A computer program and data base are presented which can be used to calculate, with a personal computer, photon cross sections for scattering, photoelectric absorption and pair production, as well as total attenuation coefficients, in any element, compound or mixture, at energies from 1 keV to 100 GeV.A convenient alternative approach is to generate the cross sections and attenuation coefficients for compounds and mixtures as needed, using a personal computer. This paper describes a computer program called XCOM which carries out this task quickly on IBM-compatible personal computers, for any element, compound or mixture, at energies between 1 keV and 100 GeV. The program makes use of a database of cross sections for the elements that is stored in compressed form on a single floppy disk.The XCOM program can generate cross sections on a standard energy grid (spaced approximately logarithmically), or on a grid selected by the user,

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Tabulations are presented of the atomic form factor, F(x,Z), and the incoherent scattering function, S(x,Z), for values of x (=sin (IJ/2)/X,) from 0.005 A-I to 10 9 A-1, for all elements Z=l to 100. These tables are constructed from available state-of-the-art theoretical data, including the Pirenne formulas for Z = 1, configuration-interaction results by Brown using Brown-Fontana and Weiss correlated wavefunctions for Z=2 to 6, non-relativistic Hartree-Fock results by Cromer for Z=7 to 100, and a relativistic K-shell analytic expression for F(x,Z) by Bethe and Levinger for x> 10 A-I for all elements Z =2 to 100. These tabulated values are graphically compared with available photon scattering angular distribution measurements. Tables of coherent (Rayleigh) and incoherent (Compton) total scattering cross sections, obtained by numerical integration over combinations of F2(X.z) with the Thomson formula and S (x,Z) with the Klein-Nishina formula, respectively, are presented for all elements Z= I to 100, for photon energies 100 eV (1..=124 A)lto 100 MeV (0.000124 A). The incoherent scattering cross sections also include the radiative and double-Compton corrections as given by Mork. Similar tables are presented for the special cases of terminally-bonded hydrogen and for the H2 molecule, interpolated and extrapolated from values calculated by Stewart et al. and by Bentley and Stewart using Kolos-Roothaan wavefunctions.

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The Evaluated Photon Data Library, 1997 version (EPDL97), is designed for use in photon transport calculations at Lawrence Livermore National Laboratory. This library includes photon interaction data for all elements with atomic number between Z = 1 (hydrogen) and 100 (fermium), including: photoionization, photoexcitation, coherent and incoherent scattering, and pair and triplet production cross sections. For use in applications data is provided for all elements over the energy range 1 eV to 100 GeV. This report documents the sources and treatment of the data included in this library. EPDL97 completely supersedes the earlier 1989 version of EPDL and it is highly recommended that users only use the most recent version of this library. UCRL-50400,Vol. Rev. 51 EPDL97 UCRL-50400, Vol. 6. Rev. 5 EPDL97