| Irradiation processing is a new high-tech industry,which breaksthe traditionalindustries field and infiltrates tothe filds of modern science and technology and anumber of emerging industries.It gradually becomes updated cross applicationindustrieswith considerable economic benefits and social benefits.This technology isused for insecticidal、sterilization、high polymer material modification and cropmutation breeding、seed irradiation to stimulate production and etc.these effects relyon radiation ofradioactive elements or the X-ray produced by acceleratorto changethethe molecular structurethus to produce a specific chemical effect or radiationbiological effect.According to2006statistics,by2006,the number of60Co irradiationfield and accelerator irradiation fieldinSichuan province is11,54.5%,45.5%respectively.Therefore,shielding design and safety analysis of irradiated sites appearsvery important.The radiation protection and safety codesof gamma irradiation device points outthat because most places of irradiation field volume is much bigger than usingradioactive source volume,then the source is regarded as a point source to analysis andcalculation,it is bound to cause a certain error,especially when the source radioactiveactivity reachs above one millionairesCurie.The number of sources and combinationstyle in the source frame have a reflection onthe calculation results accuracy,thus usingthe non-point source model or body source model to calculate the dose rate distributionis more in line with the actual situation.This paper choose a60Co irradiation field with4million Curie activity in Sichuanas the research object.Using MCNP5to establish the practical problemsmodel in orderto calculatthe indoor and outdoor dose rate irradiation distribution.The following is themain research work in this paper.(1)Using the effect of formula calculation compared with MCNP5simulation doserate,the formula calculate effectis close to MCNP5simulation calculation value beforewithout concrete wall shielding,MCNP5program can be used to calculate the radiationdose rate of source space. (2)Use the formula calculation and MCNP5simulation irradiation dose rate valueout of shield wall found that,before usingthe variance reduction techniques,such as theRussian roulette,MCNP5simulation calculation of dose rate value is much smaller thanthat of formula,through layering the shield wall,each layer’s thickness in the threephoton free path (in shielding medium),set the importance of each layer through thephotons incident direction,formula and MCNP5simulation the dose rate value ofoutside the walls were similar, with some variance reduction techniques,MCNP5alsocan be a very good tool in solving shielding problem(3)Using MCNP5simulates radiation dose rate of point source andbody source outofirradiation chamber wall,it is concluded that,body source and point source producedthe dose rate value is different in the same position,body source is more in line with theactual situation.(4)Using MCNP5simulates irradiation dose rate distributions of indoor,it isconcluded that, in this paper,the way of arrangement source is conform to therequirements of the irradiation field,lay the foundation of calculating dose ratedistributionof complex channel,Calculation and irradiation dose rate distributionoutdoor,points out that the dose rate is relatively large in point（-1234，910，212.5）,this effect can be the basis of choosing monitoring points forenvironmental dose rate monitoring and project acceptance.(5)For4million Curie60co source,andit has a distance of2.79meters awaywall,shielding wall thickness is about1.92meters,just meet the national standard GB17568-2008about design construction and use of the norms of gamma irradiationfacilities:on the premise of maximum design source loading,the dose rate out ofshielding should not be exceeded2.5μSv.This work can provide data for afterirradiation of building, etc.Reduce the well water shlelding layer thickness,it isconcluded that a series of source under the condition of different blocking water depthin the dose rate inoue,provide reference for the accident cases,so as not to cause thestaff of the irradiation by mistake. |
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