Experiments for optical neutron detection using nuclear pumped laser

Since the nuclear pumped laser technique can be applied to optical detection of neutrons, numerical simulation and demonstration experiments have been carried out for He-Ne-Ar mixtures. Test cells filled with ³He gas (1140 torr), Ne gas (540 torr) and Ar gas (208 torr) were irradiated with thermal neutron fluxes up to about 10 ¹² n/cm²/s at the JRR-4 reactor, JAERI. In these experiments, optical output of 585.3 nm from Ne 3p-3s transitions was clearly observed. Its intensity was almost proportional to the thermal neutron flux, and these results agree with those of numerical simulation. This system can be applied to optical neutron detection. The simulation results show that the population inversion between the 3p´[1/2]₀ and 3s´[1/2]₀¹ levels of neon atoms for the cell can be achieved at the thermal neutron flux of much higher than 10¹² n/cm²/s. It is also estimated that the threshold thermal neutron flux for the population inversion is about 3×10¹² n/cm²/s for the gas cell filled with optimized gas mixtures