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Neutron dose rate for low energy deuterons on beryllium
This content has been downloaded from IOPscience. Please scroll down to see the full text. 1976 Phys. Med. Biol. 21 643 (http://iopscience.iop.org/0031-9155/21/4/014) View the table of contents for this issue, or go to the journal homepage for more
Download details: IP Address: 142.66.3.42 This content was downloaded on 08/09/2015 at 09:16
Please note that terms and conditions apply.
PHYS.MED.
BIOL.,
1976,
VOL.
21, EO. 4, 643-646.
@ 1976
XcientiJic Note
Neutron Dose Rate for Low Energy Deuterons on Beryllium R'. H. HOWELL,
PH.D.
and H. H.
BAR'SCHALL,
PH.D.t
Lawrence Livermore Laboratory, Livermore, California 94550, U.S..1.
Received 28 January 1976
Several measurements of dose rates of neutrons from deuteron bombardment of thick beryllium targetshave been reported for deuteron energies above 10 MeV (August, Theus, Attix, Bondelid, Shapiro, Surratt and Rogers 1973, Parnell, Page and Chaudhri 1971, U7eaver 1972, Weaver, Anderson, Barschall 1973). These measurements were performed primarily for and Davis applications in radiotherapy. For radiobiological experiments less penetrating neutrons can be used so that a small accelerator can serve as neutron source. We have t'herefore measured the dose rate from the bombardment of beryllium with deuterons of energies below 10 MeV to assist radiobiologists in planning experimentsin which theBe(d,n) reactionis theneutron source. I n this energyregion there is apreviousmeasurement byInada,Kawachiand of theneutron Hiramoto (1968) a t 2 - 8 MeV basedonadetermination spectrum. Deuterons were accelerated in the Lawrence Livermore Laboratory tandem Van de Graaff. They were analysedwith a 90" bendingmagnetandthen steeredthrougha series of collimators toachamber which contained the beryllium target and which was a t t h ecentre of a cubical room, of 12 m sides. The collimators and the target chamber were electrically isolated from ground and from each other. Current was typically 1 pAof atomic deuterons focused on a spot' less than 6 mm in diameter at the target position. The target is a 3.7 mm thick disk of Be metal backedby 1 mm of Ta. For all deuteron energies used, the range of the deuterons is less than the beryllium thickness. Dose was measured in a spherical tissue-equivalent plastic (Shonka A-150) ionization chamber 61 mm in outer diameter with 2.4 mm thick walls (manufactured by EG & G, Goleta, California'). The chamber was filled with tissueequivalent gas composed of 64.4% CH,, 32.5y0 CO, and 3.1% K, by volume. Thechambervolumewasdetermined by measuring its response to 6% :/-rays.Sincehighaccuracy was not necessaryfor the presentpurpose,no corrections were applied for the difference in the response of the chamber to neutrons and y-rays.
t Permanent address : Department of Suclear Engineering, Universit'y of Wisconsin, Madison, Wisconsin 53706, U.S.A.
644
R.H . Howell andHH. .
Barschall
For the dose measurements the geometric centre of the chamber was placed in line with the deuteron beam 1.0 m from the beam spot. No collimation was used between the ionization chamber and the neutron source.
Deuteron energy (MeV)
Fig. 1. Be(d, n) dose rate at 1 m from the beryllium target. The crosses are values from this work. The triangles represent data from Weaver et al. (1973). The salid dots are data from Parnellet al. (1971). The lines represent fits to data taken athigher deuteron energy: the solid line is based on the relation D = 0-000421E2~7 (Parnell et al. (1972), the dashed line on B = 0~000194EZ'g8 (August et al. 1973).
Fig. 1 shows the present measurements and the results of earlier investigations. Parnell, Oliver, Almond and Smathers (1972) have suggested that the dependence of the dose rate D on deuteron energy E may be expressed as D = aEb. If E is measuredin MeV and D ismeasuredin rad (PAmin)-l, a = 4.21 x and b = 2.7 a t adistance of 1.0 mfrom the source.This relationship is shown by the solid line in fig. 1. More recently August et al. (1973) found that, if higher deuteron energies are included, values of a = 1.94 x 10-4 and b = 2.99 provide a better fit. This dependence is shown by the dashed line in fig. 1. At the lower energies of the present measurement August's. Since bothAugust's Parnell'sconstants fit thedatabetterthan and Parnell's measurementsused a collimator, while the present measurements did not, it is not clear how close agreement should be expected. Furthermore, a smallcontribution of y-rays from the the presentmeasurementsinclude Be(d, n) reaction, and the data were not corrected for the small difference in the response of the chamber to neutrons and y-rays. The present measurements a'reconsistentwithearliermeasurementsexcept for the value a t 2.8 MeV reported by Inada et al. (1968) which is about twice as large as would be expected from the present measurements. We wish to thank Dr. J. F. Fowler for suggesting this measurement and Dr. E. Goldberg for helpful advice. This work was performed under the auspices of the U.S. Energy Research and Development Administration, W7405-Eng-48.
Neutron Dose Rate for Be(& n )
645
REFERENCES AUQUST,L. S.,THEWS,R. B., ATTIX, F. H., BONDELID, R. O., SHAPIRO,P., SWRRATT, R. E., and ROGERS, C.C., 1973, Phye. M e d . Biol., 18, 641. IXADA, T., KAWACHI, K., and HIRAMOTO, T., 1968, J . Nucl. Sei. T e c h . , 5, 22. PARNELL, C. J., OLIVER,G. D., ALMOND,P. R., and SMATHERS, J. B., 1972, Phye. M e d . Biol., 17, 429. PARNELL, C. J., PAGE, B. C., and CHAUDHRI,M. A., 1971, Br. J . Radiol., 44, 63. WEAVER,K. A., 1972, Report UCRL-51310. WEAVER,K. A., ANDERSON, J. D., BARSCHAIL, H. H., and DAVIS,J. C., 1973, Phys. Med. Biol., 18, 64.
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My IOPscience
Neutron dose rate for low energy deuterons on beryllium
This content has been downloaded from IOPscience. Please scroll down to see the full text. 1976 Phys. Med. Biol. 21 643 (http://iopscience.iop.org/0031-9155/21/4/014) View the table of contents for this issue, or go to the journal homepage for more
Download details: IP Address: 142.66.3.42 This content was downloaded on 08/09/2015 at 09:16
Please note that terms and conditions apply.
PHYS.MED.
BIOL.,
1976,
VOL.
21, EO. 4, 643-646.
@ 1976
XcientiJic Note
Neutron Dose Rate for Low Energy Deuterons on Beryllium R'. H. HOWELL,
PH.D.
and H. H.
BAR'SCHALL,
PH.D.t
Lawrence Livermore Laboratory, Livermore, California 94550, U.S..1.
Received 28 January 1976
Several measurements of dose rates of neutrons from deuteron bombardment of thick beryllium targetshave been reported for deuteron energies above 10 MeV (August, Theus, Attix, Bondelid, Shapiro, Surratt and Rogers 1973, Parnell, Page and Chaudhri 1971, U7eaver 1972, Weaver, Anderson, Barschall 1973). These measurements were performed primarily for and Davis applications in radiotherapy. For radiobiological experiments less penetrating neutrons can be used so that a small accelerator can serve as neutron source. We have t'herefore measured the dose rate from the bombardment of beryllium with deuterons of energies below 10 MeV to assist radiobiologists in planning experimentsin which theBe(d,n) reactionis theneutron source. I n this energyregion there is apreviousmeasurement byInada,Kawachiand of theneutron Hiramoto (1968) a t 2 - 8 MeV basedonadetermination spectrum. Deuterons were accelerated in the Lawrence Livermore Laboratory tandem Van de Graaff. They were analysedwith a 90" bendingmagnetandthen steeredthrougha series of collimators toachamber which contained the beryllium target and which was a t t h ecentre of a cubical room, of 12 m sides. The collimators and the target chamber were electrically isolated from ground and from each other. Current was typically 1 pAof atomic deuterons focused on a spot' less than 6 mm in diameter at the target position. The target is a 3.7 mm thick disk of Be metal backedby 1 mm of Ta. For all deuteron energies used, the range of the deuterons is less than the beryllium thickness. Dose was measured in a spherical tissue-equivalent plastic (Shonka A-150) ionization chamber 61 mm in outer diameter with 2.4 mm thick walls (manufactured by EG & G, Goleta, California'). The chamber was filled with tissueequivalent gas composed of 64.4% CH,, 32.5y0 CO, and 3.1% K, by volume. Thechambervolumewasdetermined by measuring its response to 6% :/-rays.Sincehighaccuracy was not necessaryfor the presentpurpose,no corrections were applied for the difference in the response of the chamber to neutrons and y-rays.
t Permanent address : Department of Suclear Engineering, Universit'y of Wisconsin, Madison, Wisconsin 53706, U.S.A.
644
R.H . Howell andHH. .
Barschall
For the dose measurements the geometric centre of the chamber was placed in line with the deuteron beam 1.0 m from the beam spot. No collimation was used between the ionization chamber and the neutron source.
Deuteron energy (MeV)
Fig. 1. Be(d, n) dose rate at 1 m from the beryllium target. The crosses are values from this work. The triangles represent data from Weaver et al. (1973). The salid dots are data from Parnellet al. (1971). The lines represent fits to data taken athigher deuteron energy: the solid line is based on the relation D = 0-000421E2~7 (Parnell et al. (1972), the dashed line on B = 0~000194EZ'g8 (August et al. 1973).
Fig. 1 shows the present measurements and the results of earlier investigations. Parnell, Oliver, Almond and Smathers (1972) have suggested that the dependence of the dose rate D on deuteron energy E may be expressed as D = aEb. If E is measuredin MeV and D ismeasuredin rad (PAmin)-l, a = 4.21 x and b = 2.7 a t adistance of 1.0 mfrom the source.This relationship is shown by the solid line in fig. 1. More recently August et al. (1973) found that, if higher deuteron energies are included, values of a = 1.94 x 10-4 and b = 2.99 provide a better fit. This dependence is shown by the dashed line in fig. 1. At the lower energies of the present measurement August's. Since bothAugust's Parnell'sconstants fit thedatabetterthan and Parnell's measurementsused a collimator, while the present measurements did not, it is not clear how close agreement should be expected. Furthermore, a smallcontribution of y-rays from the the presentmeasurementsinclude Be(d, n) reaction, and the data were not corrected for the small difference in the response of the chamber to neutrons and y-rays. The present measurements a'reconsistentwithearliermeasurementsexcept for the value a t 2.8 MeV reported by Inada et al. (1968) which is about twice as large as would be expected from the present measurements. We wish to thank Dr. J. F. Fowler for suggesting this measurement and Dr. E. Goldberg for helpful advice. This work was performed under the auspices of the U.S. Energy Research and Development Administration, W7405-Eng-48.
Neutron Dose Rate for Be(& n )
645
REFERENCES AUQUST,L. S.,THEWS,R. B., ATTIX, F. H., BONDELID, R. O., SHAPIRO,P., SWRRATT, R. E., and ROGERS, C.C., 1973, Phye. M e d . Biol., 18, 641. IXADA, T., KAWACHI, K., and HIRAMOTO, T., 1968, J . Nucl. Sei. T e c h . , 5, 22. PARNELL, C. J., OLIVER,G. D., ALMOND,P. R., and SMATHERS, J. B., 1972, Phye. M e d . Biol., 17, 429. PARNELL, C. J., PAGE, B. C., and CHAUDHRI,M. A., 1971, Br. J . Radiol., 44, 63. WEAVER,K. A., 1972, Report UCRL-51310. WEAVER,K. A., ANDERSON, J. D., BARSCHAIL, H. H., and DAVIS,J. C., 1973, Phys. Med. Biol., 18, 64.
