The shielding integral experiment in fission neutronics using a 252 Cf neutron source is one of the crucial methods for verifying and evaluating nuclear data quality. At high counting rates, diamond detectors tend to exhibit reduced fission fragment counting rates due to lattice damage. Although traditional parallel-plate ionization chambers have excellent radiation resistance, they suffer from inadequate timing resolution. To overcome these drawbacks, a compact cylindrical parallel-plate avalanche ionization chamber (CPPAC) was developed in this work, with a height of 25 mm and a diameter of 29 mm, that can be embedded in test samples. With the fission source closely attached to the electrode film, the detector achieves improved spatial detection efficiency while satisfying the requirements of high counting rates. This detector has a plateau length of approximately 70 V and a plateau slope of 10.6% per 100 V. By virtue of the stable gas supply and the low-pressure operating design of the CPPAC, the system achieves a time resolution of 346 ps. Under the actual operating conditions for fission fragments, the measured timing resolution of the detector is 3.28 ns (FWHM). During a 34-day test with a 252 Cf source, the detector maintained a stable counting rate of 3000 cps, with a daily attenuation rate of approximately 0.389%. The detector exhibits good long-term operational stability over 34 consecutive days of neutron spectrum measurements, with no significant performance degradation observed, providing a reliable experimental basis for studies on sustained operational stability.
Wang et al. (Fri,) studied this question.