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Energy dependence of Kodak NTA neutron personnel monitoring film
Energy Dependence of Kodak NTA Neutron Personnel Monitoring Film (Rewired
Introduction NUCLEAR track emulsion Kodak NTA is still the most widely used device for fast neutron personnel monitoring. Its energy dependence has been a matter of many studiestheoretical as well as experimental.“-5’ However, a survey of the available literature reveals certain contradictory results and it was thought worthwhile to re-investigate experimentally its energy response. I
I
I
IO
Experimental The films were exposed to neutrons from three sources: Cf-2.52, Am-Be and 14.6 MeV neutron generator. The films were kept on a specially prepared tissue-equivalent liquid phantom for neutrons at an angle of 45. and were exposed in the film holder containing 0.5mm Cd filter on both sides. Calibration of the films for each source was done giving three to four different dose-equivalents. The films were processed following a standard procedure and proton recoil tracks were scored using a Leitz ortholux microscope with an over-all magnification of x 750. The response of the films in terms of tracksjcm’/rem is presented in Table 1 for all the three sources along with DE conversion factors used for each source. Relative response normalised to Am-Be neutrons is shown in Fig. 1.
et et ~1.‘~’
Discussion It is seen from Fig. 1 that the response to Cf-252 is about 359, lower while for 14.6 MeV neutrons it is 50:~” higher as compared to that for Am-Be neutrons. The lower response in case of Cf-252 is expected and there is good agreement with the values reported in literature.‘3.5’ In case of 14.6 MeV neutrons. Table 2 presents a comparison of our value with values reported earlier.“.3,4’ Our value is in good agreement with that of CHEKA’S”’ who had calculated theoretically the energy response of NTA over the whole range of energies 0.414 MeV. He had reported that dosimeter gives too large a response for energies between 4 and 14 MeV and had therefore designed Kodak NTB film (now not produced commercially) to reduce the response of the dosimeter in this range. The responses reported by others’3.4’ were much lower than the present values and would over-estimate doses in personnel monitoring for high energy neutrons. TABLE 1
Source Cf-252 Am-Be 14.6 MeV
DE conversion factors rem/n/cm’ 3.13 x (Ref. 3.75 X (Ref. 5.79 x (Ref.
10-s 7) 1o-8 6) 1o-8 6)
15
* These calculations are for free air. On be lower as backscatter is less to that 18y). The in were dose-equivalent conversion factors given
from in Table 1.
AcknoM’letlyements-We are thankful to Dr U. MADHVANATH for suggesting this work and to Dr G. VENKATARAMAN for many useful discussions.
of
Division RadiologicalProtection Bhabha Atomic Research Centre Trombay. Bombay-400 085 India
0.
P. MASSAND D. SINGH H. K. KUNDU P. K. MARATHE
References 1. CHEKA J. A. Nucleonics 12, 40 (1954). 2. PIESCH E. Atompraxis 9, 179 (1963). 3. KNIGHT A., MARSHALL T. 0. and HARVEY C. L. Proc. Symp. on Neutron Monitoring for Radiation Protection Purposes. Vol. II, p. 171. IAEA, Vienna (1972). 4. JASIAK J. and MUSIALOWICZ T. Proc. Symp. on Neutron Monitoring for Radiation Protection Purposes. Vol. II,
Mean response tracks/cm’/rem
p. 191. IAEA. Vienna (1972). Radiation 5. Personnel Dosimetry Systems for External Exposures. Technical Reports Series No. 109, IAEA, Vienna (1970). 6. SNYDER W. S. NCRP Report No. 38, p. 46 (1971). 7. SINGH D., BISHT J. S. and MADHVANATH U. Nucl. Instrum. Meth. 151, 331 (1978).
0.98 X to4 1.51 x lo4 2.25 x lo4
249
Introduction NUCLEAR track emulsion Kodak NTA is still the most widely used device for fast neutron personnel monitoring. Its energy dependence has been a matter of many studiestheoretical as well as experimental.“-5’ However, a survey of the available literature reveals certain contradictory results and it was thought worthwhile to re-investigate experimentally its energy response. I
I
I
IO
Experimental The films were exposed to neutrons from three sources: Cf-2.52, Am-Be and 14.6 MeV neutron generator. The films were kept on a specially prepared tissue-equivalent liquid phantom for neutrons at an angle of 45. and were exposed in the film holder containing 0.5mm Cd filter on both sides. Calibration of the films for each source was done giving three to four different dose-equivalents. The films were processed following a standard procedure and proton recoil tracks were scored using a Leitz ortholux microscope with an over-all magnification of x 750. The response of the films in terms of tracksjcm’/rem is presented in Table 1 for all the three sources along with DE conversion factors used for each source. Relative response normalised to Am-Be neutrons is shown in Fig. 1.
et et ~1.‘~’
Discussion It is seen from Fig. 1 that the response to Cf-252 is about 359, lower while for 14.6 MeV neutrons it is 50:~” higher as compared to that for Am-Be neutrons. The lower response in case of Cf-252 is expected and there is good agreement with the values reported in literature.‘3.5’ In case of 14.6 MeV neutrons. Table 2 presents a comparison of our value with values reported earlier.“.3,4’ Our value is in good agreement with that of CHEKA’S”’ who had calculated theoretically the energy response of NTA over the whole range of energies 0.414 MeV. He had reported that dosimeter gives too large a response for energies between 4 and 14 MeV and had therefore designed Kodak NTB film (now not produced commercially) to reduce the response of the dosimeter in this range. The responses reported by others’3.4’ were much lower than the present values and would over-estimate doses in personnel monitoring for high energy neutrons. TABLE 1
Source Cf-252 Am-Be 14.6 MeV
DE conversion factors rem/n/cm’ 3.13 x (Ref. 3.75 X (Ref. 5.79 x (Ref.
10-s 7) 1o-8 6) 1o-8 6)
15
* These calculations are for free air. On be lower as backscatter is less to that 18y). The in were dose-equivalent conversion factors given
from in Table 1.
AcknoM’letlyements-We are thankful to Dr U. MADHVANATH for suggesting this work and to Dr G. VENKATARAMAN for many useful discussions.
of
Division RadiologicalProtection Bhabha Atomic Research Centre Trombay. Bombay-400 085 India
0.
P. MASSAND D. SINGH H. K. KUNDU P. K. MARATHE
References 1. CHEKA J. A. Nucleonics 12, 40 (1954). 2. PIESCH E. Atompraxis 9, 179 (1963). 3. KNIGHT A., MARSHALL T. 0. and HARVEY C. L. Proc. Symp. on Neutron Monitoring for Radiation Protection Purposes. Vol. II, p. 171. IAEA, Vienna (1972). 4. JASIAK J. and MUSIALOWICZ T. Proc. Symp. on Neutron Monitoring for Radiation Protection Purposes. Vol. II,
Mean response tracks/cm’/rem
p. 191. IAEA. Vienna (1972). Radiation 5. Personnel Dosimetry Systems for External Exposures. Technical Reports Series No. 109, IAEA, Vienna (1970). 6. SNYDER W. S. NCRP Report No. 38, p. 46 (1971). 7. SINGH D., BISHT J. S. and MADHVANATH U. Nucl. Instrum. Meth. 151, 331 (1978).
0.98 X to4 1.51 x lo4 2.25 x lo4
249