Neutron Multiplicity Distributions in the Spontaneous Fission of 244 Cm, 248 Cm, and 252 Cf

Abstract

The neutron multiplicities P(n) in the spontaneous fission of ²⁴⁶Cm, ²⁴⁸Cm, and ²⁵²Cf have been measured in a ³He neutron counter assembly. The efficiency ∊ for detection of a single neutron was measured to be 0.360, based on ν̄ (average number of neutrons per fission) = 3.73 for ²⁵²Cf spontaneous fission. Using this value of ∊ and assuming a Gaussian distribution p(v) for the emitted neutrons, we fitted our observed P(n), corrected for small background and pile-up effects, to the model by the method of least squares in which the Gaussian width σ_v and ν̄ were the parameters of fit. Values of p(v) were then calculated from the resulting Gaussian function. In the case of ²⁵²Cf, our values of p(v) agree well with literature values; the p(v) values for the curium isotopes have not been measured previously as far as we know. The values of ν̄ for both ²⁴⁶ Cm and ²⁴⁸Cm fall on a straight line through existing experimental values for the nuclides ²⁴²Cm, ²⁴⁴Cm, and ²⁵⁰Cm in a plot of ν̄ versus mass number; our values were 2.86 ± 0.06 and 3.14 ± 0.06 for ²⁴⁶Cm and ²⁴⁸Cm, respectively.