Revision of the harwell 240Pu source strength and ν for 235U and 252Cf

Abstract

There is now strong evidence that the intensity of the Harwell ²⁴⁰Pu neutron standard is some 2 per cent lower than the value of (2·036 ± 0·030) × 10⁴ n/sec quoted in the original calibration and relative to which $\text{ν}{}^{252}\text{Cf}$ (spontaneous) and $\text{ν}{}^{235}\text{U}$ (thermal) have been determined.