Features

The semi-spherical structure that accommodates 100 neutron detectors around the spherical vacuum chamber, at a distance of 175cm from the target position, is made of Geo-desic dome design fabricated using mild steel pipe links and hubs. The hubs are made of rings and welded to the vertexes of the geodome. The design of whole structure is is optimized to have minimum materials with light weight and strong enough to accommodate 100 detectors. The detectors are distributed on right rings with each detector inserted into the hubs at the vertexes. The reaction plane ring and two other rings out of the plane at ± 15^o with respect to the reaction plane contains 20 detectors on each ring.

The target chamber is a 100 cm diameter spherical chamber made of 4 mm thick stainless steel. The target ladder, located at the center of the chamber, can accommodate 5 targets including a beam-viewing quartz. Linear as well as rotary movement of the ladder is be possible. Inside the chamber there is an annular ring with four arms on which the fission detectors can be mounted. The arms can be rotated and the distance of fission detectors from the target can be varied. The chamber has separate flanges to accommodate vacuum feedthroughs and gas feedthroughs.

The relative detection efficiency of liquid scintillator neutron detectors is studied by measuring energy spectra of prompt neutrons from a ²⁵²Cf spontaneous fission neutron source. The neutron energies are measured using time of flight method. The zero timing signal is derived from associated γ-rays with a thin plastic scintillator. The data are collected in event by event mode, each event consisting of three parameters, viz. neutron time of flight, dynode pulse height and neutron-γ pulse shape discrimination. Electron energy calibration of the pulse height is carried out by measuring maximum Compton recoil electron energies with different γ-ray sources (¹³³Ba, ¹³⁷Cs, ⁵⁴Mn and ⁶⁰Co. Data are collected for different detection thresholds starting from 1.25 MeV to 3.0 MeV of neutron energies in a step of 0.25 MeV. The obtained energy spectrum at a particular threshold setting is compared with the standard reported spectrum of ²⁵²Cf to determine the relative neutron detection efficiency of the detector.