Energy and angular distribution of Cf-252 fission neutrons in the low energy range

Experimental and theoretical investigation of the emission of prompt fission neutrons provides information of both practical and fundamental importance. Prompt neutrons from spontaneous fission of 252Cf, adopted as an international standard have a special significance. As it is well known the energy spectrum of prompt fission neutrons from spontaneous fission of 252Cf can be described by a Maxwell distribution with a parameter of T=1-42 MeV. The different model calculations can reproduce the measured spectra within 10 percent. More precise double differential spectrum measurements are in progress at the TU in Dresden and at CENM in Geel. In the low neutron energy range, 50 keV-1.2 MeV, NE-912 glass detectors enriched in 6Li and with an absolutely determined efficiency at a distance of 350 mm from the target have been used for neutron detection. The fission fragments have been detected by two parallel-plate avalanche detectors, one of which, 5 mm far from the target gives the stop signal, while the other 35x180 mm large position sensitive detector at 72 mm far from the source divided into 36 segments of 4.5 mm width records the direction of fragment's flight. The distance between the two avalanche detectors, a flight path of 67 mm serves the distinction between the light and heavy fragments. The angular distribution of neutrons have been measured by a Δθ=6.5 deg. resolution in the 0 deg. - 180 deg. region. The effect of scattered neutrons and delayed gamma-rays have been measured. The experimental results have been compared with those of Bowman et al at two energies. The agreement is very good at 1 MeV, while at 0.5 MeV there is a small deviation. (author)