History, Overview and Recent Improvement of EGS4

Abstract

A great deal of the content of the following historical sections of this report has been plagiarised unashamedly from the original EGS3 Electron Gamma Shower Code Version 3 document authored by Richard Ford and Ralph Nelson 1 . There are several reasons for this aside from laziness. This history predates one of the author's AFB involvement with EGS and he found it very di cult to improve upon the words penned by F ord and Nelson in that original document. Moreover, the EGS3 manual is now out-of-print and this history might h a v e e v entually been lost to the ever-burgeoning EGS-community n o w estimated to be at least 6000 strong. There had been one previous attempt to give a historical perspective of EGS 2 . However, this article was very brief and did not convey the large e ort that went i n to the development of EGS. In this report the historical section on EGS4 as well as the summary of EGS3 to EGS4 conversion and the overview of EGS4 was taken directly from the EGS4 manual 3 . This is done for completeness only. The EGS4 manual gives much more detail and ought to be referred to for technical details. Finally, recent improvements to EGS4 are listed herein and represent the rst time that this information is available in one place. The reader should consult the references cited in this report for more details regarding motivation and implementation.1.1 Before EGS The Monte Carlo method was originally suggested by Ulam and von Neumann 4 , and was rst used by Goldberger 5 in order to study nuclear disintegrations produced by high-energy particles. The rst application of the Monte Carlo technique to study shower production was done by Wilson 6 . Wilson's approach w as a simple graphical-mechanical that was described as follows:The procedure used was a simple graphical and mechanical one. The distance into the lead was broken into intervals of one-fth of a radiation length about 1 mm. The electrons or photons were followed through successive intervals and their fate in passing through a given interval was decided by spinning a wheel of chance; the fate being read from one of a family of curves drawn on a cylinder: : :A word a b out the wheel of chance; The cylinder, 4 in. outside diameter by 12 in. long is driven by a high speed motor geared down by a ratio 20 to 1. The motor armature i s h e avier than the cylinder and determines where the cylinder stops. The motor was observed to stop at random and, in so far as the cylinder is concerned, its randomness is multiplied by the gear ratio: : : " from R. R. Wilson, op. cit.Although apparently quite tedious, Wilson's method was still an improvement o v er the analytic methods of the time|particularly in studying the average behavior and uctuations about the average 7 . HISTORY & O VERVIEW OF EGS4 2The rst use of an electronic digital computer in simulating high-energy cascades by Monte Carlo methods was reported by Butcher and Messel 8, 9 , and independently by V arfolomeev and Svetlolobov 10 . These two groups collaborated in a much publicized work 11 that eventuall...

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