6533

6098

كارشناسي ارشد

فيزيك هسته اي

اصفهان: دانشگاه صنعتي اصفهان، دانشكده فيزيك

1390

ده، 114ص.: مصور، جدول، نمودار

ص.ع. به فارسي و انگليسي

احمد شيراني

محمد حسن علامت ساز

17/12/90

اكبر پروازيان، ظفرا... كلانتري

1396/10/12

كتابنامه

فيزيك

فيزيك

ID6098

به فارسي و انگليسي: قابل رويت در نسخه ديجيتالي

116 Positron Life time Spectroscopy Sajjad Abedi abedys@ymail com October 5 2011 Department of physics Department of Physics Isfahan University of Technology Isfahan Iran Degree M Sc language FarsiDr Ahmad Shirani Mail shirani@cc iut ac irAbstractOne of the methods for investigating defects in metallic and non metallic solids is to measure positronlife time in these materials positron life time spectroscopy In this work by using a positron emittingsource 22Na which emits a 1 274 MeV gamma ray almost simultaneously with positron defects in themetal samples aluminum and copper and also polymer samples polyethylene poly tetra flour ethyleneand poly methyl metha crylate have been studied For this purpose a fast slow advanced coincidencesystem consisting of two BaF2 detectors two timing single channel analyzers two constant fractiondiscriminators two amplifiers two fast preamplifiers a time to amplitude converter and a fastcoincidence device were used Initially each device in the coincidence system was adjusted with thehelp of an advanced oscilloscope and then the time resolution of the coincidence system wasdetermined using a 60Co source which emits two simultaneous gamma rays of energies 1 33 and 1 17MeV The time resolution was found to be 156 74 ps After adjusting the coincidence system the 22Nasource was placed between the samples under study and then the source and the samples were placedbetween the two barium fluoride scintillators The 1 274 MeV gamma ray which is emitted from thesource almost simultaneously with the positron was considered as the start ray and the 0 511 MeVgamma ray which is created from positron annihilation with the electrons in the bulk or defect in thesample was considered as the stop ray and these gamma rays were guided into the two barium fluoridescintillators Positron life time spectra were measured in the samples under study using the timedifference between 1 274 and 0 511MeV gamma rays The spectra obtained were then analysed usingthe LT9 2 software The metal samples were analysed by methods of Auto and Ser and the polymersamples were analysed by the four component method and the positron and positronium life timecomponents and their intensities were determined The life time components in metal samples Al andCu were then used to determine the vacancies in these samples Also the life time components of ortho positronium in the polymer samples were used to determine the size of cavities in these samples with anaccurate of almost 0 1 nm 22Keyword Positron Life time Spectroscopy positronium Na Source positron life time in material coincidence system time resolution vacancy defect in samples tao eldraop

احمد شيراني

محمد حسن علامت ساز

اكبر پروازيان، ظفرا... كلانتري