Near-threshold 7Li(p,n)7Be neutrons on the practical conditions using thick Li-target and Gaussian proton energies for BNCT

• Proton enrgy from 1.85 to 1.95 MeV were studied for near threshold 7Li(p,n)7Be neutrons.
• Practical conditions were applied for RFQ type accelerator and a thick Li-target.
• Gaussian distribution of proton energies were checked for the standard deviation of 0, 10, 20 and 40 keV.
• The mean energy of 1.92 MeV protons with Gaussian distribution of 20 keV was feasible.
• The suitable thicknesses of Lead layer as gamma absorber was about 3 cm.
• The suitable thicknesses of polyethylene BDE was about 24 mm at the proton current of 13 mA.

The near threshold 7Li(p,n)7Be neutrons generated by incident proton energy having Gaussian distribution with mean energies from 1.85 to 1.95 MeV, were studied as a practical neutron source for BNCT wherein an RFQ accelerator and a thick Li-target are used. Gaussian energy distributions with the standard deviation of 0, 10, 20 and 40 keV for mean proton energies from 1.85 to 1.95 MeV were surveyed in 0.01 MeV increments. A thick liquid Li-target whose dimensions were established in our previous experiments (i.e., 1 mm-thick with 50 mm width and 50 mm length) was considered in this study. The suitable incident proton energy and physical dimensions of Pb layer which serves as a gamma absorber and a Polyethylene layer which is used as a BDE were surveyed by means of the concepts of TPD. Dose distribution were calculated by using MCNP5. A proton beam with mean energy of 1.92 MeV and a Gaussian energy distribution with a standard deviation of 20 keV at a current of 10 mA was selected from the viewpoint of irradiation time and practically achievable proton current. The suitable thicknesses of Pb gamma absorber was estimated to be about 3 cm. The estimated thickness of the polyethylene BDE was about 24 mm for an ideal proton current of 13 mA, and was 18 mm for a practical proton current of 10 mA.