The Average Number of Prompt Neutrons and the Distributions of Prompt Neutron Emission Number for Spontaneous Fission of Plutonium-240, Curium-242, and Curium-244

This research was published (in Chinese) in Chin. J. Nucl. Phys., 3, 2, 149 (1981). The average number of prompt neutron and the distributions of prompt neutron number probability P(ν) for spontaneous fission of ²⁴⁰Pu, ²⁴²Cm, and ²⁴⁴Cm relative to (²⁵²Cf) have been measured using a large gadolinium-loaded liquid scintillation counter with a co-incidence method. The results were (²⁴⁰Pu) = 2.141 ± 0.016, (²⁴²Cm) = 2.562 ± 0.020, and (²⁴⁴Cm) = 2.721 ±0.021. The measured distributions of prompt neutron number were fitted with Gaussian curves by a weighted least-squares method. The widths of Gaussian distribution are 1.149 ± 0.047, 1.159 ± 0.074, and 1.175 ± 0.098 for ²⁴⁰Pu, ²⁴²Cm, and ²⁴⁴Cm, respectively. These results as well as a previous measurement of spontaneous fission of ²⁵²Cf show the linear variation of σ with at the first order of approximation. The data were fitted by a least-squares method, and the result is given by σ = 0.980 + 0.076. This fact demonstrates the trend that the width of the excitation energy distribution of fission fragments increases with the average excitation energy of the fission fragments in the range of nuclides mentioned above.