Back-to-back gridded ionization detector technique for the determination of fragment angle and its use for the measurement of neutron angular distributions in 235U(nth,f)

A back-to-back gridded ionization chamber was used to measure the prompt neutron angular distributions after determining the fission fragment angle with incorporation of energy loss correction in the target and backing material. The correspondence of the ratio (Vg/Vc) of the grid pulse height to the collector pulse height with cos θ is made use of to derive energy loss corrected Vg and Vc values. The fragment angle is obtained from the corrected grid pulse heights after determining the calibration constants for 0 and 90 emission angles as a function of energy and mass of the fission fragments. An angular resolution of 2 to 3 [FWHM]for each fragment could be obtained over a large angular range on each side of the ionization chamber. The chamber was used along with a NE213 neutron detector to measure the angular distributions of the prompt neutrons emitted in the thermal neutron induced fission of 235U, and results of these are reported as an illustration of the present method. (orig.)