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A High Energy Electron and Photon Detector Simulation System



1 Abstract A detailed Monte-Carlo code has been developed from basic principles that simulates almost all of the basic photon and charged particle interactions. The code is used to derive the response functions of a high energy photon detector to incident beams of photons of various energies. The detector response matrice(DRM)s are calculated using this code. Deconvolution of an artificially generated spectrum is presented. The objective of the present endeavour is to develop a simple and user-friendly detector simulation code. An output pulse height spectrum is generated by the present code that may be compared directly with a measured pulse height spectrum which is the observable distribution. The aim here is not to try to develop a simulation system as detailed and sophisticated as say, the EGSnrc or GEANT4 software systems but one that has all the basic physical processes incorporated within it and one which is, at the same time, sufficiently simple so that it may be used with ease to compare results of experiments where not very elaborate and complicated calibration systems are available-hence the calibration data also has certain inherent uncertainties and limitations due to effects (of say, surrounding materials etc.) that are neither well understood nor properly taken care of. In other words the present simulation code will be very useful in applications where extremely accurate results are not needed but a few percent accuracy will suffice. The approach taken here is to develop the entire detector simulation code starting from the very basic principles, generate artificial photon input energy spectra, let these interact with the detector to give rise to output pulse height spectra. Using the detector calibration data, the pulse height spectra may be converted to equivalent output energy spectra. Since the DRMs are calculated using the same program, the output energy spectra can be deconvolved using these DRMs and the deconvolved spectra can be compared with the original input photon spectra. This procedure establishes, to a large extent, the validity and accuracy of the entire simulation code. The simulation code is written in FORTRAN 77. The GNU compiler g77 is used to compile the code. It runs under Redhat Linux 9.0 operating system. A typical run to simulate a few thousand events for input photons say, 661 keV takes a few seconds in a PENTIUM IV system. This gives the energy deposition spectrum. In order to get the pulse height spectrum one has to use the photo-multiplier dynode multiplication simulation procedure. This takes rather long time, typically more than two hours for a few thosand events of 661 keV photons. The present code is nearly 3000 lines long 1

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