Gamma-ray Energy Spectra Emitted From Iron Sphere With D-T Neutrons

The way of Compton recoil electron is used to measure the gamma-ray leakage spectra from iron spherical target assembly pulsed with 14-MeV D-T neutrons. The energy range of measured gamma-ray spectrum is 0.5-5MeV. The D-T neutrons is provided by NS-200 accelerator.Iron sphere materials have 98.5% Iron element and a few of Manganese, Carbon and Silicon elements. The density of iron sphere is 7.86g·cm-3. The sizes of iron spheres are φ(6.0cm- 12.0cm), φ(4.0cm- 16.0cm), φ(4.0cm-26.0cm),φ(4.0cm-36.0cm) and φ(4.0cm-47.6cm). The thicknesses are 3, 6, 11, 16 and 21.8cm.Measurements of Compton recoil electron spectra caused by the gamma ray are detected by a nominal 5.08cm-diam×5.08cm-long BC-501A scintillator detector. The absolute neutron yield is measured by associated a-particle method. The r-ray detection efficiency of BC-501A detector is calculated using MARTHA M-C Code. The measurements of recoil electron spectra of the gamma source Mn-54 and C-12 are compared with the calculations. The factors that affect the detecting efficiency are analyzed. The background of neutron is rejected by the technique of pulse shape discrimination.The gamma-ray leakage energy spectra φs are resolved from the Compton electron recoil spectra. The gamma ray that caused by target room is deducted by the way of combining the experiment detecting and simulated calculations. At first, measuring the electron recoil spectra of target room gamma ray. Through the resolution of spectra we get the gamma ray spectra caused by target room. Then we transform it to the zero point, the place of neutron source, and calculate the leakage gamma ray spectra φT from iron sphere caused by target room gamma ray by MCNP program. Finally we deduct it from the D-T leakage gamma ray spectra φs of iron spheres.From the analysis of gamma-ray spectrum, we find that spectra flux shows certain regularity when thickness of iron shell is increasing. The gamma flux is increasing with the thickness' increasing when thickness is less than 6cm, and it is decreasing when the thickness is more than 6cm.The leakage gamma ray of iron spheres is measured by high pure Germanium(HPGe) detector. Comparing with the BC-501A scintillator detector, four characteristic gamma rays: 846.77, 1238.282, 1771.351 and 2212.933keV caused by inelastically scattered neutrons are coincident with the BC-501 A scintillator detector. It shows that the measurements by BC-501 A scintillator detector are accurate and credible.Monte Carlo neutron-photon transport calculations are done with t-2, ENDF/B-V, ENDF/B-VI and FENDL-2 libraries and MCNP4A program. Comparisons with the measurements, the gamma spectra calculated with ENDF/B-VI, FENDL-2 and t-2 give a fair representation of the measurements, the rates of C/E are 0.91,0.95 and 0.85. However, serious discrepancies are found in calculations with ENDF/B-V library, the rate of C/E is 1.30.The measured electron recoil spectra are compared with the ERS of America Livermore Laboratory. It shows that they have good agreements.The gamma mass absorption coefficient of iron sphere is measured by high pure Germanium detector, the gamma sources are 24Na gamma ray, the r energy are 1.369MeV and 2.754MeV, and 137Cs source and 241Am -Be source, the r energy are 0.661MeV and 4.438MeV. The results show that the mass absorption coefficient is nearly exponent decay with the gamma energy, the less energy of gamma ray, the more probability of absorption in the iron sphere.