The Research On Radioactive Volume Source-less Efficiency Calibration Technology Based On The Virtual Source Theory

The calibration methods of the radioactive gas and the big source are the key technology of international study. In order to obtaine the activity of radioactive nuclide, it is very important to calibrate these voume sources, especial for proficiency test exercise of the laboratory, analysing the CTBT sample of radioactive xenon isotopes which are used to judge the property of the HPGe system and Nuclear test of the country.The relative measurement method has not realized their experimental calibration, and Monte Carlo method has large uncertainty, respectivly. Therefore, a new measurement method and experimental technology is needed. In order to avoid the using volume source and the problem of software, we need to develop source-less efficiency calibration method based on virtual source. One, a point source or a disc source is placed at virtual positon to calibrate efficiency of volume source; another, we use the software calibration to transfer the efficiency from point source or disc source to volume source. This technology is also used in the theoretical and experimental study of the heterogeneous distribution sources to obtain their detection efficiency and the boundary. The source-less efficiency calibration technology is very importance in the fields of verification of nuclear Test-ban, nuclear emergency measurement and environmental radioactivity measurement.(1) The source-less efficiency calibration based on the virtual source.The virtual source calibration theory was advanced. The layered simulation of disc source and its express of the mean value theorem of integrals were deduced by us. The virtual point source calibration method based on the efficiency function of point source was established.Then, the methodological research to calibrate boundary of polluted area using virtual point-source was advanced by us. The disc efficiency transfer code of formula was deduced to obtain volume source efficiency based on software calculation, establishing the procedure and method. We deduced the theoretical formula of source-less efficiency calibration, which used a dynamic disc source to simulate gas source, and then, a decive was designed.(2) For the small probability transport problem of large source with small detector, the method and procedure of Monte Carlo calculation were established based on the efficiency segmentation principle, the point source experiment instead of volume and the skill of point source collimated into a cone of directions in MCNP.(3) We carried out the study on the source-less efficiency calibration method based on probability density distribution. The virtual source is also used to study the theoretical and experimental method of heterogeneous distribution source, obtainning their detection efficiency. The experimental calibration method of the gas source has been developed.