Research On Measurement And Assessment Of Internal Exposure Dose Based On Lung Counting System

This research is resolving the problem about internal exposure dosemeasurement based on lung counting system, such as efficiency calibration oflow energy rays, manufacture of torso phantom, measuring low energyradionuclides in high Rn site, analysis of small peak in the spectrum, applicationof new ICRP respiratory tract model in internal exposure dose calculation. Thegoal is to master the technology of internal exposure dose measurement basedon lung counting system and to apply the technology in the practical work.Lung counting system was made of four HPGe detectors, four amplifiers,four multi-channel analyzers, and the software of analyzing and collecting thespectrum, the lead shield sharing with the Whole body counter, the aeratorsuper-induced in this research. The relation curve between efficiency and equivalentchest wall thickness was gained by experiment testing. It was researched that222Rn andits progenies in the shield and lung affected the performance of lung counting system.The efficiency was also calculated by MCNP. The result was applied to calculateinternal exposure dose using new ICRP respiratory tract model. The source ofuncertainty of the calculation result was analyzed too.The productions of my research include:(1) A torso phantom was manufactured to calibrate the efficiency of lung countingsystem. Cooperating with other departments, we used polyurethane to simulate muscle,fattiness, liver, kidney, intestines etc. The bony and cartilaginous tissues are simulatedby epoxy resins mixed with additive such as calcium carbonate. The lungs modes weresimulated by polyurethane mixed with vesicant. There were four chest plates to simulatedifferent chest wall thickness.(2) The method how to reduce the effect of Radon and its progenies in the shiedand our body while measuring low energy radio-nuclides by lung counting system. Byventilating and filtering the new air from outside the room, the concentration of Radonin the shield was reduced. By breathing, we can breathe out the Radon detained in ourbody. By decaying, the effect of the progenies in our body will be reduced. Theminimum detectable activity of222Rn、241Am（239Pu）、235U were calculated. (3) The technology of analyzing small peak in the spectrum was researched. Byexperiment testing, small peak was analyzed using wavelet analysis method.(4) The calculation of internal exposure dose is discussed based on the resultcoming from lung counting system. The retention functions in thorax region werecalculated based on ICRP publication No.66. The estimate of intake was calculated too.The values of committed effective dose can also be calculated by the method that dosecoefficients (committed effective doses per unit intake) for selected radio-nuclidesmultiply the estimate of intake.