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                Fax 0298-64-1993


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　Liseserver を介して流されて来た情報で有益と思われたものをお知らせします。

Subject:      Bremsstrahlung modeling within EGS4

     I am currently trying to carry out some beta dosimetry calculations
     using EGS4.
     In order to validate EGS4 in this context, I have generated
     bremsstrahlung spectra, by sending beta particles through a layer of
     lead and a low z material and then swapped the order of the two
     materials.  I have compared the spectra with some measured pulse
     height distributions (PHDs) and found the shapes quite dissimilar. 
     In particular the EGS4 spectra peak at a far higher energy then the
     measured PHDs. The size of the two EGS4 generated spectra compared
     with each other agrees with the relative sizes of the two measured
     PHDs. I do not think that the difference in shapes between the
     calculated spectra and measured PHD is due to measuring instrument's
     energy response, but I may have to look into this aspect in more
     detail.

     Has anyone documented a problem with either bremsstrahlung spectra
     generation or the absorption of low energy photons in lead?

     Does anyone use a method, other the the EGS4 default version, for
     generating bremsstrahling?


In response to David Spencer's request about brem modelling in EGS4.

There are several comments to be made.

1) At high energies there has been extensive benchmarking (10 to 30 MeV)
   which is reported in the following series of papers:
   Title: Forward Directed Bremsstrahlung of 10 -- 30 MeV Electrons 
          Incident on Thick Targets of Al and Pb
   Authors: B.A. Faddegon, C.K. Ross and D.W.O. Rogers
   Source: Medical Physics  17, Year: 1990, Pages: 773 -- 785

   Title: Angular distribution of bremsstrahlung from 15 MeV electrons 
          incident on thick targets of Be, Al and Pb
   Authors: B.A. Faddegon, C.K. Ross and D.W.O. Rogers
   Source: Medical Physics  18, Year: 1991, Pages: 727 -- 739

   Title: Comparisons of thick-target bremsstrahlung calculations by 
          EGS4 and ITS
   Authors: B.A. Faddegon and D.W.O. Rogers
   Source: Nuc. Inst. Meth.  A 327, Year: 1993, Pages: 556 -- 565

2) At lower energies, and even at these higher energies it is essential
   to use two modifications of EGS4, one in the brem cross sections and
   the other in the angular sampling - these are both part of the 
   standard EGS4 distribution for the last few years.  They are 
   described in:

   Title: Use of ICRU-37/NBS Collision Stopping Powers in the EGS4 
          System
   Authors: S. Duane, A.F. Bielajew and D.W.O. Rogers
   Source: NRCC Report PIRS-0177, Ottawa, March, Year: 1989

   Title: Use of ICRU-37/NBS radiative stopping powers in the EGS4 
          system
   Authors: D.W.O. Rogers, S. Duane, A.F. Bielajew and W.R. Nelson
   Source: National Research Council of Canada report PIRS-0177, 
           Year: 1989

   Title: Improved bremsstrahlung photon angular sampling in the EGS4 
          code system
   Authors: A.F. Bielajew, R. Mohan and C.S. Chui
   Source: National Research Council of Canada Report  PIRS-0203, 
           Year: 1989

This latter document also discusses brem splitting which is essential
for low energy calculations.

3) At low energies, EGS4 will not work to the extent that electron
   impact ionization is important - a fair amount of the fluorescence 
   is from impact ionization, and thus EGS4 underestimates it.  We have
   studied this somewhat and reported the results at a meeting but have 
   never published the results.

   Title: Low-energy x-ray production studies using the EGS4 code system
   Authors: Y. Namito, W.R.Nelson, S.M. Seltzer, A.F. Bielajew and 
            D.W.O. Rogers
   Source: Med. Phys. 17, (abstract), Year: 1990, Pages: 557

Dave Rogers
dave@irs.phy.nrc.ca

＜ＥＧＳ４を用いた研究の紹介＞

下記の論文が出版されました。興味をお持ちの方は、ご連絡頂ければ
別刷りをお送りします。
Y. Namito, S. Ban, H. Hirayama, N. Nariyama, H. Nakashima, Y. Nakane,
Y. Sakamoto, N. Sasamoto, Y. Asano, and S. Tanaka: Compton scattering of 
          20- to 40-keV photons, Phys. Rev. A 51, 3036-3043 (1995).

Y. Namito, S. Ban and H. Hirayama: Implementation of linearly-polarized 
          photon scattering into the EGS4 code", Nucl. Instrum. and Meth. 
          A 332,277-283 (1993).

Y. Namito, S. Ban and H. Hirayama: Implementation of the Doppler 
          broadening of a Compton-scattered photon into the EGS4 code, 
          Nucl. Instrum. and Meth. A 349, 489-494 (1994).

                                                   高エネルギー物理学研究所
                                                                 波戸　芳仁
                                                  e-mail: qv04@kekcc.kek.jp
                                                       namito@kekrc3.kek.jp
                                                           fax:0298(64)1993

K. Shin and H. Hirayama: A new Approximating Model for Gamma-Ray Buildup
          Factors of Stratified Shield
          Nucl. Sci. Eng. 118(1994)91-102.

T. Torii: Ionization efficiency of a gas-flow ion chamber used for 
          measuring radioactive gases by Monte Carlo simulation
          Nucl. Instr. Methods A356(1955)255-263.

S. Moriyama and M. Minowa: The 17 keV neutrio and search for anomalous
          γ rays in 35S decay
           Physics Letter B347(1955)152-157.

A. Endo: Calcualtion of Air Activation in an Electron Linac Facility 
           using the EGS4 Code System, JAERI-Tech 95-004(1995).