Targets for the production of neutrons from low-energy positive ion accelerators

Conference · Wed Jan 01 00:00:00 EST 1992 · Transactions of the American Nuclear Society; (United States)

OSTI ID:7033270

Brugger, R M; Luo, Xunshan; Kunze, J F ^[1]

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1. Univ. of Missouri, Columbia (United States)

To produce neutrons for neutron capture therapy at a hospital, a compact positive ion accelerator, such as a radio-frequency quadrupole machine, with a moderator blanket would be more readily accepted than a reactor with a moderator. Unfortunately, designs to date of accelerator-based epithermal neutron beams fall short of similar beams from reactors of a few megawatts. To try to identify improvements, the authors have evaluated many neutron-producing reactions. The {sup 7}Li(p,n) and {sup 3}H(p,n) continue to be the most promising for neutron yield, but both have troubles with target design. For the Li(p,n) reaction, the threshold is 1.88 MeV, but protons up to 2.5 MeV can be used with a thick target before gamma rays are produced by excitation of the first excited state in {sup 7}Be. They calculate the yield of neutrons to be 1.48 {times} 10{sup {minus}6} neutrons per proton. However, for this target, three-fourths of the heat is produced by protons below the threshold. At 2.5 MeV, the maximum neutron energy is 800 keV, and a moderator must surround the target to reduce the energies of the neutrons to less than {approximately}10 keV. This moderator significantly reduces the beam current of epithermal neutrons so that proton currents of 20 mA or more must be used to produce an epithermal beam of >1 {times} 10{sup 9} n/cm{sup 2}{center dot}s. It is suggested that a target of lithium on a high-conductivity backing would have to be 15 cm in diameter to spread this heat load. Such sizes compromise the moderator design. If a target could be designed to more effectively use the protons in the energy range where neutrons are produced, these target design problems might be overcome.

• OSTI ID: 7033270
• Report Number(s): CONF-920606-; CODEN: TANSA
• Journal Information: Transactions of the American Nuclear Society; (United States), Vol. 65; Conference: American Nuclear Society annual meeting, Boston, MA (United States), 7-12 Jun 1992; ISSN 0003-018X
• Country of Publication: United States
• Language: English

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