National Bureau of Standard:

Library, N.W. Bldg

OCT 5 1962

^ecknlcai fiote 161

EVALUATION OF UNEXPECTEDLY

LARGE RADIATION EXPOSURES

BY MEANS OF PHOTOGRAPHIC FILM

WILLIAM L MCLAUGHLIN

U. S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS

NATIONAL BUREAU OF STANDARDS

161

AUGUST 1962

EVALUATION OF UNEXPECTEDLY

LARGE RADIATION EXPOSURES

BY MEANS OF PHOTOGRAPHIC FILM

William L. McLaughlin

NBS Technical Notes are designed to supplement the Bureau's regular publications program. They provide a means for making available scientific data that are of transient or limited interest. Technical Notes may be

listed or referred to in the open literature.

For sale by the Superintendent of Documents, U.S. Government Printing Office Washington 25, D.C. - Price 15 cents
FOREWORD

This Note covers the material presented by the

author at the 1962 annual meeting of the Health Physics

Society. Work on some of the phases covered in the

report will be continued; for this reason, it is not

contemplated to publish the present results in a more

formal way.

Scott W. Smith, Chief L.S. Taylor, Chief

Radiological Equipment Section. Radiation Physics Division,

11
EVALUATION OF UNEXPECTEDLY LARGE RADIATION EXPOSURES

BY MEANS OF PHOTOGRAPHIC FIIK*

William L. McLaughlin

Conventional film types used in personnel

monitoring film badges are suitable for measuring

X- and y-radiation exposures only up to 1000 R, By

using special processing procedures, it is possible

to extend the range of the less sensitive component

of most commercial film packets up to at least

10,000 R. Limitations in precision of readings due

to changes in rate dependence, energy dependence,

and changes in the shape of the characteristic curve

in this range are discussed.

Sometimes it is important to recover photographic dosimetry data

that might be lost in routine experimental practice because the total

radiation exposure happened to be higher than the upper limit of the

useful range of the film. The useful range of photographic dosimetry

can be extended beyond its conventional upper limit of about 1000 R

by:

1. Use of Supplementary Emulsions of Low Sensitivity . Some of

the very fine-grain, spectroscopic films show a useful response to

1-Mev X-rays up to 100,000 R [l]**but these films are not always

satisfactory for dosimetry, because their latent images are not very

stable [2].

2. Developed Silver Analysis . One of the most accurate methods

for determining the amount of silver in a developed film is X-ray

fluorescence spectrometry [3]. One measures the silver K-f luorescence

excited in a piece of developed film, which is being irradiated by

X-rays. This method gives greater accuracy than routine densitometry

and is now finding wide sensitometric use. It can be utilized to

extend the upper limit of the useful range of some films by a factor

of about two. Another way to analyze the silver content in a developed

film is by activation of the silver by neutrons in a reactor thermal

column, and measuring the induced activity with a scintillation

counter [4].

3. Utilization of the Print-Out Effect . The print-out effect

begins to be useful only when the exposure is well beyond 10,000 R [5],

and in order to cover the range between 1000 and 40,000 R by this

method, the films must be given special chemical treatments prior to

exposure [6].

*This project was sponsored in part by U.S. Atomic Energy Commission.

**Figures in brackets indicate literature references at the end of this

paper.

1
4. Special Development Procedures . By using conventional developing solutions containing certain chemical retarders, or by selective

development of internal regions of the emulsion grains, it is possible

to decrease the film sensitivity and retain sufficient contrast, so that some film types achieve useful ranges up to at least 10,000 R„

This report gives results of studies at the National Bureau of

Standards on the fourth point; namely, the usefulness of several

special processing procedures for extending film dosimetry ranges.

Suppose a dosimeter film packet has been exposed beyond its normal

useful range. One would like to know how reliable would be the

exposure evaluation when one of the special development techniques

is used. People interested in increasing photographic dosimetry

ranges have tried using incomplete, localized development of the

emulsion grains [7]; that is, they would use a very slow-acting

developer for a relatively short time or they might decrease the

developer concentration or temperature, such that only the surface of

the grains would be affected. This often led to troubles in the form

of very uneven density distributions, or a tendency for the characteristic curve shapes to vary widely with exposure rate, especially in

the higher density regions. The results of this study show that these

difficulties are not so severe if one uses certain chemical retarders

in the X-ray developer, or if one develops the internal latent images

rather than the surface latent images.

Some of the more successful special development techniques are listed in the table, along with the conventional technique. Adding

200 grams of sugar to a liter of commercial X-ray developer results

in loss in film sensitivity at high density regions by a local ex- haustion effect [8] (solution 2), One gram of 6-nitrobenzimidazole

added to a liter of X-ray developer also acts to reduce the rate of

development [9] (solution 3), Similar reductions take place with the

addition of other development retarders, such as the mercaptotetrazoles

[9,10].

Development localized in internal regions of emulsion grains was achieved by using solutions which etch away part of the grain, either

during development (solutions 4 and 5) or prior to development

(solution 6) . Solution 4 is a fine-grain metol-hydroquinone

developer buffered with borax and containing 2 grams per liter of

potassium thiocyanate as a silver halide solvent. Solution 5 is an Amidol stabilization processing solution containing thiourea,

described by Levinos and Ehrlich [11]. Solution 6 is an internal

developer based on the method of Stevens [12,13], It involves bleaching away the surface of the grains with an acid dichromate bath and

then processing in a metol-hydroquinone developer containing a small

amount of sodium thiosulfate as silver-halide solvent.
TABLE

Development to Increase Useful Range of Dosimeter Films

(all at 20*C)

Solution Dev.Time

NOo ^ Development (min.)

CONVENTIONAL

1 Commercial X-ray developer 5

RETARDED

2 Commercial X-ray developer, with sugar

(200 g/^) 5

3 Commercial X-ray developer, with

6-nitrobenzimidazole (1 g/^) 5

INTERNAL

4 Metol-hydroquinone developer buffered

with borax, with thiocyanate (2 g/i) 10

5 Amidol stabilization developer, with

thiourea 3

6 Metol-hydroquinone developer buffered

with sodium carbonate, with thiosulfate,

(0.5 - 2.0 g/j^)^, preceded by acid

dichromate bleach 6

a. These numbers serve as keys on the curves of the figures.

b. The optimum amount of thiosulfate was determined experimentally for each film type.
Figure 1 shows characteristic curves of DuPont Industrial X-ray

film, type 510, exposed to Co"^ Y"^^'ii-^tion and developed in the various

solutions listed in the table. The curves marked "1" are for con- ventional commercial X-ray developer used in dosimetry, with both

emulsion sides (solid curves) and with one emulsion side removed

(dashed curves) . The other curves are for the special development

techniques. The slopes of these curves are still relatively high in

the 1000 R to 10,000 R range, although the two curves (2 and 3) for

chemically retarded development show a tendency to saturate at relatively

low density levels. The curves obtained with internal development are shown by 4, 5, 6, and 7. Curves 6 and 7 are for two different con- centrations of hypo in the developer; curve 6 was for 0.5 g/i and curve 7 was for 0.7 g/i. The fact that these curves are generally

steeper than curves 2 and 3, particularly for exposures beyond 10,000 R,

makes them more desirable from the standpoint of giving greater precision in the density measurements. If one assumes that the limits of

precision in reading the density are ± 0,02 density units, then a 5,000-R exposure reading on curve 6 would have precision limits of about

5 percent. This certainly is not as good as the 1-percent precision

limits of readings at a similar density level on curve 1, but is still

useful.

Figure 2 shows similar curves for DuPont Cine-Positive film,

type 834.-^ Again, special processing provides readings from 1000 R to

10,000 R, with a precision nearly as great as that offered by routine

processing. With some of the developers, however, this film shows

solarization.

The less sensitive component film of Kodak Personnel Monitoring

Packet, type 3, is represented in figure 3, This film type has a wider useful range than the others; however, the slopes of the curves obtained with internal development are not quite as satisfactory, the

precision limits of readings at 5000 R being as much as 10 percent for

± 0.02 density units. This film type also solarized in some instances

above 10,000 R.

Variations in the energy dependence of these film types occurred

when the various developers were used. Figure 4 shows relative sensitivity of a particular batch of DuPont Industrial X-ray film, type 510, over an effective photon energy range from 25 kev to 1000 kev, for the

The same solution numbers apply as in figure 1. The concentrations

of hypo in the developer for this film were 1.0 g/i for curve 6 and

2.0 g/i for curve 7.

2

The hypo concentrations for the development of this film type

(curves 6 and 7) were the same as those in figure 2.
different developers. It is interesting that with this very fine-grain

emulsion, the internal developers provide smaller variations in spectral

response than do the developers whose action is localized more on the

surfaces of the grain. Also, with internal development, the spectral

sensitivity is nearly constant in the lower part of the diagnostic X-ray

range

Figure 5 shows the energy dependence curves for DuPont Cine-Positive

film, type 834, which has larger emulsion grains. In this case, the

energy dependence is greater with internal development, but, as before,

the low-energy response is flatter. A similar family of curves is seen

in figure 6 for the less sensitive component of the Kodak Dosimeter

film packet.

Figure 7 shows that, although there is no rate dependence with con- ventional X-ray development up to 10,000 R/hr, relatively wide variations

in the film sensitivity occur with retarded and internal development.

These curves are for DuPont Industrial X-ray film, type 510, and show

variations in relative sensitivity, determined at about 1000 R of

exposure (except for curve 1, which was made at a lower exposure level).

The curves were plotted for different exposure rates, relative to the

sensitivity at an exposure rate of 20 R/hr, Very similar rate depend- ence curves were found for the other film types. There are variations

in curve shapes and maximum density levels with exposure rate, but

these are not as severe as when slow surface development is used. Among

these special development procedures, the one that produces the smallest

rate dependence at exposure rates up to 1000 R/hr is the internal

development with prior bleaching (curve 6) . For the very high exposure

rates, X-ray developer with sugar (curve 2) or with 6-nitrobenzimidazole

(curve 3) is more suitable.

In summary, it should be pointed out that these special development

techniques could be useful in emergencies when applied with some caution.

A set of workable procedures should be established before an emergency

arises.

The numbers shown in the graph refer to the same developing solutions

as those of figure 4.
[1

[2

[3

[4

[5

[6

[7

[8

[9

References

Mo Ehrlich and S.H. Fitch, Nucleonics 9 [3], 5 (1951)

»

W.L. McLaughlin and M, Ehrlich, Nucleonics j^ [10], 34 (1954).

L.S. Birks, "X-ray Spectrochemical Analysis," (Inter science

Publishers Inc., New York, 1959).

I.E. Berlman, Nucleonics H. [2], 70 (1952).

WoL. McLaughlin, Radiation Research 13, 594 (1960).

W.Lo McLaughlin, talk at 2nd International Congress of Radiation

Research, Harrogate, England (1962).

M. Ehrlich, "Photographic Dosimetry of X- and Gamma Rays,"

NBS Handbook 57 (1954).

H.M. Cleare and N.H. King, talk at 6th Annual Meeting of Health

Physics Society, Las Vegas , Nevada (1961).

E.T. Larson & H.A. Levine, Phot.Sci.Engng. , j., 59 (1957).

[10] K. Becker, Phot. Korr. 96, 99 (1960).

[11] So Levinos and M. Ehrlich, Nucleonics ]A [7], 72 (1956).

[12] G.W.W. Stevens, J.Phot.Scio 1, 122 (1953).

[13] M. Ehrlich and W.L. McLaughlin, J.OptoSoCoAmer, 46, 797 (1956).

1
>-\-^ 4

Z

UJD

DEVELOPMENT

COMM. X-RAY

|}CHEM. RETARDED

4.g

• INTERNAL

T

Co°" GAMMA-RAY EXPOSURE DOSE, r

Figure 1. Characteristic curves .of DuPont Industrial X-ray film, type 510,
Co°" GAMMA-RAY EXPOSURE DOSE, r

Figure 2. Characteristic curves of DioPont Cine-Positive film, type 834.
Co''" GAMMA-RAY EXPOSURE DOSE, r

Figure 3. Characteristic curves of insensitive film of Kodak Personnel

Monitoring Packet, type 3.
120

100

>

> 80

CO

LlI

if)

LlI >

Ixl

60

40

20

DEVELOPERS

COMM. X-RAY

COMM. X-RAY WITH SUGAR

COMM. X-RAY WITH 6-NBA

M-Q BORAX WITH THIOCYANATE

AMIDOL STABILIZATION

NTERNAL (0.5 g/i HYPO ) INTERNAL (0.6 g/i HYPO)

INTERNAL (0.7 g/i HYPO)

10 10^

EFFECTIVE ENERGY, Kev

10^

Figure 4. Spectral sensitivity curves of DuPont Industrial X-ray film,

type 510.

10
EFFECTIVE ENERGY, Kev

Figure 5. Spectral sensitivity curves of DuPont Cine-Positive film,

type 834o

11
1 1 1

1 1 1 1 1 1 M

/^ \

30

>

1- 8^.--/^'''^^ \ \

>

H

(/) 3 and 5/ y^ ^^->A \ z

LU 20 —

</) LJ> 2and4/ y^ Y\\ H

< 1 / \ \^\ _J 1 \ w UJ

a: 10

1 1 1 1 1 1 1 1

1 1 1 1 1 M p- 1 1 1 1 M 1 10 10^

EFFECTIVE ENERGY

10-

Figure 6, Spectral sensitivity curves of insensitive film of Kodak

Personnel Monitoring Packet, type 3.

12
10 10^ EXPOSURE DOSE RATE, r/hr

Figure 7o Rate dependence curves of DuPont Industrial X-ray film,

type 510.

* us, GOVERNMENT PRINTING OFFICE 1962 —657326 13