Characterization of quasi-monoenergetic neutron source using 137, 200, 246 and 389 MeV ⁷Li(p,n) reactions

The authors measured the neutron energy spectra of a quasi-monoenergetic ⁷Li(p,n) neutron source with 137, 200, 246 and 389 MeV protons set at seven angles (0deg, 5deg, 10deg, 15deg, 20deg, 25deg and 30deg), using a time-of-flight (TOF) method employing organic scintillators NE213 at the Research Center for Nuclear Physics (RCNP) of Osaka University. The energy spectra of the source neutrons were precisely deduced down to 2 MeV at 0deg and 10 MeV at other angles. Neutron energy spectra below 100 MeV at all angles were comparable, but the shapes of the continuum above 150 MeV changed considerably with the angle. In order to consider the correction required to derive the response in the peak region from the measured total response for high-energy neutron monitors, the authors showed the subtractions of H*(10) obtained at larger angles from the 0deg data in the continuum part. It was found that subtracting the dose equivalent at larger angles (21deg for 389 MeV, 25deg for 246 MeV and 26deg for 200 MeV) from the 0deg data almost eliminates the continuum component. This method has potential to eliminate problems associated with continuum correction for high-energy neutron monitors. (author)