NaI閃爍探測器測量感生放射性及其蒙特卡羅模擬

1、31 11 2007 11HIGH ENERGY PHYSICS AND NUCLEAR PHYSICSVol.31,No.11Nov.,2007A Measurement of the Residual Radioactivity with NaI SurveyMeter and Its MC SimulationWANG Qing-Bin1;1Kazuyoshi Masumoto2Hideo Hirayama2Tokushi Shibata21(Institute of High Energy Physics,CAS,Beijing100049,China2(Radiation Scien

2、ce Center,High Energy Accelerator Research Organization(KEK,JapanAbstract The present study shows how Monte Carlo method using EGS4code can be useful for evaluating the residual radioactivity induced in shielding concrete of accelerator facilities.By using EGS4code,the response of NaI survey meter c

3、oncerning the shielding concrete block radius and thickness are calculated.It is found that the surface dose rate is saturated when the shielding concrete radius and thickness reach40cm and30cm respectively.Under the above-mentioned conditions,the surface dose rates at position north-8 and south-9of

4、 SF cyclotron in University of Tokyo,are investigated,and compared with the experimental results obtained by NaI survey meter.It is shown that the calculation results are in good agreement with the experiments.In addition,the conversion factor of the surface dose rate to surface residual radioactivi

5、ty is obtained to be0.90(Bq·g1·(µSv·h11for60Co and1.26(Bq·g1·(µSv·h11for152Eu.By using this conversion factor,we can easily evaluate the radioactivity induced in shielding concrete of accelerator facilities from the experimental results of NaI survey meter.Key

6、 words Monte Carlo,EGS4,simulation,residual radioactivity,response,NaI survey meter1IntroductionOne of the main radiation safety issues from the decommissioning and decontamination of accelera-tor facilities and their construction is how to evalu-ate the residual radioactivity in the activated shiel

7、d-ing concrete and determine the radioactive waste1. The shielding concrete samples usually are mea-sured by gamma-ray spectrometry and several re-lated researches for measuring radioactivity in acti-vated shielding concrete have been presented in some literatures24.But the method of these researche

8、s is not suitable to measure numerous concrete samples produced from the decommissioning of the largest ac-celerator facilities.In practice,the surface dose rate is proportional to the residual radioactivity in activated shielding concrete,so one of the simple methods to evaluate the residual radioa

9、ctivity in activated shield-ing concrete is to measure the surface dose rates by NaI scintillation survey meter,and then convert these dose rates to radioactivity in Bq·g1by using the con-version factor obtained by calculation.However,it is required to know the response of NaI scintillation sur

10、vey meter to the radius and the thickness of the activated concrete block and the conversion factor of dose rate to radioactivity.In this study,the response of NaI survey meter to the concrete radius and thickness are calculated,and the self-shield property of shielding concrete with the increase of

11、 the depth of concrete is studied by EGS4 code5.In order to provide detailed information for EGS4calculations,the depth proles of principal ra-dionuclides induced in the shielding concrete of SF-cyclotron is measured by an automatic gamma-ray1072 (HEP&NP 31 The input gamma and X-ray energies wer

12、e takenfrom the Energy Level Structure Chart7for each ofthe two sources:152Eu and60Co.Double energies of1173and1333keV were used for60Co source.The en-ergy spectra deposited in the NaI crystal were scoredand converted to dose rate by G factor,which wasobtained from ALOKA Company.The number ofhistory

13、 of the calculations was determined to be10million in order to reduce statistical uncertainties.11 NaI 10731074 (HEP&NP 31SF north8SF south9experiment/(µSv·h111 NaI 1075References1Swanson W P.Radiological Safety Aspects of the Operation of Electron Linear Accelerators.Vienna:IAEA Techn

14、ical Reports Series No.188,19793Urabe I,Kobayashi K.Health Phys.,1991,60:5875914Kimura K,Ishikawa T,Kinno M et al.Health Phys.,1994, 67:6126315Nelson W R,Hirayama H,Rogers D W O.The EGS4Code System,SLAC-265.19856Kotegawa H et al.JAERI-M93-020,19937Firestone R B,Shirley V S.Table of Isotopes(CD-ROM.8Masumoto K,Toyota A,Eda K et al.Journal of Radioan-alytical and Nuclear Chemistry,2003,255:465469NaI1;1Kazuyoshi Masumoto2Hideo Hirayama2Tokushi Shibata21( 1000492(Radiation