A pulsed neutron measurement in BeO and derivation of the thermal neutron diffusion parameters from the λ (B2) curve

Abstract

The decay constant of the neutron population was measured in BeO assemblies of various sizes. Particular attention was paid to the problem of 'room return', establishment of the asymptotic mode, and the appearance of the continuous mode of decay. The best fit to the λ(B2) curve gave λa = (1.954 > 0.076) x 10 2 sec -1 Do = (1.343 + 0.011) x 10 5 sec -1 cm 2 C = (4.88 + 0.31) x 10 5 sec - 1 cm 4, for BeO density 2.96 g cm -3 at a temperature of 22oC. The parameters can be used to derive L = 26.22 + 0.51 cm λtr = 1.619 + 0.013 cm. The parameterisation of the λ(B2) curve is discussed in conjunction with the problem of deciding when agreement exists between two separate measurements.