Page 1 of 20

DOE Review Release 10/23/2020

Estimation of Neutron Flux and Neutron 

Dose Rates from Alpha-Neutron Reactions in 

Uranium and Thorium Compounds

ORAUT-OTIB-0024 Rev. 01

Effective Date: 10/08/2020

Supersedes: Revision 00

Subject Expert(s): Caleigh Samuels and Matthew H. Smith

Document Owner 

Approval: Signature on File

Matthew H. Smith, Document Owner

Approval Date: 10/05/2020

Concurrence: Signature on File

John M. Byrne, Objective 1 Manager

Concurrence Date: 10/05/2020

Concurrence: Signature on File

Scott R. Siebert, Objective 3 Manager

Concurrence Date: 10/07/2020

Concurrence: Vickie S. Short Signature on File for

Kate Kimpan, Project Director

Concurrence Date: 10/05/2020

Approval: Signature on File

Timothy D. Taulbee, Associate Director for Science

Approval Date: 10/08/2020

FOR DOCUMENTS MARKED AS A TOTAL REWRITE, REVISION, OR PAGE CHANGE, REPLACE THE PRIOR 

REVISION AND DISCARD / DESTROY ALL COPIES OF THE PRIOR REVISION.

New Total Rewrite Revision Page Change
Document No. ORAUT-OTIB-0024 Revision No. 01 Effective Date: 10/08/2020 Page 2 of 20

 

PUBLICATION RECORD

EFFECTIVE 

DATE

REVISION 

NUMBER DESCRIPTION

04/07/2005 00 New technical information bulletin to provide estimation of neutron 

doses from uranium and thorium compounds that contain low atomic 

number components. Incorporates formal internal and NIOSH review 

comments. Initiated by Cindy W. Bloom.

10/08/2020 01 Revision initiated to update neutron flux from uranium and thorium 

compounds that contain low atomic number components using 

Monte Carlo calculation methods. Incorporates formal internal and 

NIOSH review comments. Training required: As determined by the 

Objective Manager. Initiated by Matthew H. Smith.

TRADEMARK INFORMATION

MCNP® is a registered trademark of Triad National Security in the United States and/or other 

countries.

All other trademarks are the property of their respective owners.
Document No. ORAUT-OTIB-0024 Revision No. 01 Effective Date: 10/08/2020 Page 3 of 20

 

TABLE OF CONTENTS

SECTION TITLE PAGE

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

1.0 Introduction ................................................................................................................................. 6

1.1 Purpose........................................................................................................................... 6

1.2 Scope.............................................................................................................................. 6

2.0 Neutron Flux Calculations........................................................................................................... 7

2.1 Calculation of Neutron Production Rates with Sources 4C............................................. 7

2.2 Calculation of Neutron Production Rates with Sources 4C-m ......................................... 8

2.3 MCNP 6.2 Modeling........................................................................................................ 9

3.0 Neutron Flux Results ................................................................................................................10

4.0 Neutron Dose Rate Calculations...............................................................................................11

4.1 Uranium Compounds ....................................................................................................11

4.2 Thorium Compounds.....................................................................................................12

5.0 Neutron Dose Energy Fractions................................................................................................14

6.0 Conclusions ..............................................................................................................................17

References ...........................................................................................................................................19

LIST OF TABLES

TABLE TITLE PAGE

3-1 Neutron flux results...................................................................................................................10

4-1 Natural uranium per-gram ambient dose rate equivalents without alpha-emitting progeny......12

4-2 Natural uranium per-gram ambient dose rate equivalents with alpha-emitting progeny in 

secular equilibrium with 226Ra in the 238U chain and 223Ra in the 235U chain .............................12

4-3 Natural uranium per-gram ambient dose rate equivalents without alpha-emitting progeny......12

4-4 Natural uranium per-gram ambient dose rate equivalents with alpha-emitting progeny in 

secular equilibrium with 226Ra in the 238U chain and 223Ra in the 235U chain .............................13

4-5 Natural uranium per-gram ambient dose rate equivalents with alpha-emitting progeny in 

secular equilibrium with 210Po in the 238U chain and 211Po in the 235U chain..............................13

4-6 Natural thorium per-gram ambient dose rate equivalents for ThF4 in secular equilibrium 

through 224Ra ............................................................................................................................13

4-7 Natural thorium per-gram ambient dose rate equivalents for ThF4 in secular equilibrium 

through 212Po.............................................................................................................................13

4-8 Thorium isotope mix per-gram ambient dose rate equivalents for ThF4 in secular 

equilibrium through 224Ra..........................................................................................................14

4-9 Thorium isotope mix per-gram ambient dose rate equivalents for ThF4 in secular 

equilibrium through 212Po ..........................................................................................................14

5-1 Neutron ambient dose fractions for UO2 sources without alpha-emitting progeny....................14

5-2 Neutron ambient dose fractions for UO2 sources with alpha-emitting progeny in secular 

equilibrium with 226Ra in the 238U chain and 223Ra in the 235U chain..........................................14

5-3 Neutron ambient dose fractions for UO3 sources without alpha-emitting progeny....................14
Document No. ORAUT-OTIB-0024 Revision No. 01 Effective Date: 10/08/2020 Page 4 of 20

 

5-4 Neutron ambient dose fractions for UO3 sources with alpha-emitting progeny in secular 

equilibrium with 226Ra in the 238U chain and 223Ra in the 235U chain..........................................14

5-5 Neutron ambient dose fractions for U3O8 sources without alpha-emitting progeny ..................14

5-6 Neutron ambient dose fractions for U3O8 sources with alpha-emitting progeny in secular 

equilibrium with 226Ra in the 238U chain and 223Ra in the 235U chain..........................................14

5-7 Neutron ambient dose fractions for Na2U2O7 sources without alpha-emitting progeny ............15

5-8 Neutron ambient dose fractions for Na2U2O7 sources with alpha-emitting progeny in 

secular equilibrium with 226Ra in the 238U chain and 223Ra in the 235U chain .............................15

5-9 Neutron ambient dose fractions for UF4 sources without alpha-emitting progeny ....................15

5-10 Neutron ambient dose fractions for UF6 sources without alpha-emitting progeny ....................15

5-11 Natural thorium neutron ambient dose fractions for ThF4 sources without alpha-emitting 

progeny.....................................................................................................................................15

5-12 Thorium isotope mix neutron ambient dose fractions for ThF4 sources without alphaemitting progeny .......................................................................................................................15

5-13 Neutron ambient dose fractions for UO2 sources with alpha-emitting progeny in secular 

equilibrium with 226Ra in the 238U chain and 223Ra in the 235U chain..........................................15

5-14 Neutron ambient dose fractions for UO2 sources with alpha-emitting progeny in secular 

equilibrium with 210Po in the 238U chain and 211Po in the 235U chain ..........................................15

5-15 Neutron ambient dose fractions for UO3 sources without alpha-emitting progeny....................15

5-16 Neutron ambient dose fractions for UO3 sources with alpha-emitting progeny in secular 

equilibrium with 226Ra in the 238U chain and 223Ra in the 235U chain..........................................15

5-17 Neutron ambient dose fractions for UO3 sources with alpha-emitting progeny in secular 

equilibrium with 210Po in the 238U chain and 211Po in the 235U chain ..........................................16

5-18 Neutron ambient dose fractions for U3O8 sources without alpha-emitting progeny ..................16

5-19 Neutron ambient dose fractions for U3O8 sources with alpha-emitting progeny in secular 

equilibrium with 226Ra in the 238U chain and 223Ra in the 235U chain..........................................16

5-20 Neutron ambient dose fractions for U3O8 sources with alpha-emitting progeny in secular 

equilibrium with 210Po in the 238U chain and 211Po in the 235U chain ..........................................16

5-21 Neutron ambient dose fractions for Na2U2O7 sources without alpha-emitting progeny ............16

5-22 Neutron ambient dose fractions for Na2U2O7 sources with alpha-emitting progeny in 

secular equilibrium with 226Ra in the 238U chain and 223Ra in the 235U chain .............................16

5-23 Neutron ambient dose fractions for Na2U2O7 sources with alpha-emitting progeny in 

secular equilibrium with 210Po in the 238U chain and 211Po in the 235U chain..............................16

5-24 Neutron ambient dose fractions for UF4 sources without alpha-emitting progeny ....................16

5-25 Neutron ambient dose fractions for UF4 sources with alpha-emitting progeny in secular 

equilibrium with 226Ra in the 238U chain and 223Ra in the 235U chain..........................................16

5-26 Neutron ambient dose fractions for UF4 sources with alpha-emitting progeny in secular 

equilibrium with 210Po in the 238U chain and 211Po in the 235U chain ..........................................16

5-27 Neutron ambient dose fractions for UF6 sources without alpha-emitting progeny ....................17

5-28 Neutron ambient dose fractions for UF6 sources with alpha-emitting progeny in secular 

equilibrium with 226Ra in the 238U chain and 223Ra in the 235U chain..........................................17

5-29 Neutron ambient dose fractions for UF6 sources with alpha-emitting progeny in secular 

equilibrium with 210Po in the 238U chain and 211Po in the 235U chain ..........................................17

5-30 Natural thorium neutron ambient dose fractions for ThF4 sources without alpha-emitting 

progeny.....................................................................................................................................17

5-31 Natural thorium neutron ambient dose fractions for ThF4 sources with alpha-emitting 

progeny in secular equilibrium through 212Po ............................................................................17

5-32 Thorium isotope mix neutron ambient dose fractions for ThF4 sources without alphaemitting progeny .......................................................................................................................17

5-33 Thorium isotope mix neutron ambient dose fractions for ThF4 sources with alpha-emitting 

progeny in secular equilibrium through 212Po ............................................................................17
Document No. ORAUT-OTIB-0024 Revision No. 01 Effective Date: 10/08/2020 Page 5 of 20

ACRONYMS AND ABBREVIATIONS

Ci curie

cm centimeter

DOE U.S. Department of Energy

ENDF Energy Nuclear Data Format

ft feet

g gram

hr hour

MCNP Monte Carlo N-Particle

MeV megaelectron-volt (1 million electron-volts)

n neutron

NIOSH National Institute for Occupational Safety and Health

NIST National Institute for Standards and Technology

ORAU Oak Ridge Associated Universities

s second

SRDB Ref ID Site Research Database Reference Identification (number)

TBD technical basis document

TENDL TALYS Evaluated Nuclear Data Library

TIB technical information bulletin

U.S.C. United States Code

Z atomic number

α alpha particle

§ section or sections
Document No. ORAUT-OTIB-0024 Revision No. 01 Effective Date: 10/08/2020 Page 6 of 20

1.0 INTRODUCTION

Technical information bulletins (TIBs) are not official determinations made by the National Institute for 

Occupational Safety and Health (NIOSH) but are rather general working documents that provide 

historical background information and guidance to assist in the preparation of dose reconstructions at 

particular sites or categories of sites. They will be revised in the event additional relevant information 

is obtained about the affected site(s). TIBs may be used to assist NIOSH staff in the completion of 

individual dose reconstructions.

In this document, the word “facility” is used as a general term for an area, building, or group of 

buildings that served a specific purpose at a site. It does not necessarily connote an “atomic weapons 

employer facility” or a “Department of Energy (DOE) facility” as defined in the Energy Employees 

Occupational Illness Compensation Program Act of 2000 [42 U.S.C. § 7384l(5) and (12)].

1.1 PURPOSE

Based on a review of Revision 00 of this document – specifically its use of older experimental data –

the Oak Ridge Associated Universities (ORAU) Team conducted a study to examine the feasibility of 

using modern computer codes such as the MCNP (Monte Carlo N-Particle) 6.2 transport code – in 

conjunction with the TENDL (TALYS Evaluated Nuclear Data Library) data libraries, the Sources 4C 

code, and the modified Sources 4C-m code – to calculate accurate values for the magnitude of the 

neutron flux from the following compounds: UO2, UO3, U3O8, Na2U2O7, UF4, UF6, ThF4, and Th(NO3)4. 

TENDL is a cross-section library that was produced with results from the TALYS code. It is used by 

MCNP to simulate particle interactions. TALYS is a software package that simulates nuclear 

reactions. In addition, neutron dose rate values for these compounds were calculated for use in 

project technical basis documents (TBD) for sites that processed the compounds listed above. In 

most cases, the data presented here will be used by site TBD authors and subject matter experts to 

derive annual neutron dose from work with these compounds to assign to energy employees who may 

not have been monitored for neutron radiation. Examples of these sites include: Mallinckrodt

Chemical Company, Linde Ceramics Plant, Nuclear Materials and Equipment Corporation, Battelle 

Laboratories, and United Nuclear Corporation in Hematite, Missouri.

1.2 SCOPE

Sources 4C and Sources 4C-m calculate neutron magnitude and spectra from (α,n) interactions, 

spontaneous fission, and delayed neutrons. The (α,n) spectra from these outputs as the source in 

MCNP are used. With these sources, MCNP was used to simulate the transport of the neutrons and 

to calculate the fluence both within the material, at 1 ft, and 3 ft.

TENDL is a cross-section library. MCNP uses cross-section libraries to model the transport of 

particles through materials. Unlike cross-section libraries provided with the MCNP 6.2 distribution, 

TENDL contains (α,n) cross-sections. Therefore, if proven to be accurate, TENDL would enable 

MCNP to model the (α,n) reaction, eliminating the need for Sources 4C and 4C-m. 

Volume-averaged neutron flux was calculated for the first seven compounds of interest using four

methods:

1. Calculations based on data from Revision 00 of this document (ORAUT 2005);

2. Combined application of Sources 4C and MCNP 6.2;

3. Combined application of Sources 4C-m and MCNP 6.2; and 

4. Application of MCNP 6.2 with TENDL (α,n) cross-section libraries. 
Document No. ORAUT-OTIB-0024 Revision No. 01 Effective Date: 10/08/2020 Page 7 of 20

 

Volume-averaged neutron flux for the eighth compound, Th(NO3)4, was calculated with the first and 

last method only due to software limitations.

ORAUT (2020a) provides the Sources 4C and 4C-m input files. ORAUT (2020b) and ORAUT (2020c)

contain the MCNP 6.2 input files based on Sources 4C and 4C-m neutron production rates, 

respectively. ORAUT (2020d) provides the MCNP input files based on TENDL data libraries, and

ORAUT (2020e) discusses the TENDL data.

Results from each method were compared.

Neutron dose rate calculations (at distances of 1 ft and 3 ft) were then derived from the neutron flux 

information – specifically from Sources 4C and 4C-m results. The 1 ft and 3 ft distances are 

reasonable bounding distances for activities performed by energy employees. Other distances and 

specific geometries can be modeled, if needed, using the methods discussed in this document.

2.0 NEUTRON FLUX CALCULATIONS

2.1 CALCULATION OF NEUTRON PRODUCTION RATES WITH SOURCES 4C

The Sources 4C code calculates the neutron production rates and neutron spectra from spontaneous 

(α,n) fission reactions and delayed neutron emission (Perry and Wilson 1981). The production rates 

and spectra can be calculated in four situations: a homogeneous mixture of alpha-emitting material 

and low atomic number (low-Z) target material, an interface between a region of alpha-emitting 

material and a region of target material, a monoenergetic alpha beam incident on a low-Z target, or a 

three-region interface in which a third region lies between a region of alpha-emitting material and a 

region of low-Z target material. In this study, Sources 4C was used to calculate neutron production 

rates for the compounds. These production rates were later applied in the development of source 

definitions in MCNP 6.2. 

All compounds – as listed above in Section 1.1 – were modeled as solid, homogeneous mixtures. 

The atomic fraction of each element was determined from the chemical formula of the compound. 

Natural abundance data for each isotope were taken from “Atomic Weights and Isotopic Compositions 

with Relative Atomic Masses” from the National Institute for Standards and Technology (NIST) 

Physical Measurement Laboratory (Coursey et al. 2020). The atomic fraction of each target isotope 

was determined by multiplying the natural abundance of the isotope by the atomic fraction of its 

element in the compound. For all compounds, the atomic density Ni of each alpha emitter was 

determined as: 

(2-1) γ ρi A

i

N N

M =

where

γi = abundance of isotope i

ρ = physical density of the compound (g/cm3) 

NA = Avogadro’s number

M = molecular weight of the compound (g) 

The isotopic abundances were also taken from Coursey et al. (2020). The physical densities for UO2, 

U3O8, UF4, and UF6 were taken from Characteristics of Uranium and its Compounds (DOE 2001). 

The physical density of UO3 was taken from Cameco UO3 Materials Analysis (Hill et al. 2012). The 

physical density for Na2U2O7 was taken as the average of the values in Table A.28 of Stimulant Basis 

for the Standard High Solids Vessel Design (Peterson et al. 2017). The physical density for ThF4 was 
Document No. ORAUT-OTIB-0024 Revision No. 01 Effective Date: 10/08/2020 Page 8 of 20

 

taken from WolframAlpha (2020) to maintain consistency with Revision 00. The density for Th(NO3)4

was taken as the average from Table 12 of Analytical Characterization of the Thorium Nitrate 

Stockpile (Mattus, Hermes, and Terry 2003). 

The molecular weights for Na2U2O7 and Th(NO3)4 were calculated from standard atomic weights in 

Coursey et al. (2020). The molecular weight for all other compounds was taken from the National 

Institute of Standards and Technology “Chemistry WebBook” (DOC 2020). 

Sources 4C presents several limitations. The primary limitation is a hardcoded 6.5-MeV alpha energy 

threshold for oxygen and a 6.0-MeV threshold for fluorine. This threshold disables the evaluation of 

all compounds through the full decay chain. Therefore, the Sources 4C method was only applied to 

uranium compounds without progeny, uranium oxides assumed to be in equilibrium through 223Ra, 

and thorium tetrafluoride assumed to be in equilibrium through 224Ra. Neutron production rates from

Th(NO3)4 could not be obtained with Sources 4C due to a lack of nuclide-level branching data for 14N.

2.2 CALCULATION OF NEUTRON PRODUCTION RATES WITH SOURCES 4C-m 

Sources 4C-m is a modified version of Sources 4C, which enables the evaluation of neutron 

production from (α,n) reactions over an extended alpha energy range (Montague 2018) by removing

the hardcoded energy limit for the (α,2n) energy threshold. Neutron production rates were extended 

to these higher energies with the application of 2005 TENDL cross-section data. Sources 4C-m was 

then used to calculate neutron production rates for the compounds. These production rates were later 

applied in the development of source definitions in MCNP 6.2. 

Neutron production rates were determined with Sources 4C-m for all uranium compounds without 

progeny, all uranium compounds assumed to be in equilibrium through 223Ra, and all uranium 

compounds assumed to be in equilibrium through the entire decay chain. 

Specifically, there were three cases considered for all uranium compounds:

1. No alpha-emitting progeny present, 

2. Alpha-emitting progeny are assumed to be present and in secular equilibrium through 226Ra in 

the 238U chain and through 223Ra in the 235U chain, and

3. Alpha-emitting progeny are assumed to be present and in secular equilibrium through 210Po in 

the 238U chain and through 211Po in the 235U chain. 

The first case was examined with all three modeling techniques. Based on results and resource 

requirements, Sources 4C and Sources 4C-m were chosen for examination of cases 2 and 3. Case 3 

was only examined with Sources 4C-m because the emission energies exceed the capabilities of 

Sources 4C. 

Neutron production rates were determined with Sources 4C-m for thorium tetrafluoride assumed to be 

in equilibrium through 224Ra, and for thorium tetrafluoride assumed to be in equilibrium through the 

entire decay chain. Neutron production rates from Th(NO3)4 could not be obtained with Sources 4C-m 

due to a lack of nuclide-level branching data for 14N.

Sources 4C has a pedigree that Sources 4C-m lacks. The original code has been validated against 

measured spectra and the development of the code has been published in reviewed journals. To the 

best of my knowledge, Sources 4C-m has only been validated against Sources 4C and has not been 

published in a reviewed journal.
Document No. ORAUT-OTIB-0024 Revision No. 01 Effective Date: 10/08/2020 Page 9 of 20

 

2.3 MCNP 6.2 MODELING

MCNP 6.2 is a commonly used radiation transport code with a wide range of applications (Werner et 

al. 2013). In combination with Sources 4C and Sources 4C-m, MCNP 6.2 was used to simulate the 

volume-averaged neutron flux from each compound. Sources 4C and Sources 4C-m do not account 

for neutron interactions with matter, only production rates. This study used MCNP 6.2 to account for 

self-attenuation.

Each compound was modeled as a solid sphere with a radius of 1 cm (V = 4.18879 cm3) in a vacuum. 

All materials were defined using atomic fractions determined by multiplying the natural abundance of 

the isotope by the atomic fraction of its element in the compound. A neutron source was 

homogenously distributed throughout the sphere. The energy spectrum of the source was determined 

by the (α,n) neutron production rates calculated with Sources 4C and Sources 4C-m. The volumeaveraged neutron flux was tallied over a volume of the sphere in which charged particle equilibrium 

exists (r = 0.99 cm; V = 4.06438 cm3). This constraint was chosen for comparison purposes with 

Sources 4C (and 4C-m), which assume the material is infinite.

All materials were defined using atomic fractions determined by multiplying the natural abundance of 

the isotope by the atomic fraction of its element in the compound. All neutron cross-section data were 

pulled from the ENDF71x cross-section library (continuous energy neutron cross-section data tables 

published by Los Alamos National Laboratory) (Conlin et al. 2013). 

MCNP 6.2 Modeling Using TENDL Cross-Section Libraries

MCNP 6.2 was also used to determine the volume-averaged neutron flux without the aid of Sources 

4C or Sources 4C-m. The same geometry and material definitions were used as in previous cases, 

but the source was defined as an alpha emitter with an energy probability distribution corresponding 

to the decay of alpha emitters in the material. For each isotope, alpha emission energy and intensity 

data were taken from Rad Toolbox (Eckerman and Sjoreen 2013). The probability of each alpha 

energy was determined by multiplying the corresponding intensity by the relative activity of the parent 

isotope. 

TENDL cross-section libraries were applied to model alpha interactions within the material (TENDL is 

a database of cross-section data that can be used by MCNP to model the interactions of particles in 

materials). The TENDL libraries are nuclear data libraries developed by the Paul Scherrer Institute 

and the International Atomic Energy Agency (previously developed by NRG Petten) using the T6 

codes (Koning and Rochman 2012). For a more in-depth discussion, the reader is referred to ORAUT 

(2020e). Neutron interactions were determined by the ENDF71x cross-section library as in the 

previous section.

Low count rates lead to high statistical errors for the uranium oxides. Therefore, for each of these 

compounds, two files were run with altered material compositions: one in which all oxygen was 

assumed to be 17O and one in which all oxygen was assumed to be 18O. The total volume-averaged 

neutron flux was determined in post-processing as: 

(2-2) ΦΦ Φ a a ,O-17 O-17 ,O-18 O-18 = + f f

where

fa,i = atomic fraction of isotope i 

Φi = volume-averaged neutron flux of isotope i. 
Document No. ORAUT-OTIB-0024 Revision No. 01 Effective Date: 10/08/2020 Page 10 of 20

 

Calculation Based on Revision 00 (ORAUT 2005) 

The volume-averaged neutron flux Φ was back-calculated from the dose rates and isotope properties 

in Tables 5-1, 5-2, 6-1, and 6-2 of Revision 00 as (ORAUT 2005):

Φρ ω( ) (2-3) = × ×× j iii ∑ a Y

where

ρj = physical density of element j in the compound (g/cm3) 

ωi = mass fraction of isotope i

ai = specific activity of isotope i (Ci/g) 

Yi = neutron yield of isotope i [1/(s-Ci)]. 

Flux was calculated for all uranium compounds covered in Revision 00 (ORAUT 2005) without 

progeny and all thorium compounds covered in Revision 00 were assumed to be in equilibrium 

through 224Ra.

3.0 NEUTRON FLUX RESULTS

Magnitudes of the volume-averaged neutron flux for each compound and each method of calculation 

[calculations based on Revision 00 data (ORAUT 2005)], combined application of Sources 4C and 

MCNP 6.2, combined application of Sources 4C-m and MCNP 6.2, and application of MCNP 6.2 with 

TENDL (α,n) cross-section libraries are displayed in Table 3-1.

Table 3-1. Neutron flux results. 

1 

Compound

2 

Revision 00 

(n/s-cm3)

3

Sources 4C 

and MCNP 6.2 

(n/s-cm3)

4

Sources 4C-m 

and MCNP 6.2 

(n/s-cm3)

5

MCNP 6.2 and 

TENDL 

(n/s-cm3)

6

% difference 

between 

Columns 3 and 5

UO2 6.87E-03 1.89E-03 1.91E-03 1.67E-03a 12.4a

UO3 4.32E-03 1.53E-03 1.54E-03 1.67E-03a 8.8a

U3O8 5.00E-03 1.69E-03 1.66E-03 1.21E-03a 33.1a

Na2U2O7 1.29E-02 5.01E-03 6.65E-03 9.08E-04a 138.6a

Na2U2O7 1.29E-02 5.01E-03 6.65E-03 1.47E-03b 109.3b

UF4 3.02E-01 1.55E-01 1.47E-01 1.43E-01a 8.1a

UF6 1.88E-01 1.09E-01 1.09E-01 9.94E-02a 9.2a

ThF4 3.24E-01 1.60E-01 1.57E-01 1.67E-01a 4.3a

Th(NO3)4 5.67E-04 Not applicable Not applicable 2.32E-04a Not applicable

a. Results produced with TENDL 2014 cross-section library.

b. Results produced with TENDL 2015 cross-section library.

Compounds evaluated in this study are listed in the first column. The volume-averaged neutron flux 

as calculated from the values in Revision 00 (ORAUT 2005) are listed in column 2. These values are 

consistently higher than those calculated with simulations. The third column lists the volumeaveraged neutron flux as calculated with MCNP 6.2 using the neutron production rates from Sources 

4C. Revision 00 results and Sources 4C results show disagreement with a percent difference ranging 

from 53% to 114%. Column 4 lists the volume-averaged neutron flux as calculated with MCNP 6.2

using the neutron production rates from Sources 4C-m. These values are in good agreement with 

those in the previous column with a maximum percent difference of 28%. The fifth column lists the 

volume-averaged neutron flux determined by MCNP 6.2 calculations alone using TENDL crosssection libraries.

The final column lists the percent difference between the column 3 flux values (as calculated with 

MCNP 6.2 using Sources 4C production rates) and the column 5 flux values (determined by MCNP 
Document No. ORAUT-OTIB-0024 Revision No. 01 Effective Date: 10/08/2020 Page 11 of 20

 

6.2 calculations using TENDL cross-section libraries). For the majority of the compounds (UO2, UO3, 

UF4, UF6, ThF4), the values agree within statistical uncertainty. Sources 4C results typically show 

±17% agreement with measured results (Perry and Wilson 1981). MCNP 6.2 results for these 

compounds were calculated with 10% relative error.

The MCNP 6.2 results for U3O8 were calculated to approximately 5% error due to statistical 

uncertainty. Although the values from U3O8 do not show agreement within statistical error, the 

absolute difference is only 4.8 × 10-4 n/s-cm3. 

Na2U2O7 was the only compound that showed greater than a 100% difference between the flux as 

calculated with MCNP 6.2 and Sources 4C production rates and the flux determined by MCNP 6.2

calculations alone using TENDL libraries. Since 2008, an updated TENDL library has been released 

every year or two. At the time this work was completed, 9 libraries had been released (now 10). 

Unlike other isotopes contained in the compounds of interest, the 23Na (α,n) cross-sections showed 

significant differences between the 2014 release and the 2015 release. Based on the cross-section 

data used in Sources 4C (from published sources) and the other TENDL releases, the increased 23Na

(α,n) cross-sections in the 2015 release were likely in error.

4.0 NEUTRON DOSE RATE CALCULATIONS

Neutron production rates and spectra from (α,n) interactions for UO2, UO3, U3O8, Na2U2O7, UF4, and 

UF6 were determined with Sources 4C. The neutron spectra were used as the energy distribution of a 

neutron point source in MCNP simulations used to calculate an ambient dose rate equivalent. In 

these simulations, the neutron fluence per source neutron was tallied at 1 and 3 ft from the neutron 

point source in air. ICRP Publication 74 conversion coefficients were used to convert the neutron 

fluence into ambient dose rate equivalent. The ambient dose rate equivalent from 1 g of natural 

uranium or natural thorium was calculated as the product of the ambient dose rate equivalent per 

source neutron, the neutron production magnitude (as determined by Sources 4C), and the density of 

uranium or thorium in the compound (ICRP 1997). 

4.1 URANIUM COMPOUNDS

Neutron dose rate values for the compounds discussed in this document were calculated and are 

shown in this Section (uranium compounds) and Section 4.2 (thorium compounds) for use in dose 

reconstruction project TBDs for sites that processed these compounds. In most cases, the data 

presented here will be used by site TBD authors and subject matter experts to derive annual neutron 

dose from work with these compounds to assign to energy employees who may not have been 

monitored for neutron radiation. Examples of these sites include (but are not limited to) Mallinckrodt 

Chemical Company, Linde Ceramics Plant, Nuclear Materials and Equipment Corporation, Battelle 

Laboratories, and United Nuclear Corporation in Hematite, Missouri.

Table 4-1 shows the ambient dose rate equivalents at 1 and 3 ft from 1 g of natural uranium when no 

alpha-emitting progeny are considered. Table 4-2 shows the ambient dose rate equivalents at 1 and 

3 ft from 1 g of natural uranium when alpha-emitting progeny through 223Ra and 226Ra are assumed to 

be in secular equilibrium.
Document No. ORAUT-OTIB-0024 Revision No. 01 Effective Date: 10/08/2020 Page 12 of 20

 

Table 4-1. Natural uranium per-gram ambient dose rate 

equivalents without alpha-emitting progeny (rem/hr-g).a

Chemical form 1 ft 3 ft

UO2 3.22E-12 3.57E-13

UO3 4.19E-12 4.65E-13

U3O8 3.90E-12 4.32E-13

Na2U2O7 1.31E-11 1.45E-12

UF4 4.45E-10 4.93E-11

UF6 5.35E-10 5.94E-11

a. Source: Sources 4C results.

Table 4-2. Natural uranium per-gram ambient dose rate 

equivalents with alpha-emitting progeny in secular 

equilibrium with 226Ra in the 238U chain and 223Ra in the 

235U chain (rem/hr-g).a

Chemical form 1 ft 3 ft

UO2 7.64E-12 8.48E-13

UO3 9.95E-12 1.10E-12

U3O8 9.25E-12 1.03E-12

Na2U2O7 2.71E-11 3.01E-12

a. Source: Sources 4C results.

The (α,n) neutron production calculations of Sources 4C are limited to alpha energies below 6.5 MeV 

for oxygen targets and below 6 MeV for fluorine targets. Therefore, no alpha-emitting progeny were 

considered for UF4 or UF6 and the full chain was not considered for any compounds using Sources 

4C. Sources 4C-m extends the (α,n) cross-section library enabling calculations for increased alpha 

energies. Therefore, the calculations were repeated using Sources 4C-m neutron production rates 

and spectra. Table 4-3 shows the ambient dose rate equivalents at 1 and 3 ft from 1 g of natural 

uranium when no alpha-emitting progeny are considered. Table 4-4 shows the resulting equivalents 

when alpha-emitting progeny through 223Ra and 226Ra are assumed to be in secular equilibrium. 

Table 4-5 shows the equivalents when alpha-emitting progeny through 210Po and 211Po are assumed 

to be in secular equilibrium.

Table 4-3. Natural uranium per-gram ambient dose rate 

equivalents without alpha-emitting progeny (rem/hr-g).a

Chemical form 1 ft 3 ft

UO2 3.21E-12 3.56E-13

UO3 4.18E-12 4.63E-13

U3O8 3.88E-12 4.31E-13

Na2U2O7 1.70E-11 1.89E-12

UF4 4.32E-10 4.79E-11

UF6 5.19E-10 5.76E-11

a. Source: Sources 4C-m results.

4.2 THORIUM COMPOUNDS

As for the uranium compounds, the ambient dose rate equivalents were calculated for ThF4 at 1 and 

3 ft. Table 4-6 shows the equivalents from 1 g of natural thorium when alpha-emitting progeny 

through 224Ra are assumed to be in secular equilibrium. Table 4-7 shows the equivalents when alphaemitting progeny through 212Po are assumed to be in secular equilibrium.
Document No. ORAUT-OTIB-0024 Revision No. 01 Effective Date: 10/08/2020 Page 13 of 20

 

Table 4-4. Natural uranium per-gram ambient dose rate 

equivalents with alpha-emitting progeny in secular 

equilibrium with 226Ra in the 238U chain and 223Ra in the 

235U chain (rem/hr-g).a

Chemical form 1 ft 3 ft

UO2 7.61E-12 8.44E-13

UO3 9.91E-12 1.10E-12

U3O8 9.22E-12 1.02E-12

Na2U2O7 3.54E-11 3.93E-12

UF4 1.10E-09 1.23E-10

UF6 1.33E-09 1.47E-10

a. Source: Sources 4C-m results.

Table 4-5. Natural uranium per-gram ambient dose rate 

equivalents with alpha-emitting progeny in secular 

equilibrium with 210Po in the 238U chain and 211Po in the 

235U chain (rem/hr-g).a

Chemical form 1 ft 3 ft

UO2 3.84E-11 4.26E-12

UO3 5.01E-11 5.56E-12

U3O8 4.65E-11 5.16E-12

Na2U2O7 1.21E-09 1.34E-10

UF4 9.44E-09 1.05E-09

UF6 1.14E-08 1.26E-09

a. Source: Sources 4C-m results.

Table 4-6. Natural thorium per-gram ambient dose rate 

equivalents for ThF4 in secular equilibrium through 224Ra

(rem/hr-g). 

Method 1 ft 3 ft

Sources 4C 5.33E-10 5.91E-11

Sources 4C-m 5.21E-10 5.78E-11

Table 4-7. Natural thorium per-gram ambient dose rate 

equivalents for ThF4 in secular equilibrium through 212Po 

(rem/hr-g). 

Method 1 ft 3 ft

Sources 4C-m 3.67E-09 4.07E-10

Dose rates from Th(NO3)4 were not calculated due to the lack of nuclide-level branching data for 14N in 

the Sources 4C and Sources 4C-m codes.

Using the same method, the ambient dose rate equivalents at 1 and 3 ft were calculated for ThF4

based on the thorium isotope mixture at Mallinckrodt. This mixture is included here based on the 

information in – and potential use with – Section 5.4.2 of ORAUT-TKBS-0005, Basis for Development 

of an Exposure Matrix for the Mallinckrodt Chemical Company St. Louis Downtown Site and the St.

Louis Airport Site, St. Louis, Missouri (ORAUT 2010). This mixture consisted of 88.4% 232Th and 

11.6% 230Th. Table 4-8 shows the ambient dose rate equivalents from 1 g of the thorium mixture 

when 232Th alpha-emitting progeny through 224Ra are assumed to be in secular equilibrium. Table 4-9 

shows the equivalents when 232Th alpha-emitting progeny through 212Po are assumed to be in secular 

equilibrium.
Document No. ORAUT-OTIB-0024 Revision No. 01 Effective Date: 10/08/2020 Page 14 of 20

 

Table 4-8. Thorium isotope mix per-gram ambient dose 

rate equivalents for ThF4 in secular equilibrium through 

224Ra (rem/hr-g).

Method 1 ft 3 ft

Sources 4C 2.02E-06 2.24E-07

Sources 4C-m 1.89E-06 2.10E-07

Table 4-9. Thorium isotope mix per-gram ambient dose 

rate equivalents for ThF4 in secular equilibrium through 

212Po (rem/hr-g). 

Method 1 ft 3 ft

Sources 4C-m 1.90E-06 2.10E-07

5.0 NEUTRON DOSE ENERGY FRACTIONS

Neutron spectra data from Sources 4C and 4C-m were used to generate Tables 5-1 to 5-33 to assist 

with the entry of neutron dose information (based on the dose rate data provided in Section 4.0) into 

IREP. The energy bins in each table correlate to the available bins available in IREP. In addition, the 

ambient [(H*10)] dose conversion values (DCFs) given in OCAS-IG-001, External Dose 

Implementation Guideline [NIOSH 2007], should be used with the data presented here to properly 

enter organ dose into IREP. 

Table 5-1. Neutron ambient dose fractions for 

UO2 sources without alpha-emitting progeny.

a

Neutron energy group Dose fraction

<10 keV 2.50E-06

10–100 keV 5.21E-04

0.1–2 MeV 3.95E-01

2–20 MeV 6.04E-01

a. Source: Sources 4C results.

Table 5-2. Neutron ambient dose fractions for 

UO2 sources with alpha-emitting progeny in 

secular equilibrium with 226Ra in the 238U chain 

and 223Ra in the 235U chain.

a

Neutron energy group Dose fraction

<10 keV 3.31E-06

10–100 keV 6.71E-04

0.1–2 MeV 3.64E-01

2–20 MeV 6.35E-01

a. Source: Sources 4C results.

Table 5-3. Neutron ambient dose fractions for 

UO3 sources without alpha-emitting progeny.

a

Neutron energy group Dose fraction

<10 keV 2.51E-06

10–100 keV 5.22E-04

0.1–2 MeV 3.95E-01

2–20 MeV 6.05E-01

a. Source: Sources 4C results.

Table 5-4. Neutron ambient dose fractions for 

UO3 sources with alpha-emitting progeny in 

secular equilibrium with 226Ra in the 238U chain 

and 223Ra in the 235U chain.

a

Neutron energy group Dose fraction

<10 keV 3.31E-06

10–100 keV 6.72E-04

0.1–2 MeV 3.64E-01

2–20 MeV 6.35E-01

a. Source: Sources 4C results.

Table 5-5. Neutron ambient dose fractions for 

U3O8 sources without alpha-emitting progeny.

a

Neutron energy group Dose fraction

<10 keV 2.51E-06

10–100 keV 5.22E-04

0.1–2 MeV 3.95E-01

2–20 MeV 6.04E-01

a. Source: Sources 4C results.

Table 5-6. Neutron ambient dose fractions for 

U3O8 sources with alpha-emitting progeny in 

secular equilibrium with 226Ra in the 238U chain 

and 223Ra in the 235U chain.

a

Neutron energy group Dose fraction

<10 keV 3.31E-06

10–100 keV 6.72E-04

0.1–2 MeV 3.64E-01

2–20 MeV 6.35E-01

a. Source: Sources 4C results. 
Document No. ORAUT-OTIB-0024 Revision No. 01 Effective Date: 10/08/2020 Page 15 of 20

 

Table 5-7. Neutron ambient dose fractions for 

Na2U2O7 sources without alpha-emitting 

progeny.

a

Neutron energy group Dose fraction

<10 keV 1.66E-05

10–100 keV 3.78E-03

0.1–2 MeV 8.12E-01

2–20 MeV 1.84E-01

a. Source: Sources 4C results.

Table 5-8. Neutron ambient dose fractions for 

Na2U2O7 sources with alpha-emitting progeny in 

secular equilibrium with 226Ra in the 238U chain 

and 223Ra in the 235U chain.

a

Neutron energy group Dose fraction

<10 keV 1.30E-05

10–100 keV 2.86E-03

0.1–2 MeV 8.36E-01

2–20 MeV 1.61E-01

a. Source: Sources 4C results.

Table 5-9. Neutron ambient dose fractions for 

UF4 sources without alpha-emitting progeny.

a

Neutron energy group Dose fraction

<10 keV 2.77E-06

10–100 keV 6.44E-04

0.1–2 MeV 9.61E-01

2–20 MeV 3.79E-02

a. Source: Sources 4C results.

Table 5-10. Neutron ambient dose fractions for 

UF6 sources without alpha-emitting progeny.

a

Neutron energy group Dose fraction

<10 keV 2.77E-06

10–100 keV 6.42E-04

0.1–2 MeV 9.61E-01

2–20 MeV 3.80E-02

a. Source: Sources 4C results. 

Table 5-11. Natural thorium neutron ambient 

dose fractions for ThF4 sources without alphaemitting progeny.

a

Neutron energy group Dose fraction

<10 keV 4.16E-06

10–100 keV 1.08E-03

0.1–2 MeV 8.26E-01

2–20 MeV 1.73E-01

a. Source: Sources 4C results.

Table 5-12. Thorium isotope mix neutron 

ambient dose fractions for ThF4 sources without 

alpha-emitting progeny.

a

Neutron energy group Dose fraction

<10 keV 1.35E-06

10–100 keV 4.80E-04

0.1–2 MeV 9.60E-01

2–20 MeV 3.92E-02

a. Source: Sources 4C results.

Table 5-13. Neutron ambient dose fractions for 

UO2 sources with alpha-emitting progeny in 

secular equilibrium with 226Ra in the 238U chain 

and 223Ra in the 235U chain.

a

Neutron energy group Dose fraction

<10 keV 3.21E-06

10–100 keV 6.50E-04

0.1–2 MeV 3.68E-01

2–20 MeV 6.32E-01

a. Source: Sources 4C-m results.

Table 5-14. Neutron ambient dose fractions for 

UO2 sources with alpha-emitting progeny in 

secular equilibrium with 210Po in the 238U chain 

and 211Po in the 235U chain.

a

Neutron energy group Dose fraction

<10 keV 2.09E-06

10–100 keV 4.19E-04

0.1–2 MeV 2.68E-01

2–20 MeV 7.31E-01

a. Source: Sources 4C-m results.

Table 5-15. Neutron ambient dose fractions for 

UO3 sources without alpha-emitting progeny.

a

Neutron energy group Dose fraction

<10 keV 2.47E-06

10–100 keV 5.02E-04

0.1–2 MeV 3.99E-01

2–20 MeV 6.01E-01

a. Source: Sources 4C-m results.

Table 5-16. Neutron ambient dose fractions for 

UO3 sources with alpha-emitting progeny in 

secular equilibrium with 226Ra in the 238U chain 

and 223Ra in the 235U chain.

a

Neutron energy group Dose fraction

<10 keV 3.21E-06

10–100 keV 6.51E-04

0.1–2 MeV 3.67E-01

2–20 MeV 6.32E-01

a. Source: Sources 4C-m results.
Document No. ORAUT-OTIB-0024 Revision No. 01 Effective Date: 10/08/2020 Page 16 of 20

 

Table 5-17. Neutron ambient dose fractions for 

UO3 sources with alpha-emitting progeny in 

secular equilibrium with 210Po in the 238U chain 

and 211Po in the 235U chain.

a

Neutron energy group Dose fraction

<10 keV 2.09E-06

10–100 keV 4.19E-04

0.1–2 MeV 2.68E-01

2–20 MeV 7.32E-01

a. Source: Sources 4C-m results.

Table 5-18. Neutron ambient dose fractions for 

U3O8 sources without alpha-emitting progeny.

a

Neutron energy group Dose fraction

<10 keV 2.47E-06

10–100 keV 5.02E-04

0.1–2 MeV 3.99E-01

2–20 MeV 6.01E-01

a. Source: Sources 4C-m results.

Table 5-19. Neutron ambient dose fractions for 

U3O8 sources with alpha-emitting progeny in 

secular equilibrium with 226Ra in the 238U chain 

and 223Ra in the 235U chain.

a

Neutron energy group Dose fraction

<10 keV 3.21E-06

10–100 keV 6.50E-04

0.1–2 MeV 3.68E-01

2–20 MeV 6.32E-01

a. Source: Sources 4C-m results.

Table 5-20. Neutron ambient dose fractions for 

U3O8 sources with alpha-emitting progeny in 

secular equilibrium with 210Po in the 238U chain 

and 211Po in the 235U chain.

a

Neutron energy group Dose fraction

<10 keV 2.09E-06

10–100 keV 4.19E-04

0.1–2 MeV 2.68E-01

2–20 MeV 7.32E-01

a. Source: Sources 4C-m results.

Table 5-21. Neutron ambient dose fractions for 

Na2U2O7 sources without alpha-emitting 

progeny.

a

Neutron energy group Dose fraction

<10 keV 1.87E-05

10–100 keV 4.48E-03

0.1–2 MeV 8.56E-01

2–20 MeV 1.40E-01

a. Source: Sources 4C-m results.

Table 5-22. Neutron ambient dose fractions for 

Na2U2O7 sources with alpha-emitting progeny in 

secular equilibrium with 226Ra in the 238U chain 

and 223Ra in the 235U chain.

a

Neutron energy group Dose fraction

<10 keV 1.43E-05

10–100 keV 3.35E-03

0.1–2 MeV 8.73E-01

2–20 MeV 1.23E-01

a. Source: Sources 4C-m results.

Table 5-23. Neutron ambient dose fractions for 

Na2U2O7 sources with alpha-emitting progeny in 

secular equilibrium with 210Po in the 238U chain 

and 211Po in the 235U chain.

a

Neutron energy group Dose fraction

<10 keV 4.24E-06

10–100 keV 9.67E-04

0.1–2 MeV 7.10E-01

2–20 MeV 2.89E-01

a. Source: Sources 4C-m results.

Table 5-24. Neutron ambient dose fractions for 

UF4 sources without alpha-emitting progeny.

a

Neutron energy group Dose fraction

<10 keV 3.34E-06

10–100 keV 8.23E-04

0.1–2 MeV 9.66E-01

2–20 MeV 3.31E-02

a. Source: Sources 4C-m results. 

Table 5-25. Neutron ambient dose fractions for 

UF4 sources with alpha-emitting progeny in 

secular equilibrium with 226Ra in the 238U chain 

and 223Ra in the 235U chain.

a

Neutron energy group Dose fraction

<10 keV 3.37E-06

10–100 keV 7.72E-04

0.1–2 MeV 9.48E-01

2–20 MeV 5.16E-02

a. Source: Sources 4C-m results.

Table 5-26. Neutron ambient dose fractions for 

UF4 sources with alpha-emitting progeny in 

secular equilibrium with 210Po in the 238U chain 

and 211Po in the 235U chain.

a

Neutron energy group Dose fraction

<10 keV 2.35E-06

10–100 keV 6.29E-04

0.1–2 MeV 6.96E-01

2–20 MeV 3.03E-01

a. Source: Sources 4C-m results.
Document No. ORAUT-OTIB-0024 Revision No. 01 Effective Date: 10/08/2020 Page 17 of 20

 

Table 5-27. Neutron ambient dose fractions for 

UF6 sources without alpha-emitting progeny.

a

Neutron energy group Dose fraction

<10 keV 3.34E-06

10–100 keV 8.22E-04

0.1–2 MeV 9.66E-01

2–20 MeV 3.32E-02

a. Source: Sources 4C-m results.

Table 5-28. Neutron ambient dose fractions for 

UF6 sources with alpha-emitting progeny in 

secular equilibrium with 226Ra in the 238U chain 

and 223Ra in the 235U chain.

a

Neutron energy group Dose fraction

<10 keV 3.37E-06

10–100 keV 7.71E-04

0.1–2 MeV 9.48E-01

2–20 MeV 5.16E-02

a. Source: Sources 4C-m results.

Table 5-29. Neutron ambient dose fractions for 

UF6 sources with alpha-emitting progeny in 

secular equilibrium with 210Po in the 238U chain 

and 211Po in the 235U chain.

a

Neutron energy group Dose fraction

<10 keV 2.34E-06

10–100 keV 6.28E-04

0.1–2 MeV 6.96E-01

2–20 MeV 3.03E-01

a. Source: Sources 4C-m results.

Table 5-30. Natural thorium neutron ambient 

dose fractions for ThF4 sources without alphaemitting progeny.

a

Neutron energy group Dose fraction

<10 keV 4.37E-06

10–100 keV 1.19E-03

0.1–2 MeV 8.24E-01

2–20 MeV 1.74E-01

a. Source: Sources 4C-m results.

Table 5-31. Natural thorium neutron ambient 

dose fractions for ThF4 sources with alphaemitting progeny in secular equilibrium through 

212Po.a

Neutron energy group Dose fraction

<10 keV 1.89E-06

10–100 keV 5.03E-04

0.1–2 MeV 5.83E-01

2–20 MeV 4.17E-01

a. Source: Sources 4C-m results.

Table 5-32. Thorium isotope mix neutron 

ambient dose fractions for ThF4 sources without 

alpha-emitting progeny.

a

Neutron energy group Dose fraction

<10 keV 1.86E-06

10–100 keV 6.43E-04

0.1–2 MeV 9.65E-01

2–20 MeV 3.46E-02

a. Source: Sources 4C-m results.

Table 5-33. Thorium isotope mix neutron 

ambient dose fractions for ThF4 sources with 

alpha-emitting progeny in secular equilibrium 

through 212Po.a

Neutron energy group Dose fraction

<10 keV 1.86E-06

10–100 keV 6.43E-04

0.1–2 MeV 9.64E-01

2–20 MeV 3.52E-02

a. Source: Sources 4C-m results.

6.0 CONCLUSIONS

Volume-averaged neutron flux was calculated for the compounds using four methods. Results show 

agreement for UO2, UO3, U3O8, UF4, UF6, ThF4, and Th(NO3)4, which demonstrates the feasibility of 

using MCNP 6.2 with TENDL cross-section libraries to produce accurate neutron flux. However, 

results from the MCNP 6.2 with TENDL cross-section libraries method did not show agreement with 

the other methods for Na2U2O7. Therefore, caution is indicated when applying this method to 

compounds containing sodium. 

Values for neutron dose rate were also calculated (using input from Sources 4C and 4C-m). Dose 

rate values calculated using the methods presented here for UO2, UF4, and ThF4 compounds differed 

from previous revision values by as much as 92%, 55%, and 40%, respectively. However, given the 

small magnitude of these values, the overall effect on calculations of energy employee annual dose 
Document No. ORAUT-OTIB-0024 Revision No. 01 Effective Date: 10/08/2020 Page 18 of 20

 

based on these data is expected to be small. In addition, there were small overall decreases in the 

neutron flux values calculated for all compounds in comparison with the previous version of this 

document. Finally, the methods described here are based on the latest available modeling methods.

Information regarding the neutron energy dose fractions – for use with entering the dose data into 

IREP – have been updated from the previous revision and are provided based on the spectral data 

from Sources 4C and 4C-m. 

Finally, if site-specific needs require the modeling techniques discussed here to address uranium 

compounds with different enrichment values, recycled uranium, or non-natural thorium compounds 

(e.g., triple separated), contact the ORAUT Principal Scientist for External Dosimetry for assistance.
Document No. ORAUT-OTIB-0024 Revision No. 01 Effective Date: 10/08/2020 Page 19 of 20

 

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