تحليل طيف اشعه ي گاماي آشكارساز( Nal(Tl با استفاده از كد MCNP

چكيده انگليسي :

Analysis of Gamma Ray Spectra from NaI Tl Detector Using the MCNP Code Khalid Rahmani rahmani kh377@yahoo com March 8 2011 Department of Physics Isfahan University of Technology Isfahan 84156 83111 Iran Degree M Sc Language Farsi Dr Ahmad Shirani Mail shirani@cc iut ac irAbstractIn this thesis gamma rays spectra measured by a NaI Tl 3 in 5 in 16 in detector were analyzed Forthis a series of radioactive sources emitting gamma ray of known energies together with a 137Cs source were measured with the detector To determine the location of peaks in the measured spectra APTECsoftware was used Determination of peak channel in the spectrum of 137Cs source showed that the peaksshift to lower channel by time To calibrate the detector properly the peaks of other sources were shiftedwith a linear relationship using the peak of 137Cs source in each spectrum and the spectrum of 137Cs whichwas measured alone the first spectrum measured Then the detector was calibrated using peakstransmission To remove background under the peaks and determine FWHM of detector the spectrum ofeach source was determaind with the MCNP code without Gaussian distribution for the peaks and wassubtracted from experimental spectrum Fitting a Gaussian function on pure peaks FWHM in the energieswere computed FWHM defined function in MCNP code was fitted on obtained FWHM for severalenergies then FWHM was obtained for energy range of 0 06 MeV to 2 6 MeV Next to determine countsrelated to each energy in the spectrum of sources that emit more than one gamma and overlap in theexperimental spectrum the experimental spectrum of these sources were built For this the energy spectraof the sources were first simulated with MCNP code using Gaussian Energy Broadening GEB Thensimulated spectra were summed and normalized so that measured spectra were made Making experimentalspectrum by use of simulated spectra allow to calculate the number of counts of each energy This methodis also used to determine the counts related to any peak in a compound spectrum This was done for bothsources of 60Co and 133Ba In 60Co source due to high efficiency of the detector in addition to determinenumber of counts in energies of 1 173 MeV and 1 332 MeV the number of counts in sum peak energy2 505 MeV was also determined Calculation of counts of three peaks give the possibility of estimatingactivity of 60Co source without having the efficiency of the detector and it was done In the measuredspectrum source of 133Ba the peaks overlap together due to poor resolution of NaI Tl detector and thispeaks overlapping makes determination of counts regarding to each peak impossible For solution thisdifficult first using MCNP code each energy emitted from the source is simulated In what follows thesesimulated spectra are added to build another spectrum which is very similar to the measured spectrum Finally this built spectrum makes the counting of the area peaks possible Even this method to determinecounting for energy of 0 160 MeV which is placed on the backscattered peak and its intensity is low insource is also possible Accurate simultion experimental spectrum shows that proposed method can be usedfor determining counts in peaks that overlap in measured spectra This method can even determine thecounts for energies that have low intensity in source due to high efficiency of NaI Tl 3 in 5 in 16 indetector Keyword NaI Tl detector FWHM simulation of spectra gamma ray MCNP code

رحماني، خاليد

تحليل طيف اشعه ي گاماي آشكارساز( Nal(Tl با استفاده از كد MCNP

FWHM , شبيه سازي طيف