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Intense neutron source based on 79 MeV deuterons bombarding beryllium
NUCLEAR INSTRUMENTS AND METHODS 154 ( 1 9 7 8 )
399-400 : ©
N O R T H - H O L L A N D PUBLISHING CO.
L E T T E R S TO T H E E D I T O R INTENSE N E U T R O N S O U R C E BASED ON 79 MeV DEUTERONS BOMBARDING BERYLLIUM* GEORGE H. HARRISON and ELIZABETH B. KUB1CZEK
Division of Radiation Research, University ~71Malyland School o[ Medicine, 660 W. Redwood Street, Baltimore, Malyland 21201, U.S.A. Received 24 January 1978 and in revised form 30 March 1978 At fixed target power density in d-Be neutron sources for materials damage studies, the neutron fluence and helium production per neutron in irradiated material rapidly increases with incident deuteron energy.
Experiments have been performed at the University of Maryland Cyclotron to characterize the physical properties of fast neutron beams produced by bombarding Be targets with 79 MeV deuterons (d(79)+Be neutrons). These measurements were directed towards the selection of the most suitable neutron beams for use in radiation therapy. The types of nuclear data we gathered can be related to other areas of applications as well; in this note we describe the d ( 7 9 ) + B e reaction as an intense fast neutron source for fusion reactor radiation damage studies. The dose rate for d + B e neutrons in tissue has been measured at a n u m b e r of deuteron energies between 15 and 80 MeV ~,2). The dose per incident deuteron increases rapidly with deuteron energy, approximately as E 3 , where Ed is the deuteron energy. Since the dose-to-fluence conversion factor varies slowly for neutron energies above 10 MeV ~), we can expect a corresponding increase in neutron fluence as E d increases. Thus we can expect approximately an eight-fold increase in the fluence measured from a Be source at Ed = 39.9 MeV 4), if the energy were doubled to 79 MeV. This means that in the ideal geometry described in ref. 4, the fluence would be about 2.9 × 10 ~2 n / I C ~ sr ~ at 79 MeV, ignoring changes in geometry due to the two cm thick Be target required at the higher energy. We have attempted to verify these ideas by means of a dosimetric m e a s u r e m e n t of d ( 7 9 ) + B e neutrons at an angle of 20 ° from the beam axis and at a distance of 13.5 cm from the target. The dose was measured to be 11 rad/~C t using the methods de* Supported in part by American Cancer Society Grant DT-21 and National Cancer Institute Grant CA 188807-01.
scribed in ref. 1. By using parameterized dose-tofluence conversion factors3), and angular dose distribution dataS), this measured dose corresponds to 2.4× 10 ~2 n ~C ~ sr 1 which is about seven times higher than the fluence reported at 39.9 MeV. There are two possible advantages in using high energy deuterons to produce neutrons for fusion reaction materials damage studies: 1) For the same neutron flux, much lower power densities in the production target will occur at higher incident deuteron energies. This is because the flux is proportional to iaE~, where id is the deuteron beam current, and the power dissipated in the target is idE d , So that the target power is proportional to (neutron flux)Ea 2 The power density will decrease even more rapidly with increasing Ej due to the increasing deuteron range over which to distribute the power. The result is that target cooling will be less critical at higher Ed. 2) For the same neutron flux, there will be a higher proportion of spallation events and heliu m production in materials of interest, as Eu increases. It is these p h e n o m e n a which are of particular interest in materials damage studies. Again, medically-related dosimetric studies provide information to confirm these ideas; for ~2C and ~60 we demonstrated a significant increase in the proportion of spallation events, especially those leading to helium production as the mean neutron energy increases from 16 to 31 MeV ~). Measurements of neutron-induced reaction cross sections at high energies for materials of interest will quantitate the increased proportion of spallation events obtained at high incident Ed, relative to the same cross sections near 1 4 M e V neutron energy.
400
o
H. HARRISON
AND E. B. KUBICZEK
Thus the materials damage from high energy neutrons can be related to damage expected from 14 MeV neutrons. References l) G. H. Harrison, C. R. Cox, E. B. Kubiczek and J. E. Robinson, Radiat. Res. (accepted for publication).
2) L. S. August, F. H. Attix, G. H. Hefting, P. Shapiro and R. B. Theus, Phys. Med. Biol. 21 (1976) 31. 3) A. Rindi, Health Phys. 33 (1977) 264. 4) M. J. Saltmarsh, C. A. Ludemann, C. B. Fulmer and R. C. Styles, ORNL Report (1976) ORNL/TM-5696. 5) j. p. Meulders, P. Leleux, P. C. Marq and C. Pirart, Phys. Med. Biol. 211 (1975) 235.
399-400 : ©
N O R T H - H O L L A N D PUBLISHING CO.
L E T T E R S TO T H E E D I T O R INTENSE N E U T R O N S O U R C E BASED ON 79 MeV DEUTERONS BOMBARDING BERYLLIUM* GEORGE H. HARRISON and ELIZABETH B. KUB1CZEK
Division of Radiation Research, University ~71Malyland School o[ Medicine, 660 W. Redwood Street, Baltimore, Malyland 21201, U.S.A. Received 24 January 1978 and in revised form 30 March 1978 At fixed target power density in d-Be neutron sources for materials damage studies, the neutron fluence and helium production per neutron in irradiated material rapidly increases with incident deuteron energy.
Experiments have been performed at the University of Maryland Cyclotron to characterize the physical properties of fast neutron beams produced by bombarding Be targets with 79 MeV deuterons (d(79)+Be neutrons). These measurements were directed towards the selection of the most suitable neutron beams for use in radiation therapy. The types of nuclear data we gathered can be related to other areas of applications as well; in this note we describe the d ( 7 9 ) + B e reaction as an intense fast neutron source for fusion reactor radiation damage studies. The dose rate for d + B e neutrons in tissue has been measured at a n u m b e r of deuteron energies between 15 and 80 MeV ~,2). The dose per incident deuteron increases rapidly with deuteron energy, approximately as E 3 , where Ed is the deuteron energy. Since the dose-to-fluence conversion factor varies slowly for neutron energies above 10 MeV ~), we can expect a corresponding increase in neutron fluence as E d increases. Thus we can expect approximately an eight-fold increase in the fluence measured from a Be source at Ed = 39.9 MeV 4), if the energy were doubled to 79 MeV. This means that in the ideal geometry described in ref. 4, the fluence would be about 2.9 × 10 ~2 n / I C ~ sr ~ at 79 MeV, ignoring changes in geometry due to the two cm thick Be target required at the higher energy. We have attempted to verify these ideas by means of a dosimetric m e a s u r e m e n t of d ( 7 9 ) + B e neutrons at an angle of 20 ° from the beam axis and at a distance of 13.5 cm from the target. The dose was measured to be 11 rad/~C t using the methods de* Supported in part by American Cancer Society Grant DT-21 and National Cancer Institute Grant CA 188807-01.
scribed in ref. 1. By using parameterized dose-tofluence conversion factors3), and angular dose distribution dataS), this measured dose corresponds to 2.4× 10 ~2 n ~C ~ sr 1 which is about seven times higher than the fluence reported at 39.9 MeV. There are two possible advantages in using high energy deuterons to produce neutrons for fusion reaction materials damage studies: 1) For the same neutron flux, much lower power densities in the production target will occur at higher incident deuteron energies. This is because the flux is proportional to iaE~, where id is the deuteron beam current, and the power dissipated in the target is idE d , So that the target power is proportional to (neutron flux)Ea 2 The power density will decrease even more rapidly with increasing Ej due to the increasing deuteron range over which to distribute the power. The result is that target cooling will be less critical at higher Ed. 2) For the same neutron flux, there will be a higher proportion of spallation events and heliu m production in materials of interest, as Eu increases. It is these p h e n o m e n a which are of particular interest in materials damage studies. Again, medically-related dosimetric studies provide information to confirm these ideas; for ~2C and ~60 we demonstrated a significant increase in the proportion of spallation events, especially those leading to helium production as the mean neutron energy increases from 16 to 31 MeV ~). Measurements of neutron-induced reaction cross sections at high energies for materials of interest will quantitate the increased proportion of spallation events obtained at high incident Ed, relative to the same cross sections near 1 4 M e V neutron energy.
400
o
H. HARRISON
AND E. B. KUBICZEK
Thus the materials damage from high energy neutrons can be related to damage expected from 14 MeV neutrons. References l) G. H. Harrison, C. R. Cox, E. B. Kubiczek and J. E. Robinson, Radiat. Res. (accepted for publication).
2) L. S. August, F. H. Attix, G. H. Hefting, P. Shapiro and R. B. Theus, Phys. Med. Biol. 21 (1976) 31. 3) A. Rindi, Health Phys. 33 (1977) 264. 4) M. J. Saltmarsh, C. A. Ludemann, C. B. Fulmer and R. C. Styles, ORNL Report (1976) ORNL/TM-5696. 5) j. p. Meulders, P. Leleux, P. C. Marq and C. Pirart, Phys. Med. Biol. 211 (1975) 235.