Neutron Yield from the Spontaneous Fission of²⁵²Cf (bar nu)

Abstract

The average number of neutrons ( V ) emitted per fission event in the spontaneous fission of 252Cf has been determined by separate absolute measurements of the fission rate and the neutron emission rate per mg of a solution of californium chloride. The fission rate was determined by a hitherto untried method based on fission-fission coincidences, and the neutron emission rate was determined by the well-known manganese sulphate bath technique. The measurements were carried out during the period 1968 to 1972, and several provisional values of V have been released from time to time. The results have now been subjected to a rigorous statistical treatment in which correlations were treated by covariance matrices.The value for V (total) for 252Cf is (3.7509 k 0.0107) neutrons per fission. This value supersedes all previously released provisional values.

Improved measurements of the neutrino mixing angle θ 13 with the Double Chooz detector

“…The window is set to be 3.5 < E vis < 10 MeV for the numerator to select only Gd capture (small fraction of C captures are also included) and 0.5 < E vis < 10 MeV for the denominator to include H captures. In order to suppress background contamination in the 252 Cf data, two cuts are applied in addition to the standard IBD selection criteria: 1) E vis > 4 MeV where E vis is the visible energy of the prompt signal; 2) more than one neutron are detected after the prompt signal ( 252 Cf emits 3.8 neutrons on average [32]). 2) is applied to eliminate a correlated background contribution.…”

The Ratio of the Thermal Neutron Capture Cross-Sections for Hydrogen and Manganese and its Impact on the Measurement of Neutron Source Emission Rates by Manganese Bath Techniques

“…One of the most important motivations in the struggle for higher accuracy in manganese bath measurements is the demand for high accuracy in the measurement of ij, the average number of neutrons emitted per fission in the spontaneous fission of z52Cf [3]. The work of reference [2] was based on a spherical bath of diameter 0.48 m and the NPL radium-beryllium photoneutron source 3 B, whereas the more recent V measurement of reference [3] was based on a larger bath (0.98 m in diameter) and various z52Cf neutron sources. The apparent crosssection ratio in the latter case would be sensitive to an entirely different set of the corrections mentioned in Sect.…”

“…For the Cf source alone it makes no difference whether the calculated or the measured corrections for neutron leakage are used and therefore it was decided to use measured corrections throughout the least-squares fitting procedure. This enables the long-counter detection efficiency, y , which is regarded as independent of source spectrum and bath size [3], to become an optional floating variable.…”

Tagging fast neutrons from a 252 Cf fission-fragment source

“…The weighted average α-particle energy is ∼6111.69 keV. The prompt-neutron yield is ∼3.75 neutrons per fission event [5,6]. The resulting fast-neutron energy spectrum follows the Watt distribution [7] and is very well known, with a most-probable energy of 0.7 MeV and an average energy of 2.1 MeV.…”