100 Time after Proportional Approxima- 
80 irradiation parts tion 
A- After | hour (hours) 
60F —g-after 10 min at 130°C | Ss Ta 
C- After 8 days at room temp. 0.1 
40 1 
0.2 
3 30 O03 \ 
oO | 
S | 
§ 0.5 ; 
aes | day 06 Good 
= at 
2 !0 2 days 0. 
é 8 3 days os | 
3 100 4 days Oh 
= 6 days 
a 8 days TD *i0> + 
: 2 weeks Hel| 
5 3 weeks 1.2 . 
Q Erased glass | month 13 nob 
2 © Nonerased glass 1000 dee ee! 
“2 months ‘14 oa 
4 months 1:5. E +; 
6 months 16 ane 
10° 2 3 4 6 8 106 2 34 6 8 [7 \ 
arid eavteone ( ese weass pet Are a 
Dose (rep) 10,000 lyear a 
FIG. 8. Comparison of optical densities of nonerased glasses and 
glasses subjected to ten successive exposure-erasure cycles 
An example can best illustrate this 
use of the scale. Assume that an 
optical density of 1.00 (3-mm glass) is 
obtained at 4,500 A, three days after 
the irradiation (glass was heated, 
60 min after irradiation, for 10 min at 
130° C). The time scale shows that 3 
days represents about four-fifths of the 
distance to 8 days. An optical density 
reading of 1.00 intercepts the fading 
area between the two curves at doses 
corresponding to the dose range of 4.7— 
5.380 X 10° rep. However, it inter- 
cepts the fading area four-fifths of the 
vertical distance between the fading 
curves, at about 5.15 X 10° rep. (Lin- 
ear interpolation of the logarithmic 
scale is reasonably accurate for small 
time intervals). The total dose is, 
therefore, 5.15 x 10° rep. 
Use of Fig. 4 for a calibration curve 
when other sources or dose rates are 
used must take into account fading 
during irradiation, if the exposure is 
long. The fading that takes place dur- 
ing irradiation is not known. How- 
ever, the use of the heat treatment after 
irradiation will reduce appreciably the 
effect of the amount of time that 
elapses after irradiation, since it appar- 
ently eliminates the centers that are 
10 
FIG. 9. Nomogram for estimating de- 
crease in optical densities of glasses after 
different time intervals following irradia- 
tion and heating 
most unstable and that have a high 
probability of fading in the initial pe- 
riods. For greatest accuracy, calibra- 
tion doses should be delivered in times 
comparable with those to be encoun- 
tered in use. 
Considerations for Use 
Restrictions in the use of the silver- 
activated phosphate glass dosimeter, 
such as avoidance of extreme tempera- 
tures and excessive exposure to light, 
are not difficult to fulfill in practice. 
Fading during and after exposure, and 
the energy dependence below 200 kev 
(7) are disadvantages, but these can be 
minimized by various techniques and 
do not detract appreciably from the 
value of the dosimeter. 
Megarep dosimetry is not precluded 
by the appreciable decrease in sensi- 
tivity there. It is necessary, however, 
to apply careful experimental tech- 
niques to attain the precision that is 
readily available with lower doses. 
The degree of precision desired is 
variable with different needs and the 
latter should dictate the experimental 
methods used in this high-dose region. 
It would be desirable for suppliers 
of this glass to develop formulations 
that would saturate at higher dose 
levels than silver-phosphate glass. 
This would help develop glass dosim- 
etry to its fullest potentialities. 
BIBLIOGRAPHY 
1. J. H. Schulman, NRL Memorandum Report 
266 (1954) 
. H. Rabin, NRL Memorandum Report 309 
(1954) 
3. J. H. Schulman, C. C. Klick, H. Rabin, 
Nucveonics 13, No. 2, 30 (1955) 
4. B. E. Proctor, S. A. Goldblith, A.E.C. Quar- 
terly Progress Report July 1, 1954 to Septem- 
ber 30, 1954, on Contract AT(30-1)-1164. 
5. J. H. Schulman, R. J. Ginther, C. C. Klick, 
R. S, Alger, R. A. Levy, J. Appl. Phys. 22, 
1479 (1951) 
6. J. H. Schulman, W. Shurcliffe, R. J. Ginther, 
F. H. Attix, Nucteonics 11, No. 10, 52 
(1953) 
7. J. H. Schulman, R. J. Ginther, C. C. Klick, 
NRL Reprint 65-52 (1952) 
8. M. Eicher, Developmental study of the use of 
Vycor glass for gamma ray dosimetry. Re- 
search Report, Project NM 006 012. 04. 
69 Vol. 12, 147-166, May 1954, Naval Medi- 
cal Research Institute 
9. G. E. Blair, Data on a megaroentgen dosime- 
ter system. (Bausch and Lomb Chemical 
Research Lab. Report, 1955) 
10. S. Davison, S. A. Goldblith, B. E. Proctor, M. 
Karel, B. Kan, C. J. Bates, Nucureonics 11, 
No. 7, 22 (1953) 
11. J. C. Trump, K. A. Wright, A. M. Clarke, 
J. Appl. Phys. 21, 345 (1950) 
12. H. Rabin, W. E. Price, Nucteonics 18, No. 
3, 33 (1955) 
13. B. E. Proctor, S. A. Goldblith, S. Davison, 
NYO 3345 (1955) 
eo okey ok 
Contribution No. 275, Department of 
Food Technology, Massachusetts Institute of 
Technology, Cambridge, Mass. 
te 
