GAMMA-DOSE CHARACTERIZATION OF THE NEUTRON FIELD IN THE SIGMA-SIGMA-IRRADIATION FACILITY

We present a method to estimate the gamma dose in a neutron field usin g a parametrization of the doses measured with thermoluminescent detec tors. The source for the high neutron fluences was the Sigma Sigma fac ility, a uranium multishell sphere placed in the thermal column of the VVRS reactor of the INPE Bucharest, which has a high precision neutro n fluence calibration (4%) and a very well defined neutron spectrum. T he photon spectrum inside the Sigma Sigma, degraded by absorption and Compton scattering was simulated with a Monte Carlo method, The doses, up to 150 Gy, were measured with thermoluminiscent detectors (TLDG Mg F2(Mn) and CaF2) calibrated up to 8 MeV with radioactive sources and i n the bremsstrahlung radiation of the IPTRD-Bucharest linear electron accelerator. A rough model for separating the contribution of prompt a nd delayed gammas is used to calculate the doses for different time ch aracteristics of irradiation. For the Sigma Sigma facility, the ratio between the prompt gamma dose and the neutron fluence is (1.73 +/- 0.0 9) pGy cm(2)/neutron; the contribution of the delayed gamma depends on the time characteristics of the irradiation, The method can be used t o evaluate the gamma dose in any fission environment if the gamma and neutron spectra are approximately known.