NBS Measurement Services:
Center for Radiation Research

The Center for Radiation Research is a major component of the National Measurement Laboratory in the National Bureau of Standards. The Center provides the Nation with standards and measurement services for ionizing

radiation and for ultraviolet, visible, and infrared radiation; coordinates and furnishes essential support

to the National Measurement Support Systemfor ionizing radiation; conducts research in radiation related

fields to develop improved radiation measurement methodology; and generates, compiles, and critically

evaluates data to meet major national needs. The Center consists of five Divisions and one Group.

Atomic and Plasma Radiation Division

Carries out basic theoretical and experimental research into the • Atomic Spectroscopy

spectroscopic and radiative properties of atoms and highly ionized • Atomic Radiation Data

species; develops well-defined atomic radiation sources as radiometric • Plasma Radiation

or wavelength standards; develops new measurement techniques and

methods for spectral analysis and plasma properties; and collects,

compiles, and critically evaluates spectroscopic data. The Division

consists of the following Groups:

Radiation Physics Division

Provides the central national basis for the measurement of far ultra- • Far UV Physics

violet, soft x-ray, and electron radiation; develops and disseminates • Electron Physics

radiation standards, measurement services, and data for for these radia- • Photon Physics

tions; conducts theoretical and experimental research with electron,

laser, ultraviolet, and soft x-ray radiation for measurement applications; determines fundamental mechanisms of electron and photon interactions with matter; and develops advanced electron- and photon-based

measurement techiques. The Division consists of the following Groups:

Radiometric Physics Division

Provides national measurement standards and support services for ultra- • Spectral Radiometry

violet, visible, and infrared radiation; provides standards dissemination • Spectrophotometry

and measurement quality assurance services; conducts research in optical • Radiometric Measurement Services

radiation, pyrometry, photometry, and quanton radiometry; and develops

spectroradiometric and spectrophotometric standards and calibration

procedures. The Division consists of the following Groups:

Develops,

Radiation

operates,

Source

and

and

improves

instrumentation

major NBS radiation

Division

facilities • Accelerator

^

Research

including the electron Linac and race track microtron; develops, • Linac Operations

designs, and builds electronic and mechanical instrunentation for • Electronic Instrinentation

radiation programs and facilities; provides national leadership • Mechanical Instrunentation

in the standardization of nuclear instrumentation; and develops

new competence in radiation sources and instrunentation. The

Division consists of the following Groups:

ionizing Radiation Division

Provides primary national standards, measurement services, and basic

data for applications of ionizing radiation; develops new methods of

chemical and physical dosimetry; conducts theoretical and experimental

research on the fundamental physical and chemical interactions of

ionizing radiation with matter; provides essential standards and measurement support services to the National Measurement Support

System for Ionizing Radiation; and develops and operates radiation

sources needed to provide primary radiation standards, fields, and

well-characterized beams of radiation for research on radiation

interactions and for development of measurement methods. The Division

consists of the following Office and Groups:

• Office of Radiation Measurement

• Radiation Theory

• Radiation Chemistry and Chemical

Dosimetry

• Neutron Measurements and Research

• Neutron Dosimetry

• Radioactivity

• X-Ray Physics

• Dosimetry

Nuclear Physics Group

Engages in forefront research in nuclear and elementary particle physics;

performs highly accurate measurements and theoretical analyses which

probe the structure of nuclear matter; and improves the quantitative

understanding of physical processes that underlie measurement science.
NBS MEASUREMENT SERVICES:

ALPHA-PARTICLE CALIBRATIONS

J. M. Robin Hutchinson

Center for Radiation Research

National Measurement Laboratory

National Bureau of Standards

Gaithersburg, MD 20899

U.S. DEPARTMENT OF COMMERCE, Malcolm Baldrige, Secretary

NATIONAL BUREAU OF STANDARDS, Ernest Ambler, Director

Issued July 1987
Library of Congress Catalog Card Number: 87-619849

National Bureau of Standards Special Publication 250-5

Natl. Bur. Stand. (U.S.), Spec. Publ. 250-5, 34 pages (July 1987)

CODEN: XNBSAV

Commercial products— materials and instruments— are identified in this document for the sole pur- pose of adequately describing experimental or test procedures. In no event does such identification imply recommendation or endorsement by the National Bureau of Standards of a particular product; nor does it imply that a named material or instrument is necessarily the best available for the purpose

it serves.

U.S. GOVERNMENT PRINTING OFFICE

WASHINGTON: 1987

For sale by the Superintendent of Documents, U.S. Government Printing Office, Washington, DC 20402-9325
PREFACE

The calibration and related measurement services of the National Bureau

of Standards are intended to assist the makers and users of precision

measuring instruments in achieving the highest possible levels of

accuracy, quality, and productivity. NBS offers over 300 different

calibration, special test, and measurement assurance services. These

services allow customers to directly link their measurement systems to

measurement systems and standards maintained by NBS. These services

are offered to the public and private organizations alike. They are described in NBS Special Publication (SP) 250, NBS Calibration Services

Users Guide .

The Users Guide is being supplemented by a number of special

publications (designated as the "SP 250 Series") that provide a detailed description of the important features of specific NBS

calibration services. These documents provide a description of the:

(1) specifications for the service; (2) design philosophy and theory;

(3) NBS measurement system; (4) NBS operational procedures; (5)

assessment of measurement uncertainty including random and systematic

errors and an error budget; and (6) internal quality control procedures

used by NBS. These documents will present more detail than can be

given in an NBS calibration report, or than is generally allowed in

articles in scientific journals. In the past NBS has published such

information in a variety of ways. This series will help make this type

of information more readily available to the user.

This document (SP 250-5), NBS Measurement Services: Alpha-Particle

Cal ibrat ions , by J. M. R. Hutchinson, is the fifth to be published in

this new series of special publications. It describes the calibration

of alpha-particle sources submitted to NBS for calibration of either

their 2tt steradian emission rate or their total activity (see test

numbers 43030C and 43030D in the SP 250 Users Guide). Inquiries

concerning the technical content of this document or the specifications

for these services should be directed to the author or one of the

technical contacts cited in SP 250.

The Center for Radiation Research (CRR) is in the process of publishing

21 documents in this SP 250 series, covering all of the calibration

services offered by CRR. A complete listing of these documents can be

found inside the back cover.

NBS would welcome suggestions on how publications such as these might

be made more useful. Suggestions are also welcome concerning the need

for new calibration services, special tests, and measurement assurance

programs

.

George A. Uriano Chris E. Kuyatt

Director Director

Measurement Services Center for Radiation Research

1 1

1
ABSTRACT

This document describes the alpha-particle calibration services offered

by the Radioactivity Group of the National Bureau of Standards (NBS)

(Scheduled Calibrations; 43030C and 43040C; formerly 8.2H and 8.21). The

fundamental measurement quantities are defined, the measurement approach is

described (or reviewed), and the operating procedures are described from the

point of view of the calibration technician or metrologist. The measurement

uncertainties, and how they are estimated, are described. Methods for

maintaining and assessing quality control, e.g., international comparisons,

MQA programs, etc. are also briefly reviewed.

Key words: alpha particle; calibrations; counters; emission rate;

radioactivity; standards

1v
TABLE OF CONTENTS

Page

Abstract iv

List of Tables vi

List of Figures vii

1. Introduction 1

2. Description of Service 1

3. Design Philosophy and Theory 2 3.1. 2Tra Proportional Counter 3

3.2. O.STra Counter 8

4. Description of Systems 11

4.1. 2TTa 11

4.2. O.STTa 11

5. General Operational Procedures 12

5.1. 27ra 12

5.2. O.STTa 13

6. Step-by-Step Procedures 13

6.1. Procedure for Using the 2-na Counter 13

6.2. Procedure for Using the O.Sttu Def i ned-Sol id-Angl e Counter .. 15

7. Calibration Service Procedure 17

7.1. Customer Contact 17

7.2. General Procedure 17

7.3. Test Folders 17

8. Uncertainty Components 18

8.1. Counter Geometry 19

8.2. Extension and Non-Uniformity of Source 20

8.3. Sel f -Absorption and Scattering from Source and Support 20

8.4. Scattering off Counter Wall 20

8.5. Transmission through Collimator Edge 20

8.6. Scattering in/on Detector 20

8.7. Background 20

8.8. Dead-Time 20

8.9. Extrapolation to Zero Pulse Height 20

8.10. Setting of 400 keV Discrimination Level 20

8.11. Counting Statistics 21

9. Quality Control 21

10. References 22

11. Appendices

A: Report of Calibration (27r) A-1

B: Report of Calibration (O.Stt) B-1

V
LIST OF TABLES

Page

Table 1. Specifications for calibrations using the 2TTa proportional

counter and the O.STra defined solid angle counter 2

Table 2. Approximate relative scintillation efficiencies of various

commercially available materials at room temperature 10

Table 3. Listing of count rate correction factors and typical la

uncertainties for 2it and O.Stt measurements 18

vi
LIST OF FIGURES

Page

Fig. 1. 2tt solid angle alpha counter 3

Fig. 2. Pulse height spectrum for O.Stt solid angle alpha counter 4

Fig. 3. Relative count rate as a function of counter voltage for 2t\

solid angle alpha counter 5

Fig. 4. Relative count rate as a function of source position for 2tt solid angle alpha counter 5

Fig. 5. Ratio of 2t\ counting rate to activity as a function of source thickness 7

Fig. 6. Schematic of O.Stt defined-sol id-angle alpha counter 8

Fig. 7. Count rate versus angle of emission for O.Stt solid angle

alpha counter 9

vii

1. Introduction

Alpha particles emitted from radioactive sources are measured at the

National Bureau of Standards (NBS) in two systems, the 2tt steradian proportional counting system (denoted "2iTa" system) and the O.Stt steradian CsI{Tl)

scintillation system (denoted "0.87ra" system). The full energy of the alpha

particles are absorbed in the counting gas in the first system and in the

scintillator in the second system. A ("frequency") spectrum of alpha-particle

counts in a counting period versus alpha-particle energy deposited in either

the gas or scintillator is collected and displayed in a multichannel analyzer.

Overall counting rates are determined from sums of all or parts of these

spectra as discussed below.

2. Description of Service 43030C and 43040C (previously 8.2H and

8.21, respectively)

Alpha-particle sources are submitted by outside laboratories to NBS for

calibration of either their 2it steradian emission rate or of their total

activity, i.e., emission rate into 4it including those alpha particles self

absorbed by the source — that is, the total number of radioactive atoms that

decay per unit time regardless of the fate of the resulting emissions.

Emission rate is measured in alpha-particles per second detected in 2u

geometry - in this case by the 2tt proportional counter. Because the resulting

pulse-height distribution is continuous down to zero energy and alpha

particles cannot always be separated from pulses produced by recoiling

daughters (~ 100 keV) in the proportional counter, sometimes only pulses above

an arbitrary cutoff of 400 keV are counted and certified in the emission

rate measurements. (This is discussed further in the Operational Procedures

section.) Activity, Ng, is measured in becquerels (Bq), the SI unit which is

also dimensional ly "per second," and represents the total number of alpha

particles per second produced by the purely alpha-particle emitting source. Emission rate, N2^, is measured on the NBS 2it a-particle proportional counter

and activity is usually measured with the 0.8Tr a-particle counter, both of

which are described in the main body of the text. Calibrations are checked by

simultaneously calibrating a previously-calibrated standard source (see

page 11).

Typical calibration reports for 2TTa-emi ssion rate measurement and

0.8TTa-parti cl e emission rate are given in Appendices A and B.

Sources submitted by the customer to NBS for calibration must satisfy

certain requirements. The source thickness must be such that more than

99.5 percent of the alpha particles emitted have an energy greater than

400 keV. Packaging for all sources must be in compliance with Department of

Transportation (DOT) and Nuclear Regulatory Commission (NRC) regulations.

Copies of regulations may be obtained from Operations Division, Office of

Hazardous Materials, Department of Transportation, Washington, D.C. 20590.

Postal regulations prohibit mailing radioactive materials which require a caution label under DOT regulations. Alpha-particle solid sources must be

^Numbers in brackets indicate literature references at the end of this

document.

1
supplied in special source holders such that the active area is not touched by

any material. For sources measured in the 2iTa counter (Calibration 43030C)

the diameter of the source must be less than 10 cm and that of the active

surface less than 9 cm. For the O.Sira counter (Calibration 43040C) , the

maximum diameter is only 1.6 cm.

Further specifications for these calibration services are given in the

following table. (Table 1)

Table 1. Specifications for calibrations using the Zua proportional counter

and the O.STia defined solid angle counter.

Calibration 43030C Calibration 43040C

Counting System NBS 2Tra proportional Counter NBS O.S-rra definedsol id-angl e-counter

Sources Calibrated for: Alpha-particle emission rate Total activity

into 2iT Steradians either (in Bq)

above 400 keV or extrapolated

to zero keV (in s-i)

Nominal Uncertainty (~ 3a) 1.5 percent 1.5 percent

Activity Range ~ (0.4 - 10'+) s-i ~ (40 - 10"+) s"!

Maximum Source Diameter 10 cm (9 cm active surface) 1.6 cm

3. Design Philosophy and Theory

The 27ra-proportional counter [2] is used because it records alpha

particles with little interference from emitted beta particles or gamma rays.

In the proportional counter, all alpha particles leaving the source into the

forward hemisphere ionize atoms in the counting gas, with the number of ions

produced proportional to the a-particle energy deposited. The electrons

released in the ionization are accelerated in an electric field toward a collecting electrode, multiplying their number by impact ionization. The

resulting electrical pulse is electronically amplified, and sorted as to pulse

height. The fact that the source is "internal" (inside the counter) allows

all emitted particles to be recorded without absorption by possible counter

casings. (For further discussion of proportional counters see NCRP 58 [3].)

The advantage of this detection system is that sources up to 10 cm in

diameter can be measured; however, because of the high detection efficiency

and count rate limitations in the electronics, the measurements are limited to sources with activities of less than 20,000 Bq. At the lower end, count rates

should be greater than 10 times background which is on the order of 0.06 s-^.

2
3.1. Z-na Proportional Counter ^

The calibration of alpha-particle sources started at the National Bureau

of Standards (NBS) in the early 1950's [5]. The alpha-particle detector used consisted of a 12-cm-di ameter hemispherical gas-flow proportional counter as shown m Fig. 1. This counter has been in use constantly since that time and

IS still much used today. Such 2tt counters are extremely versatile, and it

may still be true today that, if one were limited to a single detector, the 2 tt gas-flow proportional counter would be the detector of choice. Because these

counters are so versatile and so widely used, I would like to make the

following observations and suggestions about their use as accurate alpha- particle detectors.

12 CENTIMETER DIAMETER PROPORTIONAL COUNTER CHAMBER

1 STAINLESS STEEL

2 RUBBER "0" RING

3 ALUMINUM

4 PLEXIGLASS

5 BRASS

6 TUNGSTEN .002" DIA. WIRE

7 SOURCE

Fig. 1. 2t\ solid angle alpha counter

^Excerpted from Lucas [4].

3
Extrapolation to Zero Pulse Height — Regardless of the type of detection

system used, an accurate determination of the total alpha-particle count rate

requires that the alpha-particle pulse-height spectrum be recorded and extrapolated to zero pulse height, as shown in Fig. 2. The high count rate at low

channel numbers is primarily due to system noise. At NBS we generally fit to

a second-order polynomial, although a simple first-order polynomial (straightline extrapolation) is often adequate. When the pulse-height spectrum is

extrapolated to zero pulse-height in this way, the total count rate remains

almost constant despite a large change in the system gain, whereas the count

rate above a fixed discrimination level varies significantly with the same change in the system gain. The effect of using an extrapolation-to-zero pulse

height is demonstrated in Fig. 3 in terms of a plot of relative count rate versus counter voltage and in Fig. 4 in terms of a plot of relative count rate versus point-source position.

100 200 300 400 500 600 700 800 900 1000

CHANNEL NUMBER

Fig. 2. The pulse-height spectrum from a sample of 239pu in the NBS 0.8it

def ined-geometry counter, showing the extrapolation to zero pulse

height.

4
1.2 14 1.6 COUNTER VOLTAGE (kV)

1.8

F1g. 3. Relative count rate versus counter voltage for the NBS 2-ua

proportional counter (see Fig. 1). An ^'^^kn point source was located

in the center of the chamber. The counting gas was P-10 at

atmospheric pressure. The solid line is the count rate extrapolated

to zero pulse height. The dashed line is the count rate above a fixed discrimination level.

1 .01

1.00

2 099

3

8 0.98 >

u

cr.

0.97

0.96

0.95

1 1 1 1

1

-

^"^^^^^^^^"5"-^ ^^^^^

1 1 1 1 1

/

/

/

/

1

1 PERPENDICULAR PARALLEL

1 TO WIRE LOOP TO WIRE LOOP

1

1

, i , , , , 1 1 1 1 I

Fig. 4. Relative count rate versus position for an ^'tiAm point source in the

NBS 27ra proportional counter (see Fig. 1). The counter voltage was 1400 V. The counting gas was P-10 at atmospheric pressure. The

solid line is the count rate extrapolated to zero pulse height. The

dashed line is the count rate above a fixed discrimination level.

5
Maximum Source Size — For uniformly high detection efficiency (1.000 ± 0.005) from the surface of an extended source, the source diameter should not

be larger than about one half of the counter diameter. The maximum permissible source size using this criterion depends upon the electric field distribution within the counter (especially the shape and position of the anode wire

loop) and upon the composition of the counting gas (for example, it is larger

for P-10 than for methane [6]) and can be determined for any given counter by

plotting the count rate versus the position of a point source. Figure 4 shows

such data for our 2Tra counter at NBS under normal operating conditions (1 atm

of P-10 gas, 1400 V). Note the difference when the pulse-height spectrum is

extrapolated to zero pulse height.

Counting Gas — In a proportional counter the counting gas serves two

purposes

:

1. It provides a medium in which an alpha particle can dissipate its

kinetic energy to form free electrons and ionized atoms or molecules.

2. It provides a medium in which the free electrons so formed can be

accelerated in the presence of an electric field to produce additional ionization (that is, electron multiplication and hence amplification or "gas gain").

Methane and P-10 (90 percent argon, 10 percent methane) are the gases

most often used for gas-flow proportional counters. The gas of choice in any

given system or for any given application depends upon a number of factors,

including cost, availability, purity, and background count rate. There are also other considerations. A much higher electric field ( that is, a much

higher anode voltage) is required in methane than in P-10 for the same average

electron multiplication, and the electron multiplication in methane is less

affected by the presence of small concentrations of electronegative gas impurities, such as 0„ and H2O. However, if the pulse-height spectrum is extrapolated to zero pufse height, the effect of the change in system gain due to the

presence of impurities in the counting gas will be minimal, even with P-10.

Scattering — For reasons of stability and convenience, an alpha-particle

source is commonly mounted on a flat metal backing. When such a source is

measured in a detector having 2tt geometry, the 2tt counting rate, 02^^, is

generally not one half of the activity, Nq, because some of the alpha

particles initially emitted downward are backscattered into the sensitive

volume of the detector, while some of the alpha particles initially emitted

upward are scattered or absorbed in the source or both. As a result, the

measured C2^/Nq ratio can vary significantly from 0.50. This is shown in

Fig. 5, which is from the latest and most comprehensive [7] of a number of

papers dealing with this subject. The unit-less parameter d shown in Fig. 5 is the thickness of the source material expressed as a fraction of the alphaparticle range in the same material. Note that, even for a weightless source,

the correction can be very significant. Although the range in the source

material is often poorly known, it can be calculated from Cg^Ng measurements

on a few thick (d > 0.2) sources using the equations given m Lucas [8].

6
Fig. 5. Calculated and experimental values of Co/Nq as a function of source thickness, d, expressed as a fraction of\he alpha-particle range in

the same material (UO2 and U3OQ). See Ref. 1 for complete details.

7
3.2. O.Sira Counter

The O.Sira counter, the so-called Robinson counter [9,10], after the

designer of the instrument, is a CsI(Tl) scintillation counter, with defined

solid angle, and a three dimensional central baffle (Fig. 6). Alpha particles

striking the scintillator produce light flashes proportional to the energy

imparted. These flashes are transformed to electrical pulses and amplified

for pulse-height analysis. The baffle is designed such that the detection

efficiency is insensitive to positional changes in the source with respect to

the detector. As shown in [9], a 10 mm vertical or horizontal displacement of

the source results in a count rate change on the order of 0.1 percent. This

detector should not be used with sources with diameters greater than 1.6 cm. However, since the efficiency is approximately 40 percent of that of the 2tt counter, maximum source activities can be correspondingly greater. Unfortunately, the background is significantly higher than that in the 2tt counter and,

therefore, the minimum activity sources are significantly higher - on the

order of 40 Bq.

Fig. 6. Schematic of O.Stt def i ned-sol id-angl e alpha counter.

8
In about 1960 an experimental investigation 2 of the energy and angular

distributions of the emitted and scattered alpha particles was carried out at

NBS by Walker [2]. Her results for all emitted alpha particles at various

angles are shown in Fig, 7. Backscattered alpha particles are all emitted

within about 20° of the plane of the source (70° to 90° in Fig. 6). Therefore

if the solid angle subtended by the detector is such as to exclude all alpha

particles emitted within 20° or more of the plane of the source, then the

scattering correction, and the uncertainty associated with it, is eliminated.

The slight slope in the central portion of the curve was apparently due to the

center of rotation of the detector not being coincident with the source. Figure 7 also shows the angles subtended by several of the def i ned-geometry

counters now in use at NBS for the standardization of alpha-particle sources.

3 40

o

o

20

^

^4tf 0 40 80

ANGLE

Fig. 7, Count rate versus angle of emission for alpha particles emitted by

2iopo that had been deposited on the surfaces of platinum and monel

disks, (0 is perpendicular to the surface of the disk.) See Ref. 2 for complete details. Also shown are the angles subtended by the

detectors in several of the def i ned-geometry counters in use at NBS.

^Excerpted from Lucas [4],

9
Several def ined-geometry counters have been described 1n the literature

[9-12], One problem that arises in the use of such counters, especially those

with large solid angles, is that the geometry is very dependent upon the

position of the source in the counter, A very clever design for a highgeometry counter that almost eliminates such position dependence over a wide

range of horizontal and vertical displacements of the source was described by

Robinson [10] and is shown in Fig. 6. The inner and outer baffles together

define a detection geometry that varies less than 0.2 percent in solid angle

from any point within ± 20 mm horizontally and within ± 1 mm vertically of the mean center position.

To obtain the highest accuracy from a def i ned-geomet ry counter, it is

desirable to minimize the energy loss and the scattering in the region between

the alpha-particle source and the col 1 imator(s) and detector. As a result

most [10, 11], but not all [9, 12], counters of this type are operated with

the chamber under vacuum and with a solid scintillator as the alpha-particle

detector, A question that always arises is, "What is the detection efficiency

of the solid scintillator?" Our results at NBS indicate that the alphaparticle-detection efficiencies of our commercially prepared inorganic scintillation crystals [cesium iodide (thallium) and calcium fluoride (europium)]

and organic scintillation plastics are at least 0.999. The alpha-particledetection efficiencies of zinc sulfide (silver) layers are considerably more

variable because this material is available only in the form of microcrystal

line powder that must be deposited as a thin layer (often with a binder) to

form a suitable detector. Nonetheless, for carefully prepared deposits,

efficiencies of 0.999 appear to be reproducibly attainable [10]. There are,

however, important differences between the various solid scintillators,

especially in relative light output for alpha particles compared with beta

particles and gamma rays. Table 2 lists a number of commonly used scintillators, their relative light outputs, and their a/ B response ratios.

Table 2. Approximate relative scintillation efficiencies of various commercially available materials at room temperature. The relative light

output of sodium iodide (thallium) per unit energy deposited by beta

particles is taken as 1.00.

Solid

Scintil 1 ator

Relative Light Output per Unit Energy Deposited

a 3 a/

3^

ZnS(Ag) 2.0 1. 2.0

CsI(Tl) 0.4 0.5 0.8

NaI(Tl

)

0.5 = 1.00 0.5

CsBr(Tl) 0.05 0.15 0.3

KBr(Tl

)

0.01 0.04 0.25

CaF2(Eu) 0.1 0.4 0.25

; , NaCl (Ag) 0.01 0.04 0.2

Organic 0.02 0.25 0.08

^For ionization detectors (gaseous or solid state) this ratio is equal to 1.0.

10
If one is counting a source that emits only alpha particles, the a/

6

response ratio is not of significance. Mechanical and chemical properties

would be the basis on which to select a scintillator. But if the source also

emits beta particles or gamma rays or both, or if these radiations constitute

an important part of the background, then the a/ 3 response ratio may be the

most important parameter in the choice of a scintillator. For example,

suppose that one is counting 5,5-MeV alpha particles in the presence of

500-keV conversion electrons and that both types of particles deposit their

full energies in the scintil 1 ator, ^ if the scintillator is zinc sulfide

(silver), the light output due to the alpha particles will be more than

20 times that due to the conversion electrons. Hence the conversion electrons

may be readily discriminated against on the basis of pulse height. If the

scintillator is an organic plastic, the light outputs due to the two types of

particles will be the same. In this case it will not be possible to

discriminate against the conversion electrons on the basis of pulse height.

4, Description of Systems

4.1. Z-na : The Zua proportional counter system is pictured in Figure 1. The source is centered inside the counter and sits on the aluminum base plate.

Alpha particles emitted into the sensitive volume ionize counting gas (P-10)

atoms which are attracted and cascade to the positively charged anode loop

where they are collected. The pulse of charge is presented to a charge

sensitive preamplifier after which the pulse is amplified to overload. The

resulting spectrum is collected in a multichannel analyzer.

By amplifying to overload, the condition is nearly satisfied that all

alpha particles, regardless of energy, will be detected in the data collection

system — the multichannel analyzer. Consequently under these conditions,

extrapolation to zero pulse height is more easily accomplished because the

low-energy region can be examined in detail,

4.2, 0,8Tra : The 0,8TTa CsI(Tl) scintillation "Robinson" counter is shown in

Fig. 6, The source is mounted on the "source mount" and the enclosed volume

between it and the scintillator is flushed with hydrogen gas to permit the

alpha particles to move with minimum loss of energy. The outside baffle and

the Al stop are accurately machined with tolerances on the order of 0,005 cm

so that the detection geometry is known to approximately 0,1 percent. Light

pulses are collected in the light pipe and passed into the phototube. The

resulting pulses are amplified to overload as with the 2tt system and the

spectrum is collected in a multichannel analyzer.

Without the inside baffle, the source geometrical factor would be sensitive to vertical positioning of the source. As explained by Robinson [10],

the three dimensional central baffle is so designed that changes in the

geometrical factor defined by the outside baffle due to changes in source position, are offset by equal and opposite changes in the screening of the

alpha-particle beam by the central baffle. Hutchinson et al . [9] have shown

^In actual practice, one generally tries to minimize the energy deposition of

the beta particles and gamma rays by using a solid scintillator that is just

thick enough to stop the alpha particles.

11
that for a vertical displacement of 0.4 cm or a horizontal displacement of

1 cm of the source from the central position, the change in the count rate

varies by less than 0.3 percent.

A big advantage of this counter relates to the fact that multiplyscattered alpha particles, essentially all of which are emitted at grazing

angles to the source, are not detected. The difficult problem of estimating

the backscattering contribution is thus avoided.

The total efficiency for this geometry, eq o^, of the counter was deduced

from measurements on thin sources with the Z-n and O.Stt counters for different

values of atomic number, Z, of the backing material [9].

The 2tt count rate, No^, divided by the O.Stt count rate, Ng^g^, was plotted as a function of 2, and extrapolated to Z = 0 where, theoretically,

^O.Stt = No.8n/2N2TT = ^0.3^^0.

A schematic diagram of the spectrum for either the 2tt or O.Stt counter is

shown in Fig. 2. The multichannel analyzer is set to integrate counts above a level just above noise. The number of true counts in the noise region are estimated by means of an extrapolation of the flat part of the spectrum to zero pulse height.

5. General Operational Procedures

5.1. 2jTa: After the source has been introduced into the counter and the sensitive volume flushed until the pulses observed on the pulse-height analyzer

have reached their maximum height, the counting procedure is initiated.

Typically, the counting proceeds in the order: background, standard reference

source, submitted source, background. The counting times are adjusted so that

10^ counts from the source are collected (corresponding, of course, to 0.1

percent statistical uncertainty). These total counts are collected usually

over five repetitions, or approximately 2 x 10^ counts per measurement.

The functioning of the instrument is checked by comparing the measurement

results for the standard, corrected for decay, and the background with

previous results.

Five collection windows are set covering the lower end of the spectrum

for the purpose of obtaining an extrapolation in the case where the total

number of counts into 2tt are required. The extrapolation is based on the

assumption that the "true" tail of the spectrum (Fig. 2) can be represented as

a flat horizontal line with a height corresponding to the spectrum minimum.

In many cases, the customer asks not for total alpha-particle-emission

rate into 2tt, but instead, the rate for those emitted with energies above

400 keV. In this case, a rough energy calibration is performed using the

a-particle "peak" obtained at a lower known gain setting to avoid saturation

as a reference (the a energies can be obtained from the Nuclear Data File).

The spectrum above the 400 keV point is integrated. In either case, background is subtracted and the result, reduced to counts per second, is entered

onto the calibration certificate (Appendices A and B). The random uncertainty

is taken as the internal standard deviation of the mean of the five repetitions with a total of 10^ counts. The corresponding random uncertainty would

12
be 0.1 percent if other components of variation are all zero. A comparison of

the internal standard deviation and, in this case, 0.1 percent is referred to

as the "index of dispersion" test. So-called systematic errors are estimated

at the la level and are added in quadrature. In the example given in

Appendix A, there are only two such components, the inaccuracies in the selection of the pulse height at 400 keV and in the system dead time. When

appropriate, uncertainty due to extrapolation of the a spectrum to zero energy

should be taken into account. The overall uncertainty quoted in the certificate is three times the calculated combined uncertainty [13].

5.2. O.STra : Generally the same procedure for data collection and reduction is

employed with the O.Sna as with the 2T\a counter. Only activity measurements

are made with the O.Stt counter, therefore all measurements involve extrapolated values to which a calibration factor of 1/eg = 5.0638 is applied (see

reference 5). A sample certificate is shown in Appendix B. The one significant operational difference from the 2-na counter is that the correct

source height must be determined by varying the vertical position of the source through screwing the mount in or out as required. The count rates will

go through a maximum (as shown in Fig. 8 from [4]) representing the correct

vertical setting.

6. Step-by-Step Procedures '^

SAFETY PRECAUTIONS

The following procedures have been developed to ensure the safety of the

operator. It is important that they be followed meticulously in the order

given.

6.1. Procedure for Using the 2-na Counter:

• To Start

Turn on electronics (NIM BIN).

Turn on Air pressure valve (to raise and lower top of counter).

Raise top of counter by pulling handle up si owly .

Place source in center of counter, handling the source with gloves to

prevent possible contamination.

Lower top of counter by pulling handle down si owly .

Turn on gas (P-10, Argon-Methane) at main valve and adjust diaphragm

control to about 2-3 lbs/in^.

Open black knob on regulator and flush rapidly for about 10 minutes.

Turn on high voltage, ( + )1425 volts, at start of flushing.

'^Assembled by P. A. Mullen.

13
Reduce flow to approximately 60 cc/min; observe flow rate on small

flowmeter on top of counter.

Connect amplifier to oscilloscope and observe pulses, usually with coarse

gain at 16.

Connect amplifier to analyzer (at attenuator box).

Adjust coarse gain first to 4 and estimate energy calibration (keV/ch),

using approximate midpoint of peak area.

Set desired integrals on analyzer (see sample data sheet).

Set teletype keyboard to "data".

Turn on teletype punch.

Raise coarse gain to 16 and begin counting.

• To Change Source

Turn teletype punch to "off" and keyboard to "local."

Cut off high voltage by turning off switch (not by turning "pots" to

zero)

.

Turn off gas flow at black knob.

Open counter by raising top si owly .

Remove source carefully.

Place next source in center of counter.

Lower top of counter si owly .

Turn on gas at black knob.

Continue as above.

• To Shut Down

Turn off electronics (high voltage at switch and NIM BIN).

Turn off gas (close black knob, main valve, and release the diaphragm

control )

.

Remove source or blank carefully.

Turn off air pressure valve.

Turn off teletype.

Take smears of counter and immediate area and count at Health Physics.

14
6.2. Procedure for Operating the O.STra Def i ned-Sol id-Angl e Counter:

« To Start

Turn on electronics (NIM BIN) and high voltage interlock box.

High voltage power supply switch must be off.

Remove lead from interlock to breechblock.

CAREFULLY remove breechblock (which is also source mount) by unscrewing

it.

Be ready to support the block when it comes free.

Place source in center on top of block (spacers for sources of various

diameters in drawer under counter).

Replace block and turn to stop position CAREFULLY, (Care should be taken

not to advance source to the point of contact with the central

baffle,)

Replace lead from interlock.

Turn on gas (hydrogen) at main valve and adjust diaphragm control to

about 4 lbs/in2. (The gas is exhausted directly to the outside.)

Open black knob between regulator and flow meter and flush for about

10 minutes, at 3 L.P.M, as indicated on flow meter.

Turn on high voltage, (+)1500 volts, at start of flushing.

Reduce flow rate to about 0.5 L.P.M,; observe flow rate on flow meter.

Connect amplifier output to oscilloscope and observe pulses.

Connect amplifier output to analyzer at attenuator input; coarse

gain = 4, fine gain = 3.20.

Set desired integrals on analyzer (see sample data sheet).

Set teletype keyboard to "data."

Turn on teletype punch.

Begin counting.

15
To Change Source

Turn teletype punch to "off" and keyboard to "local."

Turn off high voltage at on-off switch.

Turn off gas flow by closing black knob.

Remove interlock lead.

CAREFULLY unscrew and remove block ; be prepared to support the weight of

the block when it comes free.

Remove source.

Place next source in center of top of block.

Continue as above.

To Shut Down

Turn off electronics (high voltage at switch and NIM BIN).

Turn off gas (close black knob, main valve, and release the diaphragm).

Remove interlock lead.

Remove source carefully.

Take smears of block and counter area and count at Health Physics.

Replace block and turn to stop position.

Turn off interlock control.

Turn off teletype.

Source Position

Horizontal — The available spacers fit most source diameters that we encounter. For those sources of a different diameter, a new spacer can

be made, or the source may be centered on the block and secured with a minimum of double-stick tape. The tape method is not recommended for

thin source mounts such as thin platinum.

Vertical — The optimum vertical position for counting a source will vary

with the thickness of the source mount, and the type of deposit

(electroplated, vacuum evaporation, or dried deposit). This position is

determined by counting the source (or one of a batch of similar sources)

at the "0" turns or stop position, which is the point at which the block

is against the bottom of the counter. Then, count at each 1/4 or 1/2

turn down, to the point where the count obviously decreases. These

measurements can be plotted as count-rate-vs-breechbl ock position, and

the operating point selected. The position which is thus determined can then be used for sources of the same configuration.

16
7. Calibration Service Procedure

7.1. Customer Contact

a. Give specifications for physical dimensions and activity limits (and

fee)

.

b. Emphasize that source container must protect active area from contact

with anything.

c. Request customer to specify on purchase order what type calibration,

i.e., 2t\ emission rate or activity.

d. Give time frame (do not promise what you cannot deliver).

e. Request any other useful information (user telephone number, etc.).

f. Request customer to call when ready to send sources.^

g. Give correct addresses — 1) shipping

2) mailing.

h. Send calibration booklet.

7.2. General Procedure

a. Submit completed NBS-364 to Health Physics for approval before

arrival of material

b. Notify Dr. Roald Schrack of the arrival and departure of all

Plutonium and uranium.

c. Accept material from Health Physics.

d. Calibrate, calculate, and write report.

e. Complete any necessary forms (64, 77, 796A).^

f. Package material (in original container(s) if possible).

7.3. Test Folders

a. Request test folder from OPMS on receipt of material to be

cal ibrated.

b. Note dates material received, returned.

^Shipments sometimes go astray (even after they arrive at NBS), so it is

useful to know when they are shipped to NBS and try to follow up on them.

^Give information for 796A to person typing shipping order.

17
8. Uncertainty Components

The corrections and uncertainty components considered are given in

Table 3.

Table 3. Listing of count rate correction factors and typical la

uncertainties for 2tt and O.Biv measurements.

2t\ Counter O.Stt Counter

Correction

Typical

Correction

Factor

Typical

Uncertainty

(%)

la

Typical

Correction

Factor

Typical

Uncertainty

(%)

la

Counter geometry {^) 2.000 0.05 40.000 0.05

Extension and non- uniformity of source (E)

1.000 0.05 1.005

0.0-5

Self-absorption and scattering

from source and support (Sg)

1.100 0.5 1.000 0.05

Scattering off counter wall (S^.) 1.000 0.02

Transmission through

collimator edge (T^)

1.000 0.02

Scattering in/on detector (Sq) 1.000 0.01 1.000 0.01

Transmission through

detector (no count) (Tq) 1.000 0.01 1.000 0.01

Background (B) 0.999 0.01 0.990 0.01

Deadtime (J) 1.010 0.01 1.010 0.01

Extrapolation to zero pulse height (x)

1.050 0.5 1.010 0.5

Setting of 400 keV

discrimination level (D)

1.000 0.6

Counting Statistics 0.1 1.000 0.1

18
Although this table lists typical uncertainties, one could, by using

these numbers, derive typical total uncertainties for the various measurements

by combining the relevant uncertainty components in quadrature and multiplying

by an arbitrary factor of 3. The measurements and these "typical"

uncertainties in percent are follows:

(i) 2Tr count rate above 400 keV 1.3

(ii) 2t\ count rate extrapolated to zero energy 1.5

(iii) activity derived from 2t\ count rate extrapolated to zero energy and corrected by theoretical 2tt/Nq factor [8] . . . 2.2

(iv) activity from O.STra measurements 1.6

In Table 3 typical corrections and uncertainties associated with the

determination of alpha-particle activity are given. A source with a diameter

of 4 cm, a thickness equal to one fourth of the alpha-particle range, and an activity of 2000 s"i is assumed. These uncertainties will vary in individual cases depending on such factors as source size, source uniformity,

alpha-particle energy, impurities, interfering radiations and count rate to

background ratio. Appendices A and B give examples of uncertainty computation

in two specific cases. Uncertainties for other sample measurements will, in

general, be different from these two examples but are nearly always within

0.5 percent in the quoted overall uncertainty. A number of the entries in

Table 3 have been considered and evaluated but are normally negligible and are

not included in the examples given in Appendices A and B.

The uncertainty estimates are given at roughly the la level. For the

most part the table is self explanatory. Symbols used in this section are identified in Table 3.

The measurement equation for the 2t\ counter giving the count rate into

2Tr, C2^, in terms of the gross rate, 62^.

(Go - ) ^2. -

I - J ^

(Note: If an estimate of activity is desired, the right hand side must be

multiplied by nS., and X must be used.)

The measurement equation for the O.Stt counter giving the total activity,

A, in terms of the gross rate, Gg^g^, is

A = ^^"'n

" n'^^^ S T S^T.X (1-J) accDD

where the symbols are defined in Table 3. Now follow some notes on the sources of error:

8.1. Counter Geometry : The uncertainty in ^^(0.811) is estimated from possible

differences between the calculated values, previously described, based on alternate extrapolations to Z = 0.

19
8.2. Extension and Non-Uniformity of Source : If the source is large enough,

it will impinge on the region of point-source position for which the response

of the detector is significantly (>0.1 percent) different from that at the

center. These effects have been previously described in the Design

Philosophly and Theory Section.

8.3. Sel f -Absorption and Scattering from Source and Support : This effect is

very much larger for 2tt sources because, as previously pointed out, back and

forward scattered particles involve those alphas which are coming off the source at grazing angles. For even moderately thick sources, this correction

could be quite significant for 2tt sources yet be completely insignificant in

0.8tt geometry because the 0.8Tr counter measures those forward directed,

relatively scatter-free, particles. As discussed on page 6 under Scattering , the activity of an alpha-particle-emitting source can be obtained from the 2Tr extrapolated 2t\ counting rate using a theoretical 2tt/Nq counting rate [8],

8.4. Scattering off Counter Wall : This effect does not exist in the 2tt counter because alpha particles do not reach the wall. The dimensions of the

0.8Tr counter are such that very rare large-angle scattering would be required

to produce such events.

8.5. Transmission through Collimator Edge : This applies only to the O.Su

counter and is negligible based on the range of alpha particles in the

collimator material.

8.6. Scattering in/on Detector : This is a conceivable, but entirely negligible, effect for these counters as in the Transmission through Detector .

8.7. Background : This is not observed as being variable with time and could

supposedly be driven down through collection of massive statistics.

Generally, enough counts are accumulated to reduce the background uncertainty

contribution to less than 0.1 percent.

8.8. Dead -time : The expression for dead-time correction is given in the

measurement equations for uncompensated systems. However, the multichannel

analyzer, which is the dominant source of dead-time losses, has a highly

precise dead-time compensator so that for a one percent dead time correction,

for example, the uncertainty due to this effect is entirely negligible.

8.9. Extrapolation to Zero Pulse Height : The shapes of the spectra in the low

energy region have significant curvature. Consequently, an extrapolation

based on the minimum value has significant uncertainty.

8.10 Setting of 400 keV Discrimination Level : For 2tt calibrations for which

the customer requests the 2tt emission rate above 400 keV, the discriminator

setting at that level carries a significant degree of uncertainty. The reason

for this is that the gain for a loop anode proportional counter is doublevalued because of the asymmetrical electric field lines in the counter. Thus

any energy calibration will have some ambiguity and carries with it a relatively large uncertainty.

20
8.11 Counting Statistics : The standard deviation of the mean of repeated

counts is taken as the basic measure of statistical uncertainty.

The overall uncertainty is estimated by summing in quadrature, the

standard errors of all calculated or estimated uncertainties and multiplying

by a factor of three which then gives approximately a 99 percent confidence

1 evel

.

9. Quality Control

The day-to-day control of the instruments uses a known standard which is

measured at the time of a calibration.

Cross checks between the counters and other specialized counters such as the O.Itt counter [4] are also performed. For example, a given calibration

will be performed and a quick cross check of this source on another counter

will be made. Such checks provide a feeling for the quality of source, a check on the functioning of the calibration counting system, and cross calibration in the (unlikely) event that questions are raised at a later date.

The only large international i ntercompari son of alpha-particle-emitting

sources was performed under the sponsorship of the BIPM in 1963 on a solution

of 2'+iAm. The agreement of NBS with the international average was in the 0.1

percent range. It was concluded at that time that the calibration of

alpha-particle emitters was well understood and no futher international

comparisons have been made on alpha-particle emitters.

21
REFERENCES

1. NBS Special Publication 250 , "NBS Calibration Services Users Guide

1986-88," G. A. Uriano, et al . , Editors, U.S. Department of Commerce,

National Bureau of Standards, U.S. Government Printing Office, Washinton,

D.C, July 1986.

2. Walker, D.H. "an Experimental Study of the Backscatteri ng of 5.3-MeV

Alpha Particles from Platinum and Monel Metal", Int. J. Appi . Radiat.

Isotopes , 1_6, 183 (1965).

3. NCRP Report 58, A Handbook of Radioactivity Measurements Procedures,

Section 3.7 "Alpha Particle Counting", Mann, W.B. (ed) National Council

' on Radiation Protection and Measurements, Washington (1978).

4. The Standardization of Alpha-Particle Sources. L.L. Lucas. Proceedings of

the ASTM Conference of Effluent and Environmental Radiation Surveillance,

July 9-14, 1978, Johnson, Vermont, in ASTM Spec. Tech. Publ . 698.

American Society for Testing and Materials (ASTM), pp. 342-354 (1980).

5. Temmer, G.M. and Wycoff, J.M., "Alpha-Ray Measurements Program" National

Bureau of Standards, Report No. 2598, 1953.

6. Hawkings, R.C., Merritt, W.F., and Craven, J.H. in Recent Developments

and Techniques in the Maintenance of Standards , Her Magesty's Stationary

Office, London, 1952, p. 35.

7. Hutchinson, J.M.R., Lucas, L.L., Mullen, P. A. "Study of the Scattering

Correction for Thick Uranium-Oxide and Other a-Particle Soures-II:

Experimental", Int. J. Appl . Radiat. Isotopes , 27 , 43 (1976).

8. Lucas, L.L, and Hutchinson, J.M.R. "Study of the Scattering Correction

for Thick Uranium-Oxide and Other a-Particle Sources-I: Theoretical",

Int. J. Appl. Radiat. Isotopes , 27, 35 (1976).

9. Hutchinson, J.M.R. , Naas, C.R., Walker, D.H., Mann, W.B. "Backscatteri ng

of Alpha Particles from Thick Metal Backings as a Function of Atomic

Weight", Int. J. Appl . Radiat. Isotopes , 19^, 517 (1968).

10. Robinson, H.P. in Metrology of Radionuclides , International Atomic Energy

Agency, Vienna, Austria, 1960, p. 147.

11. Jaffey, A.H., Flynn, K.F., Bentley, W.C., and Karttunen, J.O., Phys. Rev.

C 2. 1974, p. 1991.

12. Bambynek, W.B. in Standardization of Radionuclides, International Atomic

Energy Agency, Vienna, Austria, 1960, p. 147.

13. Giacomo, P. "News from BIPM, " Metrologia 17, 73 (1981).

22
(Rev 2-86) Appendix A

U.S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS

QAITHERSBURO. MARYLAND 20899

REPORT OF CALIBRATION

for

Bendii Field Engineering Corporation

Grand Junction Operations

Grand Junction, Colorado

Radionucl ide Amer ic iujn-241

Source identification 4904M-F-79

Act ivity 1.528 I 102 Bq ^2)

Reference time March 24, 1986

Half life

Overall uncertainty

432.2 years <3)

1.5 percent

Measuring instrument "0.8n'a counter

Dale D. Hoppes, Group Leader

Radioactivity Group

Center for Radiation Research

[ndall S. Caswell, Chief

Ionizing Radiation Division

Center for Radiation Research

Gaithersburg, MD 20899

March 31, 1986

NBS Test No. 236927

Notes on next page

A - 1
NOTES

^1) This source was said by the customer to be aniericium-241. No

checks were made for impurities at NBS.

(2) Including scattered alpha particles.

(3)

(4)

(5)

From the Evaluated Nuclear Structure Data File, August, 1980

One mean tropical year = 365.2422 d.

The overall uncertainty is three times the value found from

combining quadratical ly the standard deviations of the mean,

or approximations thereof, of the following:

a) one standard deviation of the

mean of 10 measurements 0.07 percent

b) count rate extrapolation

to zero energy 0.50 percent

c) system live time 0.05 percent

Defined-sol id-angle counter with scintillation detector.

For further information contact J.M.R. Hutchinson or S.J. Walker at

(301) 921-2396 or (FTS) 921-2396.

4904M-F-79

A - 2
FOAM NBS-US

(NCV. IJ-4*) Appendix B U.S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS

WASHINGTON, O.C. 20214

REPORT OF CALIBRATION

for

Department of the Air Force

HQ Aerospace Guidance and Metrology Center

Nevark Air Force Station, Ohio

Radionucl ide Plutoniunr-23 9

Source identification

2n alpha-particle

counting rate

8-03 8-1

214.0 s-1 (D*

Reference time December 30, 1985

Overall uncertainty 1 .5 percent (2)

Measuring instrxunent

Dale D, Hoppes, Group Leader

Radioactivity Group

Center for Radiation Research

NBS 2na proportional counter

Randall S. Caswell, Chief

Ionizing Radiation Division

Center for Radiation Research

Gaither sburg, MD 20899

January 2, 1986 *Notes on next page

NBS Test No. 45133

B
NOTES

The number of alpha particles with energies greater than 400 keV

counted per second in a 2n-steradian geometry (including those

sea t tered)

.

The overall uncertainty is three times the value found from

combining quadra t ica 1 ly the standard deviations of the mean,

or approximations thereof, of the following:

a) one standard deviation of the

mean of 10 measurements 0.1 percent

b) selection of pulse height at

400 keV 0.5 percent

c) system live time 0.05 percent

For further information contact J.M.R. Hutchinson (301) 921-2396 or (FTS)

921-23 96.
FORM NBS-1 )4A (REV.1 1-84)

U.S. DEPT. OF COMM. BIBLIOGRAPHIC DATA

SHEET (See instructions)

1. PUBLICATION OR

REPORT NO. NBS/SP-250/5

2. Performing Organ. Report No. 3. Publication D a te July 1987

4. TITLE AND SUBTITLE

NBS Measurement Services:

Alpha-Particle Calibrations

5. AUTHOR(S)

J.M.R. Hutchinson

6. PERFORMING ORGANIZATION (If joint or other than NBS. see instructions)

NATIONAL BUREAU OF STANDARDS

U.S. DEPARTMENT OF COMMERCE

GAITHERSBURG, MD 20899

7. Contract/Grant No.

8. Type of Report & Period Covered

Final

9. SPONSORING ORGANIZATION NAME AND COMPLETE ADDRESS fStreet, City, State. ZIP)

Same as item 6

.

10. SUPPLEMENTARY NOTES

Library of Congress Catalog Card Number: 87-619849

Document describes a computer program; SF-185, FlPS Software Summary, is attached,

11. ABSTRACT (A 200-word or less factual summary of most significant information, if document includes a si gnificant

bibliography or literature survey, mention it here)

TlT^s document describes the alpha-particle calibration services offered

by the Radioactivity Group of the National Bureau o"^ Standards (NBS)

(Scheduled Calibrations; 43030C and 43040C; formerly 8.2H and 8.21). The

fundamental measurement quantities are defined, the measurement approach is

described (or reviewed), and the operating procedures are described from the

point of view of the calibration technician or metrologist. The measurement

uncertainties, and how they are estimated, are described. Methods for

maintaining and assessing quality control, e.g., international comparisons,

MQA programs, etc, are also briefly reviewed.

12. KEY WORDS (Six to twelve entries; alphabetical order; capitalize only proper names; and separate key words by semicolons)

alpha particle; calibrations; counters; emission rate;

radioactivity; standards

13. AVAILABILITY

Unl imited

1331 For Official Distribution. Do Not Release to NTIS

Order From Superintendent of Documents, U.S. Government Printing Office, Washington, DC

20402.

Order From National Technical Information Service (NTIS), Springfield, VA 22161

14. NO. OF

PRINTED PAGES

34

15. Price

USCOMM-DC 85-6006

PUBLICATIONS IN THE SP 250 SERIES FROM THE CENTER FOR RADIATION RESEARCH

SP 250-1 NBS Measurement Services:

Spectral Radiance Calibrations

J.H. Walker, R.D. Saunders, and A.T. Hattenburg

SP 250-2 NBS Measurement Services:

Far Ultraviolet Detector Standards

L.R. Canfield and N. Swanson

SP 250-3 NBS Measurement Services:

Radiometric Standards in the Vacuum Ultraviolet

J.Z, Klose, J.M. Bridges, and W.R. Ott

SP 250-4 NBS Measurement Services:

Fricke Dosimetry in HighEnergy Electron Beams

C.G. Soares, E.L. Bright and M. Ehrlich

SP 250-5 NBS Measurement Services:

Alpha-Particle Calibrations

J.M.R. Hutchinson

SP 250-6 NBS Measurement Services:

Regular Spectral Transmittance

K.L. Eckerle, J.J. Hsia, K.D. Mielenz,

and V.R. Weidner

SP 250-7 NBS Measurement Services:

Radiance Temperature Calibrations

W.R. Waters, J.H. Walker, and A.T, Hattenburg

SP 250-8 NBS Measurement Services:

Spectral Reflectance

V.R. Weidner and J.J. Hsia

SP 250-9 NBS Measurement Services:

Calibration of Beta-Particle-Emitting

Ophthalmic Applicators

J.S. Pruitt

SP 250-10 NBS Measurement Services:

Radioactivity Calibrations with the "4ir" Gamma Ionization Chamber, and Other

Radioactivity Calibration Capabilities

J.M. Calhoun

SP 250-11 NBS Measurement Services:

Dosimetry for High-Do?e Applications

J.C. Humphreys^ D. Hocken, and W.L. McLaughlin

SP 250-12 NBS Measurement Services: Neutron Personnel Dosimetry

R.B. Schwartz

SP 250-13 NBS Measurement Services:

Activation Foil Irradiation

with Californiun Fission Sources

G.P. Lamaze and J. A. Grundl

SP 250-14 NBS Measurement Services:

Activation Foil Irradiation by Reactor Cavity Fission Sources

G.P. Lamaze and J. A. Grundl

SP 250-15 NBS Measurement Services:

Photometric Calibrations

R.L. Booker and D.A. McSparron

SP 250-16 NBS Measurement Services:

Calibration of X-Ray and Gamma-Ray

Measuring Instruments

P.J. Lamperti, T.P. Loftus, and R. Loevinger

SP 250-17 NBS Measurement Services:

The NBS Photodetector Spectral Response

Calibration Transfer Program

E.F. Zalewski

SP 250-18 NBS Measurement Services: Neutron Source Strength Calibrations

E.D. McGarry and E.W. Boswell

SP 250-19 NBS Measurement Services:

Calibration of Gamma-Ray-Emitting

Brachytherapy Sources

J.T. Weaver, T.P. Loftus, and R. Loevinger

SP 250-20 NBS Measurement Services:

Spectral Irradiance Calibrations

J.H. Walker, R.D. Saunders, J.K. Jackson,

and D.A. McSparron

SP 250-21 NBS Measurement Services:

Calibration of Beta-Particle

Radiation Instrumentation and Sources

J.S. Pruitt, C.G. Soares, and M. Ehrlich
U.S. Department of Commerce

National Bureau of Standards

Gaithersburg, MD 20899

Official Business

Penalty for Private Use $300