History overview and recent improvements of EGS4

Abstract:  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 byFord and Nelson in that original document. Moreover, the EGS3 manual is now out-of-print and this history mighthaveeventually been lost to the ever-burgeoning EGS-communitynow 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 wentinto 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.