During the early years of Stanford Linear Accelerator Center (SLAC), many shielding studies were done to verify or modify shielding equations in existence at that time for high-energy electron accelerators. Many, if not most, of those formulae had only limited experimental verification, especially shielding from radiation produced by electron beams with energies greater than a few hundred MeV. As experimental verification proceeded, and as sophisticated Monte Carlo simulations emerged, both at SLAC and at other electron accelerators around the world, we realized that incorporating the results into a fairly simple computer program was the logical next step, and so the SHIELD code was born. Over a period of many years, SHIELD was modified and refined and received fairly broad dissemination to high-energy electron laboratories and synchrotron light sources. However, documentation of the code, now called SHIELD11 after much iteration, was absent.
SHIELD11 documentation is now available in the form of a SLAC report (SLAC-R-737) which
Included in the appendix of SLAC-R-737 is the physics involved in the five-component model that we developed; namely, the production and attenuation of the radiation emanating from a thick target when struck by a high-energy electron beam. Hopefully this will aid those who use SHIELD11 to assure that the code is used properly--i.e., with an understanding of its strengths and, especially, its limitations. To facilitate this, a complete listing of the Fortran77 code is given at the end of the report. We believe strongly in producing code that is "self documenting" and we hope we have accomplished this by providing a lot of commentary within the code.
The SHIELD11 code and its documentation have been placed on an anonymous-ftp site at SLAC that can be accessed by using a browser (e.g., Microsoft Internet Explorer) with the following address:
The following two files have been placed in this directory:
Both can be downloaded to your computer by right-clicking with your mouse and selecting (for example) the "Copy to Folder" option.
The second file provides instructions on how to uncompress the shield11.tar.gz file into its directory structure for running with a Fortran77 compiler. The README file in the main directory explains the directory structure and the files therein. The SLAC-R-737 report itself is located in the subdirectory called "/documentation" in the form of a portable document format (PDF) file (or an equivalent postscript file).
SLAC-R-737 was written with the following three ideas in mind:
The descriptions and examples given in this report are meant to serve as guides for using SHIELD11 and, while not complete, will at least aid users in adapting the abilities of the code to their own particular needs.
It should be noted that Monte Carlo codes, such as EGS, FLUKA, and MCNP, while more universal and complete, are most often quite time consuming. When using such codes, the user should first do back-of-the-envelope calculations which SHIELD11 provides. The accuracy and/or precision of SHIELD11 may not be as good as the more rigorous Monte Carlo methods, yet still should be, and often have been shown to be, good enough for most shielding studies, since uncertainties in beam targeting, materials, angles, and especially beam loss, usually are greater than any imprecision in the SHIELD11 code itself.
Finally, we note that new experiments and Monte Carlo studies can provide the means for improving the models which are employed in SHIELD11, and we encourage our accelerator health physics colleagues to continue in this effort.