Proof-of-principle Study of Photon-nuclear Transmutation Based on 7Li (p,γ)8Be Reaction

Abstract

With the development of economy, there is an increasing need of nuclear energy, which means that nuclear waste transmutation is becoming more and more important. Usually, there are two ways to preform nuclear transmutation, one of which is neutron transmutation. Neutron transmutation is the main way to process most of nuclear waste, including almost all transuranic elements and several kinds of fission products. However, the reaction cross sections of some fission products are small for neutron transmutation. So, it is worthwhile to develop an auxiliary way. Photon nuclear transmutation could be a reasonable way to process nuclear waste when the intensity of high energy gamma beam reaches a certain level. There are several different methods to produce high energy gamma rays, like Bremsstrahlung, in-flight positron annihilation, laser Compton backscattering (LCS) and (p,γ) resonant reactions. High energy gamma rays from Bremsstrahlung have very low production rate. The methods of LCS and in-flight positron annihilation need large-scale electron accelerators. Gamma rays from (p,γ) resonant reactions are based on tandem accelerators, which is only working on hundreds of kilovolts voltage. It makes (p,γ) resonant gamma source a very attractive way to be used in nuclear waste transmutation, since it has a relatively low cost. With the technology development of high intensity proton beam accelerator, the beam intensity can reach more than 100 mA. Under such condition, the gamma beam intensities can be improved greatly. Then, (p,γ) resonant gamma source becomes a promising way to process nuclear wastes. There are some different reactions can be used to produce high energy gamma rays, 7Li(p,γ)8Be resonant reaction is the best choice among them. The gamma ray energies from this reaction, 14.8 and 17.6 MeV, just locate in the giant resonance region. The experiment was done by using the 2×1.7 MV tandem acceleration at China Institute of Atomic Energy. Gamma rays emitted from 7Li(p,γ)8Be reaction were detected by HPGe detector. In order to get maximized gamma ray yield, the LiF target was positioned 45° to the proton beam direction. The 197Au target was parallel placed with the LiF target while it was irradiated by high energy gamma rays. It has been irradiated for 3.85 h. After irradiation, the 197Au target was placed in the low background chamber. A Compton suppressed HPGe spectrometer was used to measure the decay gamma rays from 196Au. The transmutation rate from this experiment is finally obtained to be (586.83±22.98)s-1 under the proton beam intensity at 0.81 μA for an 18.5 mm diameter and 2 mm thick gold target. The experimental results lay a technical foundation for the experimental study of photon nuclear transmutation by using (p, γ) resonant gamma source.

Keywords

• photon-nuclear transmutation
• high energy gamma ray
• resonance reaction
• nuclear waste