ANALYSIS OF EPITHERMAL NEUTRON-PRODUCTION BY NEAR-THRESHOLD (P,N) REACTIONS

A recent advance in portable accelerator neutron source development wa s research on production of epithermal neutrons by near-threshold char ged-particle reactions. When the projectile energy is accurately contr olled at an energy close to the reaction threshold, the neutrons produ ced will have energies less than or around 100 keV and can be used wit h little or no moderation or filtration in neutron capture therapy. Al though the total neutron yield is lower than at higher proton energies , the epithermal neutron flux may be sufficiently intense because of t he softer energy spectrum and the requirement for less neutron moderat ion. This paper presents an analysis of the main characteristics of ep ithermal neutron production by this method using the Li (p,n) reaction as an example. The energy, yield and angular characteristics of neutr on emission are discussed. The achievable epithermal fluxes are comput ed from experimental data. The results are used to assess the feasibil ity of near-threshold production of epithermal neutrons for neutron ca pture therapy with compact accelerators such as a RFQ proton accelerat or. The results indicated that, using a Li3N target, 1 mA of 2 MeV pro tons will produce 10(9) n/cm(2)/s with an average energy of 83 keV whi le 5.6 mA of 1.91 MeV protons can produce 10(9) n/cm(2)/s with an aver age energy of 45 keV. (C) 1997 Elsevier Science Ltd. All rights reserv ed.