2NCorr SPDP Introduction

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The neutron efficiency and acceptance of our detector array varies highly non-uniformly over the range of two-neutron opening angles ([math]\theta_{nn}[/math]). This is due to the detector array's non-spherically symmetric geometry, and to its varying neutron detection efficiency as a function of both position and energy (see figure).

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  Measured opening angle distribution of neutrons from the spontaneous fission of Cf252.

For this reason, every measured distribution is made meaningful by normalizing against a "control" distribution. This is done by diving the values of the measured distribution by the control distribution on a bin-by-bin basis. For [math]\theta_{nn}[/math], the control distribution is made by looking at pairs of two separate pulses, and if there is a neutron event in both pulses, the opening angle between the two events is calculated. Since no information can be shared between neutrons of different pulses, the control distribution is completely free of all two-neutron correlations, but it is nonetheless subject to the usual effects of detector geometry and efficiency as a function of position and energy. So what is meant by "angular correlation" here, is the measured event rate relative to a totally uncorrelated neutron source.

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  Angular correlation of neutrons (E>1.5 MeV) from the SF of Cf252. In this case, the normalizing distribution is taken from neutron pairs corresponding to separate fission event triggers, instead of separate pulses.










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