Development of New Neutron Detectors for Accident Dosimetry

New detectors and measuring techniques are proposed to improve the assessment of individual dose received from persons involved in a criticality accident. The aim was to reduce the number of detectors in the conventional detector combinations, to use sensitive activation reactions and to measure the dose of intermediate and fast neutrons directly. The proposed neutron detectors for the dosimeter combination are: (a) Arsenic, to detect slow and intermediate neutrons up to 1 MeV by the 75As(n, y) 76As reaction (half-life of 76As is 26.4 h); (b) Phosphorus, to detect fast neutrons above a threshold of 2 MeV by the 31P (n, γ) 31Si reaction (half-life of 31Si is 2.6 h), and slow neutrons by the 31P(n, γ) 32P reaction (half-life of 32P is 14 d); (d) A polycarbonate detector (Makrofol E) as a nuclear track detector to detect fast neutrons above a threshold of 0.5 MeV by elastic scattering and (n,a) reactions in carbon and oxygen. The S-activity of 76As, 31Si and 32P can be measured directly in As2S3 glass and in phosphate glass by means of the β-induced Cerenkov effect. It uses a liquid scintillation counter set up as for tritium measurements. The calibration of the detectors was performed by calculations of the detector sensitivity for different neutron spectra and by irradiation with different neutron sources at different ctiticality installations. After an accident a first estimation of the neutron dose is obtained by a β-counting of the arsenic phosphate glass, which indicates the surface adsorbed dose or the total neutron fluence directly. It is energy independent over the range of intermediate and fast neutrons. (author)