Monte carlo calculation and fusion neutronics

Five topics in fusion neutronics simulated by means of monte carlo method are as follows: (1) Measurement of low energy neutron spectrum by slowing down time method: Slowing down time following injection of D-T pulsed neutron into a medium corresponds to an average energy of neutron. The number of time dependent neutrons counted is convertible to the number of energy dependent neutrons, or neutron energy spectrum. This method is suitable for measurement of neutron energy spectrum within the range of 1eV-10keV. Time dependent neutron transport calculation are made by monte carlo code, MCNP. (2) Response functions of γ-ray detector: γ-ray spectra measured by organic liquid scintillation detector (NE213) for Cs-137 (γ ray; 0.662 MeV) and by NaI (Tl) detector for Na-24 (γ ray; 1.369, 2.754MeV) are compared with response functions calculated by monte carlo code, MARTHA and the MCNP, respectively. (3) Accuracy evaluation of secondary gamma-ray data: Secondary γ-ray spectra caused by D-T neutron in various depths of iron experimental system are compared with the calculation results of the MCNP. (4) Correction of β-ray energy loss in experimental samples: The β-ray energy loss of P-32 in a sulphur sample is measured by a total energy absorption spectrometer which is developed for decay heat measurement, and compared with the MCNP calculation. (5) Experiment analysis for decay heat of tungsten: Tungsten is considered as the first wall material of function reactor. W-187 is produced by (n, γ) reaction of W-186. The activity of W-187 is measured at various depths in tungsten plate (thickness, 12mm). Calculation results by monte carlo method gave a good agreement with the values obtained by experiments. (M. Suetake)