α Spectrometry Solution Spectrum Based On Monte Carlo Simulation

Plutonium is a highly toxic radionuclide. Once breathing into the plutonium, thepeople will have serious internal radiation, and initiate life-threatening. So plutoniumaerosol measured accurately and real time is very necessary. The measurement ofplutonium aerosol will be affected by radon and its daughters in the air. Theconcentration of radon and its daughters is3-5orders of magnitude more than theconcentration plutonium aerosol in workplace, so the concentration plutonium aerosolmeasured accurately and real time is very difficult. People have used the decay law,stripping spectrometry, energy screening method, and aerosol particle size gradingplus energy screening the plutonium aerosol measurements in the context of radon.Stripping spectrum algorithm is very widely.Currently, Stripping spectrum methods are used Function fitting, cubic splinefunction method, etc. Abroad try to analyze α spectrum using the Monte Carlo method,but the domestic No one try this. This paper attempts to use this method to strippingspectrum of transuranium elements and radon daughter mixed α spectrum, and do acomparison with the use of function fitting method.The MCNPX model is established According to the Ion Implantation typedetector （PIPS） detecting the α spectroscopy, then the αparticles of²⁴¹Am（5.486MeV）、²¹⁸Po（6.0MeV）、²¹⁴Po（7.69MeV） and the source covered with a layerof plastic wrap are simulated. The alpha spectroscopy spectrum parameters withMCNPX simulation method is modified.This paper uses the radon daughter standard source of Canada Pylon to make afilm radon daughter source, then put this film covering on the source. So theapproximate experimental condition is established, and using MCNPX to simulatethis. This paper has tried stripping spectrum algorithm based on the weighted leastsquares method to simulate the spectrum α spectrometry.A comparison between the Monte Carlo simulation results with the function fitting results is made. The results showed that A comparative analysis of databetween the two methods is made. Both methods are approximately equal in theallowed error range with7.5%.The values of MCNPX simulation、function fitting andexperiment under long measurement time are approximately equal in the allowederror range with10%, but for short measurement time there are large relativedeviations between MCNPX simulation value and experiment value,so were functionfitting value and experiment value. The main reason for this phenomenon is thatmeasurement time is too short, so that the statistical error is too large,as well as thesize of the particles of the²⁴¹Am source and the size of aerosol particles in thesimulation are is not considered.The setting of the initial value has a certain impact on the fitting result when thefunction fitting method is used. Using the method of fitting function, there is verystrong dependence on the initial value,so Monte Carlo simulation is a better choice inthe case of the scope of the initial value can not be determined.Besides, when using the MCNPX program simulation²⁴¹Am source cover withplastic wrap, thickness of the film （a difference of1um） has a relatively large impacton α spectroscopy peak position, FWHM the tailing parameter. Using the method ofcomparison between simulation and experiment can improve the accuracy of thethickness of film quality with alpha particle measurement method.