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Advances Toward a Stable Sensitive Iron Dosimeter

Advances Toward a Stable Sensitive Iron Dosimeter 1'"'0./ depths of 0, 2, 5, 10, and 15 em. and areas of 25, 100, and 400 sq. em. and infinite area for radiations in the range 50 to 1,250 kev. The energy absorbed, expressed as depth dose, was obtained for a number of incident spectra and compared with experimentally determined depth dose curves. The results were in good agreement. 1 Graduate Student, Physics Department, University of Saskatchewan. 2 Head of Physics Division, Ontario Cancer Institute and Professor of Physics, University of Toronto. Formerly, Professor of Physics, University of Saskatchewan. acid (0.4 gm./liter) can give G 130 under suitable conditions. There appear to be drift considerations with systems investigated to date when G > 45. Wavelengths of absorption and transmission, pH range to provide known complexing and to keep the iron from adhering to container walls, temperature control of solutions, and the kind of groups being added are all items of importance. Some insight is being gained as to the effect on sensitivity of some of the functional groups in the additive organic acids. 1 From the Radiological Laboratory, University of California School of Medicine, San Francisco, Calif. GAIL D. ADAMS, Ph.D., and WILLIAM R. BALKWELL, B.A. Neutron-Insensitive Gamma-Ray Dosimeter! R. S. CASWELL, Ph.D. Utilization of the conventional ferrous sulfate dosimeter indicates the desirability of a chemical system which exhibits greater stability and is more sensitive to energy absorbed from radiation. Greater apparent sensitivity has been achieved (a) by comparing with a potentiometer the single electrode potentials of irradiated against unirradiated solutions, (b) by concentrating the ferric ion in a solution on an ion exchange column, and (c) by using aqueous solutions other than that proposed by Fricke. The potentiometer method is somewhat more difficult than that using the DU spectrophotometer and has not been exploited. The column concentration is successful, although in at least one case the resin in the column appears to cause a small amount of oxidation of ferrous to ferric ion. Most of our work to date is concerned with other solutions. A cursory examination of many metal cations showed that iron exhibited the greatest sensitivity and it has been adopted throughout. To stabilize the system, additive chemicals have been sought which would form complexes both with ferrous and with ferric ions. Addition of inorganic anions generally produces a dosimeter not more sensitive than that of Fricke. Addition of organic acids can produce a dosimeter of greater or lesser sensitivity, apparently depending on the groups contained in the acid, as well as on spectral considerations. Some of these dosimeters also exhibit long-term stability. Our current standard has a G of 40 or so and has exhibited no observable change in the absence of irradiation since being mixed in June 1956. The composition is as follows: To 1 N H 2S0 4 add 7 X 10- 4 molar benzoic acid and then 7 X 10- 4 molar Fe+ 2 as FeS04. The optical density is read at 2715 A. Having stabilized the ferrous system, for example with benzoic acid, further additions of aliphatic organic acids can increase or decrease the sensitivity. Oxalic acid (1.5 gm./liter) gives a G 60. Tartaric 1'"'0./ A gamma-ray dosimeter for mixed radiation dosimetry with a neutron sensitivity of ~2 per cent (on the basis of absorbed dose in tissue) has been developed. This instrument consists of a graphite-wall, hclium-Crx-filled proportional counter operated at pressures of the order of 5-40 em. Hg. Large pulses due to heavy particle recoils produced by neutrons, such as carbon recoils from the walls and helium recoils in the gas, are discarded. Small pulses due to secondary electrons produced by gamma rays are recorded and are weighted according to height (i.e., according to the amount of current represented by each pulse) (1). The counter acts as a Bragg-Gray cavity, the "current" serving as a measure of the gamma-ray dose. Gamma-ray sensitivity is independent of energy to within ±20 per cent from 1.25 Mev (C 0 60) to 47 kev. Some indication of the incident gamma-ray spectrum may be obtained from the gamma-ray pulse height distribution. The counter container (outside the graphite lining) is made of thin aluminum to minimize production of gamma rays in the walls by inelastic scattering of the incident neutrons. Detection of these gamma rays by the counter represents neutron sensitivity, since the initiating particles are neutrons. Tests were made with 2.5 Mev H2(d,n)He 3 neutrons. The counter indicated an absorbed dose which was 2 per cent of the measured fast-neutron dose. This value is the sum of two contributions: (a) the gamma-ray contamination of the neutron radiation (the true gamma-ray dose) and (b) the neutron sensitivity of the dosimeter. Since we do not know the gamma-ray contamination of the neutron field, we obtain only an upper limit on the neutron sensitivity of the counter. Efforts are being made to decrease the gamma-ray contamination of the neutrons by redesigning the target assembly to minimize gamma-ray production by inelastic scattering. This instrument operates at low dose rates (~200 mrad/hr.), below the useful range of the gamma-ray http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Radiology Radiological Society of North America, Inc.

Advances Toward a Stable Sensitive Iron Dosimeter

Adams, Gail D.; Balkwell, William R.
Radiology , Volume 68 (1): 101 – Jan 1, 1957
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Publisher
Radiological Society of North America, Inc.
Copyright
Copyright © 1957 by Radiological Society of North America
ISSN
1527-1315
eISSN
0033-8419
DOI
10.1148/68.1.101a
Publisher site
See Article on Publisher Site

Abstract

1'"'0./ depths of 0, 2, 5, 10, and 15 em. and areas of 25, 100, and 400 sq. em. and infinite area for radiations in the range 50 to 1,250 kev. The energy absorbed, expressed as depth dose, was obtained for a number of incident spectra and compared with experimentally determined depth dose curves. The results were in good agreement. 1 Graduate Student, Physics Department, University of Saskatchewan. 2 Head of Physics Division, Ontario Cancer Institute and Professor of Physics, University of Toronto. Formerly, Professor of Physics, University of Saskatchewan. acid (0.4 gm./liter) can give G 130 under suitable conditions. There appear to be drift considerations with systems investigated to date when G > 45. Wavelengths of absorption and transmission, pH range to provide known complexing and to keep the iron from adhering to container walls, temperature control of solutions, and the kind of groups being added are all items of importance. Some insight is being gained as to the effect on sensitivity of some of the functional groups in the additive organic acids. 1 From the Radiological Laboratory, University of California School of Medicine, San Francisco, Calif. GAIL D. ADAMS, Ph.D., and WILLIAM R. BALKWELL, B.A. Neutron-Insensitive Gamma-Ray Dosimeter! R. S. CASWELL, Ph.D. Utilization of the conventional ferrous sulfate dosimeter indicates the desirability of a chemical system which exhibits greater stability and is more sensitive to energy absorbed from radiation. Greater apparent sensitivity has been achieved (a) by comparing with a potentiometer the single electrode potentials of irradiated against unirradiated solutions, (b) by concentrating the ferric ion in a solution on an ion exchange column, and (c) by using aqueous solutions other than that proposed by Fricke. The potentiometer method is somewhat more difficult than that using the DU spectrophotometer and has not been exploited. The column concentration is successful, although in at least one case the resin in the column appears to cause a small amount of oxidation of ferrous to ferric ion. Most of our work to date is concerned with other solutions. A cursory examination of many metal cations showed that iron exhibited the greatest sensitivity and it has been adopted throughout. To stabilize the system, additive chemicals have been sought which would form complexes both with ferrous and with ferric ions. Addition of inorganic anions generally produces a dosimeter not more sensitive than that of Fricke. Addition of organic acids can produce a dosimeter of greater or lesser sensitivity, apparently depending on the groups contained in the acid, as well as on spectral considerations. Some of these dosimeters also exhibit long-term stability. Our current standard has a G of 40 or so and has exhibited no observable change in the absence of irradiation since being mixed in June 1956. The composition is as follows: To 1 N H 2S0 4 add 7 X 10- 4 molar benzoic acid and then 7 X 10- 4 molar Fe+ 2 as FeS04. The optical density is read at 2715 A. Having stabilized the ferrous system, for example with benzoic acid, further additions of aliphatic organic acids can increase or decrease the sensitivity. Oxalic acid (1.5 gm./liter) gives a G 60. Tartaric 1'"'0./ A gamma-ray dosimeter for mixed radiation dosimetry with a neutron sensitivity of ~2 per cent (on the basis of absorbed dose in tissue) has been developed. This instrument consists of a graphite-wall, hclium-Crx-filled proportional counter operated at pressures of the order of 5-40 em. Hg. Large pulses due to heavy particle recoils produced by neutrons, such as carbon recoils from the walls and helium recoils in the gas, are discarded. Small pulses due to secondary electrons produced by gamma rays are recorded and are weighted according to height (i.e., according to the amount of current represented by each pulse) (1). The counter acts as a Bragg-Gray cavity, the "current" serving as a measure of the gamma-ray dose. Gamma-ray sensitivity is independent of energy to within ±20 per cent from 1.25 Mev (C 0 60) to 47 kev. Some indication of the incident gamma-ray spectrum may be obtained from the gamma-ray pulse height distribution. The counter container (outside the graphite lining) is made of thin aluminum to minimize production of gamma rays in the walls by inelastic scattering of the incident neutrons. Detection of these gamma rays by the counter represents neutron sensitivity, since the initiating particles are neutrons. Tests were made with 2.5 Mev H2(d,n)He 3 neutrons. The counter indicated an absorbed dose which was 2 per cent of the measured fast-neutron dose. This value is the sum of two contributions: (a) the gamma-ray contamination of the neutron radiation (the true gamma-ray dose) and (b) the neutron sensitivity of the dosimeter. Since we do not know the gamma-ray contamination of the neutron field, we obtain only an upper limit on the neutron sensitivity of the counter. Efforts are being made to decrease the gamma-ray contamination of the neutrons by redesigning the target assembly to minimize gamma-ray production by inelastic scattering. This instrument operates at low dose rates (~200 mrad/hr.), below the useful range of the gamma-ray

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Radiology – Radiological Society of North America, Inc.

Published: Jan 1, 1957

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