Development of passive neutron detection system from thermal to fast using SSNTD detectors

In personnel neutron monitoring, only neutrons above 100 KeV can be measured with PADC (poly allyl diglycol carbonate) detectors for dose evaluation but neutron dose contribution below 100 KeV cannot be measured due to 100 KeV threshold for PADC. In this work, a detector system was developed to measure neutrons from thermal to fast using PADC detectors. Three sets of PADC detectors were loaded in cassettes normally used for thermoluminescence dosimetry. Two sets of PADC detectors were covered with lithium tetra borate radiator, out of which one was bare and other was covered with 1 mm cadmium. Thermal neutron measurements were carried by counting the alpha tracks from (n,á) reaction of 6Li and 10B present within lithium tetra borate radiator, Thermal neutrons were measured from the difference in the alpha track densities of the two detectors. Fast neutron measurements were carried by counting the recoil tracks of hydrogen, carbon and oxygen present within the detector located at the centre of the cassette. It was observed that in case of 252Cf neutron source having average energy as 2.2 MeV the response was more for bare and polyethylene cover mode than 241AmBe neutron source having average energy as 4.5 MeV for same combination. Further in case of 14 MeV neutron source there was not much change in response when compared with 252Cf and 241Am-Be neutron source. Thermal neutron measurements were carried by taking the difference between the tracks in bare and cadmium cover mode of PADC covered with lithium tetra borate radiator. The angular response of the detector system was checked by exposing the detector system to 241Am fast neutron source for various angles. It was found that the detector system is angular dependent. The thermal neutron dose measurement ranges from 0.65 μSv to 2.6 mSv whereas fast neutron dose ranges from 0.1 mSv to 310 mSv. In this detector system thermal and fast neutrons can be measured in same detector system using different chemical etching times