Draft 

ADVISORY BOARD ON 

RADIATION AND WORKER HEALTH 

National Institute for Occupational Safety and Health 

REVIEW OF THE SITE PROFILE FOR THE 

STANFORD LINEAR ACCELERATOR CENTER 

Contract No. 200-2009-28555 

Prepared by 

Joseph Fitzgerald 

Ron Buchanan 

William James 

S. Cohen & Associates 

1608 Spring Hill Road 

Suite 400 

Vienna, Virginia 22182 

Saliant, Inc. 

5579 Catholic Church Road 

Jefferson, Maryland 21755

December 2011 

Disclaimer 

This document is made available in accordance with the unanimous desire of the Advisory Board on 

Radiation and Worker Health (ABRWH) to maintain all possible openness in its deliberations. However, 

the ABRWH and its contractor, SC&A, caution the reader that at the time of its release, this report is predecisional and has not been reviewed by the Board for factual accuracy or applicability within the 

requirements of 42 CFR 82. This implies that once reviewed by the ABRWH, the Board’s position may 

differ from the report’s conclusions. Thus, the reader should be cautioned that this report is for 

information only and that premature interpretations regarding its conclusions are unwarranted.

 
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Document No. 

SCA-TR-SP2011-0011 

Effective Date: 

December 20, 2011 

S. COHEN & ASSOCIATES: 

Technical Support for the Advisory Board on

Radiation & Worker Health Review of 

NIOSH Dose Reconstruction Program Revision No. 

0 – (Draft) 

Review of the Site Profile for the Stanford 

Linear Accelerator Center Page 2 of 86 

Task Manager: 

________________________ Date: ___________ 

Joseph Fitzgerald 

Supersedes: 

N/A 

Project Manager: 

________________________ Date: ___________ 

John Mauro, PhD, CHP 

Reviewer: 

 John Mauro 

Record of Revisions 

Revision 

Number Effective Date Description of Revision 

0 (Draft) 12/20/2011 Initial issue 

0 (Draft) 

PA-Cleared 

version 

01/04/2012 Some information from the original report relating to statutory and regulatory 

interpretations has been removed from this Privacy Act-cleared version, as well 

as the names of some individuals to protect their privacy. 
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TABLE OF CONTENTS 

Acronyms and Abbreviations ..........................................................................................................5 

1.0 Executive Summary.............................................................................................................8 

1.1 Summary of Primary Findings.................................................................................9 

1.2 Strengths ................................................................................................................11 

1.3 Opportunities for Improvement .............................................................................11 

2.0 Scope and Introduction ......................................................................................................13 

2.1 Review Scope.........................................................................................................13 

2.2 Assessment Criteria and Methods..........................................................................14 

2.2.1 Objective 1: Completeness of Data Sources.............................................15 

2.2.2 Objective 2: Technical Accuracy..............................................................15 

2.2.3 Objective 3: Adequacy of Data.................................................................15 

2.2.4 Objective 4: Consistency among Site Profiles..........................................15 

2.2.5 Objective 5: Regulatory Compliance and Quality Assurance ..................15 

2.3 Dose Reconstruction under EEOICPA..................................................................16 

2.4 Report Organization...............................................................................................16 

3.0 Vertical Issues....................................................................................................................17 

3.1 Secondary Findings................................................................................................29 

3.1.1

.......................................................................................37 

Finding 6: Incomplete Basis for Environmental External Dose from

Neutron Skyshine

3.1.2

.............................................................................................39 

Finding 7: Back Extrapolation of Occupational Environmental 

Photon Doses

3.1.3

.......................41 

Finding 8: Unsupported Assumptions for Calculation of 

Environmental Internal Dose from Onsite Releases to Air

4.0 Overall Adequacy of the Site Profile as a Basis for Dose Reconstruction ........................45 

4.1 Objective 1: Completeness of Data Sources.........................................................45 

4.2 Objective 2: Technical Accuracy..........................................................................47 

4.3 Objective 3: Adequacy of Data.............................................................................48 

4.4

.............................................................................................................49 

Objective 4: Consistency among Site Profiles and Other NIOSH 

Documents

4.5 Objective 5: Regulatory Compliance and Quality Assurance ..............................51 

4.6 Inconsistencies and Editorial Errors in the Site Profile .........................................51 

5.0 References..........................................................................................................................55 

Attachment 1: Potential Radiation Fields at SLAC......................................................................60 

Attachment 2: Summary of Site Expert Interviews......................................................................63 
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NOTICE:

LIST OF TABLES 

Table 1. Neutron Dosimetry vs. Time Period...............................................................................18 

Table 2. Dose Equivalent Fractions for Low-Energy and High-Energy Neutrons.......................20 

Table 3. Impact of Detector Energy Dependence Issues..............................................................21 

Table 4. Photon and Beta Dosimetry at SLAC.............................................................................26 

Table 5. Environmental Photon Monitoring and Data..................................................................39 

Table 6. Lifetime Dose Summary for [EE]...................................................................................43 

Table 7. Recommended Updates to Table 2-1, Pages 11–12 of the Site Profile. .........................54 

LIST OF FIGURES 

Figure 1. Neutron Spectrum from 46.6 GeV Electrons through Iron and Concrete.....................19 

Figure 2. Neutron Spectra at SSRL through 2 ft of Concrete.......................................................19 

Figure 3. Neutron Dose Conversion Factors (Flood 1995)...........................................................25 

Figure 4. Handwritten Note of Early Doses..................................................................................44 
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ACRONYMS AND ABBREVIATIONS 

ACL Administrative Control Limit 

Advisory Board 

or ABRWH Advisory Board on Radiation and Worker Health 

AEC U.S. Atomic Energy Commission 

ALARA As Low as Reasonably Achievable 

AMAD Activity Median Aerodynamic Diameter 

AMS Air Monitoring System 

ANL-E Argonne National Laboratory-East 

AWE Atomic Weapons Employer 

BDE Beam Dump East 

BF3 Boron Trifluoride 

BNL Brookhaven National Laboratory 

Bq Becquerel 

BSOIC Beam Shutoff Ion Chamber 

BSY Beam Switch Yard 

CAM Continuous Air Monitor 

CEDE Committed Effective Dose Equivalent 

CERN European Organization of Nuclear Research 

CF Correction Factor 

CFR Code of Federal Regulations

Ci curie 

cm centimeter 

DAC Derived Air Concentration 

DE Dose Equivalent 

DOE U.S. Department of Energy 

DOELAP Department of Energy Laboratory Accreditation Program 

dpm disintegrations per minute 

DU Depleted Uranium 

EEOICPA Energy Employees Occupational Illness Compensation Program Act of 2000 

EPA U.S. Environmental Protection Agency 

ES&H Environmental Safety and Health 

ESA End Station A 

eV electron volts 

FFTB Final Focus Test Beam 

ft foot 

FRC Federal Records Center 

g gram 

GERT General Employee Radiation Training 

GeV Gigaelectron volts 
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GM Geiger Mueller 

GR Giant Resonance 

GSD Geometric Standard Deviation 

HEPA High Efficiency Particulate Air 

HHS Health and Human Services 

HPI Health Physics Instrument 

hr hour 

Hz Hertz 

ICRP International Commission on Radiological Protection 

ICRU International Commission on Radiological Units and Measurements 

in inch 

IREP Interactive RadioEpidemiological Program 

l liter 

keV kiloelectron volt 

LANL Los Alamos National Laboratory 

LBNL Lawrence Berkeley National Laboratory 

LCLS LINAC Coherent Light Source 

LiF Lithium fluoride 

LINAC Linear Accelerator 

LLNL Lawrence Livermore National Laboratory 

LLD Lower Limit of Detection 

m3 cubic meter 

mA milliamp 

MAPEP Mixed Analyte Performance Evaluation Program 

MBq Megabequerels 

MDD Minimum Detectable Dose 

MeV megaelectron-volt, 1 million electron-volts 

MFD Mechanical Fabrication Department 

MMAD Mass Median Aerodynamic Diameter 

mR milliroentgen 

mrem millirem 

mSv milliSievert 

mV millivolt 

MW Megawatt 

NaI Sodium Iodide 

NAVSEA Naval Sea System Command 

NCRP National Council on Radiation Protection 

NIOSH National Institute for Occupational Safety and Health 

NLCTA Next Linear Collider Test Accelerator 

NTA Nuclear Track Film Type A 

ODTS Occupational Dose Tracking System 
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NOTICE:

OIO Office of Independent Oversight

ORAUT Oak Ridge Associated Universities Team 

ORPS Occurrence Reporting and Processing System 

OTIB ORAUT Technical Information Bulletin 

pCi picocurie 

PEP Positron Electron Project 

PIC Pocket Ionization Chamber 

PMS Perimeter Monitoring System 

PNNL Pacific Northwest National Laboratory 

POC Probability of Causation 

PPE Personal Protective Equipment 

PuBe Plutonium Beryllium 

PuLi Plutonium Lithium 

QC Quality Control 

R Roentgen 

RAMSY Radioactive Material Storage Yard 

RadCon Radiological Control 

RCA Radiological Control Area 

RCO Radiological Control Organization 

RCT Radiological Control Technician 

RDC Radiation Detection Company 

RF Radio Frequency 

RMS Remote Monitoring System 

RP Radiation Protection 

RWP Radiological Work Permit 

SC&A S. Cohen & Associates 

SEC Special Exposure Cohort 

SLAC Stanford Linear Accelerator Center National Accelerator Laboratory 

SLC SLAC Linear Collider or Stanford Linear Collider 

SPEAR Stanford Positron-Electron Asymmetric Ring 

SRDB Site Research Database 

SSRL Stanford Synchrotron Radiation Lightsource 

Sv sievert 

TA Technical Area 

TBD Technical Basis Document 

TIB Technical Information Bulletin 

TLD Thermoluminescent dosimeter 

μm micron 

yr Year 
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1.0 EXECUTIVE SUMMARY 

This draft report presents the results of an independent review conducted by S. Cohen and 

Associates (SC&A, Inc.) of ORAUT-TKBS-0051, Site Profile for the Stanford Linear 

Accelerator Center (ORAUT 2007a), which was issued by the National Institute for 

Occupational Safety and Health (NIOSH) as a summary site profile document. SC&A 

conducted this review during the period of May 2010 through August 2011. 

This review was conducted in accordance with the Advisory Board’s Data Access and Interview 

Procedures (ABRWH 2009a) and SC&A’s Board-approved Standard Operating Procedure for 

Performing Site Profile Reviews (SC&A 2004). SC&A evaluated the site profile for 

completeness, technical accuracy, adequacy of data, compliance with regulatory objectives, and 

consistency with other site profiles. Review criteria and methods are described in greater detail 

in Section 2.0 of this report. 

The Stanford Linear Accelerator Center National Accelerator Laboratory, known as SLAC, was 

established in 1962 at Stanford University in Menlo Park, California. SLAC is home to a 

20 GeV, 2-mile linear electron accelerator that was originally established to conduct particle 

physics research, but has evolved to a multi-purpose laboratory for astrophysics, photon science, 

accelerator, and particle physics research. The 2-mile linear electron accelerator (LINAC) was 

constructed over a period of 4 years. The first electron beam was accelerated through the entire 

length of the machine on May 21, 1966. The accelerator proper is housed in a concrete tunnel 

25 feet underground. Parallel to the accelerator at ground level is the klystron gallery, which 

contains all the components and devices for the acceleration of the subterranean electron beam. 

The Stanford Synchrotron Radiation Lightsource (SSRL) is a national facility for the utilization 

of synchrotron radiation in many fields of scientific investigation collocated at SLAC. A 

smaller, self-contained test band linear accelerator, the Next Linear Collider Test Accelerator 

(NLCTA), is used to test x-band technology, which allows for faster acceleration of particles. 

A brief description of the processes that create radiation fields at a high-energy electron 

accelerator is presented in Attachment 1 of this report. Potential external exposures include 

photon and beta radiation while the accelerator is operating or when it is off, and neutron 

radiation while the accelerator is operating. Potential internal exposure may result from 

exposure to activated air or invasive work on beamline/components, experimental targets, the 

shielding, and the beamstops. The dominant dose contribution to workers at SLAC is external 

exposure. 

SC&A conducted a site visit from January 24–28, 2011, comprised of a document review and 

unclassified site expert interviews. SLAC provided SC&A staff members with access to the 

intranet, where additional documents were captured. Data retrieved were made available to 

NIOSH via the O-drive. Interviews were conducted with 26 former and current SLAC workers, 

including personnel from radiological control (RadCon) and dosimetry; environmental 

monitoring and waste management; accelerator operations; medical; and maintenance and crafts. 

The purpose of these interviews was to obtain first-hand accounts about past radiological 

controls, personnel monitoring programs, and site operations. Attachment 2 of this report is a 

summary of information provided to SC&A by the SLAC site experts. 
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This draft report was prepared at the request of the Advisory Board and covers ORAUT-TKBS0051, Site Profile for Stanford Linear Accelerator Center, Rev. 01 (ORAUT 2007a). As part of 

its evaluation, SC&A also reviewed other documents that were considered relevant, including the 

following: 

 Relevant technical information bulletins (TIBs) 

 Select documents that were referenced in the SLAC Site Profile 

 Documents contained in the NIOSH Site Research Database (SRDB) 

 Documents retrieved from data capture at SLAC 

This review found that the NIOSH site profile for SLAC fails to fully characterize some key 

issues that are fundamental to guiding dose reconstruction. In several sections of the technical 

basis document (TBD), contemporary data are applied across all years of operation, without 

regard to changes in accelerator power, beam modifications, and improvements in the 

radiological control program. Unsubstantiated basis is another concern that impacts multiple 

aspects of this review—NIOSH does not provide adequate documentation of data, assumptions, 

and methods to support their conclusions and facilitate technical review. This observation is 

applicable to neutron correction factors (CFs) and occupational environmental dose. The 

evaluation of internal hazards in the site profile is limited in scope; it is based on qualitative 

rather than quantitative analysis of available data, as well as incomplete analysis of internal 

hazards. Occupational medical dose is summarily dismissed with language that appears to 

exclude all x-rays from dose reconstruction. A lack of quality assurance reviews of incoming 

data may have led to incomplete claimant information and potential underestimate of dose. 

1.1 SUMMARY OF PRIMARY FINDINGS 

A summary of SC&A’s primary findings for the SLAC site profile is presented below. Detailed 

discussions of all findings and observations are found in Section 3.0 of this report, “Vertical 

Issues.” 

Finding 1: Incomplete Basis for External Neutron Dose Adjustments 

SC&A found that the CFs recommended by NIOSH for SLAC’s neutron dosimeters are not 

adequately supported by the information presented in the site profile. The TBD contains several 

discussions of neutron energy spectra, as well as information and analysis concerning various 

neutron instruments, area monitors, and dosimetry systems. However, most of this information 

is not clearly connected to the few important CFs the dose reconstructor will actually use. Some 

recommendations in the TBD are based on a very limited evaluation of complex radiation fields 

and dosimetry issues. In several cases, NIOSH fails to explain how assumptions and estimates 

were derived from reference documents. The CFs are presented without sufficient supporting 

documents or details, and they are applied across all time periods for the entire accelerator 

complex, disregarding variations in neutron energy spectra for different times and facilities. 

SC&A was able to derive most of the CFs in Table 6-6, but several concerns were noted in 

regard to underlying data and assumptions. Although the subject of neutron radiation and its 

associated dosimetry at SLAC received reasonable coverage in the site profile, there are several 
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neutron energy ranges in which reconstructed neutron doses may not adequately reflect the doses 

received by the workers. 

Finding 2: Lack of Extremity Monitoring and Low-Energy Photon Calibration 

The site profile does not adequately address extremity monitoring or low-energy photon 

calibrations. The characterization of common sources of exposure (Table 2-5, page 15, of the 

TBD) shows that contact dose rates are orders of magnitude higher than dose rates at 30 cm for 

most of the components tested. Handling of these activated components could present 

significant dosimetry geometry issues. The dose to extremities, lower sections of the body, and 

areas of the head (if leaning over components) could be significantly greater than the recorded 

dose from a monitor worn on the chest area. However, the TBD does not discuss dosimetry 

geometry factors, and there is no indication that extremity monitoring was needed or performed 

at SLAC. 

In addition, dosimeters were apparently not calibrated for low-energy photon exposures before 

the Department of Energy Laboratory Accreditation Program (DOELAP) accreditation of the 

Panasonic UD-802 system in the mid-1990s. These issues were identified in the Department of 

Energy (DOE) Tiger Team report (DOE 1991) as deficiencies in the external dosimetry program 

at SLAC. Many of these deficiencies were corrected after the Tiger Team inspection, but dose 

reconstructions for workers exposed to these conditions before the corrections were implemented 

may need additional consideration and/or adjustment factors to compensate for these 

deficiencies. 

Finding 3: Assessment of Internal Dose from Enhanced Radon and Thoron in the Tunnels 

Radon and thoron (Rn-220) gases above typical building background levels may have caused 

internal doses that need to be accounted for when a claimant worked in the accelerator tunnel or 

other underground structures with low air ventilation (fresh air exchange) levels. Enhanced 

radon and thoron levels are considered in other site profiles where underground concrete 

structures exist, but no consideration is given to this potential source of internal dose in the 

SLAC site profile. If radon studies were conducted at SLAC, as indicated by a site expert, 

NIOSH should obtain the record of results and evaluate the validity and applicability of the data 

to account for occupational radon and thoron doses in dose reconstruction. 

Finding 4: Incomplete Characterization of Internal Radiological Hazards at SLAC 

The TBD fails to discuss and consider potential internal exposure from special projects 

historically and currently conducted at SLAC. Although the handling of radioactive materials 

and samples during special projects does not necessarily indicate a need for routine bioassay, it 

does suggest that special bioassay and air sampling efforts may have been needed to identify 

exposures during unusual situations or incidents. Further research should be conducted to 

identify source terms beyond routine accelerator operations, identify internal monitoring that 

may have been done, and evaluate the relative potential for internal exposures. The outcome of 

this analysis should be included in the TBD to inform dose reconstructors. This analysis should 

take into consideration the field and personnel monitoring practices of the time. 
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In addition, because potential internal exposure at SLAC is more likely incidental rather than 

chronic, the TBD should identify incidents and significant unexpected contamination events that 

occurred. Examples include the W-181 personnel contamination incident (SLAC 1969), residual 

contamination from poor machining clean-up practices (SLAC 1994a), and spread of 

contamination events (SLAC 1994b). 

1.2 STRENGTHS 

The TBD discusses the site, activities occurring at the site, and the characteristics of radiation 

exposure. It addresses radiation characteristics associated with electromagnetic cascades, 

activation products and internal dose, external fields from activation, beta dose, neutron spectra, 

and synchrotron radiation. Table 2-1, “Area Information,” provides a well-organized and 

informative overview of facilities, periods of operation, access and shielding considerations, and 

radiation sources and fields. 

Occupational external dose, acknowledged as the primary source of exposure at SLAC, was 

analyzed in detail, considering badging requirements, administrative practices affecting data 

interpretation and recording, and the responsiveness of various detectors and dosimeters to 

workplace radiation fields. In particular, the subject of neutron radiation and its associated 

personnel and environmental monitoring at SLAC were discussed at some length in the site 

profile. The TBD acknowledges technical challenges and limitations affecting neutron detection 

and presents extensive information concerning various neutron instruments, area monitors, 

dosimetry systems, and thermoluminescent dosimeter (TLD) readout parameters (mV/mrem, 

etc.). Detailed analysis is presented, particularly in Appendix A, in an effort to apply 

information from multiple studies and theoretical calculations to the challenges of SLAC’s broad 

energy spectra. 

1.3 OPPORTUNITIES FOR IMPROVEMENT 

While the TBD provides detailed information concerning the history, developments, and 

facilities at SLAC, there are bases and assumptions that can be strengthened and improved. 

Recommendations to support bases and assumptions, as well as completeness of dose 

reconstruction efforts, include the following: 

 Evaluation of the completeness of medical records provided by the site for dose 

reconstruction 

 Evaluation of the availability of internal monitoring and incident reports provided by the 

site for dose reconstruction 

 Validation of missed external dose protocols against information available in the 

dosimetry log 

 Linkage of external dosimetry log information with claimant files 

 Demonstration that neutron energy spectra used for development of neutron CFs are 

bounding for all exposure conditions 
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 Demonstration that dose estimates derived from contemporary air sampling and 

contamination monitoring data are bounding for all accelerator power levels, locations, 

and periods of operation 

In addition to the technical findings presented in this report, SC&A noted a process concern in 

regard to worker outreach. No worker outreach meetings were held during the development or 

revision of the SLAC site profile. In addition, SC&A’s search of the SRDB did not produce any 

documentation of NIOSH site expert interviews for SLAC. An e-mail correspondence with site 

radiological control staff is the only source of worker input identified in the SRDB. Information 

obtained during SC&A site expert interviews indicates that NIOSH may have conducted limited 

site expert interviews with radiological control personnel at SLAC, but SC&A was unable to 

confirm this information. The absence of worker outreach meetings indicates a procedural 

noncompliance with the Oak Ridge Associated Universities Team (ORAUT) procedure 

ORAUT-PROC-0097 (ORAUT 2005b). The absence of worker outreach meetings and the 

scarcity of documented communication with SLAC personnel represent weaknesses in the 

completeness of data sources.
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2.0 SCOPE AND INTRODUCTION 

The review of the Site Profile for the Stanford Linear Accelerator Center (ORAUT 2007a) was 

authorized by the Advisory Board at its May 19–21, 2010, meeting in Augusta, Georgia, and was 

conducted between May 2010 and August 2011 by SC&A’s team of health physicists and 

technical personnel. All of the pertinent records reviewed were unclassified. This review was 

performed in accordance with Data Access and Interview Procedure (ABRWH 2009a), which 

provides for appropriate onsite coordination and data access protocols in conjunction with the 

Advisory Board, NIOSH, and DOE, and with Department of Energy Classification Review of 

Documents (ABRWH 2009b), which provides for appropriate security clearance reviews. 

SC&A understands that site profiles are living documents, which are revised, refined, and 

supplemented with NIOSH technical information bulletins (TIBs) as required to help dose 

reconstructors. Site profiles are not intended to be prescriptive or necessarily complete in terms 

of addressing every possible issue that may be relevant to a given dose reconstruction. However, 

future revisions in the SLAC site profile would serve to mitigate some of the gaps and issues 

raised in this report. 

2.1 REVIEW SCOPE 

The Advisory Board on Radiation and Worker Health (Advisory Board) is mandated to conduct 

an independent review of the methods and procedures used by NIOSH and its contractors for 

dose reconstruction. As a contractor to the Advisory Board, SC&A has been charged to support 

the Advisory Board in this effort by independently evaluating a select number of site profiles that 

correspond to specific facilities at which energy employees worked and were exposed to ionizing 

radiation. 

This report provides a review of the TBD related to historical occupational exposures at SLAC: 

 ORAUT-TKBS-0051, Site Profile for the Stanford Linear Accelerator Center, Rev. 01 

(ORAUT 2007a). 

To date, the site profile has not been supplemented by site-specific TIBs, but there are two 

generic TIBs that provide additional guidance to the dose reconstructor: 

 ORAUT-OTIB-0006, Technical Information Bulletin: Dose Reconstruction from 

Occupationally Related Diagnostic X-ray Procedures, Rev. 03-D, December 21, 2005 

(ORAUT 2005a). 

 ORAUT-TIB-0055, Technical Basis for Conversion from NCRP Report 38 Neutron 

Quality Factors to ICRP Publication 60 Radiation Weighting Factors for Respective 

IREP Input Neutron Energy Ranges, June 5, 2006 (ORAUT 2006). 
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SC&A also reviewed other pertinent documents, including those cited on the NIOSH SRDB. 

SC&A has critically reviewed the SLAC TBD, as well as supplementary and supporting 

documents, against the following three evaluation criteria: 

 Determine the completeness of the information gathered by NIOSH, with a view to 

assessing its adequacy and accuracy in supporting individual dose reconstructions

 Assess the technical merit of the data/information

 Assess NIOSH’s guidelines for the use of the data in dose reconstructions

SC&A’s review of the SLAC site profile and supplemental documentation focuses on the quality 

and completeness of the data that characterized the facility and its operations, and on the use of 

these data in performing dose reconstruction. The review was conducted in accordance with 

SC&A Standard Operating Procedure for Performing Site Profile Reviews (SC&A 2004), which 

was approved by the Advisory Board. 

The review is directed at “sampling” the site profile analyses and data for validation purposes. 

The review does not provide a rigorous quality control process, whereby actual analyses and 

calculations are duplicated or verified. The scope and depth of the review are focused on aspects 

or parameters of the site profile that would be particularly influential in dose reconstructions, 

bridging uncertainties, or correcting technical inaccuracies. 

The SLAC site profile document serves as site-specific guidance to support dose reconstructions 

for EEOICPA claimants. It provides the health physicists who conduct dose reconstructions on 

behalf of NIOSH with consistent general information and specifications to support their 

individual dose reconstructions. This report was prepared by SC&A to provide the Advisory 

Board with an evaluation of whether and how the TBD can support dose reconstruction 

decisions. 

The basic principle of dose reconstruction is to characterize the radiation environments to which 

workers were exposed, and to determine the levels of exposure the workers received in that 

environment through time. The hierarchy of data used for developing dose reconstruction 

methodologies is dosimeter readings and bioassay data, coworker and workplace monitoring 

data, and process description information or source term data. 

 

2.2 ASSESSMENT CRITERIA AND METHODS 

SC&A is charged with evaluating the approach set forth in the site profiles that is used in the 

individual dose reconstruction process. These documents are reviewed for their completeness, 

technical accuracy, adequacy of data, consistency with other site profiles, and compliance with 

the stated objectives, as defined in SC&A Standard Operating Procedure for Performing Site 

Profile Reviews (SC&A 2004). This review is specific to the SLAC site profile; however, items 

identified in this report may be applied to other facilities, especially facilities with similar source 

terms, exposure conditions, and mobile workforces. The review identifies a number of issues 

and discusses the degree to which the site profile fulfills the review objectives delineated in 

SC&A’s site profile review procedure (SC&A 2004). 
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2.2.1 Objective 1: Completeness of Data Sources 

SC&A reviewed the site profile with respect to Objective 1, which requires SC&A to identify 

principal sources of data and information that are applicable to the development of the site 

profile. The three elements examined under this objective are (1) determining if the site profile 

made use of available data considered relevant and significant to the dose reconstruction, 

(2) investigating whether other relevant/significant sources are available, but were not used in the 

development of the site profile, and (3) determining if worker input was considered in the 

development of the site profile. 

2.2.2 Objective 2: Technical Accuracy 

Objective 2 requires SC&A to perform a critical assessment of the methods used in the site 

profile to develop technically defensible guidance or instructions, including evaluating field 

characterization data, source term data, technical reports, standards and guidance documents, and 

literature related to processes that occurred at SLAC. The goal of this objective is to analyze the 

data according to sound scientific principles, and then evaluate this information in the context of 

dose reconstruction. 

2.2.3 Objective 3: Adequacy of Data 

Objective 3 requires SC&A to determine whether the data and guidance presented in the site 

profile are sufficiently detailed and complete to conduct dose reconstruction, and whether a 

defensible approach has been developed in the absence of data. In addition, this objective 

requires SC&A to assess the credibility of the data used for dose reconstruction. The adequacy 

of the data identifies gaps in the facility data that may influence the outcome of the dose 

reconstruction process. For example, if a site did not monitor all workers exposed to neutrons 

who should have been monitored, this would be considered a gap and thus an inadequacy in the 

data. An important consideration in this aspect of our review of the site profile is the scientific 

validity and claimant favorability of the data, methods, and assumptions employed in the site 

profile to fill in data gaps. 

2.2.4 Objective 4: Consistency among Site Profiles 

Objective 4 requires SC&A to identify common elements within site profiles completed or 

reviewed to date, as appropriate. In order to accomplish this objective, the SLAC TBD was 

compared to other TBDs, particularly those referenced in the site profile and those related to 

frequently visited facilities. This assessment was conducted to identify areas of inconsistencies 

and determine the potential significance of any inconsistencies with regard to the dose 

reconstruction process. 

2.2.5 Objective 5: Regulatory Compliance and Quality Assurance 

Objective 5 requires SC&A to evaluate the degree to which the site profile complies with stated 

policy and directives contained in 42 CFR Part 82. In addition, SC&A evaluated the TBD for 

adherence to general quality assurance policies and procedures utilized for the performance of 

dose reconstructions. 
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NOTICE:

2.3 DOSE RECONSTRUCTION UNDER EEOICPA 

[Introductory text from this section that relates to statutory and regulatory interpretations 

has been redacted.] 

SC&A’s draft report and preliminary findings will subsequently undergo a multi-step resolution 

process. Resolution includes a transparent review and discussion of draft findings with members 

of the Advisory Board Work Group, petitioners, claimants, and interested members of the public. 

Prior to and during the resolution process, the draft report is reviewed by the DOE Office of 

Health, Safety, and Security to confirm that no classified information has been incorporated into 

the report. 

All review comments apply to Rev. 01 of the SLAC site profile document, which is the most 

recently published version. Site expert interviews were conducted with former and current 

SLAC site workers to assist SC&A in obtaining a comprehensive understanding of the radiation 

protection program, site operations, and historic exposure experience. 

Attachment 1 to this report contains a brief description of the processes that create radiation 

fields at a high-energy electron accelerator. This information provides a foundation for 

understanding workers’ exposure potential at SLAC. 

Attachment 2 to this report contains a summary of the collective interviews conducted by SC&A 

during the course of this review and approved by interviewees. 

2.4 REPORT ORGANIZATION 

In accordance with directions provided by the Advisory Board and with site profile review 

procedures prepared by SC&A and approved by the Advisory Board, this report is organized into 

the following sections: 

(1) Executive Summary 

(2) Scope and Introduction 

(3) Vertical Issues 

(4) Overall Adequacy of the Site Profile as a Basis for Dose Reconstruction 

Based on the issues raised, SC&A prepared a summary list of findings, which is presented in the 

Executive Summary. Issues are designated as primary findings if SC&A believes they represent 

deficiencies that need to be corrected and pose the potential for substantial impact on at least 

some dose reconstructions. Issues can be designated as secondary findings if they simply raise 

questions, which, if addressed, would further improve the site profile and may possibly reveal 

deficiencies that will need to be addressed in future revisions of the site profile. Detailed 

analyses of the primary and secondary findings are provided in Section 3.0 of this report. 

Section 4.0 summarizes the evaluation of the TBD with respect to the stated objectives in SC&A 

Standard Operating Procedure for Performing Site Profile Reviews (SC&A 2004). 
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3.0 VERTICAL ISSUES 

Finding 1: Incomplete Basis for External Neutron Dose Adjustments 

Despite a large volume of information and analysis presented in the site profile on the topic of 

neutron dosimetry, the bases, assumptions, and calculations supporting NIOSH’s Correction 

Factor (CFs) for dose reconstruction are incomplete. There are several neutron energy ranges for 

which the adjusted neutron dose may not adequately reflect or bound doses received by workers. 

A brief description of the process that creates the radiation fields at a high-energy electron 

accelerator is presented in Attachment 1 of this report. Neutrons, ranging in energy from the 

thermal range [0.025 electron volts (eV)] up to several hundred megaelectron volts (MeV), may 

be found in occupied areas of the SLAC facility during accelerator operation. As NIOSH 

acknowledges in the TBD, neutron dosimeters did not respond to the entire spectrum of neutrons 

present at SLAC. Adjustments to recorded neutron doses are needed to compensate for the 

dosimeters’ sensitivity or lack of sensitivity to specific ranges of the energy spectrum. 

The subject of neutron radiation and its associated dosimetry at SLAC received reasonable 

coverage in the site profile, with material in Section 2, Section 4, Section 6, and Attachment A. 

The TBD acknowledges technical challenges and limitations affecting neutron dosimetry and 

presents extensive information concerning various neutron instruments, area monitors, dosimetry 

systems, and readout parameters for thermoluminescent dosimeters (TLDs). Detailed analysis is 

presented, particularly in Appendix A of the TBD, in an effort to apply information from various 

studies and theoretical calculations to the challenges of monitoring SLAC’s broad neutron 

energy spectra. However, the technical information is somewhat scattered and segmented. 

Rather than flowing directly from the information and analysis presented in the TBD, the CFs 

and their underlying assumptions are often presented as short statements without sufficient detail 

or supporting data. Even where references are provided, it is difficult to determine how NIOSH 

used the referenced information to generate the values and assumptions presented in the TBD. 

This complicated the technical review considerably. 

To develop this finding, SC&A condensed and digested information from multiple sections of 

the TBD, attempted to reproduce NIOSH’s derivation of neutron CFs, and evaluated the 

technical basis as understood by the reviewers. SC&A was able to derive most of the CFs 

presented in Table 6-6, but several concerns were noted in regard to underlying data and 

assumptions. SC&A’s interpretations and concerns are presented below for each aspect of this 

review. 

Neutron Dosimetry Systems 

Table 1 summarizes the types of neutron dosimetry used at SLAC during specific time periods 

(from ORAUT 2007a, Table 6-6, pg. 34). 
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Table 1. Neutron Dosimetry vs. Time Period 

1961–6/1971 Nuclear track emulsion, Type A (NTA) film badge 

7/1971–1995 Lithium fluoride (LiF) Albedo TLD 

1996–3/2000 Panasonic TLD [calibrated w/unmoderated Cf-252] 

4/2000–2001 Panasonic TLD [calibrated w/moderated Cf-252] 

2002–2005 Landauer Columbia Resin 39 (CR-39) 

 

Characterizing Neutron Spectra 

The site profile identifies energy dependence issues associated with each neutron dosimetry 

system. Characterization of the radiation fields encountered by workers during these time 

periods is an essential step in adjusting doses to account for these issues. Multiple statements in 

the site profile acknowledge the significant challenges posed by the wide range of neutron 

energies at SLAC: 

 Page 19: Neutron spectra of concern for personnel exposure probably vary significantly. 

[Emphasis added.]

 Page 57: In the field, dose determination is more difficult because the neutron spectra 

extend to much higher energies than the calibration sources and most instruments. 

[Emphasis added.]

 Page 57: There are several measurements used to qualify the 5- and 6-in. moderated 

TLDs as a measurement tool (Liu et al. 2000). These instruments are characterized as 

providing information on the neutrons only below 20 MeV. Neutrons above 20 MeV are 

characterized as having up to as much dose in the SLAC radiation fields as the lower 

energy neutrons. [Emphasis added.]

 Page 57: For the SLAC radiation fields, the spectrum as well as the dose equivalent have 

not been readily available, so generating useful information for calibration has been very 

difficult. [Emphasis added.]

It appears that NIOSH relied on three neutron spectra measurements from 1997 (Vylet et al. 

1997) to assign the fraction of neutrons to each of the five Interactive RadioEpidemiological 

Program (IREP) energy bins and to derive CFs for dosimetry systems used at SLAC across 

several time periods. These measurements are described below. 

Main Accelerator FFTB2 [Final Focus Test Beam 2] Measured Neutron Energy Spectra

A measurement was made at the beam dump of the main electron accelerator (Vylet et al. 1997). 

The parameters were as follows: 

 46.6 gigaelectron-volt (GeV) electrons 

 16o

 downstream of beam dump 

 Through 4 ft of iron plus 5 ft of concrete 

 Used Bonner spheres and plastic scintillators (20-MeV threshold) detectors 

 Neutron dose rate was ~20 millirem (mrem)/hour (hr) 

 Resulting neutron energy spectrum shown in the TBD (Figure 2-5), presented below in 

Figure 1: 
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Reproduced from ORAUT 2007a, Figure 2-5, pg. 18 

Source: Vylet et al. 1997 

Figure 1. Neutron Spectrum from 46.6 GeV Electrons through Iron and Concrete 

SSRL-LINAC and SSRL-SPEAR [Stanford Positron Electron Asymmetric Ring] Measured

Neutron Energy Spectra

Measurements were made at SSRL accelerators with the electron beam striking a Faraday cup 

(Vylet et al. 1997). The parameters were as follows: 

 120-MeV electrons (LINAC); 2.3-GeV electrons (SPEAR) 

 90o

 to beamline 

 Through 2 ft of concrete 

 Used Bonner spheres and plastic scintillators (20-MeV threshold) detectors 

 Neutron dose rate was not provided 

 Resulting neutron energy spectra shown in the TBD (Figure 2-6) , presented below in 

Figure 2: 

Reproduced from ORAUT 2007a, Figure 2-6, pg. 19 

Source: Vylet et al. 1997 

Figure 2. Neutron Spectra at SSRL through 2 ft of Concrete 
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The measurements used to derive several CFs for adjusting claimants’ neutron doses were 

obtained in 1997 under specific operating conditions. The TBD fails to demonstrate that these 

measurements are representative of the moderated neutron fields at various locations and time 

periods at SLAC. Shielding conditions, location, beam angles, reflected radiation (such as 

backscatter and skyshine), and other factors could significantly change the neutron energy 

spectra from those present under the specific measurement conditions of the 1997 data. This 

could significantly alter the fraction of undetected neutron dose from low-energy and highenergy neutrons, especially as beam energies changed over time. Several site experts 

interviewed by SC&A reported that accelerator beam power has decreased consistently from a 

peak period in the early 1970s, due to improvements in beam maintenance and modifications. It 

is not clear how a few neutron spectra obtained in the late 1990s can adequately characterize or 

bound dose corrections for workers at all affected locations and times throughout the site’s 

history. 

Dose Equivalent Fractions 

The spectral data from the 1997 measurements were sorted into the five IREP neutron energy 

bins and combined with the flux-to-dose equivalent (DE) factors in National Council on 

Radiation Protection (NCRP) publication NCRP 38 (NCRP 1971) to determine the fraction of 

the DE that falls below or above a certain neutron energy. The dose fractions for the five 

neutron energy bins are listed in Table 6-5 of the TBD in the column labeled “NCRP 38 Dose 

Fraction.” This column also lists the fraction of the DE that falls below the NTA film neutron 

energy threshold of 0.800 MeV and the CR-39 threshold of 0.050 MeV for each of the neutron 

spectra (ORAUT 2007a, pg. 34). 

The following table summarizes the “NCRP 38 Dose Fraction” data from TBD Table 6-5 

(ORAUT-TKBS-0051, page 34) that is pertinent to specific detection limitations identified for 

SLAC’s neutron dosimeters. Because NIOSH did not describe its calculations and assumptions 

or indicate which tables from NCRP 38 were used, SC&A was unable to verify the DE fractions 

reported in TBD Table 6-5. 

 

Table 2. Dose Equivalent Fractions for Low-Energy and High-Energy Neutrons 

Location 

Electron 

Energy 

(GeV) 

Dose Fraction 

<0.8 MeV 

(NTA Threshold) 

Dose Fraction 

<0.05 MeV 

(CR-39 Threshold) 

Dose Fraction 

>20 MeV 

(High Energy) 

SSRL-LINAC 0.120 0.386 0.075 0.018 

SSRL-SPEAR 2.3 0.289 0.082 0.099 

FFTB2 46.6 0.120 0.016 0.463 

Estimating Percentages of Undetected Low-Energy and High-Energy Neutrons 

For some neutron dosimetry systems, NIOSH used the “NCRP 38 Dose Fraction” data to 

estimate how much of the DE was not detected due to the dosimeter’s insensitivity to certain 

neutron energies. These data play a significant role in the derivation of CFs, particularly for 

NTA film, Landauer CR-39 TLDs, and the Panasonic TLDs calibrated with unmoderated 

neutrons (1996–March 2000). Table 3 summarizes several energy dependence issues identified 

by NIOSH for these neutron dosimetry systems. The fourth column presents SC&A’s 
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understanding of how NIOSH used the 1997 neutron spectral data to derive the “Impact” values 

listed in Table 6-6 of the TBD (ORAUT 2007a, pg. 34). 

Table 3. Impact of Detector Energy Dependence Issues 

Detector System Issue Impact SC&A Interpretation of NIOSH Basis 

(Apparent use of neutron spectral data) 

NTA Film Badge Insensitive below 

800 keV 

Lose 12%–40% FFTB2 dose fraction <0.8 MeV = 12% 

SSRL-LINAC dose fraction <0.8 MeV = 38.6% 

(rounds up to 40%) 

Panasonic TLD 

(1996–3/2000) 

Not measure highenergy neutrons Lose 2%–50% SSRL-LINAC dose fraction >20 MeV = 1.8% 

(rounds up to 2%) 

FFTB2 dose fraction >20 MeV = 46.3% 

(rounds up to 50%) 

Landauer 

CR-39 

Insensitive below 

50 keV 

Lose 1.6%–8% FFTB2 dose fraction <0.05 MeV = 1.6% 

SSRL-SPEAR dose fraction <0.05 MeV = 8.2% 

(rounds down to 8%) 

NTA Film Badge 

& 

Landauer 

CR-39 

Not detect heavy 

recoils 

Lose 30%–40% 

of 50%–2% 

SSRL-LINAC dose fraction >20 MeV = 1.8% 

(rounds up to 2%) 

FFTB2 dose fraction >20 MeV = 46.3% 

(rounds up to 50%) 

Assumption described in TBD: 30%–40% loss 

at energies above 10–50 MeV 

NIOSH assumes 30%–40% of the high-energy dose fraction is not detected by NTA film and 

Landauer CR-39 TLDs. This estimate is described in the TBD as follows (ORAUT 2007a, 

pg. 54): 

Above 10 to 50 MeV, carbon and oxygen recoil and spallation become important. 

The NTA and Neutrak [CR-39] systems probably do not respond to them. There 

are no calibration sources in this energy range, so testing cannot occur. Based 

on ICRU [International Commission on Radiation Units and Measurements] 

Report 63 (1999, Figure 7.19) an estimated 30% to 40% of the dose equivalent in 

this energy range is lost. [Emphasis added.] 

NIOSH does not explain how ICRU Report 63 (ICRU 1999) was used to estimate that 30%–40% 

of the dose from high-energy neutrons was lost to detection by NTA film and CR-39 TLDs. No 

further explanations or calculations are provided to show how this estimate was derived. 

Without this information, SC&A could not verify the calculated values or the assumptions used. 

The TBD also does not discuss the relevance of ICRU’s data to the high-energy neutron fields 

encountered by SLAC workers throughout the years when these dosimetry systems were in use. 

Derivation of Correction Factors for Neutron Dosimetry Systems 

NIOSH lists the “Total Impact” for each dosimeter system and time period in Table 6-6 of the 

TBD (ORAUT 2007a, pg 34); these are the overall CFs applied by the dose reconstructor to 

adjust the recorded neutron dose. The TBD does not describe the derivation of these CFs, which 
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complicated the technical review. SC&A was able to derive most of the CFs presented in 

Table 6-6, but several concerns were noted in regard to underlying data and assumptions. The 

following analysis of neutron CFs reflects SC&A’s understanding of NIOSH’s approach. 

It appears that NIOSH used a simple average of two values to quantify the impact of each issue 

listed in Table 3 above. For example, the fraction of the DE in the high-energy range (>20 MeV) 

was determined to range from about 2% (in the SSRL-LINAC spectrum) to about 50% (in the 

FFTB2 spectrum). NIOSH apparently took the average of these two values (26%) to represent 

how much of the DE is from high-energy neutrons. Similarly, the estimated 30%–40% loss of 

detection for high-energy neutrons is apparently represented as the average, 35%. 

The CFs that compensate for undetected low-energy and high-energy neutrons on the basis of the 

“NCRP 38 Dose Fractions” from the 1997 neutron spectra measurements may be obtained using 

the following equation: 

Total Impact = 1/[1 – (threshold fraction lost + high-energy fraction lost)] 

Using this approach, the following corrections would be calculated for these systems: 

1. NTA Film Badge (1961–June 1971) 

a. Insensitive below 800 keV: Lose 12%–40% 

(0.12 + 0.40)/2 = 0.26 

Assume 26% of DE was not detected due to low-energy neutrons 

b. Not detect heavy recoils: Lose 30%–40% of 50%–2% 

(0.30 + 0.40)/2 = 0.35 

(0.02 + 0.50)/2 = 0.26 

0.35 * 0.26 = 0.09 

Assume 9% of DE was not detected due to high-energy neutrons 

c. SC&A calculated combined CF: 1/[1 - (0.26 + 0.09)] = 1.53

d. NIOSH “Total Impact:” Multiply by 1.53 +/- 0.14 

2. Landauer CR-39 TLD (2002–2005) 

a. Insensitive below 50 keV: Lose 1.6%–8% 

(0.016 + 0.08)/2 = 0.048 (rounds up to 0.05) 

Assume 5% of DE was not detected due to low-energy neutrons 

b. Not detect heavy recoils: Lose 30%–40% of 50%–2% 

(0.30 + 0.40)/2 = 0.35 

(0.02 + 0.50)/2 = 0.26 

0.35 * 0.26 = 0.09 

Assume 9% of DE was not detected due to high-energy neutrons 

c. SC&A calculated combined CF: 1/[1 - (0.05 + 0.09)] = 1.16

d. NIOSH “Total Impact:” Multiply by 1.12 +/- 0.04 

Disagreement: SC&A’s result is higher by ~4% compared to NIOSH’s result. 

Using simple arithmetic means of high and low values to derive CFs appears to be overly 

simplistic. This approach fails to account for the amount of time a worker may have spent in one 
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accelerator field compared to the other, as well as the accelerators’ respective contribution to the 

overall radiation field as a function of space and time. 

Correction factors (CFs) for the other neutron dosimetry systems used at SLAC are not based 

primarily on the “NCRP 38 Dose Fractions.” Each of these CFs is evaluated separately below. 

3. LiF Albedo TLD (1971–1995) 

a. NIOSH “Total Impact:” Multiply by 0.56. GSD [geometric standard deviation] of 

2.5. 

b. SC&A interpretation: 1/1.8 = 0.56

The CF of 1.8 is mentioned in the TBD (ORAUT 2007a, pg 63): 

The neutron dose equivalent for the SLAC LiF system used from 1971 

should be reduced by a factor of 1.8 with a GSD of 2.5 [14].1

 The large 

uncertainty is likely due to different albedo neutron responses to different 

spectra at SLAC; there was no attempt to evaluate the different spectra to 

which individuals were exposed. To attempt such an evaluation would 

have been a time-consuming task that would likely have been 

unsuccessful. The correction is due to the fact that SLAC conservatively 

erred on the side of over-reporting the neutron dose equivalent. 

The basis for this CF is not expressly identified in the TBD. If it is based on NIOSH’s 

detailed analysis of response characteristics of albedo TLD systems (ORAUT 2007a, 

pp. 59–62), the derivation is not clear. A factor of 1.8 is listed in Table A-1 (ORAUT 

2007a, pg. 58) in Column 6, Row 12; this value is associated with TLDs in a 6-in water 

moderator exposed to CERN (European Organization for Nuclear Research) neutron 

fields with concrete shielding. It is not readily apparent why TLDs exposed in a 6-in 

water moderator to CERN concrete-shielded neutrons are representative of the neutron 

fields workers were exposed to at all locations at SLAC throughout this time period. 

4. Panasonic TLD (1996–March 2000) 

a. Use unmoderated rather than moderated Cf for dose evaluation: 

Divide by 7. GSD of 2.5. 

Assume the dose of record was overestimated by a factor of 7. 

b. Not measure high-energy neutrons: Lose 2%–50% 

[SC&A incorporated the 30%–40% assumption for high-energy neutron detection. 

The TBD does not indicate if this factor applies to the Panasonic TLD.] 

(0.02 + 0.50)/2 = 0.26 

0.35 * 0.26 = 0.09 

Assume 9% of DE was not detected due to high-energy neutrons. 

c. SC&A calculated combined CF: 1/[1 - 0.09] × 1/7 = 0.16 

d. NIOSH “Total Impact:” Multiply by 0.14. GSD of 2.5. 

Disagreement: SC&A’s result is higher by ~14% compared to NIOSH’s result. 

1

 [Annotation provided in TBD]. Rohrig, Norman D. ORAU Team. Health Physicist. April, 2006. 
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NIOSH did not incorporate a correction for undetected high-energy neutron dose into the 

combined CF—the combined CF (“Multiply by 0.14”) is equivalent to the first issue 

impact (“Divide by 7”). This accounts for the discrepancy between SC&A’s calculation 

and the CF listed in Table 6-6. The TBD does not indicate if the 30%–40% estimate for 

the percentage of high-energy neutrons lost to detection, described above for NTA film 

and CR-39 TLDs, is applicable to the Panasonic TLD. 

Some contradictions were noted in different sections of the TBD regarding calibration of 

the Panasonic TLD during this time period. It appears that the TLDs were calibrated 

using unmoderated (i.e., higher-energy) neutrons, but NIOSH assumes workers were 

exposed primarily to lower-energy moderated neutrons. Multiplying the dose of record 

by 1/7 (0.14) reduces the assigned dose to compensate for the TLD’s higher sensitivity to 

lower-energy neutrons. The final sentence in Attachment A describes this position 

(ORAUT 2007a, page 63): 

We understand that the reported neutron doses for the Panasonic system 

until March 2000 were based on the unmoderated 252Cf spectrum, 

resulting in reported doses being about a factor of 7 too large (Flood

[1995]). [Emphasis added.]

If the statement quoted above correctly represents NIOSH’s position, the following 

statements should be revised to improve clarity and consistency. 

 Table 6-6, Column 3, Row 4 (ORAUT 2007a, pg. 34): 

o Current wording: Use unmoderated rather than moderated Cf for dose 

evaluation. [Emphasis added.] 

o Suggested wording: Unmoderated rather than moderated Cf was used for 

dose evaluation. [Emphasis added.]

 Section 6.3.3.2, second paragraph, second sentence (ORAUT 2007a, pg. 32): 

o Current wording: ...between 1996 and March 2000, the Panasonic system 

used the dose response for a moderated 252Cf neutron source... [Emphasis 

added.] 

o Suggested wording: ...between 1996 and March 2000, the Panasonic system 

used the dose response for an unmoderated 252Cf neutron source... [Emphasis 

added.] 

There still remains the important issue of how the correction factor of 1/7 was derived 

and how it was determined that workers were exposed mainly to lower-energy moderated 

neutrons. It is important for NIOSH to clarify this analysis, as it supports a decision to 

reduce a worker’s neutron dose by a factor of 7 for a period of 4 years. SC&A reviewed 

the cited reference (Flood 1995) to determine the source and rationale of the 1/7 CF. The 

following figure, excerpted from this document (Flood 1995, pg. 4), appears to be 

relevant: 
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 Dose Conversion 

 Factors 

 Element 1 

 mR*/mrem 

Unmoderated (High 

Energy) Cf-252 

Neutrons 0.222 

Moderated (Low 

Energy) Cf-252 

Neutrons 1.546 

Figure 3. Neutron Dose Conversion Factors (Flood 1995) 

NIOSH’s CF appears to be a ratio of Flood’s dose conversion factors for unmoderated 

and moderated Cf-252 neutrons. 

CF = Unmod response/Mod response = 0.222/1.546 = 1/7 = 0.14 

The CF should incorporate all of the energy dependence issues identified in the TBD, and 

inconsistencies in wording should be corrected. Considering the significance of a 

decision to reduce a worker’s reported neutron dose by a factor of 7, the TBD does not 

adequately explain NIOSH’s derivation of this CF, nor does it support the underlying 

assumption that workers were mainly exposed to lower-energy moderated neutrons 

(similar to moderated Cf-252 neutrons). 

5. Panasonic TLD (April 2000–2001) 

a. May overcompensate for high-energy neutrons 

b. NIOSH “Total Impact:” None. GSD of 2.5. 

According to the TBD, moderated Cf-252 neutrons were used to calibrate the Panasonic 

TLDs during this period (ORAUT 2007a, pg 32): 

Dose using the Panasonic system was defined from the response to the 

moderated 252Cf source. Beginning in March 2000 (Flood [2000]), in 

consideration of the high-energy neutron peak at 80 to 100 MeV, the dose 

conversion factors were divided by 2, which effectively doubled the 

reported neutron dose equivalent. [Emphasis added.] 

In Table 6-6, NIOSH recommends no further adjustments [other than those recommended 

by the International Commission on Radiological Protection (ICRP)] to the neutron dose 

of record, because the recorded dose may already overcompensate for high-energy 

neutrons. The TBD provides no further details concerning the rationale for dividing dose 

conversion factors by 2, or if that adjustment correctly compensated or overcompensated 

for undetected high-energy neutrons. While the Flood document (Flood 2000, pg. 43) 

provides some additional details, the rationale appears to be based on the assumption that 

approximately 50% of the DE is from high-energy neutrons. SC&A’s concern about 
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oversimplified assumptions in regard to complex and varied neutron spectra have been 

discussed in earlier segments of this finding. 

In summary, despite a large volume of information and analysis presented in the TBD on the 

topic of neutron dosimetry, the CFs that are actually used to adjust recorded neutron dose are not 

adequately supported. The TBD recommendations are based on a very limited treatment of 

complex radiation fields and dosimetry issues. Several components of the recommended CFs are 

based on simple averages of upper and lower values that may not represent the radiation fields to 

which workers were exposed. The 1997 neutron spectral measurements are based on limited 

parameters, and the TBD fails to demonstrate that these measurements are representative of the 

moderated neutron fields at various locations and time periods at SLAC, especially as beam 

power changed over time. Dose fraction values in Table 6-5 could not be verified without 

additional information on NIOSH’s use of NCRP 38 (NCRP 1971). Similarly, the reference to 

ICRU Report 63 (1999, Figure 7.19) was not sufficiently detailed to support an assumption that 

30%–40% of the DE from high-energy neutrons was not detected by NTA film or CR-39 TLDs. 

Several other assumptions and CFs appear in the TBD without sufficient explanations or 

supporting data. Without sufficient support for NIOSH’s “Total Impact” CFs, SC&A cannot 

conclude that neutron dose reconstruction adequately reflects or bounds the doses received by 

workers. 

Finding 2: Lack of Extremity Monitoring and Low-Energy Photon Calibration 

The site profile does not adequately address the need for, or the lack of, extremity monitoring at 

SLAC. In addition, significant monitoring and calibration for beta and low-energy photon 

exposures do not appear to have occurred before approximately 1996. These issues require 

further investigation and should be addressed in the TBD. 

As described in Attachment 1 of this report, the energy spectra of the photons created at SLAC 

can range from several keV up to near the maximum energy of the electron beam. The photon 

energies of most concern from a health protection aspect (outside the shielding) range from 

approximately 30 keV to several MeV at SLAC. When the accelerator is not operating, exposure 

comes from activated materials (e.g., targets, beamline components, structural materials, and air). 

Adequate beta/photon monitoring would include dosimetry that is responsive and appropriately 

calibrated for field exposure conditions: 

 Photons: 30 keV to 3 MeV, both while the accelerator is operating and when it is off. 

 Betas: keV and MeV range, both while the accelerator is operating and when it is off. 

The following table summarizes the types of photon and beta dosimetry used at SLAC as a 

function of time: 

Table 4. Photon and Beta Dosimetry at SLAC 

Photon Beta 

1961–1971 Type 2 film Type 2 film 

1972–1995 TLD None 

1996–2001 TLD TLD 

2002–2005 TLD TLD 
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SLAC’s photon/beta dosimetry system throughout its operating history appears to be similar to 

the standard photon/beta dosimetry used at most institutions during these periods. This 

dosimetry accounts for prompt photons outside the shielding during accelerator operations and 

photons from activated materials. It would detect the photons emitted from the klystrons (300–

400 keV) and synchrotron radiation (in the 30-keV energy range). 

It is not apparent from the TBD if dosimetry geometry issues were considered for SLAC. 

Handling of activated components could present significant dosimetry geometry issues, 

including extremity exposures that could be much higher than the whole-body recorded doses. 

There is no indication that extremity monitoring was needed or performed. However, the 

characterization of common sources of exposure (Table 2-5, page 15 of the TBD) shows that 

contact dose rates are orders of magnitude higher than dose rates at 30 cm for most of the 

components tested. The dose to extremities, lower sections of the body, and areas of the head (if 

leaning over components) could be significantly greater than the recorded dose from a monitor 

worn on the chest area. This issue is applicable to the calibration facilities as well as the 

accelerators and experimental areas. 

Beta and low-energy gamma exposure are important to the reconstruction of dose for skin 

cancers. The TBD acknowledges that synchrotron radiation includes x-rays below 30 keV. 

Furthermore, the site profile indicates beta radiation is 10% to 30% of the gamma dose. Before 

approximately 1996, there does not appear to have been significant monitoring and/or calibration 

for beta or low-energy gamma exposures (see Table 6-2, pg. 31, for a summary of recorded dose 

practices). In Section 6.3.1, “Site Dosimetry Technology,” calibration of dosimetry for lowenergy photon exposures is not mentioned before the DOELAP accreditation of the Panasonic 

UD-802 system in the mid-1990s (ORAUT 2007a, pg. 30). 

These issues were identified in the DOE Tiger Team report (DOE 1991) as deficiencies in the 

external dosimetry program at SLAC. Many of these deficiencies were corrected after the Tiger 

Team inspection; however, dose reconstructions for workers exposed to these conditions before 

the corrections were implemented may need additional consideration and/or adjustment factors 

to compensate for these deficiencies. 

Finding 3: Assessment of Internal Dose from Enhanced Radon and Thoron in the Tunnels 

Radon and thoron gases above typical building background levels may have caused internal 

doses that need to be accounted for when a claimant worked in the accelerator tunnel or other 

underground structures with low air ventilation (fresh air exchange) levels. Enhanced radon and 

thoron levels are considered in other site profiles where underground concrete structures exist, 

but no consideration is given to this potential source of internal dose in the SLAC site profile. 

According to the introduction section for ICRP Publication 65 (ICRP 1993): 

The naturally radioactive noble gas radon (222Rn) is present in the air outdoors 

and in all buildings, including workplaces. It is thus an inescapable source of 

radiation exposure both at home and at work. High radon levels in air can occur 

in buildings, including workplaces, in some geographical locations. This applies 

particularly in workplaces such as underground mines, natural caves, tunnels, 
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medical treatment areas in spas, and water supply facilities where ground water 

with a high radon concentration is treated or stored. 

The SLAC site profile states that radiation from naturally occurring radon present in 

conventional structures is not considered occupational exposure. SC&A maintains that an 

accelerator tunnel, intentionally placed underground due to the very high radiation fields and 

immense shielding requirements associated with accelerator operations, is not a conventional 

structure. It is assumed that higher levels of radon and thoron exist in the tunnel than in a 

conventional structure. The tunnel walls are under soil, and the gas in the soil contains a higher 

level of radon and thoron than is present in the ambient air above ground. Gas from the soil 

enters through walls and floors into the tunnel, where penetrations and building materials allow 

diffusion from the soil into the tunnel’s air. 

The importance of this potential exposure is reinforced by a study (Oki et al. 1999), which 

measured radon concentrations in accelerator tunnel air several times higher than the 

concentration in a nearby building basement (280 Bq/m3

 versus 50 Bq/m3 for Rn-222). The 

particle size measured for Po-218 in the study was several times smaller in the tunnel than in the 

building basement (0.03 μm vs. 0.2 μm), which would increase the comparative lung dose from 

this radon decay product. 

If radon and thoron enter the tunnel air via soil gas penetration, and if fresh air exchange is not 

adequate, there may be potential for elevated concentrations higher than typical buildings onsite 

that are above ground. Discussions during SC&A’s site expert interviews seem to indicate that 

the level of fresh air ventilation in accelerator tunnels at SLAC varies and can be low at times. 

The TBD mentions radon as a consideration affecting job-specific air sampling, but it does not 

discuss radon dose assignment for work in the tunnels: 

Air-sampling results on job activities have resulted in a negligible signal above a 

contemporary radon background measurement (Gooch 2005). Air samples are 

taken near but outside the work area prior to work to get radon background 

results. Air sample results are then compared to these results until the radon has 

been allowed to decay, after which they are compared to instrument background. 

(ORAUT 2007a, pp. 26–27) 

According to a site expert, a radon study was completed in the tunnel at SLAC during the late 

1980s using track etch detectors provided and analyzed by a vendor laboratory. This is a wellestablished measurement method. At times in the past, a national certification process was in 

place for vendors to demonstrate the quality of their analyses. 

In summary, radon and thoron gases above typical building background levels may have caused 

internal doses that need to be accounted for when a claimant worked in the accelerator tunnel or 

other underground structures with low air ventilation (fresh air exchange) levels. NIOSH should 

locate the records of radon studies conducted at SLAC and evaluate the validity and applicability 

of the data to account for occupational radon and thoron exposures in dose reconstruction. 
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3.1 SECONDARY FINDINGS 

Finding 4: Incomplete Consideration of Internal Exposure Potential from Routine 

Operations 

Section 5.0 of the TBD accepts the analysis from the SLAC internal dosimetry TBD (Kase et al. 

1993; Tran 2005), indicating that a conventional internal bioassay program was unnecessary, 

because workers were unlikely to receive a committed effective dose equivalent (CEDE) of 100 

mrem/yr. These determinations were made based on the regulatory requirements for operational 

internal dosimetry programs. While SLAC’s determination is suitable in this context, it is not an 

appropriate basis for NIOSH to disregard internal dose contributions under the compensation 

program. The SLAC site profile does not provide a thorough quantitative analysis of organ dose 

demonstrating that internal dose potential is negligible in the context of the compensation 

program. SC&A recommends additional consideration of issues affecting internal exposure 

potential, including the source term, modeling assumptions, contamination surveillance and air 

sampling data, and the completeness of bioassay records available for dose reconstruction. 

Section 5.0, “Occupational Internal Dose,” describes NIOSH’s rationale for excluding internal 

dose assignment in dose reconstruction. The TBD states that internal dose was not a routine or 

typical exposure occurrence at the site (i.e., any significant internal dose would be unusual and 

likely from a major incident). The only time a dose reconstructor should assign internal doses 

for a claimant is when internal monitoring is identified in the claimant’s file provided by SLAC. 

According to the TBD (ORAUT 2007a, pg. 27): 

Based on these considerations, no internal dose should be assigned for all SLAC 

employees unless an intake is identified in the worker files. 

The TBD mentions as its basis: 

 Absence of significant removable radioactivity 

 Insignificance of internal dose potential compared to external dose 

 Active air-sampling and contamination control programs demonstrating minimal hazard 

 Lack of internal dose measurements in claimant files 

Published studies from accelerator facilities (nationally and internationally) show some level of 

concern about internal monitoring and characterizing exposures, from earlier years through the 

last decade of high-energy accelerator work (Patterson et al. 1969, Patterson and Thomas 1973, 

Lucci et al. 1973). A CERN study, for example, warns about neglecting potential hazards of 

internal exposure (Charalambus and Rindi 1967): 

In spite of the fact that internal contamination has not been found so far in 

persons and that smear tests or air measurements do not normally show high 

contamination level, a potential hazard exists in the machine and it is possible to 

find highly activated machine parts. Consequently, the hazard for internal 

contamination should be followed up in parallel with the danger from external 

radiation. 
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While the internal dose may be neglected for regulatory purposes, NIOSH should consider the 

potential internal dose in the context of the compensation program and organ dose. 

The following radionuclides have been associated with activated components of accelerator 

hardware at SLAC: Na-22, Na-24, Ca-45, Sc-46, V-48, Cr-51, Mn-52, Mn-54, Fe-55, Fe-59, 

Co-56, Co-57, Co-58, Co-60, Zn-65, and Cu-64 (Busick and Warren 1969, Donahue 1991, 

SLAC 1994a). Several other radionuclides can be produced in metal components, varying by 

material composition and the types of reactions likely to occur. The lists of radionuclides in 

Section 2 of the TBD appear incomplete in comparison to applicable studies and modeling of 

induced activities at other sites (Patterson and Thomas 1973, Tesch 1991, Oki et al. 1994, 

Numajiri et al. 1994, Endo et al. 2004, Oishi et al. 2005). Activated cooling water contains 

tritium; other liquids, such as pump oils, are known to contain tritium as well. Other radioactive 

materials include Be-7 and C-11 from air activation. Induction of radionuclides in concrete can 

occur, although this is not specifically addressed in the TBD. Endo et al. (2004) measured H-3 

and C-14 in one study. Oishi et al. (2005) detected Na-24, Sc-47, Ca-47, and Mn-54, along with 

other radionuclides in another study. NIOSH’s analysis should include thorough consideration 

of the source term to support bounding assumptions. 

The TBD indicates that an electron accelerator does not generate significant removable 

radioactivity; most of the activity induced by the accelerator is within the structure of materials 

exposed to the beam. The principal risk for internal exposure identified in the SLAC site profile 

is the generation of respirable radioactive aerosols during occasional machining activities, such 

as sawing, drilling, grinding (used rarely), and welding. The bulk of SLAC’s machining 

experience has been with copper and stainless steel. The TBD cites the following references as 

demonstrating that the CEDE from machining activated materials would be trivial in comparison 

to the external exposure received (Busick and Warren 1969, Donahue 1989, and Donahue 1991). 

The focus of Busick and Warren (1969) was to establish operational guidelines for machining of 

activated hardware in machine shops and other environments. The paper mentions personal air 

sampling use during machining operations “with negative results;” neither Busick and Warren 

(1969) nor the TBD provides details on this air sampling. The authors go on to say the specific 

activity in irradiated copper, stainless steel, or aluminum would have to reach proportions that 

would create external whole-body radiation protection problems before measureable airborne 

exposure becomes significant. SC&A’s site expert interviews indicate that external exposure 

rates did result in High Radiation Areas in some situations. Busick and Warren caution that their 

analysis does not consider long-term buildup of radioactive contamination on machines and 

machine shop areas. SC&A notes that resuspension of loose contamination from buildup of dust 

and debris may have led to skin, ingestion, and inhalation exposures if precautions were not 

adequate. 

SLAC has used modeling of possible inhalation exposures from the induced radionuclides that 

could occur in high-energy accelerators (Donahue 1989, 1991), along with some air sampling 

studies, as a basis to assume radionuclide intakes under routine conditions are insignificant. It 

should be noted that SLAC’s basic position on internal dose from normal operations has 

continued through current operations, supported by more recent reviews and revisions to SLAC’s 

dosimetry technical documents (e.g., Tran 2005, Sit 2000). 
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Section 2.0 of the TBD includes the following statement (ORAUT 2007a, pg. 13), which is also 

echoed in Section 5.0: 

Donahue (19892

, 1991, p. 10) compared the possible internal dose to the external 

dose for a machining process and showed that the internal dose by this pathway is 

about 10-6 of the external dose (see the next to the last column of Table 2-2). 

Because the external dose would be received during the setup of the machining 

process, the relative contribution from internal dose would be much smaller. 

These ratios depend on the assumed exposure and decay times, material mass 

being machined, and detailed machining practices; however, the conclusion that 

internal exposure is trivially small in comparison to the external dose remains 

true. 

2

 The 1989 reference contains an error (cm vs m) that results in erroneous 

concentrations a factor of 10,000 larger.

As cited in the TBD, Donahue (1991) calculated estimates of the internal radiation exposure 

relative to the external exposures from machine shop operations during cutting, grinding, and 

welding operations performed on activated beamline components. Donahue (1989, 1991) 

concluded internal doses from these activities were such small fractions of the external dose that 

there was no need to account for the internal dose. However, the Donahue (1989, 1991) 

modeling of intakes and doses calculated were challenged by a study from Germany (Tesch 

1991). The conclusion of the opposing study directly points out their disagreement with SLAC’s 

conclusion (Tesch 1991): 

Our conclusions do not agree with the work of Donahue [Donahue (1989, 1991)], 

who came to the conclusions that internal dose can be neglected compared with 

the external dose. The three main reasons for this difference are: The activities 

for iron given in Table 3 of Reference 3 [Donahue, 1991] are too low. They 

produce a dose rate of 0.14 mSv.h-1 instead of 1 mSvh-1 at a distance of 30 cm. 

The ventilation rate of 8.5 m3

.min-1 of the test set-up in Reference 2 [Donahue, 

1989] was used, whereas a rate of 1 m3

.min-1 appears to us to be more realistic. 

A detailed discussion of the lung dose equivalent is absent. Furthermore, the 

nuclide distribution we obtained experimentally deviates from Swanson’s 

theoretical values, especially in the case of copper. 

In their modeling, both Donahue and Tesch determined dose estimates by comparing modeled air 

concentrations that could have been inhaled to the specific Derived Air Concentration (DAC) 

regulatory limit for each radionuclide. The DAC limits at that time were based on the old 

standard default particle size of 1 μm AMAD (Activity Median Aerodynamic Diameter); current 

health physics practice uses a default assumption of 5 μm AMAD. Table 4 of Donahue (1991) 

shows various maintenance activities with metal components, such as pipe cutting, sawing, and 

torch cutting with different tools, could generate a wide range of particle sizes [0.1–10.3 μm 

Mass Median Aerodynamic Diameter (MMAD), which equates to AMAD assuming uniform 

radionuclide distribution within the particles]. It should be noted that the data in Table 4 is based 

on empirical airborne particle size data from another research facility (Newton et al. 1987), 
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which was assumed to be applicable for this modeling. By including a wide range of particle 

sizes in Table 4, Donahue (1991) appears to accept that some types of machining may have led 

to possible sub-micron particle size exposures, depending on the specific materials and methods 

involved. For example, torch cutting and welding can produce very small particle aerosols in 

more insoluble forms, due to oxidation enhancement by the heat. When creating aerosols of 

unusually small particle sizes far into the sub-micron (<1 μm) range, deposition in the alveolar or 

pulmonary region of the lung increases by factors even greater than 2 (ICRP 1994a). Increases 

in lung doses for insoluble particles produced by extremely hot processes can be expected. 

In addition to the Newton et al. (1987) study referenced by Donahue (1991), several studies in 

international literature have shown the airborne radionuclide particle size distributions at those 

accelerator locations characterized are different than the default AMAD assumption of 5 μm, 

which is typically used in absence of site-specific particle size data (Yokoyama et al. 2007, 

Endo et al. 2001, Kondo et al. 1984, Muramatsu et al. 1988, Oki et al. 1994, Oki et al. 1999). 

The TBD discusses doses from induced radionuclides. However, consideration of other studies 

indicates that NIOSH’s estimates may be significantly low. For example, Be-7, S-38 and Na-24 

aerosols were determined to have very small particle sizes, with mean radii of approximately 

0.03 μm (Kondo et al. 1984, Muramatsu et al. 1988), which could increase lung dose from these 

airborne contaminants found in accelerator tunnels. 

Another issue that complicates accurate modeling of airborne contamination releases from heat 

cutting of activated metals is the fuming rate of radionuclides. This issue has also been studied 

closely (Oki et al. 1994). In this study, it is apparent that different radionuclides fume (i.e., 

vaporize and condense to form airborne particulates) at different rates from the metals. The 

different rates are apparently related to the thermal properties of the radioactive and matrix 

elements. The composition of the fumes to which the worker is exposed may not be directly 

proportional to that of the solid material being handled. Therefore, it appears improper to 

assume that the radionuclides come out of the heated material at uniform rates in mass and 

activity ratios that are the same as the material’s induced activity concentration (Bq/gram) ratios. 

In regard to the relative exposure risk from internal versus external radiation, NIOSH should 

consider published studies on airborne radionuclide hazards that SC&A has cited here from 

Japanese high energy accelerators. These studies indicate that the ratio of internal dose to 

external dose will increase significantly depending on the length of time that elapses between the 

material’s exposure to inducing reactions and the work activities that generate airborne particles 

(welding, sawing, etc.). Researchers have pointed out that in some situations, for materials that 

have been allowed to sit unexposed to inducing reactions for periods of time, the external 

radiation can diminish significantly due to the decay of shorter-lived gamma-emitting 

radionuclides. The two longest-lived radionuclides induced, Fe-55 and Ni-63, stay at significant 

levels, but they are not detected proportionally by external dose rate measurements, because they 

do not emit easily detected penetrating radiations (Oki et al. 1992, Numajiri 1994). Given 

sufficient time post-irradiation, Fe-55 and Ni-63 could become the dominant radionuclides, 

increasing the relative significance of these nuclides in the internal exposure and dose potential 

from machining activities. Assumptions about the relative significance of internal and external 

dose from activated metals may not be applicable to all relevant situations. 
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Carbon-11, which is typically assumed to be only an external dosimetry issue, was studied 

thoroughly for possible internal dose consequence and in some tunnel work exposure scenarios. 

It was found to have an internal dose contribution up to 29% of the total dose from C-11 (Endo 

et al. 2001). Thus, if this scenario occurs, almost one-third of the total dose from the C-11 

exposure may not be accounted for by doing external dosimetry alone. Researchers have also 

gone further with characterizing the airborne radionuclide hazards of induced radioactivity of air 

(Cl-38, Cl-39, S-38, and Br-82), which may affect internal dose estimates from tunnel work 

(Yokoyama et al. 2007, Kanda and Yoshioka 2007). 

Regarding the full spectrum of possible inhaled radionuclides at accelerators, the assumption that 

internal dose potential is negligible has not been demonstrated in the context of the compensation 

program. Additional quantitative analysis is warranted. 

Air Sampling and Contamination Control 

The DOE Tiger Team came to SLAC in the early 1990s. Among its observations, the Tiger 

Team identified weaknesses in radiation safety training for staff, documentation of surveys, and 

radiological records. As a result of this evaluation, major improvements to the radiation 

protection program were initiated. Rigorous procedures and policies based on Navy procedures 

were implemented. The documentation became more frequent, structured and formalized. 

Improvements in the radiological surveillances included a strong emphasis on continuous job 

coverage during radiological work. SLAC procured more sensitive instrumentation and 

implemented self-frisking practices. 

The DOE Tiger Team inspections identified weaknesses in the air sampling program to the point 

that the program was not sufficient to demonstrate compliance with DOE Order 5480.11. The 

report raises the following concern (DOE 1991): 

The SLAC 5480.11 implementation plan indicates air monitoring requirements do 

not apply to SLAC. Two samples, taken in 1972, augmented by a tutorial paper 

serve as a basis for obviating the need for air sampling during cutting operations 

at the open storage area. This information does not support the conclusion that 

air monitoring is unnecessary during cutting and welding operations. 

While the air sampling and contamination control programs are active now, the statement above 

implies that workplace air sampling was not consistently performed throughout the operation of 

the site. If air sampling was not consistently performed during earlier periods, greater emphasis 

is placed on effectiveness of any engineering (ventilation) controls, and proper performance of 

surface and personal contamination monitoring by workers and radiological control staff. Lack 

of air sampling data complicates the bounding of past potential exposures in the absence of 

routine bioassay. The TBD presents data for historical airborne and contamination levels from 

work areas to justify the position that intakes did not occur at SLAC. These data are limited 

primarily, although not exclusively, to the 1990s and 2000s. 

It is likely that the relative hazard at SLAC has changed over time. The site has undergone 

major improvements in beam control and maintenance, mostly performed from the mid-1970s 
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through the 1980s. Site experts indicated the contamination detected at SLAC came about from 

past high-energy operations of the LINAC, the Beam Switch Yard (BSY), and the end stations 

starting in the 1960s and ending in the mid-1970s. As the energy and average power of the 

accelerator has dropped, reductions in external dose and contamination levels have resulted, 

lowering the internal exposure potential over time. The TBD should demonstrate that airborne 

radioactivity and contamination level data are representative of all periods of operations, 

particularly when accelerator power was at its maximum. 

Organ Dose 

According to Tesch (1991), Donahue (1991) lacks a detailed discussion of the lung DE and 

focuses only on the effective dose in assessing the relative contribution of internal dose. The 

potential committed dose to an individual organ/tissue concentrating the radionuclide (and to 

nearby organs for penetrating radiations) can be many times higher than the resulting effective 

dose. Section 5.0 of the TBD acknowledges this (ORAUT 2007a, pg. 26): 

For the principal isotopes generated at SLAC, (H-3, Na-24, Sc-46, Mn-54, Fe-55, 

and Co-60) the highest organ dose is 1 to 10 times the effective dose equivalent 

and most of it is delivered in the first year after the intake. 

The TBD does not provide sufficient information for SC&A to evaluate this statement. The 

source of this statement is not identified in the TBD, and the relative organ dose from the 

radionuclides is not specified as a point of comparison to external dose. The statement above 

emphasizes that organ doses received from potential intakes can exceed effective dose 

determined in cited dose estimates. Dose reconstructors are concerned with organ doses, which 

contribute to POC calculations used in determining compensation. Organ dose must be kept in 

mind when reviewing determinations of the significance of possible internal doses, whether 

estimated from modeling or any other methods of assessment. Contribution of internal dose 

relative to external dose, as presented in the Donahue (1989, 1991) studies, is irrelevant for dose 

reconstruction and compensation decisions. In order to exclude the dose contribution from 

internal dose, the TBD must demonstrate that internal dose to all organs is negligible. 

Lack of Internal Dose Measurements in Claimant Files 

The lack of internal dose measurements in claimant files is not sufficient justification for 

neglecting internal dose, unless there is reasonable confidence that the files provided by the site 

are complete. Potential sources of internal monitoring data include dosimetry files, medical files, 

incident reports, and other relevant sources in the historical archive. The SC&A onsite review 

yielded a series of in-vivo counts unknown to personnel supplying information for claimant files. 

An additional report on a W-181 personnel contamination incident was identified in a medical 

file (SLAC 1969). 

Given the episodic nature of potential internal exposures, knowledge of radiological incidents 

becomes imperative. Radiological Control (RadCon) staff interviewed by SC&A indicated there 

is no incident database. According to some RadCon staff, occurrences such as personal 
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contamination events are documented on survey forms and include laboratory analysis to identify 

the radionuclide. These records are not likely captured in the dosimetry file. 

It would be prudent for NIOSH to confirm the completeness of internal monitoring data provided 

for claimants before assuming that the absence of data substantiates the absence of internal dose 

potential. 

Summary 

The site profile does not provide sufficient justification for neglecting internal dose for routine 

invasive operations, such as machining of activated components, and from existing area 

contamination. Theoretical models used to demonstrate minimal potential for internal dose 

contained questionable assumptions. Donahue (1989) presents a theoretical calculation of 

internal dose in comparison with external dose. Tesch (1991) challenges Donahue’s conclusion 

that internal dose can be neglected on the basis of assumed ventilation rate, absence of a detailed 

discussion of lung DE and organ dose consideration, and assumed radionuclide distribution. Oki 

et al. (1994) also concludes that different radionuclides fume at different rates from the metals, 

due to the thermal properties of the radioactive and matrix elements. Publications from other 

accelerators conclude internal doses can be a significant fraction of external dose when using 

organ dose. 

While air sampling and contamination surveys are discussed in the TBD, the data are limited and 

detailed analyses are not presented. Insufficient data prevent SC&A from fully evaluating 

NIOSH’s conclusions. The TBD makes use of mostly contemporary data, which may not be 

reflective of periods of maximum accelerator power. The TBD should quantitatively 

demonstrate these data are bounding for all accelerator power levels, locations, and periods of 

operation. A thorough analysis would consider changes in engineering and administrative 

controls, use of personal protective equipment, radiological surveillance policies, and instrument 

capabilities. 

Contribution of internal dose should be considered in the context of the compensation program, 

rather than an operational health physics program (i.e., allowing no monitoring at 100 mrem per 

year CEDE), with the TBD quantitatively demonstrating that organ dose is negligible. 

Furthermore, there is an indication that the absence of internal monitoring records in claimant 

files is partially an artifact of the availability of these data to SLAC staff. Additional 

investigation of data completeness is needed before a lack of monitoring records can be 

interpreted as a lack of internal exposure potential. 

Finding 5: Incomplete Claimant Medical Records for Historical Workers 

Section 3.0 of the TBD summarizes the methodology used to assign dose from medical x-rays 

required as a condition of employment. The TBD states (ORAUT 2007a, pg. 20): 

Medical examinations for most DOE contractors usually involved chest X-rays. 

Such routine X-rays contribute dose that is included in the Interactive 

RadioEpidemiological Program (IREP) POC calculations. The SLAC medical 
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department reports that it never gave such routine X-rays. Current medical 

documents do not identify chest X-rays as part of the examination process 

(Gherman 2006). 

The TBD indicates 20 out of 27 individuals submitting claims contained no medical information. 

Based on the lack of medical x-rays in the files and statements provided by the SLAC medical 

department, the TBD concludes the following (ORAUT 2007a, pg. 20): 

Based on this information, this analysis concludes that SLAC gave no X-ray 

examinations that EEOICPA dose calculations need to include. 

While the TBD acknowledges x-rays were given to beryllium workers at SLAC, it does not 

consider assignment of dose for beryllium-related x-rays. This is in contrast to other site 

profiles, such as Rocky Flats (ORAUT 2007b), where annual x-rays provided to beryllium 

workers are acknowledged and included in EEOICPA dose calculations. Although a 

recommendation for semi-annual x-rays for beryllium workers was apparently not implemented 

at Brookhaven National Laboratory (BNL), the site profile gives no indication that x-rays 

provided to a claimant for this purpose would be excluded from dose calculations. Rather, the 

BNL site profile states, “Dose reconstructors should assign dose according to the number of 

photofluorograhy and 14-in × 17-in posterior-anterior chest x-rays in the claim file records if 

they are provided” (ORAUT 2010, pg. 48). A review of the reference cited by NIOSH (Pindar 

1965) indicates that chest x-rays were provided as early as 1964–1965 for “beryllium work.” 

Because x-rays for “beryllium work” were provided under a different contract than the routine 

“radiation medical exams” described in Pindar (1965), SC&A is unable to determine the 

frequency or technique factors of x-rays provided to beryllium workers at SLAC. 

Interviews and reviews of medical records during SC&A’s site visit revealed two important 

issues. First, medical records are stored onsite for active employees only. Remaining medical 

records are maintained at the nearby Federal Records Center (FRC). According to records staff, 

if the Medical Department is unable to provide an accession number to pull records from the 

FRC, claimants’ medical records are not obtained and provided to NIOSH or the Department of 

Labor. The Medical Department has accession numbers available to retrieve records only for 

employees whose employment ended after 1990. While there is an electronic list of recent 

records sent to the FRC, historical records require a hand search of disposition schedules to 

obtain accession numbers. For those claimants terminating prior to 1990, medical staff currently 

does not have accession numbers and is not able to retrieve medical records. As a result, 

historical medical records are most likely incomplete. 

Medical staff interviewed by SC&A stated there was never an x-ray machine onsite at SLAC; 

x-rays were done offsite if indicated. A limited number of SLAC employees have been screened 

for beryllium sensitization; a screening chest x-ray was offered to these individuals and 

performed offsite if the employee consented to the x-ray. These x-rays were mostly performed at 

Alliance Occupational Health Center or Work Force Medical. As far as Medical can see, only 

one-time chest x-rays were performed on those who consented (with no follow-up screening). 
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As a part of the onsite review, SC&A identified and reviewed a set of historic medical records 

located at the FRC. While it appears that routine chest x-rays were not received by all 

employees, SC&A found a subset of employees was sent offsite for chest x-rays. Chest x-ray 

reports received from an offsite vendor indicated both posterior-anterior and lateral chest x-rays 

were performed. Most of the x-rays found in the historical medical records were associated with 

pre-employment assessments. These observations suggest the TBD is incorrect in assuming 

employment-related x-rays were limited to beryllium workers. In the limited sample of records 

reviewed, SC&A was unable to identify commonality among the workers who received x-rays as 

compared to those who did not. Further review of historical medical practices and records is 

recommended. 

SC&A also performed a review of 28 claimant files. SC&A noted one case in which the Energy 

Employee’s medical records listed two chest x-ray exams (1976 and 1980); NIOSH assigned 

annual x-ray examination doses in the dose reconstruction report for this claimant, which was an 

over-estimate dose reconstruction. This dose assignment contradicts the conclusion of TBD 

Section 3: “SLAC gave no x-ray examinations that EEOICPA dose calculations need to 

include.” If situations exist in which assignment of dose is warranted based on information in 

the claimant medical file, the TBD should provide sufficient guidance to assure consistency of 

practice among dose reconstructors. 

In summary, a more comprehensive onsite review of medical records should be conducted to 

ascertain whether medical records for all claimants are captured from the historical archives. 

The TBD should provide more detail regarding x-rays provided to beryllium workers, including 

a basis for assigning or not assigning occupational medical dose. Historical medical records 

and/or medical practices should be reviewed to determine other factors for which x-rays may 

have been indicated for occupational purposes. The TBD should also provide clear direction to 

dose reconstructors in regard to assignment of dose from x-rays based on information in the 

claimant medical file. Given that no medical records were provided to NIOSH for 20 of 27 

claimants, and significant obstacles to records retrieval have been communicated by site experts, 

it is not claimant favorable to assume no occupational medical dose without further evaluation. 

3.1.1 Finding 6: Incomplete Basis for Environmental External Dose from Neutron 

Skyshine 

SC&A did not have sufficient information to evaluate the annual neutron dose values reported in 

Table 4-6 of the TBD (ORAUT 2007a, pp. 25–26), particularly for years when the TBD 

indicates that environmental neutron monitoring data are not available or are not useful. The site 

profile does not provide adequate detail to support technical review of the calculated or 

extrapolated dose estimates. 

NIOSH assumes that the only measurable neutron dose to unmonitored workers was from 

neutrons resulting from skyshine. This is a reasonable assumption for an electron accelerator 

with controlled access, such as SLAC. NIOSH used the data from environmental Perimeter 

Monitoring Station (PMS) neutron detectors to estimate annual environmental neutron doses to 

personnel. These are Boron Trifluoride (BF3) detectors surrounded by a moderator with a 

cadmium cover and are calibrated to read out in mrem of neutron dose. 
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Some neutron PMS data are listed in the TBD [see Table 4-3 (1972–1979) and Table 4-4 (1980–

1989)]. NIOSH applied corrections to generate estimates of environmental neutron doses from 

the PMS measurements. Despite some confusion in the wording of Section 4.3.3 (“Two 

corrections” in the first sentence vs. “three corrections” in the last sentence), SC&A is fairly 

confident that NIOSH utilized the following corrections: 

 A CF of 1.51 +/- 0.53 compensates for the difference in neutron energy spectra used for 

calibration compared to skyshine neutrons. The derivation of this factor is discussed on 

page 59 of the TBD (Attachment A). 

 Equation 4-1 (TBD page 25) compensates for the different distances that the PMS 

detectors and buildings were located from the source of the skyshine neutrons. 

 A correction is made for annual work hours (occupational exposure time) as compared to 

the continuous exposure of the detector: 2,000 hrs/8,766 hrs = 0.228. 

NIOSH used the above data and CFs to generate a “Neutron skyshine annual dose” for each year 

at various buildings onsite. These values are listed in Table 4-6 of the TBD and are used by the 

dose reconstructor to assign neutron dose to unmonitored workers. SC&A did not have access to 

details such as the distances, measured doses, and calculations used by NIOSH to derive the net 

neutron dose from the “PMS detector accelerator neutrons” and “Neutron background” data 

provided in Tables 4-3 and 4-4. Without this information, SC&A could not replicate and/or 

verify the annual doses listed in Table 4-6. 

According to the text on pages 22–25 of the TBD (ORAUT 2007a), the only useful PMS 

environmental data available were for 1972–1979 (as shown in Table 4-3) and 1980–1989 (as 

shown in Table 4-4). However, Table 4-6 lists annual doses for every year from 1966–2005. 

According to the TBD, “Estimates for the early years were generated by extrapolation from the 

1972 values. Estimates for later years when TLDs were used were based on the latest years of 

monitor operation” (ORAUT 2007a, pg. 25). The values in Table 4-6 for 1966–1971 do not 

match those for 1972, and the values for 1990–2005 do not match those for 1989. Since the site 

profile states that data from these years are not available or are not useful for various reasons, it 

should demonstrate how the maximum dose values for these years were generated. If the data 

from some other years were used and/or dosimeter lower limits of detection (LLD) values were 

used, the approach should be described. Additionally, Table 4-6 should clarify if the “annual 

dose” values represent 8,766 hours per year or 2,000 hours per year exposure. 

SLAC’s semi-annual radiation reports to the Atomic Energy Commission (AEC) would be an 

appropriate source of data for validating the maximum dose values listed in Table 4-6. The PMS 

was set up and running at least as early as 1965. Each current PMS system includes a pair of 

BF3 detectors and Geiger-Mueller (GM) detectors to measure skyshine neutrons and photons, 

respectively. The neutron and gamma dose data were collected and recorded in the same manner 

as that from 1972–1979. These data were reported to the AEC in semi-annual radiation reports. 

Recovery and review of these data would serve to validate maximum dose values listed in 

Table 4-6. 
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3.1.2 Finding 7: Back Extrapolation of Occupational Environmental Photon Doses 

SC&A did not have sufficient information to evaluate the data and methodology used by NIOSH 

to estimate annual dose from ambient environmental photons. Applying relatively recent 

environmental photon dose data to the 1966–1994 time period does not appear to be technically 

sound, especially since the accelerator operated at its highest power in the early 1970s. When 

applying contemporary data to earlier periods, NIOSH should demonstrate technical equivalency 

or account for differences in operational parameters, monitoring locations, and monitoring 

results. 

According to Section 4.3 of the TBD, a program was in place from the start of accelerator 

operations using eight PMSs to measure ambient gamma and neutron fields near the site 

boundaries. The monitoring stations originally used GM counters for photon detection and BF3

detectors for neutrons. The TBD indicates that the gamma monitor readings were the same 

regardless of whether the accelerator was on or off, presumably throughout the period when GM 

counters were used. After 1990, the ambient photon radiation levels were measured with highsensitivity TLDs. Table 5 lists the environmental photon detection methods and data availability 

for the years of operation, as gleaned from TBD Section 4.3.2 and related data tables (ORAUT 

2007a, pp. 22–25). 

Table 5. Environmental Photon Monitoring and Data 

Time Period Detector Type Data Status 

1966–1970 GM Not found 

1971 GM Combined gamma and neutron data are not useful for dose reconstruction. 

1972–1979 GM Photon data are not reported in TBD – characterized as indistinguishable from 

natural background. 

1980–1990 GM PMS locations changed in 1980 (text, page 23) or 1983 (Figure 4-1 caption). 

Photon data are not reported in TBD. 

Several PMSs were out of service each year from 1983–1990 (Table 4-4). 

Apparently, all stations were out of service in 1988 (Table 4-4) and from 

1990 to the third quarter of 1991 (text, page 23). 

1991–1992 TLD TLD program was initiated near end of 3rd quarter 1991. 

All neutron & gamma results were <1 mrem both years. 

1993–2001 TLD Net annual TLD photon doses for 7 PMS stations are reported in TBD 

Table 4-5. 

2002 TLD Results were compromised by inadequate attention to storage times. 

2003–2004 TLD Results “were not reported.” TBD does not explain why. 

NIOSH used TLD measurements obtained from 1995–2001 at the PMS with the highest 7-year 

total dose to calculate an average environmental photon dose. This environmental dose is 

assigned only to unmonitored workers. The approach is described in the TBD (ORAUT 2007a): 

Page 23: 

The largest total dose for the 7 yr from 1995 to 2001 was 82.5 mrem at PMS6. 

This location is near LINAC Sector 20 (radiation from klystrons) far away from 

the site buildings. Dose reconstructors should assign a 3-mrem/yr photon dose 
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based on the exposure for 2,000 (40 hr/wk for 50 weeks) of 8,766 hours that the 

TLDs were exposed (82.5 ÷ 7 × 2,000 ÷ 8,766). 

Page 25: 

Assignment of an annual photon dose of 3 mrem as discussed above in Table 4.5 

[4-5] is recommended. This value should be assumed to encompass the critical 

uncertainty range. Dose reconstructors should not add these doses if the energy 

employee was monitored. 

SC&A has several concerns regarding the use of contemporary data for back extrapolation. The 

dose value of 3 mrem/year for environmental photons is based on data from 1995–2001, when 

the accelerator was not operating at the same power as it had in previous years. During SC&A’s 

site interviews, several current and retired staff members indicated that accelerator beam power 

has decreased consistently and significantly over the period from the early 1970s to the 1990s 

due to improvement in beam maintenance, engineering, and control. These changes have 

lowered the external radiation levels, particularly adjacent to the operating area, as a result of the 

direct correlation between accelerator power and ambient radiation levels. 

Other factors affecting technical equivalency are difficult to evaluate. The TBD does not 

provide PMS GM counter data and does not discuss detection levels or adjustment factors used 

to derive photon dose from GM counters. This makes it difficult to ascertain the equivalency of 

dose values obtained prior to and after the implementation of TLDs. The TBD mentions one 

change in PMS locations; it seems to imply that PMS locations were otherwise stable over time, 

but this is not directly stated. The document is not internally consistent regarding when the PMS 

locations were changed (1980 or 1983). While the TBD mentions the use of area monitors 

around the research yard, these results are not taken into consideration when bounding the 

photon dose potentially received by unmonitored workers. These readings may be more 

representative of dose received by onsite workers in some cases. 

It is not clear why the PMS results from 1993 and 1994 were excluded from the dose estimate 

calculation, but this decision has no significant impact on the dose estimate. Performing the 

calculation using all available photon dose data from Table 4-5 (1993–2001 instead of 1995–

2001) produced essentially the same results for average annual photon dose at the site boundary. 

In summary, the TBD fails to demonstrate that 3 mrem/year is an appropriate estimate of 

environmental photon dose for unmonitored workers at SLAC as a function of location and time. 

There is insufficient evidence to demonstrate technical equivalency in operational parameters, 

monitoring station location, and monitoring results over time. Changes in accelerator power and 

detection limits, in particular, bring into question the use of back extrapolation to assign ambient 

environmental photon doses. 
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3.1.3 Finding 8: Unsupported Assumptions for Calculation of Environmental Internal 

Dose from Onsite Releases to Air 

Section 4.2.1 of the TBD concludes that environmental internal doses from onsite releases to air 

are negligible, but the discussion and data provided in the TBD to support this assessment is 

limited. NIOSH obtained estimates of air activity releases from SLAC annual environmental 

reports; these estimates were calculated based on beam power, the air distance traversed, and 

access made to the beam areas (ORAUT 2007a, Page 21). 

The bases supporting the decision to exclude ambient internal dose from dose reconstruction are 

incomplete and inadequately supported. The quantitative discussion is limited to Cl-38 and 

Cl-39. The calculated dose is estimated from calculated chlorine emissions in 1993, which does 

not represent the period of maximum beam power at SLAC. 

Table 4-1 of the TBD shows a history of reported total activity released by year (primarily 

Ar-41). Table 4-1 is based on measured values, in contrast to Table 4-2, which is based on 

calculated values. Table 4-1 indicates the highest measured environmental releases occurred in 

1972 and 1975, and releases diminished significantly after 1975. This information is consistent 

with the time period of peak operating power levels at SLAC as described by site experts. The 

data confirm that emissions in the earlier years are much greater than in more recent years. 

According to site expert interviews, the current environmental monitoring utilizes confirmatory 

measurements with the Air Monitoring Systems (AMSs). Air is pumped from the vent in an 

accelerator housing into a pressurized and low-background tank where a GM detector is used to 

measure the short-lived airborne radionuclides produced inside the housing (Attachment 2). 

McCall and Jenkins (1966) identify N-13, O-15, H-3, C-11, Ar- 41, Be-7, Cl-38, and Cl-39 as 

radioactive air emissions, in decreasing order of saturation activity. A 2-hour waiting period 

allows for decay of short-lived radionuclides. Beryllium-7 and other radionuclides typically 

assumed to only be in a gaseous state have been found to exist in particulate forms in 

accelerators (Endo et al. 1995, Endo et al. 2001, Muramatsu et al. 1988). Radioactive effluents 

include H-3, C-11, N-13, and Ar-41. Assuming NIOSH is taking this position, the TBD should 

state no particulate emission occurred and discuss the rationale for this assumption, such as 

HEPA filtration of all applicable exhaust or other methods used to prevent release of particulates 

to the environment. Dose calculations within later environmental reports principally base the 

ambient internal dose calculations on N-13, O-15, C-11 and Ar-41. The only radionuclides 

NIOSH considers as contributors to occupational environmental internal dose are Cl-38 and 

Cl-39. The rationale for exclusively selecting Cl-38 and Cl-39 is unclear. Further quantitative 

justification demonstrating that other air emissions contribute negligible dose should be included 

in the site profile. 

 

Dose coefficients for radionuclides released to the environment and potentially giving 

environmental internal dose were based on an assumed 5 μm AMAD and Type M absorption 

class. Per the ICRP guidance (ICRP 1995, ICRP 1996), the default particle size for estimating 

environmental exposures is 1 μm AMAD. Although Energy Employees covered under the 

EEOICPA are occupational workers and not members of the public, the modeling for 

environmental scenarios is applicable for environmental dose, rather than normal occupational 
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exposure scenarios. In other words, the individuals are like members of the public who are 

closer to the release point, and the airborne contamination they may be exposed to likely has 

properties similar to public exposure scenarios. 

The calculated environment airborne release quantity in 1993 for chlorine (Cl-38 and Cl-39) is 

0.36 Ci. Using a dispersion factor of 4.5 × 10-4 s/m3, NIOSH calculated an airways dose of 

about 0.053 mrem/year for an individual located at the site boundary. Although the TBD 

recognizes that “site buildings are somewhat closer resulting in slightly larger doses,” it does not 

attempt to quantitatively adjust the boundary dose (i.e., member of the public) to a dose 

representative of workers within the site boundary. The TBD should attempt to estimate the 

actual dose to the highest exposure locations onsite, to determine the potential impact of distance 

ratios and short distance site-specific dispersion modeling (building wake effects, etc.). 

The total calculated chlorine release for 1993 is assumed for all years, but no rationale or defense 

is provided in the TBD. NIOSH may have selected 1993 as the year of highest estimated release 

activity to maximize estimates of particulate radionuclide dose contribution, but the TBD does 

not state this rationale or provide data to demonstrate it. The assumed release activity for 

chlorine appears to come from the addition of Cl-38 and Cl-39 from Table 4-2, “Airborne 

Release Quantities (Ci),” which are based on calculated values. Table 4-1, “Reported Total 

Activity (Ci) Released by Year, Primarily 41Ar,” indicates the highest measured environmental 

releases occurred in 1972 and 1975, which corresponds to the time period of peak operating 

power levels mentioned by site experts. The relative contributions of other airborne emissions 

would similarly increase with power levels. The TBD should demonstrate that the combined 

airborne release quantity of Cl-38 and Cl-39 would bound the total release quantities for years of 

peak power. 

In summary, NIOSH should quantitatively demonstrate that annual environmental internal doses 

total less than 1 mrem based on clearly defined and justified assumptions. The completeness of 

the source term, the particle size, and quantitative adjustments for onsite versus boundary dose 

should be taken into consideration. The TBD does not adequately validate the assumption that 

Cl-38 and Cl-39 emission data from 1993 are representative or bounding for all years of 

operation and periods of maximum accelerator power. 

Finding 9: Lack of Adequate and Accurate Dose Records Prior to 1974 

SC&A’s review of 28 claimant files indicates that most workers’ exposures to photon and 

neutron radiation were generally not excessive and were fairly low in magnitude compared to 

most DOE facilities. This would be expected for an electron accelerator. However, neutrons 

were a measurable part of the total external dose. From 1974 to present, workers’ dose records 

include badge cycle results that distinguish between photon deep dose and neutron dose. Prior to 

1974, claimant files contain annual summaries of external monitoring results that are not broken 

into dose components (i.e., photon and neutron). SC&A questions the validity of the 

assumptions used by NIOSH to estimate neutron and photon dose components. NIOSH has not 

validated that these assumptions are claimant favorable based upon available data. They failed 

to capture the methodology in the TBD. 
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From the 28 claimant files reviewed by SC&A, it appears that the DOE files provided to NIOSH 

for dose reconstruction purposes contain detailed dose data for 1974 to present. However, 

detailed dose data are rarely provided to NIOSH for employment periods from the beginning of 

SLAC operations through 1973. This observation appears to reflect a transition to an electronic 

database for dosimetry data in 1974. Claimant files for earlier employment periods typically 

include a letter from SLAC’s Environmental Safety and Health (ES&H) Division containing a 

statement similar to the following: 

Please note that the reported lifetime dose before 1974 (about [xxx] mrem) were 

obtained from the archived records of the personal dose reports. Dose records 

after 1974 are currently maintained electronically in our Occupational Dose 

Tracking System (ODTS) computer data base. 

In almost all cases reviewed, the DOE files do not include details of the dose or copies of 

original forms. It does not appear that pre-1974 badge cycle dosimetry data have been provided 

to NIOSH for any of the claims analyzed to date. In some cases, as in the following example, a 

summary table is provided in the claimant file: 

Table 6. Lifetime Dose Summary for [EE] 

(From archived paper records) 

Year CEDE [mrem] 

1966 45 

1967 0 

1968 0 

1969 84 

1970 0 

1971 660 

1972 33 

1973 0 

Total: 822 

Occasionally, a handwritten note (see Figure 4 below) is found in the margin of the DOE file 

listing the years and associated doses. 
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Figure 4. Handwritten Note of Early Doses 

SC&A reviewed some of the dose reconstruction reports for these claims and found that NIOSH 

divides the pre-1974 doses into half photon and half neutron exposures when assigning doses. 

NIOSH also assigns missed dose, based on the LLD of the dosimetry system, for each potential 

exchange cycle from the start of employment through 1973. No data validation is discussed in 

the TBD to support the practice of estimating half photon and half neutron dose for doses 

recorded prior to 1974. If the dose record is correct and complete, this approach may result in an 

overestimate of dose, most likely an extreme overestimate for non-radiation workers, such as 

administrative personnel. However, it could result in an underestimate of dose for radiation 

workers if the summarized data tables or notes are not based on verified dose records. 

Additionally, it is questionable if the present method used by NIOSH would be considered 

plausible and reasonably accurate. 

SC&A interviews with SLAC dosimetry personnel indicate that external dosimetry data from 

1961 through 1973 are available as printouts from Radiation Detection Company (RDC) by 

cycle. SC&A located copies of RDC dosimetry reports during the site visit and found that they 

include penetrating x-ray, gamma, and neutron dose. While many of these dosimetry reports are 

available on the SRDB, the results have not been linked to claimant files. There is no indication 

in the SLAC TBD that dose data received in summary tables or handwritten notes are verified 

against these original dosimetry reports. Since data for photon and neutron dose are available in 

dosimetry logs for exposures prior to 1974, these data could be used for dose reconstruction, 

eliminating the need for estimates and assumptions about the dose component fractions. At a 

minimum, the available RDC reports should be used to validate that NIOSH’s assumptions about 

dose components are claimant favorable; the methodology and validation should be documented 

in the TBD. 

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4.0 OVERALL ADEQUACY OF THE SITE PROFILE AS A BASIS FOR 

DOSE RECONSTRUCTION 

The SC&A procedures call for both a “vertical” assessment of a site profile, for evaluating 

specific issues of adequacy and completeness, and a “horizontal” assessment, considering how 

effectively the profile satisfies its intended purpose and scope. This section addresses the latter 

objective in a summary manner by assessing: 

(1) How, and to what extent, does the site profile satisfy the five objectives defined by the 

Advisory Board? 

(2) How usable is the site profile as a generalized technical resource for the dose 

reconstructor when individual dose records are unavailable? 

(3) Have generic technical or policy issues been identified that transcend any single site 

profile and need to be addressed by the Advisory Board and NIOSH? 

4.1 OBJECTIVE 1: COMPLETENESS OF DATA SOURCES 

The TBD discusses the site, activities occurring at the site, and the characteristics of radiation 

exposure. The primary focus is on accelerator operation, with some consideration given to 

invasive work with beamline/components. The TBD fails to discuss and consider potential 

exposure from special projects conducted at SLAC. 

Consideration of the radionuclides that may be found in sufficient quantities to impact internal 

dose potential is incomplete. The TBD may not be considering the full spectrum of induced 

radionuclides, including those discovered at other accelerators that should be used in modeling 

and estimating potential internal doses at SLAC. Further research should be conducted to 

characterize significant source terms and to evaluate the relative potential for internal exposure. 

The outcome of this analysis should be included in the TBD to inform the dose reconstructors. 

Radon and thoron (Rn-220) gases above typical building background levels may have caused 

internal doses that need to be accounted for when a claimant worked in the accelerator tunnel or 

other underground structures with low air ventilation (fresh air exchange) levels. No 

consideration is given to this potential source of internal dose in the SLAC site profile. 

According to a site expert, a radon study was completed in the tunnel at SLAC during the late 

1980s, using track etch detectors provided and analyzed by a vendor laboratory. NIOSH should 

obtain the record of results and evaluate the validity and applicability of the data for assignment 

of occupational internal dose. 

A review of internal monitoring data sources should be conducted to ascertain whether complete 

records for all claimants are captured from dosimetry files, medical files, and other relevant 

sources, including historical archives. The SC&A onsite review yielded a series of in-vivo 

counts unknown to personnel who retrieve information for claimant files. The TBD should also 

identify incidents and significant unexpected contamination events, such as the W-181 personnel 

contamination incident identified in a medical file (SLAC 1969). This analysis should consider 
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the field and personnel monitoring practices of the time, including documentation of incidents in 

field monitoring records, rather than personal dosimetry files. 

Although it was determined during interviews that SLAC has performed a significant amount of 

occupational radiological air sampling during higher exposure risk situations, these data were not 

shown or discussed adequately in the site profile. Further discussion of air concentrations 

detected in worker breathing zones and general work areas should be included in the site profile 

to validate the assumption there was no missed internal dose. 

SC&A interviews with SLAC dosimetry personnel indicate that external dosimetry data from 

1961 through 1973 are available as printouts from RDC by cycle; however, claimant files 

typically contain summary doses without copies of original RDC monitoring data. SC&A 

located a copy of all RDC dosimetry reports during the site visit. Furthermore, many of these 

logs are available on the SRDB; however, the data are not linked to individual claimant files. 

The RDC data provides sufficient detail to differentiate between photon and neutron dose, 

whereas summary data requires assumptions be made. 

A more comprehensive onsite review of medical records should be conducted to ascertain 

whether medical records for all claimants are captured from the historical archives. Indication 

from site expert interviews is that medical records are not pursued for individuals terminating 

prior to 1990. The TBD should include a provision for assigning dose from x-rays based on 

information in the claimant medical file, as opposed to assignment of no occupational medical 

dose (as mentioned in the TBD), or assignment of annual occupational medical dose (as 

observed in a dose reconstruction report). A review of the reference cited by NIOSH (Pindar 

1965) indicates that chest x-rays were provided as early as 1964–1965 for “beryllium work.” 

The contract number under which x-rays were provided for beryllium workers is noted in Pindar 

(1965). This contract may provide additional information regarding the frequency and/or 

technique factors of x-rays provided to beryllium workers at SLAC. It seems likely that 

contracts and invoices from offsite medical providers, similar to Pindar (1965), can be located 

for other time periods, shedding light on the uncharacterized subset of workers who received 

occupationally related x-rays at SLAC. 

Site boundary PMSs measure potential real-time external dose, which includes skyshine or direct 

radiation doses that the public may receive. These systems were set up and running at least as 

early as 1965. Each current PMS system includes a pair of BF3 detectors and GM detectors to 

measure skyshine neutrons and photons, respectively. The neutron and gamma dose data were 

collected and recorded in the same manner as that from 1972–1979. These data were reported to 

the AEC in semi-annual radiation reports. Recovery and review of these data would serve to 

validate maximum dose values listed in Table 4-6. Site experts have confirmed that 

environmental monitoring reports were prepared prior to 1971. 

The solicitation and consideration of input from site experts and other workers is important to 

ensuring the adequacy and completeness of the site profile and the subsequent dose 

reconstruction. NIOSH appears to have neglected or underutilized this invaluable resource. No 

worker outreach meetings were conducted during the development of the SLAC site profile. In 

addition, SC&A’s search of the SRDB did not produce any documentation of NIOSH site expert 
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interviews for SLAC. An e-mail correspondence with site radiological control staff is the only 

source of worker input identified in the SRDB. Information obtained during SC&A site expert 

interviews indicates that NIOSH may have conducted limited site expert interviews with 

radiological control personnel at SLAC, but documentation of these interviews is not available 

on the SRDB. SC&A interviews also indicate that radiological control personnel were afforded 

the opportunity to review the site profile, but no documentation was found to support this 

information. Because worker outreach meetings and site expert interviews provide valuable 

opportunities for NIOSH to obtain information and insights into site operations and safety 

programs, this omission represents a weakness in the completeness of data sources. 

4.2 OBJECTIVE 2: TECHNICAL ACCURACY 

Table 2-5 of the TBD (ORAUT 2007a, pg. 15) shows that the contact dose can be orders of 

magnitude greater than the dose at 30 cm for most components tested. Therefore, the dose to 

extremities, lower sections of the body, and areas of the head (if leaning over components) could 

be significantly greater than the recorded dose from a monitor worn on the chest area. This issue 

is also applicable to the calibration facilities. However, the TBD does not discuss dosimetry 

geometry factors, and there is no indication that extremity monitoring was needed or performed 

at SLAC. 

Additionally, before approximately 1996, there does not appear to have been significant 

monitoring and/or calibration for beta or low-energy gamma exposures (see Table 6-2, pg. 31, 

for a summary of recorded dose practices). As indicated in the TBD, there was no apparent 

calibration of dosimetry for low-energy photon exposures before DOELAP accreditation in the 

mid-1990s (ORAUT 2007a, pg. 30). This is an area that needs further investigation and should 

be addressed in the TBD for SLAC. 

Despite a large volume of information and analysis presented in the TBD on the topic of neutron 

dosimetry, the CFs that are actually used to adjust recorded neutron dose are not adequately 

supported. Several components of the recommended CFs are based on simple averages of upper 

and lower values that may not represent the radiation fields to which workers were exposed. The 

1997 neutron spectral measurements are based on limited parameters, and the TBD fails to 

demonstrate that these measurements are representative of the moderated neutron fields at 

various locations and time periods at SLAC, especially as beam power changed over time. Dose 

fraction values in Table 6-5 could not be verified without additional information on NIOSH’s use 

of NCRP 38 (NCRP 1971). Similarly, the reference to ICRU Report 63 (1999, Figure 7.19) was 

not sufficiently detailed to support an assumption that 30%–40% of the DE from high-energy 

neutrons were not detected by NTA film or CR-39 TLDs. Several other assumptions and CFs 

appear in the TBD without sufficient explanations or supporting data. Without sufficient support 

for NIOSH’s “Total Impact” CFs, SC&A cannot conclude that neutron dose reconstruction 

adequately reflects or bounds the doses received by workers. 

Section 4.2.1 of the TBD concludes that environmental internal doses from onsite releases to air 

are negligible, but the discussion and data provided in the TBD to support this assessment are 

limited. The TBD states that the only radionuclides contributing to occupational environmental 

internal dose are Cl-38 and Cl-39. It assumes that calculated estimates of chlorine releases from 
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1993 are representative of bounding doses for all years of operation at SLAC. This assumption 

is questionable, because both prompt and residual radiation fields have declined significantly 

from periods of maximum power in the early 1970s. The estimate of dose to workers also uses 

an inappropriate particle size, assuming 5 μm AMAD for worker exposure rather than 1 μm used 

in the calculation of environmental exposures. The TBD acknowledges that site buildings are 

closer to the releases than the site boundary, but it does not attempt to estimate the actual dose to 

the highest exposure locations onsite. The assumptions used in the calculation of onsite internal 

dose from airborne releases should be further validated. The completeness of the source term, 

the particle size, and lack of quantitative adjustment for onsite versus boundary dose should be 

addressed. 

According to the text on pages 22–25 of the TBD, the only useful PMS environmental data 

available were for 1972–1979 (as shown in Table 4-3) and 1980–1989 (as shown in Table 4-4). 

Data were not available for 1966–1971; data from 1991–2005 were monitored with TLDs, which 

precluded differentiation between accelerator-produced radiation and background. However, 

Table 4-6 lists data for every year from 1966–2005. The TBD on page 25 states, “Estimates for 

the early years were generated by extrapolation from the 1972 values. Estimates for the later 

years when TLDs were used were based on the latest years of monitor operation.” The TBD 

should demonstrate how the maximum dose values were calculated for years when useful 

environmental data were not available. Additionally, it is not stated if the values in Table 4-6 

assume 8,766 hours per year or 2,000 hours per year exposure. 

4.3 OBJECTIVE 3: ADEQUACY OF DATA 

During the site interviews, several current and retired staff reported accelerator beam power has 

decreased consistently since the peak period in early 1970s, due to improvement in beam 

maintenance and modifications. As a result, external radiation levels have decreased. Applying 

relatively recent (1995–2001) environmental photon dose data to the 1966–1994 time period, 

especially when the accelerator was operating at peak power in the early 1970s, is not a 

technically sound method to use for dose reconstruction. 

SC&A questions the basis and appropriateness of data supporting the decision to neglect internal 

dose in the absence of internal monitoring data. The basis for assignment of no internal dose 

includes the absence of internal monitoring data in claimant files, the ratio of the internal dose to 

the external dose, the analysis of contamination survey and air monitoring data, dose estimates 

based on exposure to activated water, and on exposure caused by torching of activated materials. 

Donahue (1991), Busick and Warren (1969), and the SLAC internal dosimetry TBD (Kase et al. 

1993; Tran 2005) are cited in support of NIOSH’s conclusion that no internal dose should be 

assigned. Tesch (1991) challenges Donahue’s (Donahue 1989) conclusion that internal dose can 

be neglected when compared with external dose on the basis of radionuclide dose rate produced, 

ventilation rate assumed, and absence of organ dose consideration. Publications from other 

accelerator facilities conclude that internal doses can be at significant fractions of the external 

doses to the worker, especially when looking at the organ dose (e.g., lungs). 

Studies reviewed by SC&A provide valuable information on particle size during typical 

maintenance activities at accelerator facilities. Several studies have shown the airborne 
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radionuclide particle size distributions at those accelerator locations characterized are different 

than the default AMAD assumption of 5 μm typically used in the absence of site-specific particle 

size data (Yokoyama et al. 2007, Endo et al. 2001, Kondo et al. 1984, Muramatsu et al. 1988, 

Oki et al. 1994, Oki et al. 1999). Table 4 of Donahue (1991) shows that particle sizes could have 

a wide range (0.1–10.3 μm MMAD, which equates to AMAD assuming uniform radionuclide 

distribution within the particles) in performing various maintenance work on metal components 

such as pipe cutting, and sawing and torch cutting with different tools. It should be noted that 

the data in Table 4 are based on empirical airborne particle size data from another research 

facility (Newton et al. 1987), which was assumed to be applicable for this modeling. 

A quantitative analysis demonstrating insignificant internal organ dose should be included in 

subsequent revisions of the TBD. NIOSH should review particle size studies from other 

accelerator sites to determine the appropriateness of using the default 5 μm AMAD particle size 

for internal dose calculations and for calculations justifying the decision that internal dose does 

not need to be considered. Furthermore, a validation should be completed to demonstrate that 

the mostly contemporary air sampling data used to justify the assignment of no internal dose are 

bounding. This validation should consider changes in accelerator power levels, and thus 

potential internal exposure, through time. 

The dose reconstruction method of assigning half photon and half neutron dose for doses 

recorded prior to 1974, and assigning missed photon and neutron doses for each badge exchange 

cycle prior to 1974, results in an overestimate in some cases; most likely an extreme overestimate for non-radiation workers, such as administration personnel, if the dose of record is 

correct. However, it could result in an underestimate of dose for radiation workers if the data 

provided in the summary statement (or tables or notes) are not based on verified dose records. 

Additionally, it is questionable if the present method used by NIOSH would be considered 

plausible and reasonably accurate. While dosimetry logs including penetrating x and gamma and 

neutron dose are available, no data validation supporting assigning half photon and half neutron 

dose for records doses prior to 1974 was presented in the TBD. 

4.4 OBJECTIVE 4: CONSISTENCY AMONG SITE PROFILES AND OTHER 

NIOSH DOCUMENTS 

SC&A has conducted reviews of methodologies applied for accelerator facilities at Argonne 

National Laboratory-East (ANL-E), Brookhaven National Laboratory (BNL), Lawrence 

Berkeley National Laboratory (LBNL), and Los Alamos National Laboratory (LANL), which are 

similar to that at SLAC. Site profiles from SLAC, ANL-E, BNL, LBNL, and LANL focus much 

of the analysis on occupational and environmental external dose. SLAC is unique from other 

DOE facilities reviewed to date in that its mission was focused exclusively on high-energy 

physics research, with no mission to produce radioactive material. The SLAC site profile speaks 

directly to dose associated with high-energy accelerator operations, as opposed to potential dose 

from target material. The activation products listed in the SLAC site profile are similar to those 

listed in other site profiles; however, consideration of these radionuclides in contribution to 

occupational and environmental internal dose is not always consistent. One possible reason for 

this is the availability of in-vivo and in-vitro bioassay at ANL-E, BNL, LBNL and LANL for a 

limited number of these radionuclides. 
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The SLAC site profile gives no consideration to the assignment of internal dose from enhanced 

radon and thoron in the accelerator tunnel. The lack of consideration of dose from enhanced 

radon and thoron levels is inconsistent with other site profiles where underground concrete 

structures exist. An underground accelerator tunnel is assumed to have higher levels of radon 

and thoron concentrations than exist in conventional structures. If radon and thoron enter the 

tunnel air via soil gas penetration, and if fresh air exchange is not adequate, there may be 

potential for elevated concentrations higher than typical buildings onsite that are above ground. 

This general assumption is supported by a study conducted by Oki et al. (1999), which showed 

radon concentrations measured in accelerator tunnel air were several times higher than in a 

nearby building basement (280 Bq/m3 versus 50 Bq/m3 for Rn-222). Discussions during 

SC&A’s site expert interviews seem to indicate that the level of fresh air ventilation in 

accelerator tunnels at SLAC varies and can be low at times. According to a site expert, a radon 

study was completed in the tunnel during the late 1980s, using track etch detectors provided and 

analyzed by a vendor laboratory. The TBD does not discuss any radon/thoron monitoring 

information for the site, nor does it consider internal dose from exposure to enhanced radon and 

thoron levels in the tunnel. 

One noted discrepancy between site profiles for facilities with accelerators is the selection of 

photon radiation energy and percentages for use in dose reconstruction. In the case of ANL-E 

and LBNL, all types of accelerators are grouped into a single category with an assumed photon 

distribution of 90% >250 keV photons and 10% 30–250 keV photons. These photon 

distributions are assigned for the high-energy physics area at SLAC, with different assumptions 

applied to the SSRL. The SLAC site profile recommends the dose reconstruction assume 100% 

30–250 keV photons for the SSRL, which is identical to that recommended for the National 

Synchrotron Light Source at BNL. The optimal method for presenting beta, photon, and neutron 

energies and percentages is by using available characterization data. In the absence of this, the 

method applied in the SLAC site profile, distinguishing between different accelerators and 

supporting facilities, is preferable to grouping all accelerator types. 

Some confusion exists in regard to assignment of Occupational Medical Dose. Section 3.0 of the 

site profile concludes that SLAC gave no x-ray examinations that EEOICPA dose calculations 

need to include (ORAUT 2007a, pg. 20). However, SC&A notes that some employees have 

been sent offsite for x-rays, including, but not necessarily limited to, pre-employment assessment 

and beryllium sensitivity screening. While the TBD acknowledges x-rays were given to 

beryllium workers at SLAC, it does not consider assignment of dose for beryllium and preemployment x-rays. This is in contrast to other site profiles, such as Rocky Flats (ORAUT 

2007b), where annual x-rays provided to beryllium and other workers are acknowledged and 

included in EEOICPA dose calculations. 

SC&A also notes one case in which a claimant was assigned annual dose for x-rays associated 

with employment at SLAC, which appears to contradict instruction provided in the site profile. 

The dose reconstructor is directed to assign dose according to the number of x-rays reported in 

the claimant files in the absence of default occupational medical dose assumptions. 
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4.5 OBJECTIVE 5: REGULATORY COMPLIANCE AND QUALITY ASSURANCE 

SC&A reviewed the site profile with respect to Objective 5, which requires SC&A to evaluate 

the degree to which the site profile complies with stated policy and directives contained in 

42 CFR 82. In addition, SC&A evaluated the site profile for adherence to general quality 

assurance policies and procedures utilized for the performance of dose reconstructions. 

The SLAC site profile was developed and revised in the absence of the worker outreach efforts. 

Conduct of the Worker Outreach Program, ORAUT-PROC-0097 (ORAUT 2005b), which was 

in place at the time of the site profile development, specified worker outreach activities be 

performed during the development of site profiles. No technical issues were found in this regard 

that required attention, but SC&A has previously raised concerns regarding compliance with the 

requirements of ORAUT-PROC-0097. The solicitation and consideration of input from site 

experts and other workers is important to ensuring the adequacy and completeness of the site 

profile and the subsequent dose reconstruction. 

Since ORAUT-PROC-0097 has been replaced by OCAS-PROC-012, Worker Outreach Program

(OCAS 2009), there is no longer a procedural requirement for NIOSH to conduct worker 

outreach in conjunction with site profile development. However, the objectives of worker 

outreach remain (OCAS 2009, pg. 2): 

This program provides current and former Department of Energy (DOE) and 

Atomic Weapons Employer (AWE) employees with the opportunity to obtain 

information about the Special Exposure Cohort (SEC) program and site profiles 

and to provide information for consideration and possible use in dose 

reconstructions, site profiles, and SEC petition evaluations. 

During SC&A interviews, it was evident that individuals at SLAC were not familiar with the 

EEOICPA program. By failing to conduct worker outreach meetings, NIOSH denied current and 

former workers the opportunity to receive information about EEOICPA, and to provide input to 

the site profile and the dose reconstruction process. SLAC workers also had minimal 

opportunity to contribute to site profile development through site expert interviews. Additional 

interviews and/or worker outreach activities, in accordance with OCAS-PR-012, Worker 

Outreach Program (OCAS 2009), should be considered in subsequent revisions of the site 

profile. Worker outreach efforts would benefit the site profile and may also improve awareness 

of EEOICPA at this facility. 

4.6 INCONSISTENCIES AND EDITORIAL ERRORS IN THE SITE PROFILE 

Inconsistencies and editorial errors were identified in the site profile and are detailed below. 

 Pages 7 and 12: The acronym, SSRL, is defined as Stanford Synchrotron Radiation 

Laboratory. Site experts and the SLAC website indicate the last term in this facility’s 

acronym is “Lightsource” rather than “Laboratory.” 
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 Pages 15 and 16, Table 2-5: The headings of the third and fourth columns should contain 

the units of mrem/hr, not Mrem/hr (a factor of 109 difference). 

 Page 16, Section 2.3.5: The meaning of the next to the last full sentence on this page is 

not clear; it states, “At 50 to 200 MeV, the high-energy neutrons are generated by the 

photopion process.” However, according to the contents of this section and Patterson and 

Thomas (1973), it would be more appropriate to state, “High-energy neutrons, in the 

range of 50 to 200 MeV, are generated by the photopion process.” The current text does 

not state if it is the photons or the resulting neutrons that are in the 50–200 MeV energy 

range. 

 Page 17, Section 2.3.5: The terms FFTB and FFTB2 appear multiple times (Sections 2, 

6, 7, and Attachment A). They are not defined. 

 Page 22, Section 4.3.2: The second sentence, since it follows a description of the earliest 

monitoring systems, seems to imply that the GM and BF3 detector results from “when 

SLAC began operating” are provided in the report. This does not appear to be the case: 

Table 4-3 (page 23) contains neutron data from 1972 to 1979; Table 4-4 (page 24) 

contains neutron data from 1980 to 1989; and Table 4-5 (page 25) contains photon data 

from 1993 to 2001. Perhaps the second sentence would make more sense following the 

introduction of the first data table (Table 4-3) in the second paragraph of this section. 

 Pages 24 and 25, Section 4.3.3: The first sentence of the section states, “Two corrections 

must be made for the environmental neutron dose,” referring to corrections for energy 

dependence of the dosimeter and distance dependence of the skyshine field. The final 

sentence of the section begins, “Combining all three corrections...” The additional 

correction appears to be a factor accounting for 8,766 hours of exposure for the PMS 

versus 2,000 hours of exposure for a worker. The discrepancy is confusing to the reader, 

who is left to search and/or guess which corrections are being referenced. 

 Page 25, Table 4-5: Since NIOSH selected the PMS location with the highest 7-year total 

dose as a basis for assigning environmental photon dose, a row of “7-yr Total” results 

would simplify comparison and harmonize the table with the relevant text at the bottom 

of page 23. 

 Some tables and figures in Section 4.3.2 seem to be misplaced in relation to the text. 

Figure 4-1 would be more accessible on page 23, following the description of PMS 

locations. Tables 4-4 and 4-5 would be more accessible immediately after the paragraphs 

that describe the data (both are currently located on page 23). Table 4-5 seems 

particularly out of place, since it contains photon data and is located in a section 

discussing “Corrections on Environmental External Neutron Dose.” 

 Page 25, Section 4.4, third from last sentence: This sentence describes the last paragraph 

on page 23 as being located “above Table 4.5 [4-5].” It would be appropriate for this 

sentence to precede Table 4-5, but the table is currently located on page 25 in a different 

section of the site profile, as indicated in the previous observation. 
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 Page 27, next to last paragraph: It is not obvious what this statement is intended to mean. 

Perhaps rewording it would help. Additionally, is the design dose limit initially 

500 mrem per person over the entire life of the accelerator, or 500 mrem/year per person? 

The SLAC design dose limit was initially 500 mrem based on an 

extrapolation . . . of regulatory dose limits over time to when SLAC would 

be operating. 

 Pages 34 and 35, Tables 6-5 and 6-7: The term “(%)” in Column 6 in both tables should 

be deleted; most values are not presented as percentages. In Column 6 of Table 6-7, the 

number 20 should be changed to 0.20 and the number 80 should be changed to 0.80. 

 Page 54, third paragraph: Last sentence should read Section 2.3.5, not Section 2.3.4. 

 Concerning the calibration CF of 1.51, SC&A found that the wording on pages 37 and 59 

of the TBD appear to contradict each other. Page 37 states (ORAUT 2007a): 

[13] Rohrig, Norman D. ORAU Team. Health Physicist. April, 2006. 

The correction is based on the ratio of the counts per nanorem for the PuF 

calibration spectrum and the SSRL LINAC spectrum for the PMS. 

Because the PMS will have a smaller response to the FFTB2 spectrum, 

using it would result in a larger dose by the factor 0.385/0.135. 

[Emphasis added.] 

However, on page 59 it is stated (ORAUT 2007a): 

The correction is then 0.582 ÷ 0.385 = 1.51 with an uncertainty of 35% at 

1 sigma based on the ratio 5.5/4.1 from the measured to calculated ratios 

for moderated TLDs for the CERN iron and concrete spectra. If the 

FFTB2 was appropriate, the doses received would be smaller by about a 

factor of 3 (0.385/0.135) [13]. [Emphasis added.]

From the rest of the TBD and Table A-1, SC&A assumes that the statement on page 37 is 

correct. However, this should be verified and the wording corrected. 

The following are recommendations from SLAC staff during the site expert interviews. 
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NOTICE:

Table 7. Recommended Updates to Table 2-1, Pages 11–12 of the Site Profile. 

Area Period of Operation Comment 

LINAC Tunnel 1966–present Since April 2008, only the last one-third of the tunnel has 

been used. 

Klystron Gallery 1966–present 

End Station B 1966–1985 +/- 2 years Since the B-Line was last used in the early 1980s, End 

Station B has housed the NLCTA. 

End Station C 1966–present The LCLS tunnel now passes through the area which was 

known as End Station C years ago. 

BSY 1966–present Up until the 1980s, the beam could be directed to one of 

three end stations A, B or C or to the PEP or SPEAR storage 

rings. Later, the SLC arcs were added. Now, the beams can 

be directed to the LCLS or End Station A. 

SPEAR 

SSRL 

1972–present 

PEP 1980–1991 

PEP-II 1998–April 2008 

SLC 1988–1998 

Next Linear Collider 

Test Accelerator 

1993–present 

In addition, the first damping ring was built in 1978, rather than 1984, as stated on page 12 of the 

TBD, second paragraph. 
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However, this report is pre-decisional and has not been reviewed by the Advisory Board on Radiation and Worker 

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Endo, A., Y. Oki, Y. Kanda, T. Oishi, and K. Kondo, 2001. Evaluation of Internal and External 

Doses from 11C Produced in the Air in High Energy Proton Accelerator Tunnels, Radiation 

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Endo, A., Y. Harada, K. Kawasaki, and M. Kikuchi, 2004. Measurement of depth distribution of 

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Flood, J.R., 1995. “Upper Useful Range of the Panasonic UD-802 Dosimeter,” Memorandum to 

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ICRP 1995. Age-dependent doses to members of the public from intake of radionuclides: Part 

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ICRP 1996. Publication 72, Age-dependent Doses to Members of the Public from Intakes of 

Radionuclides: Part 5 Compilation of Ingestion and Inhalation Dose Coefficients. International 

Commission on Radiological Protection, Pergamon Press, Oxford. Approved September 1995. 

ICRU 1999. Nuclear Data for Neutron and Proton Radiotherapy and for Radiation Protection, 

Report 63, International Commission on Radiation Units and Measurements, Bethesda, 

Maryland. 

Kanda, Y., A. Yoshioka, 2007. Physical and chemical forms of radionuclides of 38S, 38Cl, 39Cl, 

and 82Br, produced at a high-energy proton accelerator facility, Journal of Radioanalytical and 

Nuclear Chemistry, Vol. 273, No. 2, pp. 507–512, Akademiai Kiado, Budapest. 

Kase, K.R., R. Sit, J. Liu, H. Tran, D. Busick, and M. Grissom, 1993. Establishment of a 

Technical Basis for Internal Dosimetry at High Energy (50 GeV) Electron Accelerator Facilities. 

SLAC ID001, July 14. (SRDB Ref ID: 23307, p. 497) 

Kondo, K., H. Muramatsu, Y. Kanda, and S. Takahara, 1984. Particle Size Distribution of 7Be 

Aerosols formed in High Energy Accelerator Tunnels. International Journal of Applied 

Radiation and Isotopes, Vol. 35, No. 10, pp. 939–944, Pergamon Press, Ltd. 
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Health for factual accuracy or applicability within the requirements of 42 CFR 82. 

Liu, J.C., B. Flood, S. Rokni, R. Seefred, and R. Sit, 2000. Use of LiF and Panasonic TLDs 

inside 5” and 6” Polyethylene Moderators for Area Dose Monitoring at SLAC, RP Note 99-14, 

Rev. 1, Stanford University, Stanford Linear Accelerator Center, Stanford, California, March 21, 

2000. (SRDB Ref ID: 23300) 

Lucci, F., S. Merolli, and M. Pelliccioni, 1973. Measurements of Induced Radioactivity in Dust 

Around a 400 MeV LINAC, Health Physics 24, 411-415, Health Physics Society. 

McCall, R.C. and T.M. Jenkins, 1966. Preliminary Plan for Environmental Monitoring at 

SLAC, TN-66-9, Stanford University, Stanford Linear Accelerator Center, Stanford, California, 

March. [SRDB Ref ID: 23245] 

Muramatsu, H., K. Kondo, and Y. Kanda, 1988. Radioactive Airborne Species Formed in the 

Tunnels of a High Energy Accelerator Facility, Applied Radiation and Isotopes, Vol. 39, No. 5, 

pp. 413–419, Pergamon Press, Ltd. 

NCRP 1971. Protection against Neutron Radiation, Report 38, National Council on Radiation 

Protection and Measurements, Bethesda, Maryland. January 4, 1971. (SRDB Ref ID: 11520) 

Nelson, W.R., 1987. Properties of the EM Cascade. SLAC-PUB-4203. February 1987. 

Newton, G., M. Hoover, E. Barr, B. Wong, and P. Ritter, 1987. Collection and Characterization 

of Aerosols from Metal Cutting Techniques Typically Used in Decommisioning Nuclear 

Facilities, American Industrial Hygiene Association Journal 48 (11) (1987). 

NIOSH 2006. Scanned elevated exposure incident memos, file name: 023151_Elevated 

Exposure Incidents (1970–1974).pdf, Division of Compensation Analysis and Support, 

Cincinnati, Ohio. From NIOSH Data Capture April 13, 2006. 

Numajiri, M., Y. Oki, T. Suzuki, T. Miura, M. Taira, Y. Kanda, and K. Kondo, 1994. Estimation 

of Nickel-63 in Steel and Copper Activated at High-Energy Accelerator Facilities, Applied 

Radiation and Isotopes, Vol. 45, No. 4, pp. 509–514, Elsevier Science, Ltd. 

OCAS 2009. Worker Outreach Program, OCAS-PROC-012, Office of Compensation and 

Analysis, National Institute for Occupational Safety and Health, Cincinnati, Ohio. March 2, 

2009. 

Oishi, K., N. Nakao, K. Kosako, H. Yamakawa, H. Nakashima, M. Kawai, H. Yashima, T. 

Sanami, M. Numajiri, T. Shibata, H. Hirayama, and T. Nakamura, 2005. Measurement and 

Analysis of Induced Activities in Concrete Irradiated Using High-Energy Neutrons at KENS 

Neutron Spallation Source Facility, Radiation Protection Dosimetry, Vol. 115, No. 1-4, pp. 623–

629, Oxford University Press. 

Oki, Y., M. Numajiri, T. Suzuki, T. Miura, K. Kondo, 1992. Evaluation and Measurement of 

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However, this report is pre-decisional and has not been reviewed by the Advisory Board on Radiation and Worker 

Health for factual accuracy or applicability within the requirements of 42 CFR 82. 

Oki, Y., M. Numajiri, T. Suzuki, Y. Kanda, T. Miura, K. Iijima, and K. Kondo, 1994. Particle 

Size and Fuming Rate of Radioactive Aerosols Generated during the Heat Cutting of Activated 

Metals, Applied Radiation and Isotopes, Vol. 45, No. 5, pp. 553–562, Elsevier Science, Ltd. 

Oki, Y., K. Kondo, Y. Kanda, T. Miura, 1999. Aerosol-size distribution of radon daughter 218Po 

in the accelerator tunnel air, Journal of Radioanalytical and Nuclear Chemistry, Vol. 239, No. 3, 

pp. 501–505. Akademiai Kiado, Budapest. 

ORAUT 2005a. Technical Information Bulletin: Dose Reconstruction from Occupationally 

Related Diagnostic X-ray Procedures, ORAUT-OTIB-0006, Rev. 03-D, Oak Ridge Associated 

Universities Team, Cincinnati, Ohio. December 21, 2005. 

ORAUT 2005b. Conduct of the Worker Outreach Program, ORAUT-PROC-0097, Oak Ridge 

Associated Universities Team, Cincinnati, Ohio. December 29, 2005. 

ORAUT 2006. Technical Basis for Conversion from NCRP Report 38 Neutron Quality Factors 

to ICRP Publication 60 Radiation Weighting Factors for Respective IREP Input Neutron Energy 

Ranges, ORAUT-OTIB-0055, Rev. 00, Oak Ridge Associated Universities Team, Cincinnati, 

Ohio. June 5, 2006. 

ORAUT 2007a. Site Profile for the Stanford Linear Accelerator Center, ORAUT-TKBS-0051, 

Rev. 01. Oak Ridge Associated Universities Team, Cincinnati, Ohio. August 17, 2007. 

ORAUT 2007b. Rocky Flats Plant – Occupational Medical Dose, ORAUT-TKBS-0011-3, 

Rev. 01, Oak Ridge Associated Universities Team, Cincinnati, Ohio. April 23, 2007. 

ORAUT 2010. Site Profile for the Brookhaven National Laboratory, ORAUT-TKBS-0048, 

Rev. 01, Oak Ridge Associated Universities Team, Cincinnati, Ohio. April 26, 2010. 

Patterson, H.W., A. de G. Low-Beer, and T.W. Sargent, 1969. Whole-Body Counting and 

Bioassay Determinations Made on Accelerator Workers, Health Physics, Vol. 17, pp. 621–625, 

Pergamon Press. 

Patterson, H., and R. Thomas, 1973. Accelerator Health Physics. Academic Press, Inc., New 

York, New York. 1973. 

Pindar, F., 1965. “Blanket Order, Palo Alto Medical Clinic, Req. 24789M,” Memorandum to D. 

Littlefield, Stanford University, Stanford Linear Accelerator Center, Stanford, California. June 

29, 1965. (SRDB Ref ID: 23251) 

SC&A 2004. SC&A Standard Operating Procedure for Performing Site Profile Reviews, Rev. 1. 

S. Cohen & Associates, Vienna, Virginia. May 13, 2004. 

SIT, R., 2000. OHP Department Airborne Activity Control Levels, SLAC-I-760-2A05O-009, 

FO#012, Rev. 6, Stanford University, Stanford Linear Accelerator Center, Stanford, California, 

October 5. SRDB Ref ID: 23364]. 
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Health for factual accuracy or applicability within the requirements of 42 CFR 82. 

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SLAC 1969. 181Tungsten Contamination Incident, by D. Busick and G. Warren, SLAC-Pub-543, 

January 1969, presented at Health Physics Society Mid-Year Topical Symposium, January 29–

31, 1969. 

SLAC 1994a. PC ORPS Occurrence Report, “Beam Switch Yard Swipes Analysis,” SAN-SUSLAC-1994-0012, Stanford Linear Accelerator Center, Menlo Park, California, November 3, 

1994. 

SLAC 1994b. PC ORPS Occurrence Report, “Loose and Fixed Radioactive Contamination,” 

SAN-SU-SLAC-1994-0011, Stanford Linear Accelerator Center, Menlo Park, California, 

October 24, 1994. 

Tesch, K., 1991. The Ratio of Internal Dose Due to Inhalation to the External Dose When 

Machining Radioactive Accelerator Components, Radiation Protection Dosimetry, Vol. 35, 

No. 3, pp. 167–171, Nuclear Technology Publishing. 

Tran, H., 2005. Technical Basis Regarding Routine Bioassay Measurements at SLAC, DG #103, 

Rev. 3.0, Stanford University, Stanford Linear Accelerator Center, Stanford, California. April 

15, 2005. 

Vylet, V., J.C. Liu, S.H. Rokni, and L.–X. Thai, 1997. “Measurements of Neutron Spectra at the 

Stanford Linear Accelerator Center,” Radiation Protection Dosimetry, Vol. 70, pp. 425–428. 

(SRDB Ref ID: 23306) 

Yokoyama, S., K. Sato, K. Manabe, H. Noguchi, H. Kaneko, Y. Oki, T. Iida, and S. Tanaka, 

2007. Ratio of Aerosol and Gases of Radioactive Chlorine and Particle Size Distribution of 

Aerosol Formed By High-Energy Proton Irradiation, Radiation Protection Dosimetry, Vol. 127, 

No. 1-4, pp. 392–397, Oxford University Press. 
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December 20, 2011 

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However, this report is pre-decisional and has not been reviewed by the Advisory Board on Radiation and Worker 

Health for factual accuracy or applicability within the requirements of 42 CFR 82. 

ATTACHMENT 1: POTENTIAL RADIATION FIELDS AT SLAC 

 

A brief description of the process that creates the radiation fields at a high-energy electron 

accelerator is helpful in understanding the potential exposures at such a facility. The term 

“electron” will be used to mean both negatively and positively charged electrons (called negative 

electrons and positrons, respectively). 

 At SLAC, electrons are accelerated in a 2-mile long pipe (beamline) up to 47 GeV (which 

is 47,000 MeV) of energy. Several smaller accelerators at the end of the beamline also 

accelerate electrons up to 120 MeV and 2.3 GeV. These beamlines are in a concrete 

tunnel covered with earth in most locations at SLAC. 

 The accelerated electrons interact with the inside of the beamline/components, 

experimental targets, the shielding, and the beamstops to create high-energy photons. 

 These high-energy photons interact with similar material to go on to create additional 

negative electrons/positrons. This is called an electromagnetic cascade or shower. The 

number of electrons and photons increases exponentially, and their energies decrease 

exponentially as they pass through material. This is illustrated in the following figure 

(Nelson 1987): 

r.l. = radiation length = distance traveled to decrease energy 

by a factor of 1/e; about 8” in concrete. 

Figure A-2. Electromagnetic Cascade 

 The energy spectra of the photons created can range from several keV up to near the 

maximum energy of the electron beam. The photon energies that are of most concern 

from a health protection aspect, outside the shielding, range from approximately 30 keV 

to several MeV at SLAC. 

 The high-energy (>10 MeV) photons go on to interact with material to produce neutrons. 

The three major interactions are as follows: 

o 10–30 MeV photons create a peak of neutrons with an energy around 1 MeV

through the Giant Resonance (GR) interaction. 
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o 30–300 MeV photons create neutrons in the 10–20 MeV range through the photo 

disintegration of nucleon pairs (so-called pseudodeuteron interaction). 

o 140 MeV–50 GeV photons create a peak of neutrons around the 80 MeV, 

(ranging from 50–200 MeV), through the photon-pion production (one, two, and 

three pion) reactions. 

This is illustrated in the following diagram (Patterson and Thomas 1973): 

Figure A-3. Neutron Production from Electromagnetic Cascade 

The magnitude and energy range of the neutrons produced depend upon the atomic 

number of the material that the photons interact with. 

 Some high-energy neutrons are degraded in energy from interactions with materials, 

resulting in neutron energy spectra in the thermal (0.025 eV) to 1 MeV range. 

 In combination, the photon and neutron interactions described above result in a broad 

spectrum of neutron energies, ranging from approximately 0.025 eV through 

200 MeV. 

 The electrons, photons, pions, and neutrons described above are produced in the 

beamline, tunnel, and shielding. Since charged particles and spallation products 

would not penetrate to work areas, the following radiation exposures are of primary 

concern for personnel dosimetry while the accelerator is running: 

o Photons in the 30 keV–3 MeV range. 

o Neutrons in the thermal (0.025 eV) up to several hundred MeV range. 

o Both photons and neutrons could emerge horizontally from the direction 

of the accelerator and vertically from radiation reflected back down to 

ground level from skyshine. Except near experimental areas and 
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NOTICE:

penetrations in the shielding, the geometry of exposure would most likely 

resemble isotropic irradiation. 

 When the accelerator is not operating, the radiation types described above are not 

produced. Exposure during these times comes from activated materials (e.g., targets, 

beamline components, structural materials, and air); these materials emit gamma rays 

in the 30 keV to 3 MeV energy range and beta particles in the keV and MeV energy 

range. 

This brief summary is a generalized view of the production of radiation fields at SLAC and 

leaves out many details; however, it will serve the purpose for health protection and dose 

reconstruction evaluation. Workers could potentially be exposed to the radiation fields listed 

below. Adequate monitoring would consist of dosimetry that is responsive to these fields, 

appropriate calibration of dosimetry, and availability of recorded results for dose reconstruction 

purposes. 

 Photons: 30 keV–3 MeV, both while the accelerator is operating and when it is off. 

 Betas: keV and MeV range, both while the accelerator is operating and when it is off. 

 Neutrons: Energies from thermal to several hundred MeV, only when the accelerator is 

operating. 

 Generally, neutrons do not dominate the radiation fields at electron accelerators, except in 

the case of skyshine. This is in contrast to proton accelerators, where neutrons are 

usually one of the dominate radiation exposures.
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ATTACHMENT 2: SUMMARY OF SITE EXPERT INTERVIEWS 

As a technical support contractor assisting the Advisory Board on Radiation and Worker Health 

(Advisory Board), SC&A has been tasked with reviewing NIOSH’s site profile for Stanford 

Linear Accelerator Center (SLAC) in Menlo Park, California. One component of SC&A’s 

review is a series of interviews with site experts, including current site workers, former site 

workers, and worker representatives. The purpose of these interviews is to obtain first-hand 

accounts of past radiological control and personnel monitoring practices, and to better 

understand how operations and safety programs were implemented at the site over time. 

Interviewees were identified through available site reports, other interviewees, and site 

personnel. This report summarizes the results of those interviews that were reviewed and 

accepted by the interviewees. 

SC&A interviewers William James and Kathryn Robertson-DeMers conducted interviews at 

SLAC in Menlo Park, California, between January 24 and January 28, 2011, as well as 

interviewing a couple participants by telephone. No Advisory Board members participated in 

these interviews. A total of 26 site experts were interviewed. 

SC&A explained that the interviews were being conducted on behalf of the Advisory Board as 

part of their review of NIOSH’s site profile report. Participants were told that the interviews 

were unclassified, and that they should not disclose any classified information. Interviewees 

were informed that interview notes with names (if authorized by the interviewee) would be made 

available to the Advisory Board. Summaries from each interview set were prepared and 

provided to the interviewees for review. Approximately 80% of the participants responded to the 

request for review; the information obtained from non-responders has been withheld from this 

master summary. 

 

The workers whose interviews are summarized below represent the time period from 1963 

through the present (January 2011). They worked throughout the research area and support 

facilities, including the 2-mile Linear Accelerator (LINAC), the Stanford Synchrotron Radiation 

Lightsource (SSRL), Stanford Positron-Electron Asymmetric Ring (SPEAR), the SLAC Linear 

Collider (SLC), the Positron Electron Project (PEP), the Next Linear Collider Test Accelerator 

(NLCTA), the Final Focus Test Beam (FFTB), the LINAC Coherent Light Source (LCLS), the 

Klystron Gallery, the Central Laboratory area, the Beam Switch Yard (BSY), the End Stations, 

Storage Areas, Building 44, Building 25, and Building 26. The areas represented by the 

interviewees include the following: 

 Accelerator Engineering 

 Accelerator Operations 

 Accelerator Operations and Safety 

 Central Laboratories 

 Dosimetry (External and Internal) 

 Environmental Compliance 

 Environmental Monitoring 

 Experimental Facilities Department 

 Experimental Particle Physics 
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 Klystron Department 

 Mechanical Design 

 Mechanical Fabrication 

 Medical 

 Operational Health Physics 

 Radiation Physics 

 Radiation Protection 

 Security 

 Waste Management (including Radioactive Waste) 

The information provided by the workers and site experts is invaluable in helping SC&A to 

better understand the operations at SLAC. This summary report is not a verbatim presentation of 

the material contained in the interview notes, nor is it a statement of SC&A findings or opinions. 

It is a consolidated summary of statements, opinions, observations, and comments that the 

interviewees communicated to SC&A. Its sole intent is to communicate to the Work Group, the 

Advisory Board, and other interested parties information acquired by SC&A during these 

interviews. Comments are included in brackets where SC&A has provided clarification on 

a statement.

Information provided by the interviewees is based entirely on their personal experience at SLAC. 

It is recognized that the site experts’ recollections and statements may need to be further 

substantiated. However, they stand as critical operational feedback and reality reference checks. 

These interview summaries are provided in that context. Key issues raised by site experts are 

similarly reflected in our discussion, either directly or indirectly. Interviews from all workers 

who reviewed and approved their individual interview summaries were consolidated into a single 

summary document. The information has been categorized into topical areas related to 

organization, facility security and access, accelerator operations, exposure potential, radiological 

control, external dosimetry, internal dosimetry, environmental monitoring, incidents and unusual 

events, radiological records, occupational medical exposure, comments on the site profile, and 

miscellaneous comments. Where conflicting observations and statements have been received, 

both perspectives have been retained in this summary report. 

With the preceding qualifications in mind, this summary has contributed to SC&A’s 

understanding of issues raised in the Site Profile Review report. 

Organization 

Historically, there were few divisions, each headed by an associate director who reported to the 

laboratory director. These divisions are now referred to as directorates, which have undergone 

name changes as well as organizational changes. For example, the Accelerator Directorate now 

includes most of the functions formerly included in the Technical Division. 

The Accelerator Engineering Division now includes the Mechanical Fabrication Department, the 

Klystron Department, the Controls Department, the Power Conversion Department, the 

Metrology Department, and other smaller groups. The Mechanical Design group works on 

assembly of accelerator components, and assembly and disassembly of new components. 
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The RadCon program was initially divided into Radiation Physics and Operational Health 

Physics. The Radiation Physics group, part of the Research Division, worked on shielding, 

radiation safety commissioning, beam parameter approvals, beam authorization sheet sign-off, 

and other tasks. Operational Health Physics was responsible for day-to-day operations in the 

field, including surveys, posting, material control, writing/issuing Radiological Work Permits 

(RWPs), and 10 CFR 835 and DOE RadCon Manual compliance activities. Before 1991, the 

staff involved with health physics and other safety issues were scattered among the divisions. 

The Environmental Safety and Health (ES&H) Division came into existence in about 1991, with 

both the Operational Health Physics group and Radiation Physics group reporting to ES&H. In 

about 2000 or 2001, Radiation Physics and Operational Health Physics were merged into one 

group, Radiation Protection. 

There are currently 30–34 personnel in the Health Physics organization. Each experimental 

facility has a safety officer, who is responsible for reviewing the hazards associated with 

experiments. Radiation Protection is brought in to consult on radiological hazards. Staff in the 

Radiation Physics group includes individuals certified as health physicists, many with PhDs. 

Facility Security/Access Control 

SLAC covers the 420-acre property. There is a perimeter fence around the entire site. There is 

nowhere in the restricted area where an individual can inadvertently enter the site. 

Security has the responsibility for the badging office onsite. There are 30 officers at SLAC that 

support the facility, with 2 flex officers who have commensurate training. There are three patrol 

officers driving around the site on routine patrol from Monday to Friday, and two on the 

weekends and after hours. 

There are two entrance gates to SLAC and two internal gates. The two main entrances are the 

Main Gate and the Alpine Gate. All employees entering the Main and Alpine gates must show a 

badge or decal, which is registered with Security. Decal registration information allows Security 

to identify the individual as necessary. Non-employees can pass through the Main Gate without 

a badge, but they must have formal business onsite. No visitor escort is required on the 

“Campus” area of the site. A badge is required to enter the Alpine Gate, Gate 17, and Sector 30 

gate. Visitors entering the restricted area are issued a temporary badge and are required to be 

escorted by an appropriately trained individual. 

Officers typically wear uniforms. They wear Personal Protective Equipment (PPE) like hard hats 

in construction areas as required, mainly for non-radiological hazards. 

Officers occasionally walk through machine shops—only when no activities are going on. They 

keep their path to the aisles and corridors and do not go near the shop equipment. They utilize 

PPE if required. 

Indefinite Delivery, Indefinite Quantity contractors, contractors that provide an indefinite 

quantity of supplies or services during a fixed period of time, have been here for non-radiological 

cleanups, but they did not require Security services. 
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Officers at SLAC have not been loaned out to other DOE facilities. 

Accelerator Operations

The budget for SLAC operations came/comes from the Department of Energy (DOE) and its 

predecessors, while Stanford University is responsible for the operation of the facility. 

From 1961–1966, prior to start-up of the accelerator beam, some staff members were doing 

accelerator work at the Stanford University campus accelerator. Project M was run by a group of 

faculty members at Stanford University. Individuals involved in the construction of SLAC 

originally came from the campus. There was a 250-MeV accelerator set up to develop the 

prototype structures eventually used for the SLAC accelerator. 

SLAC’s focus is on conducting high-energy physics experiments. No isotope production or fuel 

production is done at the accelerator. SLAC is classified as a Radiological Facility. 

2-mile Accelerator 

The 2-mile long LINAC is the main accelerator at SLAC, providing beam to various facilities. 

The LINAC was commissioned starting in 1966. As one phase of the accelerator (SLAC) was 

completed, that part of the accelerator was started up. 

 

Commissioning started at a low energy, but was increased as more of the LINAC became 

operational. In 1967, the beam energy was increased to a maximum of 20 GeV at 60 to 

180 Hertz (Hz). The maximum number of electrons per pulse ranged from 1010 to 1011. The 

Radio Frequency (RF) pulse length was approximately 3 micro-seconds. The number of 

particles per pulse times the energy is directly proportional to the beam power, which determines 

the amount of activation in targets and other devices that intercept the beam. 

For a couple of years during the early 1970s, the accelerator was run at a maximum beam energy 

of 20 GeV and a pulse rate of 180 Hz. During this period, the average beam power was higher 

than in later years. From the late 1980s through June 1998, a beam energy of up to 47 GeV with 

a lower pulse rate of 120 Hz was used. This change in operating parameters was due to the 

ability to group particles together in a single RF bucket and to compress the RF pulse, resulting 

in a need for less power. As a result of this change, some experiments could be completed with a 

beam power an order of magnitude less than was needed in the early 1970s. The ability to 

control the beam has become significantly better over time, resulting in less beam loss. 

Currently, SLAC can produce a micrometer-wide beam versus the millimeter-wide beams in the 

early days. In almost all cases, the targets are stationary. 

The power of an accelerator can be expressed by the following function: 

Power (watts) = energy (GeV) × current (amps) × repetition rate (pulses in Hz) 

SLAC was designed for about a 1-Megawatt (MW) power level, but has never run at that power 

level. The beam energy and the average beam power for experiments at SLAC were higher 10–
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15 years ago than it is currently. The beam energy has dropped from 50-GeV beam energy in the 

early years to less than 15 GeV in recent years for LCLS. The repetition rate has been reduced 

from 120 Hz to 60 Hz. The electrons per pulse have ranged from 109

 to 1012. The accelerator 

gains about 1 GeV per sector. The radiological hazards at the accelerator are proportional to the 

power of the accelerator. Thus, reduction in power has lowered the radiological hazards. In 

general, both prompt and residual radiation fields have been reduced in the last 20 years, 

compared to the periods of maximum power in the 1970s. 

The beam is directed by a series of magnets, which direct, focus and defocus the beam in the x 

and y directions. The beam can also be narrowed in the z direction. 

The accelerator normally runs 24 hours per day for 9–10 months per year. Presently, only the 

last one-third of the accelerator is used. SLAC was/is shut down every summer. The precision 

and accuracy of the machinery requires adjustment and maintenance. The summer was/is a good 

downtime, as the electrical load during the summer is unpredictable. 

SLAC Linear Collider (also known as the Stanford Linear Collider or SLC) 

SLC accelerated electrons (from the clockwise direction) and positrons (from the counterclockwise direction), allowing them to collide at a fixed point in space. The collision point was 

centered in a detector at the SLC Experiment Hall in Building 750. There are two dump rooms 

for this process. Parts of the Linear Accelerator Facility were upgraded in 1987–1998 in 

preparation for the PEP II startup. 

Stanford Positron-Electron Asymmetric Ring (SPEAR)/ Stanford Synchrotron Radiation 

Lightsource (SSRL) 

Another major facility at SLAC is the Stanford Synchrotron Radiation Lightsource (SSRL), 

which is similar to the ANL Advanced Photon Source, the BNL National Synchrotron Light 

Source, and the LBNL Advanced Light Source. 

The SPEAR is the accelerator that feeds the SSRL. The current has ranged from a few milliamps (mA) to several hundred mA. In about 1973, it used 100 mA, but now is up to about 300–

400 mA. SPEAR 2 was the result of hardware improvements on SPEAR. For SPEAR 3, the old 

machine was pulled out and replaced with an entirely new accelerator; shielding upgrades were 

added where necessary to improve the system. SPEAR and SPEAR 2 were used for colliding 

beam physics experiments. In the mid-1980s, the machine was shared between high-energy 

physics and SSRL. High-energy physics ran at <2.0 GeV and SSRL ran at 3.0 GeV. SSRL 

continues to operate at 3 GeV. 

The SSRL produces synchrotron radiation by circulating electrons through magnetic fields, 

causing them to oscillate and give off photons. The photons are used for study of target material. 

SSRL is like a super x-ray machine that allows pictures to be taken at various depths within 

surface layers of a material. For example, it allows scientists to see the biological structures of 

molecules. SSRL will soon be able to operate up to 5 Watts. The SSRL gets about 3,000 users 

per year using its x-rays for research studies. 
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In 1995 or 1996, a new program involving transuranic experiments was initiated at SSRL. By 

1996, the Actinide preparation and handling room started up, and they received their first 

shipment of plutonium alloys for analysis. SLAC is a Radiological Facility, and the associated 

inventory of materials is kept to one-half the inventory limits specified for this type of facility 

(Category III). Activity of individual samples range from several Bq to 100s of MBq. SLAC 

has handled Pu-238, Pu-239, Pu-240, Pu-241, Np-237, Am-241, U-235, U-238, Tc-99, and 

europium isotopes in the Actinide Room. All samples are prepared at their originating facility 

[LANL, Pacific Northwest National Laboratory (PNNL), or LBNL], with no sample preparation 

occurring at SLAC. SLAC requires the initiating facility to contain the samples prior to 

shipment. Depending on the hazards class of the isotope, this could involve up to three 

containments; the samples are not handled in an uncontained situation. This is required not only 

for Radiation Protection, but also to prevent contamination of the accelerator vacuum system. 

The inventory list is provided with each package, along with a list of isotopes and maximum 

activities. When samples are received, personnel swipe each container as they open the package 

and remove the sample. Monitoring of alpha-emitting isotopes takes place on a continuous basis, 

starting with receipt of samples and continuing until completion of the experimental analysis. If 

any contamination is detected on the container, it is packaged up and sent back to the originator. 

The unpackaging and handling of the samples is done in a HEPA-filtered glovebox. Workers 

have worn HEPA respirators to open the actinide containing shipping containers; however, this is 

not a requirement in most cases. The sample is taken to SSRL and inserted into the beam line for 

testing by Radiation Protection Field Operations technicians; handling of samples by 

experimenters is limited only to those personnel who have Radiation Worker II training. 

The Actinide Room and beam hutches have an alpha continuous air monitor (CAM), and glove 

bags may be used in some experiments. CAM samples are decayed to zero. If they don’t decay 

off, this would be an indication of true radioisotopes other than radon. No leaks or airborne 

contamination releases have ever been detected in the room. 

A TBD for the actinide work in SSRL was prepared. In addition, there is a safety analysis report 

for the process used. 

Positron Electron Project (PEP) 

PEP started in about 1980 and ran to 1989. It was brought back up for a period in 1991. It was 

used for high-energy physics collisions of electrons and positrons at 15 GeV per beam. There 

was one beam pipe. The electrons were circulated in the clockwise direction and the positrons in 

the counter-clockwise direction. There were six points around the ring where collisions took 

place. There were five experimental halls at Buildings 620, 640, 660, 680, and 720. These were 

beam focusing points. PEP was designed to discover new families of quarks and leptons, to 

measure the lifetimes of various short-lived mesons, and to study other aspects of electronpositron annihilation physics. 

 

PEP II (also known as the B-Factory) used the circular tunnel previously used by PEP. The 

original PEP machine was taken apart and replaced with two beam pipes. These beam pipes 

came together at one location—the Interaction Region Hall (IR2) in Building 620. Additional 
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local shielding was added in the experimental hall, because of the higher stored currents. One 

beam ran at approximately 9 GeV, while another ran at approximately 3 GeV. There were 

various instruments around the area to measure beam losses and prompt radiation. Activation 

primarily occurred at the beam dumps. 

Next Linear Collider Test Accelerator (NLCTA) 

NLCTA is a small x-band linear accelerator. This is a self-contained accelerator, which uses 

x-band technology. It was constructed to demonstrate that x-band technology could work. There 

is about four times more acceleration per meter with x-band technology than with s-band 

technology. This accelerator is now used primarily for advanced accelerator technology 

research. The accelerator is turned on and off as needed. 

Final Focus Test Beam (FFTB) 

FFTB was the test facility used to focus LINAC beams to very small sizes and deliver them to 

various kinds of experimental apparatus and targets. In 2006, the FFTB was dismantled. As a 

part of the project, SLAC dug up the concrete floor and the activated soil below the structure. 

Low levels of radioactivity were identified by gamma spectroscopy in both the concrete and soil. 

LINAC Coherent Light Source (LCLS) 

The LCLS is a powerful x-ray laser. Its C-ray pulses are millions of times brighter than the 

SSRL. The LCLS uses stop-motion pictures and examines atoms and molecules in motion. 

Beam Switch Yard (BSY), End Stations and Storage Areas 

BSY is the transition area between the LINAC and the various End Stations or other machines. 

Targets are placed at the End Stations for various experiments. The BSY is approximately 

0.75-miles long and allowed the transport of high-energy electrons and positrons to three beam 

lines—Beam Lines A, B and C. There are three large beam halls—End Station A (Building 62), 

End Station B (Building 61), and the Large Collider Hall (Building 750). The targets used at 

End Station A and End Station B were primarily liquid hydrogen. Other targets used have 

included deuterium and various other materials. SLAC has never done any heavy ion physics. 

The beam travels through the End Stations to the Beam Dump, which is located on the hillside. 

There are about 150 separate low-conductivity water systems (i.e., cooling heat exchangers) for 

cooling parts of the accelerator and support structures. 

SLAC scientists use very large detectors (i.e., the size of a truck or house) housed in shielded 

buildings to detect particles. There was 40 feet of iron shielding manufactured from World 

War II iron blocks to provide shadow shielding to protect the central beam detector from nuclear 

interactions generated by photons and secondary particles in the BSY. 

The Radioactive Material Storage Yard (RAMSY) is located in the BSY. It is used to store old 

magnets, collimators, old beam stops, concrete blocks, and steel no longer needed for accelerator 
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operation. SLAC initiated a natural Be-7 study in 2008. A couple of samples in the BSY 

showed elevated levels of Be-7 by gamma spectroscopy; no readings above background were 

identified by field instrumentation. 

There were a couple of beam targets/dumps with lead shielding, which were stored in an outdoor 

storage area (magnet storage yard). Clean-up of the storage area and removal of the 

targets/dumps was required in 2004, due to the presence of small pieces of lead found in the 

surrounding area. Low levels of activation products originating from the targets/dumps were 

also detected in the soil via gamma spectroscopy (no readings above background were identified 

by field instrumentation). Six or seven drums of soil containing activation products were 

generated by this clean-up. 

The Bone Yard was used for storage of shielding blocks from the 1960s. When experiments 

were completed, the blocks were stored here. Lead contamination was found in this area, 

requiring the area be cleaned up. Each of the shielding blocks underwent surveys by Radiation 

Protection. The blocks were moved to an area near Section 10, along the gallery, for storage. 

Klystron Gallery 

Equipment housed in the Klystron Gallery produces high-power microwave pulses that power 

the LINACs. Each klystron is like a mini-accelerator that uses bunched electron pulses to 

produce microwaves. A wave guide takes the electrons off the electron gun, runs them down to 

the tunnel, and adds them to the main beam. There are over 250 klystrons at the accelerator. 

Operations fires up as many as they need to get the desired power. Anywhere there is an 

accelerator, there is a klystron. The area around each LINAC klystron is roped off. 

Klystrons were manufactured at the Machine Shop (Building 44) and taken to the High Bay (i.e., 

Klyston Test Building) to be tested. The “Yellow Coffin” is a shielded test facility for electron 

guns and other electron-emitting devices. It is located in the building where klystrons are 

manufactured, repaired, and tested. 

Support Facilities 

The Central Laboratory Area serves as an office building and houses Material Science and 

Chemistry laboratories. Radioactive samples are not supposed to be handled in this area. There 

are no radiochemical separations conducted here. The Central Laboratory has a quick 

turnaround Machine Shop. 

The Vacuum Technicians are located at a central location and are sent out to areas throughout the 

site. Anyone from Building 25 can be sent anywhere to do a job. 

Exposure Potential 

The largest potential radiation exposure from the SLAC accelerator is a “beam-on” condition. 

Personnel entry to the 2-Mile LINAC and all experimental areas is therefore controlled if the 

accelerator is on or could be turned on. Prior to accelerator operation, all experimental areas 
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where the accelerator particles can be present are physically searched and controlled by 

accelerator operators. The accelerator has an interlock system to keep individuals out while the 

accelerator is on or could be turned on. There has never been a “beam-on” accident at SLAC 

during its operation. 

Historical studies indicate that principal worker radiation exposure was clearly from external 

radiation distributed deep in the beam stopper, beam dump, or collimator, usually made from 

copper. Lapel and high-volume air samplers were used during repairs. The results from 

machining irradiated devices clearly demonstrated that the external gamma radiation dose rate 

dominates the machinist’s occupational radiation dose. The air samples revealed background 

radiation. Most of the exposure came from machine shop set-up and was from induced 

collimator material from the external source. 

External 

The highest doses typically occurred during major shutdowns for maintenance activities, such as 

repair or upgrading of magnets and other required devices. Activation of aluminum resulted in 

Na-22 and Na-24. Activation of steel resulted in Co-57 and Co-60. Induced activity occurs at 

the beam dump and in areas where there are beam losses. The electron beam is dumped after it 

passes the target at the beam dump. There are several areas along the accelerator where the 

beam is split or lost. These areas are shielded significantly. 

The most predominant radiological exposure is from photons. During precision alignment of the 

beamline components, individuals could spend 40 hours per week in a low dose rate radiation 

field. Generally, personnel radiation doses were compressed into specific times of the year (i.e., 

during shutdown). 

Dose rates at the beam dump could be up to 1,000 R/hr when the accelerator is running. As soon 

as it is shut down, the dose rates drop to 100–200 mR/hr on contact with a few components. The 

dose rates come from activation and short-lived radioisotopes during some experiments. The 

hottest hot spots can reach 25 R/hr. 

Muons are generated from prompt radiation along the narrow beam. The FFTB housed a muon 

shield for its main dump. This area was shielded and roped off to [a point where the dose rate 

was] 0.5 mrem/hour. The shielding requirements for muons are known. External dose from 

muons is detectable by dosimeters. There are no neutrinos generated at SLAC due to beam 

operations. 

In accelerators, the principal source of radiological exposure is from work with activated 

components. Synchrotron light sources have low average beam powers, and there are few beam 

components that can get activated. Main sources of radiation [at synchrotron light sources] are 

generated as a result of losses in the ejector and the ring transition of the beam. 

A majority of the neutron exposure at the facility in the past was from exposure to neutron 

calibration sources. These calibration sources have included plutonium beryllium, plutonium 

lithium, plutonium fluoride, and Cf-252. As a result of exposure to these sources, in general, the 
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RCTs have received the highest neutron doses at the site in the past. These sources were recently 

shipped to LANL due to security requirements. 

Internal 

Internal dose is negligible at SLAC. Contamination usually comes from activated dust or 

oxidation of metals, and there are some plastics and rubbers that get activated also. 

Contamination is seen on the beam dumps and 1–2 feet around the beam dump. Insulation 

around the beam dumps also gets contaminated. Contamination is mostly inside the materials, 

which is volumetric contamination throughout the objects. 

Machining of radioactive (activated) components is a potential source of contamination. This 

activity occurs in both the accelerator area and at Buildings 25 and 26 in the Fabrication Shops, 

where activated materials are processed. Machining conducted at SLAC includes use of a 

Dremel tool or cutter to get parts out, lathing (round parts), milling (square parts), and drilling 

core samples out of the walls of the chamber (Building 26). Parts are also machined to get them 

ready for welders. There was no grinding of activated parts in Building 25; this process puts too 

many particulates in the air. Grinding (which is rarely used) is conducted at the accelerator area 

in a glove bag. They do not allow grinding or high speed cutting of activated materials in 

Building 25. When machining, a contamination area is established, and a HEPA-filtered vacuum 

is used for controlling the activated dust. This work is done under an RWP. 

Some contamination detected at the site came about from past high-energy operations of the 

LINAC, the BSY, and the End Stations starting in the 1960s and ending in the mid-1970s. 

There was a small-scale metallic Depleted Uranium (DU) Test Project in about the late 

1960s/early 1970s, where DU was considered for shielding a new physics detector. The DU was 

stored in the east end of Building 61 in the original shipping containers. There were plans to 

build a small-scale prototype of the detector to determine if the DU would result in too high a 

background [for the detector]. The DU arrived in 1/8” to 1⁄4” sheets by truck load from Oak 

Ridge. Some of these sheets were cut into smaller square sheets by machine pressure cutting. 

The DU was stored in shipping containers when not in use. The project lasted a few months. 

The researchers eventually decided to use lead sheets instead of DU for shielding the detector, 

probably because of the signal-to-noise ratio. 

One site expert indicated there was a project in the late 1980s to measure radon levels in the 

tunnel. Staff placed about 50 track-etch dosimeters obtained from a radon analysis vendor 

laboratory in the field. The concentration results reported from the laboratory did not indicate a 

significant radon exposure issue. 

Another site expert indicated there was likely an elevated natural background radon level from 

natural occurrence in the concrete tunnel. The 2-mile LINAC tunnel was ventilated with 15 fans 

before access was permitted. 

A third site expert indicated there is not a lot of air movement down in the accelerator tunnel. 

There is a possibility of enhanced natural radon levels in the tunnel. This is demonstrated by 
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observation of the occasional particulates with radon decay products collecting on hard hats, 

clothes, and badges. These items are identified as contaminated during frisking, confiscated, and 

held for survey until they decay to a non-detectable level. There are no radon exposure/dose 

issues known or currently being assessed. RadCon does a series of counts on air filters when a 

filter is suspected to have an elevated radon reading. Radon in the tunnel can be estimated from 

air sample multiple decay counts and other information, such as CAM data. These data are 

documented in survey reports. 

A site expert indicated thorium used at SLAC consisted of commercial welding rods. Radium 

was used for calibration of instruments at the health physics lab. 

One site expert indicated some thermal neutron activation occurs where cooling water and 

concrete are present. Another indicated the coolant loop does not get contaminated with 

activation products much, but is limited to tritium and Be-7. Beryllium-7 is filtered out in the 

resin bed. The highest concentration of tritium detected in water is 109

 pCi/l. Levels greater 

than 20,000 pCi/l are controlled as contamination. Personnel have been exposed to tritiated 

water with 1,000–2,000 pCi/l during a skin contamination event. SLAC has not handled any 

tritides. 

Radiological Control 

Engineering Controls 

Prior to turning on the accelerator, SLAC developed an administrative procedure requiring a 

documented physical search of all experimental areas. Health Physics and Operations personnel 

were responsible for this search. 

All entrances into the tunnel have elaborate interlock systems. There is redundancy in the 

interlock system. If an individual opens the door when the accelerator is on, the interlock system 

trips a system that shuts the accelerator off immediately. 

There is a 1-hour “cool down” period after shutdown at locations where the beam power could 

be lost. The “cool down” period is implemented at beam dump locations and locations where 

beam energy loss occurs (at points like collimators and beam dumps in the system). This is 

where the activation product hazards occur. For example, a 1-hour “cool down” period and 

initial entry radiological survey was required for Sectors 1, 2, 3, 4, 10, 18, 19, 28, 29, and 30. 

The doors stay interlocked through the “cool down” period. RadCon is the first to enter the 

tunnel to conduct surveys prior to entry of other accelerator staff. Most of the radioactive gases 

decay away within 15 minutes. In other areas, personnel can enter immediately after shutdown. 

Pocket Ionization Chambers (PICs) are assigned to personnel who enter high radiation areas. 

Each individual is responsible for recording the PIC reading upon entry and as they leave the 

tunnel. 

There is no exposure issue at SSRL now, because the interlock system protects personnel from 

prompt radiation, and the residual activation is very small. 
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Shielding calculations for accelerators and experiments have improved over time. Radiation 

physicists and Accelerator physicists work together to anticipate possible exposure scenarios that 

would produce the maximum dose. Controlled experiments are conducted, in which radiation 

levels are measured in accessible areas, while the beam is parked on various stoppers or is 

deliberately mis-steered. Additionally, there is a verification of exposure condition when 

machines are on. 

The accelerator has 27 feet of shielding in some areas. The End Station A/B has local shielding. 

Experiment-dependent shielding may also be required. When determining the shielding 

requirements, the beam parameters and beam losses are taken into account. The highest power 

experiments occurred at the End Station A (ESA) and the Beam Dump. The ESA beams were 

approximately a factor of 10 higher in average power than the SLC beam. 

One former worker indicated that the area behind ESA, including the Beam Dump East (BDE), 

was fenced off because of forward direction of secondary particles emanating from the ESA 

liquid hydrogen or deuterium target. 

The only intrusions into the tunnel have been by cats and rodents that entered through the utility 

penetrations many years ago. In one case in the mid-1990s, a feral cat was accidently irradiated 

when it entered the tunnel through a cable penetration during operation of the accelerator. The 

utility penetrations were modified to prevent further entry by animals into the accelerator via this 

route. 

Administrative Controls 

Researchers send proposals for experiments to a committee for review. This committee approves 

the research and procedures prior to work proceeding. 

An RWP is required when any machining occurs on activated materials. Prior to a job, ES&H 

comes in and does a pre-job survey of the area. Once they provide the numbers, the supervisor 

and his boss fill out the job description on the RWP form. This is signed off by the boss. ES&H 

adds the requirements for PPE, coverage, etc. Sometimes, there is an ES&H person present to 

monitor the job. The RWP is posted at the worksite. 

Personal Protective Equipment/Frisking 

A HEPA-filtered respirator is required for all welding operations as a matter of routine. 

Respirators used have either been half-face or full-face air purifying with HEPA filters (not 

Powered Air Purifying Respirators). The Mechanical Fabrication Department (MFD) has had 

various numbers of respirator-qualified staff over the years. At times, all staff was qualified, but 

the site has cut down on the number of personnel kept in the respiratory protection program over 

the years, limiting the number of staff that can perform respirator-required work. 

For several years, there was a requirement for full-body frisking of all personnel entering the 

High Radiation areas. There is no routine contamination found on PPE. In the last 17 years, 
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there have been less than 12 individuals with positive counts from frisking. Only a couple of 

these individuals had positive beta/gamma counts.

Radiological Surveillances/Instrumentation 

There is an air sampling program, which includes grab air sampling prior to and during work 

where airborne radioactivity may be generated. In the last decade, there have been a small 

number of radiological jobs requiring the use of breathing zone monitoring (performed by taking 

1-m3

 air samples within the worker’s breathing zone). When general area air sampling is used, 

the sampler is positioned between the work area and the individual’s breathing zone. Air 

sampling is conducted during the machining of activated samples. A general area air sample is 

collected in the breathing zone of the worker. Current staff has never had a hot air sample from 

machining operations of radioactive materials other than radon. 

Contamination surveys of Experiment Hutches are conducted pre-job, during work by the 

scientists, and post-job. 

A formal instrument calibration program was historically not in place. There was a departmental 

requirement to incorporate more sensitive and reliable instrumentation, both in the laboratory 

environment and in the field. Historically, radiological instrumentation included Victoreen 400s, 

Victoreen 410s, Z-tech instruments, Eberline E600s, GM detectors, and Victoreen Neutron 

Meters. At the present time, Sodium Iodide (NaI) detectors, plastic scintillators, GMs, Ludlum 

2241-2s, Miridian Health Physics Instruments (HPIs), and Eberline ASPs are used. Instrument 

calibration sources include, but are not limited to, Cs-137, Co-60, Cf-252, plutonium beryllium 

(PuBe), plutonium lithium (PuLi), and plutonium fluoride sealed sources. Instruments are sent 

offsite for neutron calibration, allowing SLAC to dispose of some of their neutron sources. For 

some field instruments, the Radcal detector is often (but not exclusively) utilized for calibration. 

The RCTs are currently responsible for instrument calibration. 

There is a tracking system maintained for all accountable and unaccountable sources. There is 

also a program in place for managing Radiation Generating Devices. 

Other 

 

Workers are allowed to have water down in the tunnel, because it is hot (110°F). 

By agreement, LLNL is also responsible for HEPA filter certification and necessary changes 

every 6 months. All checks and certifications on the system are maintained by both SLAC and 

LLNL. 

In 1992, the DOE Tiger Team came to SLAC and identified weaknesses in radiation safety 

training for staff, documentation of surveys, radiological records, etc. As a result, in about 1992, 

major improvements were made to the radiation protection program. Rigorous procedures and 

policies based on the Navy’s Naval Sea System Command (NAVSEA) 0289-0388 were 

implemented. The documentation became more frequent, structured, and formalized. There 

were improvements in the radiological surveillance of work, which included a strong emphasis 
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on continuous job coverage during radiological work. SLAC procured more sensitive 

instrumentation and implemented self-frisking practices. Training of technicians improved 

substantially after the audit. 

Prior to 1985, the radiological training at SLAC was not standardized. In about 1993, after the 

Tiger Team audit and implementation of the Department of Energy (DOE) Radiological Control 

Manual, there was an improvement in the radiological control training program. This included 

developing and giving RCT Training, General Employee Radiation Training (GERT), and 

Radiological Worker Training. 

External Dosimetry

There is good compliance with the requirement to wear personnel dosimeters in work areas. 

Personnel follow the RadCon rules at SLAC, because there is a high level of work ethics. 

Starting in 1963, everyone onsite needing access to the research area was monitored with film 

badges. Initial experiments were conducted on campus, requiring monitoring prior to the startup of SLAC. Film badges were still in use after the start-up. When the accelerator was first 

turned on, entry by visitors and non-SLAC personnel was restricted. This was done until the 

shielding could be verified as adequate. All non-SLAC personal entering the Research Yard 

were either escorted or assigned a personal monitor using a color-coded film badge holder. 

When individuals passed through the Sector 30 gate into the research/accelerator area, they were 

required to show a dosimeter for entry. In 1966–1967, SLAC used a color-coded film badge 

holder, which was worn by staff in the research yard or areas surrounding the accelerator. Red 

and green badges were used for visitors or individuals who were not expected to receive a 

measurable dose and were provided with an escort. These badges were not read unless there was 

an accident/incident. 

Security is responsible for issuing temporary dosimetry. If you enter the restricted area more 

than 8 hours in a calendar year, you must be assigned a dosimeter. 

Any personnel assigned to work only in the support buildings and areas outside of the accelerator 

operations area (e.g., administrative staff that never entered radiological control areas), including 

contractors, probably would not have been issued neutron dosimeters; they were possibly issued 

the gamma dosimeters. Presently, in general, non-radiological worker personnel do not wear 

dosimeters continuously onsite; it depends on the area they are in. One site expert indicated that 

workers in the Klystron area or the Central Laboratory were not required to wear a dosimeter 

while he was assigned there. 

All visitors were assigned dosimeters when entering the Accelerator Area in the past. Recently, 

DOE has recommended that SLAC reduce distribution of dosimeters for those not expected to 

receive 100 mrem/year. 

Dosimeters are assigned based on the following frequencies: 
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 Monthly for visitors or temporary badges (< 30 days) 

 Quarterly for ‘radiological worker trained and qualified’ personnel (gamma/neutron – 

Luxel +, J Type Dosimeter) 

 Annually for GERT qualified personnel who only enter Radiological Control Areas 

(gamma only, Luxel+, P type) 

 

This frequency dates back to at least 1973. Radiation workers were initially on a monthly 

exchange, and then changed to a quarterly frequency. Other workers and visiting scientists were 

on an annual exchange frequency. [This population included] delivery personnel, visiting 

experimenters, and public relations tours. The primary reason for this procedure was to allow 

access to the research areas, and also to act as an accident radiation dosimeter (because this 

population was not expected to be exposed to >100 mrem per year). The archived record is from 

1961–1973. 

SLAC’s current policy encourages individuals to leave dosimeters onsite in a rack. This is not 

enforceable at the present time. Historically, workers were allowed to take dosimeters home. 

SLAC developed a TLD solid state system using Li6/Li7 powder. Later, a Teflon disk-type 

dosimeter from Teledyne was implemented. These dosimeters were about the size of a dime. 

The dosimeter was designed so that it could be carried in a worker’s wallet. 

Initially, SLAC had used Radiation Detection Company (RDC) as a processing vendor. After a 

few years, SLAC was using two-chip TLDs, which included lithium fluoride and calcium sulfate. 

From 1995 to 2001, SLAC had used a Panasonic dosimeter. Since 2002, SLAC has used 

Laudauer processing services. The Landauer dosimeter is a four-element dosimeter designed to 

measure shallow dose, lens of the eye dose, photon deep dose, and neutron deep dose. A study 

conducted on the level of beta exposure at SLAC found there was so little beta dose that SLAC 

was not required to be DOELAP-certified for beta. The photon energies encountered in the field 

range from hundreds of keV to MeV. 

Neutron dosimetry has improved in quality over the years, but has always been as good as any in 

the industry for that era. NTA film was used for a short time to measure neutron dose—10%–

20% of the neutron spectrum is below 500 keV–1MeV. Following NTA film, neutron dose was 

measured with CR-39 track etch. The CR-39 is effective for energies from ~100 keV to 

~ 20 MeV, with a flat energy response from 0.1–20 MeV. Any neutron energies above 20 MeV 

are not measurable. Any positive neutron dose measured by the CR-39 is multiplied by a factor 

of two. These adjusted doses are accepted as the dose of record. 

A fraction of the low-energy neutron dose is missed with both systems. SLAC worked with a 

team from Japan to measure the neutron energy spectra at SLAC. There was a comparison of 

special detectors with field instrument response. Based on field measurements and simulations, 

they were able to quantify neutrons by energy. The results of this study are included in 

Figure 2-4 of the NIOSH site profile. With this quantitative knowledge of the neutron energies, 

the undetected neutron dose from the NTA film or CR-39 can be calculated. 
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The threshold reporting level, based on the uncertainty, is 10 mrem for quarterly and monthly 

dosimeters and 20 mrem for annual dosimeters. Values less than the Minimum Detectable Dose 

(MDD) are recorded as zero. 

A fading study was completed for the Panasonic dosimeter. The results indicated there is an 

over-correction for fading. 

Dosimeters are worn at the chest level. The source term is generally located in front of the 

individuals being exposed, because the bulk of the exposure occurs when individuals are fixing 

things. The use of extremity dosimetry is not routine, but special extremity dosimetry is used 

occasionally for assessment purposes. Multiple dosimetry is not used at SLAC. 

The standard Landauer calibration is applied to the dosimetry system. Calibrations of the 

dosimeter tend to be conservative. SLAC conducts field verification studies to validate that the 

calibration is appropriate. Historically, TLDs were calibrated using a neutron source with a 

paraffin shield inserted between the source and the TLD at various distances. A moderated BF3

detector was used for comparison. 

Six Nano-dot Transit dosimeters come with each shipment from Landauer for evaluating transit 

dose. Dosimeters are processed by SLAC using a Micro Star reader. Quality Control (QC) and 

background control dosimeters are sent in with each batch. These QC controls and background 

controls are read by Landauer. SLAC evaluates the background levels and maintains these 

values in a background file. 

In the early 1990s, SLAC participated in a blind dosimetry test of the personnel dosimetry 

system. Dosimeters were irradiated at Oak Ridge and returned to SLAC for evaluation. The 

results of the inter-comparison indicated that SLAC dosimeters had excellent precision and 

accuracy for neutrons, as well as gamma radiation. 

Dose of record has only been adjusted once [for background/transit dose]. There was a problem 

associated with the background/transit dosimeter reading high for gamma dose as a result of a 

transit exposure. An adjustment of 10 mrem was removed from the gamma doses. 

Administrative Control Level/Dosimetry Investigations 

The first director at SLAC was one of the founders of accelerator Health Physics and believed 

Health Physics should be a part of accelerator research. He established an administrative control 

limit (ACL) of 1,500 mrem per year. A few years ago, the ACL was lowered to 500 mrem. As 

the energy and average power of the accelerator has dropped, a reduction in external dose and 

contamination has resulted. 

Since 1993, only a few (maybe 1 or 2) employees have received doses of approximately 

1 rem/year, and about 200 employees received 100–200 mrem/year. In recent years, about 10 to 

15 employees get 100–200 mrem. The maximally exposed population is the MFD and the RCTs 

in Operational Health Physics. Last year’s collective dose was 165 mrem for approximately 
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3,000 users. The combination of accelerator power reduction, improvement in the ALARA and 

work planning program, and training have been important factors in lowering personnel doses. 

Any dosimeter result of 500 mrem (administrative level) or more is considered an event that 

requires investigation. As a best-management practice, the dosimetry group investigates any 

situations where individuals receive greater than 0 mrem to verify that the dose is legitimate. In 

many cases, individuals receiving dose above 500 mrem usually received the dose as a result of a 

medical treatment or exposure offsite. 

For lost dosimeters, a lost dosimeter form is completed. The form includes an area to record the 

activities conducted during the monitoring period, such as all areas where workers were 

performing their work. The individual has 15 days to locate and return the dosimeter. At the end 

of this time period, the dosimetry group starts an investigation. The dosimetry group evaluates 

the last four quarters of dosimeter results, coworkers’ doses, and area monitoring doses. A dose 

assignment is made and recorded in the investigation and dosimetry records. 

There are about 350 beta/gamma/neutron dosimeters onsite for the monitoring of area doses at 

SLAC, which are exchanged semi-annually. These dosimeters are used to verify the radiological 

postings. About 50 dosimeters are in general areas (offices, ordinary labs, etc.) outside of 

controlled areas and radiological controlled areas. These 50 dosimeters serve as background 

control dosimeters and can be used to estimate an external dose to staff members who do not 

wear dosimeters in these areas. The dosimeters used in the Radiological Environmental 

Monitoring program are processed by the dosimetry program. This program has been in place 

for quite some time. 

Internal Dosimetry 

There is a memorandum of understanding between SLAC and LLNL for bioassay services. 

Around 2007, personnel involved in the SSRL Nano-particle Program (maybe five or six) were 

sent to LLNL for baseline in-vivo counts and verification that no intakes had occurred since the 

Actinide Room started up in the 1990s. This in-vivo counting effort was done after the site 

profile was written, and therefore was not included in it. The amounts of actinides to be handled 

are limited by a “failure analysis” done for bounding doses (i.e., SLAC’s goal is to remain a low 

hazard rated facility). LANL sent staff to SLAC to work with them on setting up the hazard 

controls in the room. Only a single site expert, who was involved in the Nano-particle Program, 

indicated he received an in-vivo count (body or chest count) and submitted bioassay samples. 

Most of the contamination occurring at SLAC is from volumetric contamination. In 1993, the 

site issued the SLAC Internal Dosimetry TBD, which has undergone revision several times since 

then. This document provides justification for not conducting a routine bioassay program, and 

therefore, no routine urinalysis data are available. 

Environmental Monitoring 

For the potential radioactive effluent monitoring, the Environmental Protection Agency (EPA) 

has allowed SLAC to take confirmatory measurements. The confirmatory measurements utilize 
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the Air Monitoring Systems (AMSs) at SLAC. Air is pumped from the vent in an accelerator 

housing into a pressurized and low-background tank where a GM detector is used to measure the 

short-lived airborne radionuclides produced inside the housing. The main long-lived 

radionuclides seen are Ar-41 and C-11. The tank has a filter on the entry point, so that potential 

radioactive particulate matter can also be filtered out and measured. All measurements are 

normalized back to the machine operation condition. The airborne radioactivity released in 

recent years is not measurable. 

The beam dump for ESA is located under a hill that provides shielding. There is sufficient 

shielding for skyshine at the beam dump. In the skyshine process, neutrons can bounce 100 to 

500 feet up into the air. The atmosphere scatters a portion of the neutrons back down and causes 

the skyshine. 

The Perimeter Monitoring Station (PMS) sites were set up and running at least as early as 1965, 

before the accelerator was operational, in order to start collecting baseline background external 

radiation data. Site boundary PMSs measure potential real-time external dose, which includes 

skyshine or direct radiation doses that the public may receive. There is a book covering the 

complete initial construction of the accelerator facilities by R.B. Neal (nicknamed the “Big 

Book”) that may help identify exactly when the PMS systems were installed. 

These PMS locations were not moved from the start through the 1970s, and they collected both 

gamma/photon and neutron external radiation count data that were converted to dose. The 

gamma radiation was detected by a GM counting system, and the neutron radiation was detected 

by a BF3 counting system at each station. Each detector system was connected to a printer that 

recorded the detected radiation. The printed data were collected and converted to average dose 

rates for both gamma and neutron dose separately. Each current PMS system includes a pair of 

BF3 detectors and GM detectors to measure skyshine neutrons and photons, respectively. 

SLAC conducted the first skyshine neutron studies, which were published in Nuclear 

Instruments and Methods. The major fraction of any doses detected above background, for 

example 90% or more, are caused by the skyshine from the accelerator from neutrons, as 

described in a 1974 Health Physics Journal published study. In 1990s, a semi-quantitative 

skyshine neutron spectra study was performed. This provided the calibration factors for the PMS 

neutron detection equipment. The doses are calculated using conservative neutron energy 

assumptions. Only a small fraction of neutron dose [from skyshine] is from high energy 

neutrons, because the scattering reduces energies. The results of the neutron study were 

presented at a Health Physics Society meeting. 

SLAC prepared environmental monitoring reports prior to 1971. The external doses detected at 

the PMS sites were reported to the AEC in semi-annual “environmental radiation reports.” The 

missing data records and reports through 1970 are likely to be in a records storage system at 

SLAC. The quality of the data from pre-1971 should be as good as the quality of the data from 

1971 forward through the years of GM and BF3 detector use at the PMS. There were no 

significant technical changes in the monitoring systems during these years. 

The “Remote Monitoring System” (RMS) was designed and made at SLAC and was called 

BSOIC or “Beam Shutoff Ionization Chamber.” The counting gas was ethane to make it 
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sensitive to neutrons. A site expert believes it was a 1.5 liter ionization chamber with quality 

electronics. They were posted on the outside of each experimental building (Beam lines A, B, 

and C, and various other places); they worked very well, except when struck with a forklift. The 

ion chambers were checked with a small radioactive gamma-emitter as part of the Beam 

Checkout procedure. 

SLAC has a site-boundary environmental dose measurement program using passive dosimeters 

for photons and neutrons (currently quarterly exchange). The state of California also has passive 

monitors at the boundary, but SLAC does not have the results. 

There is a limited tritium plume near the Beam Dump East (near Building 730). A small fraction 

of the high-energy neutron beam penetrated the concrete shielding and activated the groundwater 

and soil during the 1970s. The tritium plume is about 20 feet underground, close to the beam 

dump, and is inaccessible. The situation was/is monitored and the activity has gone down over 

time. 

No drinking water is coming from any groundwater on the site. 

Waste Management

Any waste (hazardous or non-hazardous) containing a radioactive component is handled by the 

Radioactive Waste group. The Waste Management group handles only hazardous or nonhazardous (Class II) waste that does not contain a radioactive component. 

Sources of radioactive waste include activated accelerator components, resin columns from the 

accelerator cooling water filtration system, radioactive samples from the Radiation Protection 

(RP) laboratory, old sealed sources, commercial items (i.e., smoke detectors), and shielding 

components. Radioactive waste items also include gloves, PPE, well water samples, core 

drillings, soil samples, Mixed Analyte Performance Evaluation Program (MAPEP) samples for 

laboratory quality assurance, and samples from radioactive components. SLAC does not 

generate any transuranic waste as a result of accelerator operations. 

All offsite users of SSRL, and any other researchers, must take their samples back with their 

project when they leave. They do not dispose of anything the researchers bring with them. 

When applicable, waste is analyzed using Gamma Spectroscopy or Liquid Scintillation 

Counting. Any detectable quantity is reported. The primary radionuclides identified in the 

accelerator-produced waste include Na-22, Mn-54, Co-57, Co-58, Co-60, Be-7, and tritium. 

Zn-65 has been detected in some waste accelerator components. 

All waste coming out of radiological areas is surveyed and released by Radiation Protection prior 

to receipt by the Waste Management group. There is no removable radioactive contamination on 

external surfaces of waste containers routinely handled by the Radioactive Waste group. 

The Radioactive Waste group handles about a half-gallon of tritiated vacuum pump oils per year, 

which they over pack into shipping containers and ship out. Any oil from a Radioactive Material 
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Management Area requires testing for radioactive material prior to receipt by waste 

management. Oil with any detectable radioactivity goes to the Radioactive Waste group. From 

time to time, there is a leak from the accelerator cooling system (containing tritiated water) into 

the vacuum pumps (with the pump oil) that are used to create a vacuum inside the accelerator 

beamline components. The Radioactive Waste group receives tritiated vacuum pump oil about 

once per year. 

They have a storage area between Buildings 730 and 621 for large metal items that came from 

radiological areas, but are not radioactive per screening surveys (NaI and GM tube release 

surveys) and history knowledge. Shipment of this material offsite is not currently permitted, due 

to the existing DOE metal recycling moratorium for shipment. It is not likely for any surface soil 

to be contaminated from these items, as they are presumed non-radioactive. Hazardous waste is 

stored in a 90-day storage area under the requirements of Resource Conservation and Recovery 

Act. 

SLAC de-waters radioactive resins and adds absorbent to waste items containing free-standing 

water. Radioactive waste is not held for decay of short-lived isotopes onsite. 

SLAC disposes of radioactive waste in various ways. There are no burial grounds onsite. 

Commercial items, such as smoke detectors, are returned to the manufacturer for disposal when 

possible. In 2010, SLAC began a campaign to ship radioactive sources to the DOE Nevada Test 

Site for disposal. Starting in 2004, SLAC began shipping radioactive waste to Energy Solutions 

in Utah. Prior to this, waste was shipped to the DOE Hanford Site. 

Typical shipping containers for radioactive waste include steel drums and boxes; super sacks are 

used for shipping radioactive soils. 

An example of a work operation that potentially exposes personnel to radioactive contamination 

is handling radioactive resin containers. The containers are opened at the top to transfer the resin 

into a holding container, so that the water can be filtered/removed. During this work operation, 

personnel wear full personal protective clothing with RCT coverage for the job. When it is 

handled, the resin is wet. 

Radiological Records 

Following entry of dosimetry data into the Occupational Dose Tracking System (ODTS), there is 

follow-up quality control to ensure the data are correct. Reports on dosimeter results are sent to 

workers every cycle. 

There is no incident database to the best of the current staff’s knowledge. One site expert 

indicated that incident reports with personnel involvement should be in dosimetry files. Another 

site expert indicated that personal contamination events are documented on survey forms and 

include laboratory analysis to identify the radionuclide. These records are not likely captured in 

the dosimetry file. 
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The radiological surveys and air samples have been scanned back to 1990 and are available 

electronically. 

The first request for claimant dosimetry files was received in 2003. There are 5–10 requests for 

data per year. Information from the ODTS covering 1974 to present and RDC-archived 

hardcopy files from 1961 to 1973 are provided for claimants. The RDC printouts list multiple 

names per sheet. A summary of the dose is also provided. 

Occupational Medical Exposure 

The previous physician was a private subcontractor who provided medical services to SLAC. 

Prior to this, Palo Alto Medical Foundation staffed the physicians at SLAC. There was never an 

x-ray machine onsite. X-rays were done offsite if indicated. Site experts interviewed do not 

recall ever receiving medical x-rays as a part of medical physicals. 

Through review of medical records, it appears that screening x-rays were not performed for 

routine medical surveillance at SLAC. There is currently no asbestos medical surveillance 

program at SLAC, as employees do not perform asbestos abatement. A limited number of SLAC 

employees have been screened for beryllium sensitization, and a screening chest x-ray was 

offered to these individuals and performed offsite if the employee consented to the x-ray. These 

x-rays were mostly performed at Alliance Occupational Health Center or Work Force Medical, 

and as far as Medical can see, only one-time chest x-rays were performed on those who 

consented (with no follow-up screening). It appears from review of the medical records that 

these were first offered in 1998. 

Medical records are stored onsite for active employees only. Medical records for former 

employees are stored offsite. Medical has accession numbers available to retrieve records for 

employees whose employment ended after 1990. For those terminating prior to 1990, Medical 

currently does not have accession numbers and is not able to retrieve such records. Human 

Resources is involved in trying to locate these records. 

[Note: One of four requested medical records was provided for review during the interview. 

The remaining three were not available, because no accession number could be provided for 

retrieval of the records from archive. The record reviewed indicated annual exams from at least 

1966–1980. The Physical Examination Form and the Confidential Interim Medical History are 

two possible sources of information on x-rays.] 

Incidents/Unusual Events 

The Security Team is affiliated with the Emergency Response group. The site has its own fire 

department, which also responds to offsite emergencies. Officers are not authorized to go into 

the tunnels unless there is an emergency. There is a procedure in place that officers must contact 

the Radiological Control Organization (RCO) if they are required to respond to an emergency in 

a Radiological Control Area (RCA). 

[Site experts collectively discussed the following incidents at SLAC.] 
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 In about 1994 or 1995, while drilling a hole in the klystron shielding, the oil that 

surrounds the electron gun shot radiated oil out all over the place. The individual 

involved ran from Building 26 to Building 25. The individual’s clothing was confiscated 

as a result. 

 There was an incident in 1967 where an individual brought a pipe bomb into the facility. 

The detonation caused damage to a part of the LINAC. 

 A drum of radioactive concrete slurry from FFTB stored in RAMSY was found to be 

leaking in 2007. Gamma spectroscopy of a sample obtained from the general area prior 

to clean-up identified low levels of radioactivity (no readings above background were 

identified by field instrumentation). The area has been subsequently cleaned up. 

 In approximately September 1998, an incident occurred in Sector 20 with a Positron 

Target. The Thullium/Tungsten target disintegrated, resulting in the largest surface 

contamination. Smears measured a maximum of 10,000 dpm/100 cm2 beta. There was 

measureable clothing contamination as a result. One site expert believes individuals were 

sent to LBNL for chest counts following this incident. The incident was recorded in 

Occurrence Reporting and Processing System (ORPS). 

 Prior to the startup of the Actinide Room, a staff member was sent to Technical Area 

(TA)-55 at LANL to observe the operation with Pu-239. He spent a few days getting 

training from LANL so he could learn how to monitor and take precautions for alpha 

emitters. During the visit, there was a release of Pu-239. As a result, LANL required 

submittal of bioassay (~1998). He was later sent to LLNL for a follow-up count. 

One site expert indicated he was aware of no emergencies or fires in the history of SLAC 

involving dispersal of radioactive materials. 
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Comments on the NIOSH Site Profile 

Recommended updates to Table 2-1, pp. 11–12 of the NIOSH site profile. 

Area Period of Operation Comment 

LINAC Tunnel 1966–present Since April 2008, only the last one-third of the tunnel has 

been used. 

Klystron Gallery 1966–present 

End Station B 1966–1985 +/- 2 years Since the B-Line was last used in the early 1980s, End 

Station B has housed the NLCTA. 

End Station C 1966–present The LCLS tunnel now passes through the area which was 

known as End Station C years ago. 

BSY 1966–present Up until the 1980s, the beam could be directed to one of 

three end stations (A, B or C) or to the PEP or SPEAR 

storage rings. Later, the SLC arcs were added. Now, the 

beams can be directed to the LCLS or End Station A. 

SPEAR 

SSRL 

1972–present 

PEP 1980–1991 

PEP-II 1998–April 2008 

SLC 1988–1998 

Next Linear Collider 

Test Accelerator 

1993–present 

Recommended update to page 12, second paragraph, of the NIOSH site profile. 

The first damping ring was built in 1978 rather than 1984. 

[SC&A asked if it would be appropriate to apply the 1/r correction for estimating skyshine doses 

closer than the fence line, which would increase any environmental dose assigned as being same 

as the PMS doses.] 

SLAC staff indicated if the location is within tens of meters close to the source point (which 

could vary, depending on which SLAC facilities are operating), the 1/r correction would be 

appropriate, but to estimate the far-distance public doses offsite, the 1/r2

 is more appropriate. 

Assuming the claimants get a fraction of the total dose detected by the environmental dosimeters 

is appropriate. Workers are at the site only a fraction of the total hours in a year, and the 

dosimeters record the dose at the stations every moment throughout the year. 

There was a site visit conducted by Norm Rohrig [ORAUT] and two others in 2006. They went 

through a large amount of documents and scanned them. During this visit, the team interviewed 

[redacted] [SLAC], [redacted] [SLAC], and [redacted] [SLAC]. SLAC Radiological 

Protection staff received a copy of the draft NIOSH TBD and provided comments. 

In 2007, SLAC had a DOE Compliance Audit by the Office of Independent Oversight (OIO). 

The OIO team raised several issues regarding the Radiation Protection program. They took 

exception to the way SLAC implemented radiological posting in some areas. Radiation 

Protection contracted with Norm Rohrig, the NIOSH Site Profile author, to work with ex-SLAC 
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NOTICE:

Radiological Control Manager [redacted] on addressing the RWP and posting issues identified 

in the audit. SLAC did a benchmarking with similar facilities like BNL, Fermi National 

Laboratory, etc., and implemented best-management practices. 

One site expert who reviewed the NIOSH TBD found it to be very general. 

Miscellaneous 

[SC&A asked one site expert to point out health physics related differences between different 

types of accelerators.] 

There are significant differences between electron accelerators and proton and ion accelerators. 

The Fermi Accelerator is a proton accelerator and is not similar to the electron/positron 

accelerator at SLAC. Thomas Jefferson Laboratory is an electron/positron facility similar to 

SLAC. With a proton accelerator, there are approximately 100 times (2 orders of magnitude) 

more neutrons generated as prompt radiation over the whole neutron energy spectrum for the 

same power and energy of incident beam. Protons have higher mass than electrons and interact 

through nuclear reaction; they can more easily dislodge neutrons from an atom. 

Beryllium exposure at the site is minimal. There is a small amount of Be-Copper alloy.