gamma-ray dosimeter: linearity, rate 
and temperature independence, and 
neutron insensitivity. Details are 
given in Tables 1-4. 
Energy dependence. The energy 
dependence of the anhydrous chloro- 
form and anhydrous tetrachloroethyl- 
ene dosimeters somewhat parallels that 
of film (4). Peak response as meas- 
ured by acid production is directly re- 
lated to photoelectric absorption. 
Energy dependence is decreased as 
Compton scattering begins to predomi- 
nate, and the systems become energy- 
independent above 0.6 Mey. Energy 
independence down to 80 kev is achieved 
when the systemsare shielded with 0.5 
mm oi lead. 
Dose-rate dependence. Resor- 
cinol-stabilized chloroform or tetra- 
chloroethylene is rate-independent 
from 0.5 r/hr to the rates encountered 
during nuclear detonations. Dose-rate 
studies in this laboratory have been 
varied from 0.5 r/hr to 4,200 r/min. 
Temperature dependence. Both 
the anhydrous chloroform and tetra- 
chloroethylene dosimeters are inde- 
pendent (+5%) of temperature during 
irradiation in the range 5-55° C. 
TABLE 1—Relative Energy Response* 
Acid yieldt 
(mEq X 
10-§/ml/r) 
Effective 0.5-mm 
energy No lead 
Radiation sourcet (kev) lead _ shield 
100 kvp 
(0.25 mm Cu, 
1.0 mm Al fil- 
tration) 40 0.45 0.045 
150 kvp 
(0.25 mm Cu, 
1.0 mm Al fil- 
tration) 65 0.50 0.055 
260 kvp 
(0.25 mm Cu, 
1.0 mm Al, 0.5 
mm Pb filtra- 
tion) 190 0.24 0.05 
Co® 1,200 0.05 0.05 
* Hexylresorcinol-stabilized 
tetrachloroethylene system. 
+ Radiation rates varied from 30 r/min to 
300 r/min. 
t Each value represents a mean obtained 
by titrating 20 samples; titrating was done 
with 107-*-N NaOH. 
anhydrous 
20 
Linearity. The anhydrous tetra- 
chloroethylene system shows a linear 
relationship between radiation dose and 
the total acids liberated by the halo- 
genated hydrocarbon. Acid produc- 
tion is linear to doses greater than 
200,000 r regardless of the rate. 
Neutron sensitivity. It was antici- 
pated that the anhydrous systems 
would have a low response to fast neu- 
trons. For one thing the amount of 
energy imparted to a unit mass of solu- 
tion by one rep of fast neutrons is less 
than that imparted to a unit mass by 
1 rep of photons. In addition, the G 
value for similar chemical systems is 
lower for heavy particles than for 
electrons (4). 
To determine the upper limit of the 
fast-neutron response of both systems, 
an alpha source was placed in a 1-ml 
volumetric flask containing the halo- 
genated hydrocarbon. The disk was 
submerged to insure complete absorp- 
tion of all alpha particles emitted. The 
quantity of stable acids generated per 
rep of alpha energy absorbed appeared 
to be about 149 that produced per r of 
gamma rays. This seems to indicate a 
chemical conversion efficiency of 10%. 
It is assumed that the chemical con- 
version efficiencies are of the same 
order-of-magnitude for alpha particles, 
protons, and carbon recoil atoms (4). 
How the energy absorbed in 1 gm of 
tetrachloroethylene from 1 rep of fast 
neutrons compares with the energy 
absorbed from 1 r of gamma rays in 
tissue was calculated approximately as 
shown in the Appendix. The calcula- 
tions for the tetrachloroethylene system 
indicate that a maximum of 8.3% of 
the incident energy of 8-Mev neutrons 
is absorbed by the system when com- 
pared with a tissue dose. Since only 
10% of the absorbed dose is utilized, 
the neutron response of the tetrachloro- 
ethylene system, depending on the neu- 
tron spectrum, is of the order of 0.83% 
or less. That is, if exposed to 1 rep of 
fast neutrons with no gamma rays 
present the dosimeter would generate 
0.83 % as much acid as it would from 1 
rep of gammas. 
Field Use 
Both anhydrous systems have been 
tested in mixed fields of neutron and 
gamma radiation at the ORNL tower 
shielding facility, the Los Alamos 
prompt critical assembly, the Los 
Alamos Omega thermal reactor, and 
nuclear detonations. Comparison of 
TABLE 2—Relative Dose-Rate Re- 
sponse* 
Radiation ratest Acid yieldt 
(r/min) (mEq X 10~8/ml/r) 
10 0.05 
100 0.05 
1,000 0.05 
2,500 0.05 
4,250 0.05 
* Hexylresorcinol-stabilized 
tetrachloroethylene system. 
} Source: Co®°. Total dose delivered was 
10,000 r, regardless of rate. 
t Each value represents the average ob- 
tained by titrating 15 samples; titration was 
done with 107~*-N NaOH. 
anhydrous 
TABLE 3—Relative Temperature De- 
pendence* 
Temperature} Acid yieldt 
(°C) (mEq X 10-&/ml/r) 
5.0 0.047 
22.0 0.05 
37.0 0.05 
55.0 0.053 
* Hexylresorcinol-stabilized anhydrous 
tetrachloroethylene system. All samples 
were flame-sealed in 8-mm Neutraglas- 
siliconed ampules. 
+ Dosimeters exposed after 4-hr equili- 
bration in a constant-temperature water 
bath. 
t Each value represents a mean of 15 
titrations; titration was accomplished with 
10-3-N NaOH. 
TABLE 4—Acid production as a func- 
tion of total dose* 
Total doset Acid yieldt 
(r) (mEq X 10-§/ml/r) 
1,000 0.05 
10,000 0.05 
100,000 0.05 
200,000 0.045 
300,000 0.03 
* Hexylresorcinol-stabilized anhydrous 
tetrachloroethylene. 
+ Dose rate = 1,000 r/min, Co®. 
t Each value represents a mean of 15 
titrations; titration was accomplished with 
10-3-N NaOH. 
