A gas scintillation drift chamber for the 14N(n, p)14C measurement

A gas scintillation drift chamber was developed to measure the cross section of the 14N(n, p)14C reaction at the keV region. Since it contains N2 gas in addition to He gas, the reaction events can be detected with an acceptance of 4π. The 3He in the He gas is enriched to 0.2% in order to normalize the measurement. The chamber uses primary scintillation photons to determine the neutron energies by the time-of-flight method, and uses the trajectories of charged particles to discriminate the true events from events due to both the background and the 3He(n, p)3H reaction. It was shown for the first time that N2 gas works not only as a sample, as a wavelength shifter, but also as a discharge suppressor for the electron avalanche. The basic properties of the chamber were investigated experimentally: good time- (∼ 1.7 ns), spatial- (∼ 2 mm) and energy- (∼ 16% at 600 keV) resolutions were obtained. From these results, it was estimated that the 14N(n, p)14C cross section can be measured with an error of 10 ∼ 15%.