بررسي و محاسبه ي بازدهي ذاتي شمارنده هاي سوسوزن ﴿CsI(TI) , NaI(TI) با استفاده از كد محاسباتي MCNP

چكيده انگليسي :

Study and Calculation of Intrinsic Efficiency of Scintillation Counters NaI Tl and CsI Tl Using the MCNP Code Moein Shalibayk m shalibayk@ph iut ac ir Date of Submission 2011 07 13 Department of Physics Isfahan University of Technology Isfahan 84156 83111 Iran Degree M Sc Language Farsi Supervisor alamatsa@cc iut ac ir Abstract Radiation detection and measurement is a fundamental subject in nuclear physics and engineering Various instruments were developed in the last few decades to detect and measure particles with greatest accuracy Sodium Iodide NaI detectors are devices used in gamma ray detection and activity measurements Several researchers employ the Monte Carlo method for estimating the radioactivity concentration The accuracy and the performance of this statistical method make it the most suitable and adapted to this kind of simulation Its use appears clearly when the g photon contributions in the NaI Tl detector is known NaI Tl detectors are commonly used to identify and measure activities of low level radioactive sources They have high detection efficiency and operate at room temperature One of the most important parameters in the calculation of the gamma activity of environmental radioactive sources is detection efficiency It is usually determined by using calibrated standard sources Gamma detection techniques are widely used in gamma ray spectroscopy for nuclear physics medical radiography neutron activation analyses well logging and study of cosmic rays In the present research by the use of the MCNP computational code that is based and set on the Monte Carlo method at first pulse height distribution for 137 60the known sources Cs and Co with the F8 tally has been obtained for the NaI Tl detector Then the pulse height distribution has been obtained experimentally for these two sources After the comparison of simulation results with the experimental results and validation of written codes the main codes have been written The cylindrical NaI Tl detector with 3 inches length and 1 5 inches radius has been assumed Gamma radiations with energy 0 2 1 5 10 and 50 MeV have been also used and an isotropic point source has been placed in the distance d on the x axis The x axis has been assumed the symmetry axis and oriented from the detector to the source In this research only the case where the source is placed on the detector symmetry axis has been assumed The program has been run for 20 distances d from 0 00381 up to 381 cm in another word as a function of d R from 0 001 up to 100 Then the intrinsic efficiency variations versus source detector distance has been calculated for different gamma ray energies and the intrinsic efficiency variations of NaI Tl detector versus source detector distance have been analyzed for different gamma radiations It should be noted the intrinsic efficiency depends not only on photon energy but also on source detector geometric configuration The intrinsic efficiency variations have been analyzed by the Dirac theory and mean chord length of photons in the detector and mean interaction length at each energy Finally all of the previous calculations have been done for a CsI Tl detector with the same sources and geometric configuration Then the CsI Tl detector results have been compared with those of the NaI Tl detector The results showed that the variation of intrinsic efficiency graph of the both detectors have a minimum at d R 0 7 Although NaI Tl detectors have maximum light yield in comparison with the other scintillators but the results showed that NaI Tl detectors have had less intrinsic efficiency in comparison with some scintillators like CsI Tl Keywords NaI Tl detectors intrinsic efficiency MCNP Monte Carlo tally gamma radiation isotropic source mean chord length mean interaction length

شالي بيك، معين

بررسي و محاسبه ي بازدهي ذاتي شمارنده هاي سوسوزن ﴿CsI(TI) , NaI(TI) با استفاده از كد محاسباتي MCNP

آشكارسازهاي يدروسديم , مونت كارلو , تالي , اشعه ي گاما , چشمه ي همسانگرد , ميانگين مسير پيموده شده , مسير آزاد ميانگين