NBSIR 73-413

Measurement of Depth-Dose

Distributions in Carbon, Aluminum,

Polyethylene, and Polystyrene for

10-MEY Incident Electrons

J. C. Humphreys, S. E. Ctiappell. W. L. McLaughlin, and R. D. Jarrett

Applied Radiation Division

Center for Radiation Research

Institute for Basic Standards

National Bureau of Standards

Washington, D. C. 20234

November 1973

Interim Report

Prepared for Food Laboratory

U. S. Army Natick Laboratories

Natick. Massachusetts 01760

NBSIR 73-413

MEASUREMENT OF DEPTH-DOSE

DISTRIBUTIONS IN CARBON, ALUMINUM,

POLYETHYLENE, AND POLYSTYRENE FOR

10-MEV INCIDENT ELECTRONS

J. C. Humphreys, S. E. Chappell, W. L. McLaughlin, and R. D. Jarrett

Applied Radiation Division

Center for Radiation Research

Institute for Basic Standards

National Bureau of Standards

Washington, D. C. 20234

November 1973

Interim Report

This report is to be superseded by a future publication

which will receive general distribution and should be

cited as a reference. Please consult the NBS Office of Technical Information and Publications to obtain the proper citation.

Prepared for Food Laboratory

U. S. Army Natick Laboratories

Natick, Massachusetts 01760

U. S. DEPARTMENT OF COMMERCE. Frederick B. Dent. Secretary

NATIONAL BUREAU OF STANDARDS, Richard W. Roberts. Director

ABSTRACT

Depth-dose distributions of 10-MeV electrons incident on homogeneous media of carbon, aluminum, polyethylene, and polystyrene have

been measured using thin radiochromic dye-film dosimeters. Two types of

dye-film dosimeters were employed as "cavities" within the media in two

different geometrical configurations. One configuration was a stack

with the dosimeters interleaved between disks of the medium and placed

perpendicular to the incident electron beam direction. The other configuration was a wedge assembly with a single piece of dye film placed

between pieces of the medium at a small angle to the beam direction. •

The results show no significant difference between dosimeter type or

experimental arrangement. In addition, good agreement is shown in comparisons of experimental and Monte Carlo calculated depth-dose distributions characterized by such parameters as extrapolated range, depth of

peak dose, and ratio of peak to entrance dose.

Key Words: Aluminum; carbon; depth dose; depth-dose distributions;

dye-film dosimeters; polyethylene; polystyrene; radiochromic

dyes; 10-MeV electrons

ii

TABLE OF CONTENTS

Page

ABSTRACT ii

LIST OF FIGURES iv

LIST OF TABLES vi

A. INTRODUCTION 1

B. EXPERIMENTAL METHOD 4

B.l, Description of the Irradiation Facilities 4

B.2. Material-Dosimeter Arrangements Under Irradiation 6 B. 3. Optical Density Measurements 8

C. RESULTS 14

C. L Calibration of the Dosimeters 14

C.2. A Comparison of Dose Rates of the NBS and Natick

Laboratories ^°Co Y~ray Sources 18

C. 3. Depth-Dose Distributions in Electron Irradiated

Materials 20

D. CONCLUSIONS 36

D. l. Comparison of Experimental Results with Theory 36

D.2. Comparison of Nominal and Experimental Entrance

Doses 38

D.3. Comparison of Tissue and Near Tissue-Equivalent

Materials 40

D.4. Possible Negative Effects on Results by Some

Experimental Conditions 42

D.5. Suggestions for Future Experiments 43

REFERENCES 44

iii
LIST OF FIGURES

Page

1. Schematic diagram of the NBS ^°Co pool source, and dye ^

f ilm holder

,

2. "Wedge" method of mounting dye-film dosimeters in homogeneous ^

medium; (a) electron beam direction is parallel to page, (b)

electron beam direction is perpendicular to page.

3. Optical absorption spectrum of film type A, irradiated and 10

unirradiated.

4. Optical absorption spectrum of film type B, irradiated and un- 11

Irradiated.

5. ^°Co y-ray calibration curves of film type A in air or 15

nitrogen atmosphere. Optical densities measured at two wavelengths. ^

6. ^°Co y-ray calibration curves of film type B in air. Optical ]

6

densities measured at two wavelengths

.

7. 10-MeV electron depth-dose distributions in carbon and aluminum

measured with film type A.

8. 10-MeV electron depth-dose distributions in polystyrene and 23

polyethylene measured with film type A.

9. 10-MeV electron depth-dose distributions in carbon measured 24 -

with film type B.

10. lO-MeV electron depth-dose distributions in aluminum measured 25

with film type B.

11. lO-MeV electron depth-dose distributions in polystyrene 26

measured with film type B.
Page

12. 10-MeV electron depth-dose distributions in polyethylene 2?

measured with film type B.

13. Experimental and calculated 10-MeV electron depth-dose 30

distributions in carbon and aluminum.

V
LIST OF TABLES

Page

1. Comparison of Dose Rates of the NBS and Natick Laboratories 19

^°Co Y-ray Sources

2. Electron Mass Collision Stopping Power Ratios, Material to 28

Film

3. Comparison of Some Experimental and Calculated Depth-Dose 31

Parameters for the Different Materials

4. Peak and Entrance Doses of Depth-Dose Distributions 33

5. Comparison of Results of the "Stack" and "Wedge" Methods of 34

Depth-Dose Measurements

6. Comparison of Experimental and Calculated Depth-Dose Para- 37

meters for Carbon and Aluminum

7. Entrance Dose in Water from Experimental Dose in Media: Com- 39

parison of Experimental and Nominal Entrance Doses

8. Experimental and Calculated Depth-Dose Parameters of Tissue 41

and Near Tissue-Equivalent Materials for 10-MeV Electrons

vi
A. INTRODUCTION

The purpose of this study is to determine energy-deposition profiles,

or depth-dose distributions, which result from the irradiation of homogeneous materials by high-energy electrons. The data obtained in this

study will have wide application. Some examples of its use are to provide basic data for such areas as medical therapy and the radiation processing of materials.

Detailed depth-dose distributions in the irradiated media were determined by means of thin dye-film dosimeters. These dosimeters, in

effect, were small, solid-filled "cavities" in the irradiated materials.

The theory and use of such cavities in radiation dosimetry has been

thoroughly investigated and is well understood. In general, the cavities

may be filled with any material in a gaseous, liquid, or solid state [l]t

Several investigators have reported previously the successful use of dyefilm dosimeters in applications in which materials were irradiated by

broad, spatially uniform electron beams with energies up to 3 MeV [2-7].

The experimental results were compared successfully with Monte Carlo calculations which predicted the depth-dose distributions.

Two different thin dye-film dosimeters were employed in this study.

They were hexahydroxyethyl pararosani] ine cyanide in nylon (film type A)

_

Figures in brackets indicate the literature references which are listed

at the end of this report.
and malachite green methoxide in polychlorostyrene (film type B)

Calibrations of the dosimeters were accomplished by ^°Co y-ray irradiations. Previous studies have been made of their response characteristics when irradiated by photon and electron beams at various dose rates

and under various environmental conditions. They are useful over a dose

range of approximately 0.1 to 30 Mrad. It has been demonstrated further

that the response is independent of (a) type of radiation (photons or

electrons), (b) dose rate up to 10^^ rad/s, and (c) energy spectrum

(when greater than a few keV) [7-15]. For a given dose, the response

of film type A varies with relative humidity but is the same in air,

nitrogen, and vacuum; however, for a given dose, the response of film

type B is Insensitive to moisture but is different in air from that in

oxygen-free environments. Both dosimeters show a variation of response

with temperature during Irradiation. In addition, they display a change

in response if stored at elevated temperatures. For this study the films

were calibrated, stored, and read at room temperature. Also, both types

of dosimeters are sensitive to ultraviolet radiation, and hence must be

protected from sunlight and white fluorescent lighting.

The energy deposition, or absorbed dose, in the dosimeters is interpreted from calibration curves by means of optical density transmission

These dosimeters were obtained from Far West Technology ,Inc . , Goleta,

California 93017. Film type A corresponds to the manufacturer's designation of FWT-60 and film type B to FWT-70. The identification of the

commercial supplier is not intended as an endorsement but to specify

more precisely the nature of the materials used.

2
measurements. At certain visible wavelengths, there are changes in the

optical densities of the dye-film dosimeters due to irradiation. These

changes are measured at or near the wavelengths of maximum optical density

by means of a spectrophotometer or raicrodensitometer . The calibrations

consist of a curve relating change in optical density at a given wavelength to absorbed dose in the film ("cavity") material. Cavity theory,

employing appropriate stopping power relations between the medium and the

cavity material, is applied to obtain the final desired results. This

method lends itself to the measurement of high spatial-resolution distributions of absorbed dose since microdensitometer measurements can be made

in a continuous fashion across the radiographic image produced in the

film dosimeter.

In this study, homogeneous media of carbon, aluminum, polyethylene,

and polystyrene have been irradiated with normally incident, 10-MeV electron beams to doses between 1 and 3 Mrad. The depth-dose distributions

in these materials were derived from photometric readings of thin dyefilm dosimeters placed at different depths inside these media. The

radiation measurem.ents were performed in a food processing facility using

a scanned 10-MeV electron beam that is employed for irradiating food

packages. Therefore, these data and conclusions are expected to be important in defining the relevant parameters in that application of radiation processing as well as in other areas such as sterilization of medical devices (sutures, surgical instruments, transplant apparatus), graft

polymerization (textiles, ion-exchange membranes), polymer crosslinking

(wire and cable insulators, heat-shrinkable tubing), and curing of coatings (inks, automobile parts, paint layers).

3
B. EXPERIMENTAL METHOD

B. L Description of the Irradiation Facilities

Both types of dye-film dosimeters (A and B) were calibrated

in the NBS ^°Co Y~ray pool source. Irradiations were also carried out

in the Natick Laboratories ^°Co irradiators. Comparisons of these results are given in a later section of the report.

The NBS water-shielded ^°Co y-vay source provides a dose rate

of about 10^ rad/s. It is made up of twelve encapsulated ^°Co pencils

mounted upright in a 10.5-cm diameter circle on a baseplate at the bottom

of a 3-meter deep water pool. The dye-film dosimeters were mounted in a

polystyrene holder Inside a watertight stainless-steel can during the

calibration Irradiations. The holder was sufficiently thick so as to provide electronic equilibrium conditions. The dosimeters were positioned

In the center of the source. Figure 1 is a diagram of the arrangement of

the sources, can, and film holder. During an irradiation, a constant

flow of either dry nitrogen gas or dry air was maintained around the dosimeters. This procedure provided for calibration either in nitrogen or

air and, at the same time, maintained a nearly constant ambient temperature of about 19°C.

At the Natick Laboratories, irradiations of the dye-film dosimeters were made in two different ^"Co y-ray sources separately. One

source provided a dose rate of about 40 rad/s and the other a rate of

about 1.7 X 10^ rad/s. Both sources are commercial, lead-shielded

irradiators with automatic timing control of the exposure duration. The

lower-activity source has an air-cooled irradiation chamber while the

higher-activity source has an irradiation chamber in which the temperature

4
0 I 2 3 4cm

I I L_J I I

'PIPE TO POOL SURFACE

~3 METERS

N2 GAS SUPPLY TUBE

WATER TIGHT

STAINLESS

STEEL CAN

N2 GAS FLOW SLOT>

THIN

DOSIMETERS

'ENCAPSULATED

^°Co SOURCES (12)

.BASE PLATE

Figure 1. Schematic Diagram of the NBS ^°Co Pool Source,

and Dye Film Holder.

5
is controlled by gas boiled off from liquid nitrogen. During irradiation,

dosimeters were sandwiched between plates of polystyrene which are thick

enough to provide electronic equilibrium conditions. These assemblies

were positioned at the center of each source in the irradiation chambers,

both of which were maintained at a temperature of about 25°C.

The electron source employed for the depth-dose measurements

in the various materials was the Natick Food Laboratories' linac. Beam

parameters under typical operating conditions for the irradiations were

as follows: (a) energy of 10,0 ±0.3 MeV, (b) pulse rate of 180 pulses

per second, (c) pulse width from 2 to 5.5 ys, (d) peak current from 450

to 550 mA, and (e) average current from 20C to 500 yA. The beam was

electromagnetically scanned in a vertical direction at a rate of 0.5 Hz.

The beam passed through a 0.5-mm thick aluminum window of a scan horn into

the air. At the sample irradiation position (about 20 cm from the aluminum window) the beam was about 3 cm in diameter and scanned a distance of

about 40 cm in length. A servo-controlled conveyor moved material to be

irradiated through the beam at right angles to the scan direction. For

the conditions of these measurements, the peak dose rate was approximately

10^° rad/s. The average dose rate for a complete irradiation was about

10^ rad/s.

B.2. Material-Dosimeter Arrangements Under Irradiation

For the purpose of determining depth-dose distributions, thin

dye-film dosimeters were incorporated in two arrangements in blocks of the

various homogeneous materials that were irradiated. One arrangement is

called the "wedge" method [l6] which is illustrated in Figure 2, and the

other is called the "stack" method. The square face of each block was

6
Eo

in —I

ro -

CM -

o-J oo

c/)

COo ^

0)00 (U O (30 eOA.o C U • •H a) m 0) cd

0) ^ B to •H 04

COo CO

O

4J3O

»H

O T3

•H -H

C I O O.

0) 0) ^

>^ l-t 0) O 'ri Pn Q

60

c!

a

•H cd U (U 3O

CO

C -u o o h Q)

<*Au

u

O <J 'H

<U

Q o w a

(U cd pq s --^ C r o

d)

Bu

bO 3 4J

tt) 01 raw

0)U3

00 •H 7
perpendicular to the beam direction. Polyethylene and polystyrene had

side dimensions of 15.2 cm and a thickness of 5.7 cm, carbon and aluminum had corresponding dimensions of 10 « 2 cm and 3.8 cm..

The two methods cited above were used to locate the dosimeters

in the center of each block. These methods involve assemblies of homogeneous media and dosimeters which are described as follows: (a) The

"wedge" Is a solid cylinder which is slit lengthwise on a slant at an

angle of about 9° to the beam direction. A strip of the dye-film dosimeter is placed in the slit. The two halves then are held tightly together

with a hollow cylinder of 2.5-cm outside- diameter, the cylinder being

fitted into a hole in the center of the block. (b) The "stack" is a

cylinder made up by alternately assembling disks of the block material

and squares of the dosimeters. The disks are 2.2 cm in diameter and are

0.06 cm thick for carbon and aluminum and 0.30 cm thick for polyethylene

and polystyrene. In the same manner as with the "wedge", a completed

stack is held together with a hollow cylinder, and the entire assembly is

located in the center of the block. During the irradiations, an additional piece of the dye-film was taped on the beam-entrance side of the

assembly.

B. 3. Optical Density Measurements

Before irradiation the two types of dye-film dosimeters are

transparent and almost colorless. Upon irradiation, however, they become

colored, and a plot of their optical densities versus optical wavelength

shows broad characteristic absorption peaks in the visible region of the

spectrum. Film type A develops a single broad asymmetric peak at about

601 nm (see Figure 3) while film type B exhibits two broad peaks, the

8
larger at 630 nm and the smaller at 430 run (see Figure A)

The absorbed dose received by the dosimeters is interpreted

from a measurement of the change of optical density, AOD, at or near the

absorption peaks produced by the radiation. These measurements are made

with either a spectrophotometer or a microdensitometer equipped with interference filters. In the dose range between about 0.1 and 5 Mrad, the

AOD is measured at 601 nm for film type A and at 630 nm for film type B.

From 5 to 30 Mrad, the AOD is measured at 540 nm for type A and at 430

nm for type B; this procedure is necessary because above 5 Mrad the optical densities at 601 and 630 nm are beyond the accurate measurement range

of the photometric instruments.

Spectrophotometer readings were made of optical density

changes of the dye-film dosimeters used for the ^"Co calibrations and for

those exposed in the "stack" method. Measurements of some, but not all,

of these dosimeters were made both at NBS and at Natick Laboratories.

The spectrophotometers at the two laboratories were cross-checked, and it

was concluded that for a given dosimeter the readings were identical to

within the precision of the optical density determinations.

Values of ADD at the appropriate absorption peak were de--

termined by following a two-step procedure: (1) First an CD reading was

taken at a wavelength far removed from the peaks, at 710 nm for film type

A and at 780 nm for film type B. This base-line value was subtracted

from the peak reading. This procedure corrected for the absorption,

scattering, and reflection losses that were intrinsic for each individual

dosimeter and that were not associated with the dye ion in the dosimeter,

(2) The procedure just outlined was repeated for unirradiated control

9
10
00 (O ^ CVJ

O

d

d

d

d

AiisN3a nvoiido

11
films. (3) Then the AOD for a given dosimeter is equal to step (1) minus

step (2) (see Figures 3 and 4). Care was taken to correct for an interference phenomenon that occurs with films of very uniform thicknesses

and that results in oscillations of the optical density values over

small changes in the wavelength [12,17]. The phenomenon is caused by

interference of the light which has undergone multiple reflections at the

air-dosimeter interfaces. In such cases, an average of the maxima and

minima of the interference pattern is taken as the optical density.

Microdensitometer readings were made of the dye-film dosimeters

irradiated in the "wedge" method. The optical density measurements were

taken with this instrument using narrow band-pass, Fabry-Perot interference filters which were centered on wavelengths of 600 nm for film

type A and A30 nm for film type B. A cross check was made of the response

of the m.icrodensitometer and the spectrophotometer. To accomplish this,

readings were taken on 35 dosimeters of film type A and 22 dosimeters of

film type B. The average AOD from the spectrophotometer readings was

about 1.6 percent higher than that of the microdensitometer readings for

both types of dosimeters.

In order to account for the effect of variations in thickness

for individual dye-film dosimeters, AOD for each dosimeter was divided

by its thickness in millimeters so that the variable followed with absorbed dose is the change in optical density per unit thickness in units

of AOD/mm. A dial-indicating micrometer with an accuracy of ±1% was

used to measure the thickness of each dosimeter. The nominal thickness

of the dye-films was of the order of 50 ym.

Two different batches of film type B were employed. They are

12
designated as film types B-1 and B-2. Film type B-1 was obtained from

the supplier about 2 years ago as sheets with dimensions of 20 by 25 cm,

whereas film type B-2 was obtained about a month before irradiation and

was in the form of 1 by 1 cm squares. The two batches showed slightly

different responses to radiation.

13
C. RESULTS

C.l. Calibration of the Dosimeters

The dye-film dosimeters were calibrated In the NBS ^°Co

y-ray pool source. The output of this source has been determined

previously to a high accuracy with the use of a carbon (graphite) calorimeter and a cavity Ionization chamber [l8]. Results of the dosimeter

calibrations are shown in Figure 5 for film type A and in Figure 6 for

film type B.

During the calibration irradiations, the dosimeters were embedded in a cavity within the polystyrene holder. The thickness of

material surrounding the dosimeters was such that it provided electronic

equilibrium in the cavity, that is, the material thickness was equal to

the range of the most energetic secondary electron that could be generated by photons in the polystyrene holder. From the original calibration, the ^°Co y-ray source output had been determined as the dose rate

In carbon. For any other material, the absorbed dose Is given by the

following formula [19]:

m/c

where the subscripts m and c lndicate_the material and carbon respec-

^en

tlvely; D is the absorbed dose; and is the mass energy absorption

coefficient averaged over a given energy range. Equation (1) can also be

applied to determine the dose rate by substituting D for D. For these

results, the ratio of the average mass energy absorption coefficients

14
o

ro

(UJUOt^Q)

o

UJIUi/aov

ro

O

CM E

c

OR

O

a:<

z

z

o E

c

< 5

a:CD

<

o

o

o

If)

T3

O

O

<\j Q

O O

(UJUI09) tuuu/aoV

15

•H 0)U

CO

CO

(U 0} a (U -H H -u •H & CO H C

•H <U Q

o «0o

CO -H

d) 4-i > a

>-( O

D

toM

03

>-O

CO

00a

0) iH

(U>

60 CO

m

(U

00

(14
DOSE, Mrad

Figure 6. ^°Co y-ray Calibration Curves of Film Type B in Air.

Optical Densities Measured at Two Wavelengths.

16
(of polystyrene to carbon) was taken to be equal to 1.077. This value

was within ±0.3 percent of all such ratios that exist over the range of

photon energies from 0.1 to 1.3 MeV. Ratios were computed from tabulated values of the mass energy absorption coefficients as a function

of photon energy [20].

In order to determine the absorbed dose in the dosimeters

irradiated in a medium, cavity theory was applied [l, 21, 22]. This

theory is applicable if the following conditions are met:

a. The cavity containing the dosimeter is small or thin

with respect to the range of most secondary electrons, that is, the

number of secondary electrons produced in the dosimeter must be negligible compared to the number produced in the surrounding material;

b. The electron energy spectrum at any depth must be essentially undisturbed by the presence of the cavity; and

c. The photon and electron fluence as well as energy-loss

profiles must be spatially uniform and continuous close to the cavity.

These conditions were met in all cases for the results described in this

study. Hence, if D is the absorbed dose in the medium, then, D-, the

m ' r absorbed dose in the dye-film dosimeter is

where s^ . is the ratio of the electron mass collision stopping powers

r /m

of the dosimeter to the material averaged over a given energy range.

Electron mass collision stopping powers have been calculated for a number

of materials and these values have been tabulated as a function of electron energy [23, 2h]. For the dye-film dosimeter in a polystyrene holder,

17
the following average values of the mass collision stopping power ratios

of the film to polystyrene were used; (a) film type A « 1.031 and (b)

film type B = 0.948. These average ratio values were within ±0.5 percent of all such ratios over the energy range from 0.1 to 1.3 MeV.

The results shown in Figures 5 and 6 were obtained by combining Equations (1) and (2); that is, in general

• D = D

' / • s^, . (3)

f c \ p m/c f/m

/

In this way, the measured dosimeter response of the change in optical

density was related to the absorbed dose in the dosimeter.

C.2. A Comparisoii of Dose Rates of the NBS_and the Natlck

^ ' Laboratories ^°Co y-ray Sources

;^ The output of the ^°Co y-ray irradiators at the Natick

Laboratories had been determined with the Fricke (ferrous sulfate) dosimeter, which is primarily an aqueous system. Therefore, the dose rate

specified was that in water. The equation used to find the dose in the

dye-film dosimeters was the following:

= D

f w

en

• s^, (4)

\ P / / f/m

\ / m/w

where w refers to water, and m refers to the material (polystyrene) of

/^en which the film holders were made. The value of 1 is 0.965 which

P fm/w

is within ±4 percent of the ratio values computed for polystyrene to

water between 0.1 and 1.3 MeV.

Table 1 gives a comparison of the NBS and the Natick Laboratories (one air-cooled and another nitrogen-cooled) ^ ''Co sources on the

basis of total absorbed dose in the dye-film dosimeters. Within the

limits of error, the ratio of the responses of film type A indicates the

18
Table 1

Comparison of Dose Rates of the NBS and Natick

60 t Laboratories Co y-ray Sources

A. Film Type A

Ratio of Dose Readings: NBS/Natick Laboratories

Air 0.955 ± 0.048

N2 0.980 ± 0.029

B. Film Type B

Ratio of Dose Readings: NBS/Natlck Laboratories

Film Type B-1 Film Type B-2

A 30 nm 630 nm A 30 nm 630 nm Alr(a)* 0.937±0.037 0.892±0.018 0.996±0.030 1.05A±0.063

Alr(b) 0.939+0.056 0. 992+0. OAO 0.98A±0.010 1.039±0.010

N2(a) 0.82310.016 0.837±0.008 0.930±0.056 1.013±0.030

NaCb) 0.8A2+0.03A 0.8A8±0.008 0.938±0.019 1.02A±0.010

Ai7 0.9A0 ± 0.080 1.018 ± 0.070

n7 0.838 ± 0.039 0.976 ± 0.069

Note: ^The approximate dose rates In the dosimeters at the time of

exposure were: 710 rad/s at NBS, A2 rad/s In air and

1700 rad/s In at Natick Laboratories.

Air (a) and NaCa) data are for spectrophotometrlc readings

1 to 2 days after irradiation. Air(b) and N 2(b) data are

for readings 7 months after irradiation. Air and Na data

are average values.

19
outputs of the Natick Laboratories sources are as specified by their

previous calibrations. The same conclusions can be made for film type

B-1 in the air-cooled source and film type B-2 in both sources; however,

film type B-1 does indicate a significant difference for the nitrogencooled source. The values of the ratios of the two sources were calculated by averaging all values for the individual measurements as indicated in Table 1. An associated error was assigned which is equal to the

square root of the sum of the squares of the errors assigned to the

individual measurements.

A difference was found between the two types of films (A and

B) in their post-irradiation coloration development. Film type A showed

a 2 to 3 percent increase in optical density during the first two days

following irradiation, but thereafter was stable. A gradual increase

could be seen in the optical density of film type B for several weeks

following irradiation; therefore, the time between an irradiation and a

photometric reading had to be monitored so that a proper correction factor could be applied when comparing dosimeters read at different times.

Since some of film type B-1 were read after an elapsed time of 7 months,

post-irradiation development seems not to be the cause of the results in

the nitrogen-cooled source. A satisfactory explanation of these anomalous results of the film type B-1 measurements has not been proposed to

date

C.3. Depth-Dose Distributions in Electron Irra,di,ated Materials

The four homogeneous materials irradiated by incident 10-MeV

electrons were carbon, aluminum, polyethylene, and polystyrene. The

dose versus depth curves for these materials as measured with film type
A are. shown In Figures 7 and 8, where is the incident electron energy

and is the extrapolated (practical) range. Nominal entrance doses in

water were 1.0 Mrad for carbon and aluminum and 1.5 Mrad for polyethylene

and polystyrene. The discrepancy observed in Figure 8 between stack and

wedge data in polystyrene will be discussed in a later section. The

depth-dose distributions as measured with film type B are shown in Figure

9 through 12, where p is the material (medium) density and T^ is the incident electron energy. Film type B-1 was used in the "wedge" method

measurements and film type B-2 was used in the "stack" method measurements. For these measurements, the nominal entrance dose in water was

2.0 Mrad for all materials. The doses in the homogeneous materials were

interpreted by measuring the ADD in film type B at both 430 and 630 nm

for the "stack" method. A difference in values at the two wavelengths

is noticeable for carbon (see Figure 9). This was apparently caused by

damage that occurred to the surfaces of the dosimeters and resulted in

less light transmission. Therefore, the curves were based entirely on

the 630 nm measurements since the response at this wavelength is about

four times greater than the response at 430 nm and is therefore less

sensitive to this surface effect.

The absorbed dose in the material was determined by the use

of Equation (2) which can be rewritten as

D = 7 ,^ • . (5) m m/f f

The values of the stopping power ratios used in these determinations are

given in Table 2. These values were weighted averages over the energy

range from 0.5 to 10.0 MeV. The percent variations over that energy

range also are seen to be small, especially for film type B.

21
DEPTH, cm

Figure 7. 10-MeV Electron Depth-dose Distributions in Carbon

and Aluminum Measured With Film Type A

09
-\ \

I r POLYSTYRENE

2.4

1.6

.8

o

o

UJ<no

o

2.4

1.6

.8

\

POLYETHYLENE

STACK : o

rj r4.9lcm

^e-|5.l6g/c-2 cm WEDGE : A

Re {5. 13 cm

5.39 gXm^

V

STACK- o

To = 10.0 MeV

18 cm

95 q/cTTTWEDGE: A

To = 10. 1 MeV

ft

. /5.3I

" \5.0{

cm

08 g/cm'

0

Figure 8.

1.0 2.0 3.0

DEPTH, cm

4.0 5.0 6.

lO-MeV Electron Depth-Dose Distributions in Polystyrene

and Polyethylene Measured With Film Type A.

23
CARBON

STACK

O 630 nm

A 430 nm

13

a

o

Max. Dose

= 1.69 q/cm"

= 9.95 MeV

= 2.25 Mrad

Extrapolated_ r Range ~\

3.13 cnn 5.29g/ccm

1 \^

1 \

WEDGE

.73 ^cm

0

Figure 9.

Max. Dose

To =10 MeV

= 3.02 Mrad

Extrapolated r3.20cm

Range "\5.54g/6m^

2.4 3.2

DEPTH , cm

4.0

10-MeV Electron Depth-Dose Distributions in Carbon

Measured With Film Type B.

24
2.4

1.6

.8

O

0

UJ

COO 3.2

Q

ALUMINUM

STACK

o 630nm —

^ 430 nm . , p = 2.67g/cm*

Tq =10.1 MeV —

Max. Dose = 2.80 Mrad

Extrapolated fl .95 cm

Range "15.21 g/cm^

\^ —

WEDGE To = 9.78 MeV

Max. Dose = 2.74Mrad

Extrapolated, f I. Range '\^-

95 cm

2 1 g/fcm'

1.2 DEPTH, cm

Figure 10. 10-MeV Electron Depth-Dose Distributions in Aluminum

Measured With Film Type B.

25
2.4

1.6

.8

T3

a

- 0

UJ

O 3.2 O

POLYSTYRENE

O 630 nm

STACK A 430 nm

P

' 1.05 q/cm'

To = 9.95 MeV "

V Max. Dose = 2.54 Mrad

^*N^ Extrapolated_^r4.74 cnn Range L4.98 g/cm^

—

III 11

1 \ok

1 1 -1 1 1

2.4

1.6

.8

0

WEDGE

To = 9. 78 MeV

Max. Dose = 2.89Mrad -

E/trapolated r4.75cm

Range = l4.99^cnTp

0 .8 1.6 2.4 3.2

DEPTH, cm

4.0 4.8

Figure 11. 10-MeV Electron Depth-Dose Distributions in Polystyrene

Measured With Film Type B.

26
2.4

.6

o

- 0

POLYETHYLENE

STACK o 630 nm

A 430 nm

p

= 0.956 g/cm

To = 9.95 MeV

Max. Dose = 2.34 Mrad —

Extrapolated _ 14.94 cm

Range ' 14.72 g/6m^

LU

CO

O

Q WEDGE

To = 9.78 MeV

Max. Dose = 2.81 Mrad _

Extrapolated_ ("5.44 cm

Range ^l5.20g/6m!_

2.4 3.2

DEPTH, cm

Figure 12. 10-MeV Electron Depth-Dose Distributions in Polyethylene

Measured With Film Type B.

27
Table 2

Electron Mass Collision Stopping Power

Ratios, Material to Film^

Film Type A Film Type B

Percent* Percent*

Ratio Variation Ratio Variation

Carbon 0.863 ±1.6 0.947 ±0.6

Aluminum 0.816 ±5.0 0.873 ±1.7

Polyethylene 1.016 ±3.0 1.109 ±1.6

Polystyrene 0.951 ±2.3 1.041 ±1.6

Values in the table are from reference [2ii]. *The percent variation is over the electron energy

range between 0,5 and 10 MeV.

28
Comparisons of experimental and calculated 10-MeV electron

depth-dose distributions in carbon and aluminum are shown in Figure 13.

The experimental curves were derived from the "stack" measurements using

film type B (see Figures 9 and 10) while the histograms were obtained

from Monte Carlo calculations of Berger and Seltzer [23] . The calculated results have been normalized to the experimental incident electron

fluence in each case. No comparable comparisons are shown for polyethylene or polystyrene because calculated results are not available for those

materials

Table 3 gives some of the important parameters by which the

depth-dose distributions can be characterized. The parameters listed

are: (a) the depth of maximum dose, X^, which occurs at the peak of the

distribution, (b) the experimental extrapolated range, R^, which is obtained by a linear graphical extrapolation to zero dose (or background)

of the depth-dose curve beyond the depth of maximum dose, (c) the calculated extrapolated range, R^, which is obtained in the same manner as R^

from the calculated depth-dose curves shown in Figure 13, and (d) the

average electron pathlength, R^, as determined by the continuous-slowingdown-approximation [2U, 25]. The experimental values listed are averages

obtained from data provided by the "stack" and "wedge" method measurements. A comparison of the parameters as determined by the two different

dosimeters indicate agreement to better than 2 percent for carbon, 7 percent for aluminum, and 8 percent for both polyethylene and polystyrene.

The extrapolated (or practical) range in aluminum can be

calculated from the following formula derived by Katz and P enfold [26]:

R = 0.530 E - 0.106 (6) c o 29
CO

2.8

2.4

2.0

1.6

g 1.2

1 1 1 1 1 1 1 1 CARBON

1 1 1 1

Experimental, stack.

film type B

Histogram: Berger

— \ S

and Seltzer

1 1 11 1 1 1 > 1 1 1 1 0 .8 1.2 1.6 2.0 2.4 2.8 3.2 3.6 4.0 4.4 4.

DEPTH, cm

Experimental, stack,

film type B

Histogram: Berger

and Seltzer

1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4

DEPTH, cm

Figure 13, Experimental and Calculated 10-MeV Electron Depth-Dose

Distributions in Carbon and Aluminxim.

30
Table 3

Comparison of Some Experimental and Calculated Depth-Dose

Parameters for the Different Materials'^

X

(8/

R

(^/

"ecm" ) (g/

R'ecm )

R

"ocm ) R

e /R'e R /R

e o Carbon (A)* 2. 68 5. 54 5. 75 5. 58 0. 963 0.993

Carbon (B) 2. 74 5. 42 5. 75 5. 58 0. 943 0.971

Aluminum (A) 2. 58 5. 36 5. 54 5. 84 0. 968 0.918

Aluminum (B) 2. 42 5. 21 5. 54 5. 84 0. 940 0.892

Polyethylene (A) 2. 84 5. 02 4. 79 1.048

Polyethylene (B) 2. 63 4. 96 4. 79 1.035

Polystyrene (A) 3. 11 5. 28 5. 10 1.035

Polystyrene (B) 2. 88 4. 98 5. 10 0.976

Note: X = depth of maximum dose, i.e., the peak of the depth-dose

^ distribution.

R = experimental extrapolated range obtained by graphical

extrapolation to zero dose of the depth-dose distribution.

R' = calculated extrapolated range obtained in same manner

as R from reference [23]

e R = mean electron pathlength from reference [2U ]

*

° The letter enclosed in parenthesis is the film type.

31
where R is the extrapolated (practical) range in g/cm^ and E is the

c o incident electron energy in MeV. This formula gives a value of R = 5.19

c g/cra^ for 10.0 MeV (average electron beam energy for irradiations of

aluminum with film type A), and R^= 5.16 g/cm^ for 9.94 MeV (average

beam energy for irradiations with film type B) . The experimental extrapolated ranges for the two different dosimeters in Table 3 are in

general agreement with these calculated practical ranges in aluminum.

The ratio of the values are: R /R = 1.033 for film type A, and

e c R /R = 1.010 for film type B.

e c Table 4 shows a comparison of the peak and entrance doses

in the various materials as determined by the two dosimeters and by the

two different methods of measurements. Generally, the ratio of the peak

to entrance dose, D /D , from the two different methods ("stack" or

"wedge") agree to better than 10 percent for a given material and dosimeter. If an overall average is taken, the ratio D /D for film type

' P e A is 1.41, and for film type B is 1.40. Therefore, within ±10 percent

(+10 percent for aluminum and -10 percent for polyethylene, both for

film type B) , the ratio of D /D can be taken to be 1.40 for all mater-

^ ' P e ials.

The results obtained by the "stack" and "wedge" methods are

compared in Table 5. Ratios are given of the "stack" to "wedge" methods

for the peak dose, D^; depth at the peak dose, X^; and the extrapolated

range, R^. Perhaps the most sensitive parameter for comparison is X^,

the depth at the peak dose. That parameter agrees to within 5 percent

for all materials except for polyethylene, as measured with film type B

(see Figure 12), and polystyrene, as measured with film type A (see

32
Table 4

Peak and Entrance Doses of Depth-Dose Distributions

Film Type A

Stack-S

Wedge-W (.Mraci

D (Mrad)

P

D /D

p e

S 1.06 1. 51 1. 42

Carbon W 1.06 1. 58 1. 49

s 1.19 1. 60 1. 34

Aluminum w 1.18 1. 63 1. 38

s 1.58 2. 26 1. 43

Polyethylene w 1.57 2. 26 1. 44

s 1.59 2. 12 1. 33

Polystyrene w 1 43 2. 07 1. 45

Film Type B

s 1.71 2. 25 1. 32

Carbon w 2.08 3. 02 1. 45

s 1.86 2. 80 1. 51

Aluminum w 1.74 2. 74 1. 57

s 1.89 2. 34 1. 24

Polyethylene w 2.17 2. 81 1. 29

s 1.88 2. 54 1. 35

Polystyrene w 2.00 2. 89 1. 44

*SymboIs D and

e D represent entrance dose and

dose, respectively, in the mat erial specified

33
Table 5

Comparison of Results of the "Stack" and "Wedge" Methods

of Depth-Dose Measurements

Ratio of Response; "Stack"/"Wedge""^

D X

_E

R

e

* Carbon (A) 0.956 1.050 0.996

Carbon (B) 0.745 1.026 0.955

Aluminum (A) 0.982 0.969 0.991

Aluminum (B) 1.022 0.988 1.000

Polyethylene (A) 1.000 1.025 0.974

Polyethylene (B) 0.833 0.833 0.908

Polystyrene (A) 1.024 1.214 0.957

Polystyrene (B) 0.879 0.986 0.998

Note: The symbols are: D^ = peak dose; = depth at peak

dose; and R^ = extrapolated, experimental range.

The letter in parenthesis indicates the film type.

34
Figure 8) . A close inspection of the curves indicate that the "wedge"

data for polyethylene with film type B and the "stack" data for polystyrene with film type A appear to be inconsistent with other data.

Probable causes for these results could have been (a) that in the "wedge"

the material was not forced together sufficiently tight so that a gap

existed between the material and the type B dosimeter and (b) that in

the "stack" the irradiated polystyrene block discharged during or shortly after exposure, the light from which could have caused additional

coloration of the type A dosimeters. However, overall the data indicate

that there is no significant difference in the results obtained by these

two methods

35
D. CONCLUSIONS

D.l. Comparison of Experimental Results With Theory

This study has demonstrated that thin dye-film dosimeters can

be employed successfully to det ermine depth—dose distributions in materials

.

First of all, the extrapolated ranges measured experimentally in aluminum

are in excellent agreement with the range calculated by the Katz and Penfold formula [26]. The experimental ranges are also in reasonably good

agreement with the theoretical mean pathlength, ranges of Berger and

Saltzer [2^+] as shown in Table 3. For 10-MeV electrons the calculated

pathlengths are expected to be fairly close to the experimental ranges

for low Z (atomic number) materials and become progressively larger than

the experimental ranges with increasing Z. The ratios of R^/R^ in Table

3 appear to confirm this premise. Other favorable comparisons are shown

in Table 6 where Monte Carlo calculated [23] and experimental depth-dose

distribution parameters for carbon and aluminum are compared. There is

good agreement except for the depth of the peak dose in carbon and for

the peak-to-entrance dose ratio in aluminum. Detailed comparisons of the

carbon and aluminum experimental data with the calculations are shown in

Figure 13. The measured depth-dose distributions are shifted toward the

beam-entrance surfaces of the media relative to the calculated distributions. One possible explanation of this shift could be the effect of the

0. 5 mm aluminum scan horn window which the electron beam passed through

before striking the samples. If the window thickness is added to the

material thickness of the experimental measurements, the peak dose position would be shifted toward greater depths and would account for about

half of the difference observed between the peak positions of the experi36
TABLE 6

Comparison of Experimental and Calculated Depth-Dose

Parameters for Carbon and Aluminum

Ratio of Experimental to Calculated Value^s*

X R D /D

-E. _e P e Carbon 0.826 0.953 0.986

Aluminum 0.936 0.954 0.863

Note:* Experimental values used are averages of "stack",

"wedge", and both film types from Tables 3 and 4.

Calculated values are derived from results of

Berger and Seltzer [23] shown in Figure 13. Symbols

used are the same as for the previous tables.

37
mental and calculated curves. Two other effects could cause a shift in

the experimental curves relative to the calculated results: (1) the

electron beam energy could be degraded to lower energies because of its

passage through the scan window, and (2) the electron beam could have

been not normal, having a significant divergence at the entrance to the

irradiated medium. Neither of the last two effects would appear to be

significant; however, more measurements are required to establish with

confidence these depth-dose distributions.

The experimental results strongly suggest that the "wedge"

method is equivalent to the "stack" method for measuring depth-dose distributions. In principle, for normal incidence of the electron beam,

the "stack" method is a more favorable geometrical arrangement of the dosimeters and medium than the "wedge" method in which a possibility exists

for "channeling" of some of the electrons in the gaps between the strip

of dye-film dosimeter and the medium. However, since the results show

that "channeling" is not a problem, the "wedge" is superior for most

applications because it allows continuous high-resolution measurement of

the energy-deposition profiles as well as greatly reducing the time and

effort required to handle and read the dosimeters.

D . 2 . Comparison of Nominal and Experimental Entrance Doses

Irradiation doses for the various materials were specified

initially as nominal entrance doses in water which were based on previous

measurements of the linac beam with a water calorimeter [27]. Comparisons of the nominal and experimental entrance doses in water, the latter

being determined from the doses measured for the various materials, are

shown in Table 7. The experimental entrance dose for water, D^, is given

38
Table 7

Entrance Dose in Water From Experimental Dose in Media:

Comparison of Experimental and Nominal Entrance Doses

Material

Stack-S

Wedge-W

Film

D'w

(Mr ad)

Type A

D

e (Mrad) w/m

Dw

(.Mrad;

Vd'W

Carbon S 1.0 1.06 1.136 1.20 1.20

w 1.0 1.06 1.136 1 . 20 1. 20

Aluminum s 1.0 1.19 1.222 1.45 1.45

w 1.0 1.18 1 . 222 1 . 44 1. 44

Polyethylene s 1.5 1.58 0.973 1.54 1.03 w 1.5 1.57 0.973 1 . 53 L.vl

Polysytrene s 1.5 1.59 1.035 1.65 1.10 w 1.5 1.A3 1.035 1.48 0.99

Film Type B

Carbon s 2.0 1.71 1.136 1.94 0.97 w 2.0 2.08 1.136 2.36 1.18

Aluminum s 2.0 1.86 1.222 2.27 1.14

w 2.0 1.74 1.222 2.13 1.06

Polyethylene s 2.0 1.89 0.973 1.84 0.92

s 2.0 2.17 0.973 2.11 1.06

Polystyrene s 2.0 1.88 1.035 1.95 0.98 w 2.0 2.00 1.035 2.07 1.04

Symbols are as follows: D' is the nominal entrance dose in water w

which was based on previous measurements

of the linac beam with a water calorimeter [27];

D is the experimental entrance dose in

^ the specified material;

s , is the mass collision stopping power ^ ratio of water to the material at

10 MeV;

D is the experimental entrance dose in

water

39
by modifying Equation (2) to be

D = s w 'w/m

• D

e

(7)

where sw/m is the mass collision stopping power ratio of water to the

material at 10 MeV, and is the experimental entrance dose in the specified material. Examination of the ratios of the experimental to nominal

entrance dose, D^/D^, indicates that the nominal dose was correctly specified in most cases with the exception of irradiations in carbon and aluminum for film type A and the carbon "wedge" and aluminum "stack" for film

type B.

D . 3 . Comparison of Tissue and Near Tissue-Equivalent Materials

In an effort to determine which of the two high polymer materials used in this istudy is closest to tissue in its energy-absorption

properties, a comparison is made of some of the depth-dose parameters of

the materials for 10-MeV electrons as shown in Table 8. The parameters

for tissue are taken to be those for muscle as calculated by Berger and

Seltzer [2^]. It appears that there is no clear preference for one polymer material over the other as far as being tissue equivalent. The polystyrene values are slightly higher than muscle for the range and depth

of peak parameters while the polyethylene values are slightly lower. The

Inverse is true for the stopping power values. Both materials have values

within 5 percent of the values for muscle. If measurements were made with

both materials. Interpolation between values obtained should give results

close to tissue. However, as can be seen in Table 8, water is much closer

In electron energy-absorption properties than either of the polymer materials .

40
Table 8

Experimental and Calculated Depth-Dose Parameters of

Tissue and Near Tissue-Equivalent

Materials for 10-MeV Electrons

Material

Muscle

Water

Polystyrene

Polyethylene

Range

A. 939 (a)

Depth of

Peak Dose

A. 880 (a) 2.83 (b)

5.095 (a) 3.00 (c)

5.13 (c)

A. 792 (a) 2.73 (c)

A. 99 (c)

Mass Collision

Stopping Power

(MeV • cmVs)

1.978 (a)

2.000 (a)

1.932 (a)

(a) Calculated, Berger and Seltzer

(b) Calculated, Berger and Seltzer [28].

(c) Experimental, this report.

Al
D.4. Possible Negative Effects on Results by Some Experimental

Conditions

As discussed In Section C.3., a defect existed In the polyethylene "wedge" assembly which could have caused unreliable results.

This was a result of improper machining of the two halves of the wedge,

thereby making possible an air gap between the polyethylene and the dyefilm dosimeter if the two parts of the wedge were not held together

tightly during assembly. Also, a discharge which occurred in one of the

polystyrene blocks during irradiation could have caused additional coloration to the dye-film dosimeters in that assembly. Such a discharge

happened only once in the four irradiations made of polystyrene assemblies

and did not occur during any of the irradiations of other materials.

Another adverse experimental condition was the thermal heating

of the blocks of material upon and immediately after irradiation. Temperature dependence studies of the two types of dye-film dosimeters have been

made with the films held at constant temperatures during ^°Co y-ray irradiations [12-IJ4]. Under these conditions, film type A displays a positive temperature coefficient; that is, the response to radiation increases

with increasing temperature. On the other hand, film type B exhibits a

negative temperature coefficient above room temperature under these conditions. If the dosimeters behaved in this way during the electron beam

irradiations, the difference between the responses of the two types of

dosimeters should have been as great as 40% at the peak dose for the carbon measurements. However, comparison of the peak-to-entrance dose ratios

in Table 4 for the different dosimeters shows agreement to within 5 percent. In addition, previous dose-rate studies [11 ] of film type B indicate no significant temperature dependence for fast-pulse electron irradi42
ations where the temperature reached 30 C above room temperature but

cooled to near room temperature in less than 10 seconds. Hence, thermal

heating by electron beams, where the total dose is delivered in a short

time, does not seriously affect the response of these dosimeters.

D. 5. Suggestions for Future Experiments

Since the experiments described in this report were primarily

designed to enable the Natick Laboratories to better understand the total

energy deposited and the energy-depositions profiles in irradiated food

products, it would be desirable to perform additional experiments using

the dye-film dosimeters in actual meat packages during irradiation. For

these irradiations, the dosimeters should be used in the bulk of the meat

(preferably in a "wedge" configuration) as well as perpendicular to the

electron beam near the interface of the meat and its package. Such experiments would give basic data which are relevant to energy deposition

in tissue. Also, these measurements would demonstrate more exactly how

energy is deposited in the food products under processing conditions;

that is, the effects of boundaries especially would be accounted for.

Furthermore, comparisons of measurements with the Monte Carlo calculated

predictions could be made in order to verify the applicability of these

calculations in a wide variety of similar irradiations.

43
REFERENCES

1. Burlin, T.E., Cavity-Chamber Theory, Radiation Dosimetry , Vol. 1,

Attix and W.C. Roesch, Eds., Academic Press, New York, p. 332(1968).

2. McLaughlin, W.L. , Hussman, E.K., The Measurement of Electron and

Gamma-Ray Dose Distributions in Various Media, Large Radiation

Sources and Accelerators in Industrial Processes , IAEA, Vienna,

, p. 579 (1969)

.

3. Eisen, H. , Rosenstein, M. , and Silverman, J., Electron Dosimetry

Using Chalkley-McLaughlin Dye-Cyanide Thin Films, Dosimetry in

Agriculture, Industry, Biology, and Medicine , IAEA, Vienna, p. 615

=i . V (1973).

4. Rosenstein, M. , Eisen, H., and Silverman, J., Electron Depth-Dose

'Distribution Measurements in Finite Polystyrene Slabs, J. Appl.

Phys. 43, 3191 (1972)

.

5. Eisen, H. , Rosenstein, M. , and Silverman, J., 2.00-MeV Electron

Depth-Dose Measurements in Aluminum, Copper, and Tin Absorbers

Using a Radiochromic Dye Film, Intern. J. Appl. Rad. Isotopes 23 ,

97 (1972).

6. Eisen, H. , Rosenstein, M. , and Silverman, J., Electron Depth-Dose

Distribution Measurements in Two-layer Slab Absorbers, Rad. Res.

52, 429 (1972).

7. Hussman, E.K. and McLaughlin, W.L. , Dye Films and Gels for Megarad

Dosimeters, Radiation Dose and Dose Rate Measurements in the Megarad Range , National Physical Laboratory, Teddington, England, p. 35

(1970).

44
8. McLaughlin, W.L. , Radiochromic Dye Cyanide Dosimeters, Manual on

Radiation Dosimetry , N.W. Holm and R.J. Berry, Eds., Marcel Dekker,

Inc., New York, p. 377 (1970).

9. Harrah, L.A. , Chemical Dosimetry with Doped (halostyrene) Film,

Radiation Research _4l, 229 (1970).

10. Harrah, L.A., Stored Charge Effects on Electron Dose-Depth Profiles

in Insulators, Appl. Phys. Letters r7, 421 (1970).

11. Chappell, S.E. and Humphreys, J.C., The Dose-Rate Response of a

Dye-Polychlorostyrene Film Dosimeter, IEEE Trans. Nucl. Sci. NS-19 ,

175 (1972).

12. Bishop, W.P. , Humpherys, K.C., and Randtke, P.T. , Poly (halo) styrene

Thin-film Dosimeters for High Doses, Rev. Sci. Instr. 44, 443(1973).

13. Humpherys, K.C. and Wilcox, R.L., Radiochromic Dosimetry and Rate

Effects, EG&G Report No. 1183-2218 (1969).

14. Humpherys, K.C. and Randtke, P.T., Doped Poly (halo) styrene Dosimeter Materials Studies, EG&G Report No. 1183-2267 (1971).

15. Frankhauser, W.A., Measurement of the Radiation Response of a

Radiochromic Dosimeter Exposed to a Pulsed Electron Beam Source,

EG&G Report 1183-5024 (1973).

16. Brynl6lfsson, A. and Thaarup, G., Determination of Beam Parameters

and Measurements of Dose Distribution in Materials Irradiated by

Electrons in the Range of 6 MeV to 14 MeV, Danish AEC, Riso Report

No. 53 (1963).

17. Bishop, W.P. and Benson, J.L., Operational Treatment of Multiple

Reflection Interference in the Readout of Thin-film Poly (halo) styrene Dosimeters, Sandia Laboratories Report No. SC-DR-72 0641(1972).

45
18. Petree, R. and Lamperti, P., A Comparison of Absorbed Dose Determinations in Graphite by Cavity Ionization Measurements and by Calorimetry, J. of Research Natl. Bur. Stnds. 71C , 19 (1967).

19. Weiss, J. and Rizzo, F.X., Cobalt-60 Dosimetry in Radiation Research

and Processing, Manual on Radiation Dosimetry , N.W. Holm and

R. J. Berry, Eds., Marcel Dekker, Inc., New York, p. 231 (1970).

20. Evans, R.D. , X-Ray and y-ray Interactions, Radiation Dosimetry ,

Vol. 1, F.H. Attix and W.C. Roesch, Eds., Academic Press, New York,

p. 93 (1968).

21. Chan, F.K. and Burlin, T.E., An Experimental Examination of a

General Cavity Theory Using a Solid State Dosimeter, Br. J. Radiol.

•- 43, 54 (1970).

22. McLaughlin, W.L. , Hjortenberg, P.E. , and Radak, B.B., Absorbed-Dose

Measurements With Thin Films, Dosimetry in Agriculture, Industry,

Biology and Medicine , IAEA, Vienna, p. 577 (1973).

23. Berger, M.J. and Seltzer, S.M., private communication.

24. Berger, M.J. and Seltzer, S.M. , Tables of Energy Losses and Ranges

of Electrons and Positrons, NASA SP-3012 (1964) and SP-3036 (1966).

25. Pages, L., Bertel, E. , Joffre, H. , and Sklavenitis, L., Energy Loss,

Range, and Bremsstrahlung Yield for 10-keV to 100-MeV Electrons in

Various Elements and Chemical Compounds, Atomic Data 4^, (1)1(1972).

26. Katz, L. and Penfold, A.S., Range-Energy Relations for Electrons

and the Determination of Beta-Ray End-Point Energies by Absorption,

' Revs. Mod. Phys . 24, 28 (1952).

46
Holm, N.W. and Jarrett, R.D., An Evaluation of Dosimetry Procedures

Applicable for Use in Food Irradiation, Nat. Acad, of Science, Nat.

Research Council, Publication 1273, 361 (1965).

Berger, M.J., and Seltzer, S.M., Calculation of Energy and Charge

Deposition and of the Electron Flux in a Water Medium Bombarded

with 20-MeV Electrons, Annals New York Academy of Sciences 171 ,

Art. 1, 8 (1969).

47

NBS-1 14A (REV. 7-73)

L'.S. DEPT. OF COMM. BIBLIOGRAPHIC DATA

SHEET

1. PUBLICATION OR REPORT NO.

NBSIR 73-413

2. Gov't Accession

No.

3. Recipient's Accession No.

4. TITLE AND SUBTITLE

Measurement of Depth-Dose Distributions in

Carbon, Aluminum, Polyethylene, and Polystyrene for 10-MeV

Incident Electrons

5. Publication Date November 1973

6. Performing Organization Code

7. AUTHOR(S)

J.C.Humphreys, S.E. Chappell, W.L. McLaughlin, & R.D. Jarrett

8. Performing Organ. Report No. NBSIR 73-413

9. PERFORMING ORGANIZATION NAME AND ADDRESS

NATIONAL BUREAU OF STANDARDS

DEPARTMENT OF COMMERCE

WASHINGTON, D.C. 20234

10. Project/Task/Work Unit No. 2430411

1 !• Contract /Grant No. AMXRED 73-141

12. Sponsoring Organization Name and Complete Address (Street, City, State, ZIP)

Food Laboratory

U.S. Army Natick Laboratories

Natick, Massachusetts 01760

13. Type of Report & Period Covered

Interim Report

14. Sponsoring Agency Code

15. SUPPLEMENTARY NOTES

16. ABSTRACT (A 200-v'ord or less factual summary of most significant information. If document includes a significant

bibliography or literature survey, mention it here.)

Depth-dose distributions of 10-MeV electrons incident on homogeneous media of

carbon, aluminum, polyethylene, and polystyrene have been measured using thin radiochromic dye-film dosimeters. Two types of dye-film dosimeters were employed as "cavities" within the media in two different geometrical configurations. One configuration was a stack with the dosimeters interleaved between disks of the medium and

placed perpendicular to the incident electron beam direction. The other configuration

was a wedge assembly with a single piece of dye film placed between pieces of the

medium at a small angle to the beam direction. The results show no significant difference between dosimeter type or experimental arrangement. In addition, good agreement

is shown in comparisons of experimental and Monte Carlo calculated depth-dose distributions characterized by such parameters as extrapolated range, depth of peak dose, and

ratio of peak to entrance dose.

17. KEY WORDS (six to twelve entries; alphabetical order; capitalize only the first letter of the first key word unless a proper name; separated by semicolons)

Aluminum; carbon; depth dose; depth-dose distributions; dye-film dosimeters; polyethylene; polystyrene; radiochromic dyes; 10-MeV electrons

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