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From: Giuseppe Battistoni <giuseppe.battistoni_at_mi.infn.it>
Date: Wed, 10 Jul 2013 09:58:08 +0200

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To: "Maruyama, Takashi" <tvm_at_SLAC.Stanford.EDU>
CC: "fluka-discuss_at_fluka.org" <fluka-discuss_at_fluka.org>
Subject: Re: pair production
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Dear Takashi
FLUKA contains an original algorithm which originates from the
theoretical report of Y.S. Tsai of 1974:
Pair production and bremsstrahlung of charged leptons
Rev. Mod. Phys. 46, 815-851 (1974)
Erratum: Rev. Mod. Phys. 49, 421-423 (1977)
(the erratum of 1977 is essential!)

In addition (but probably not relevant for the features that you are
eploring): the Landau-Migdal-Pomeranchuk density-dependent suppression
effect has been introduced (noticeable only at very high energies).

L.D. Landau, I.Ya. Pomeranchuk
         The limits of applicability of the theory of bremsstrahlung by
         electrons and of creation of pairs at large energies (In Russian)
         Dokl. Akad. Nauk SSSR 92, 535-536 (1953)
         Collected papers of L.D. Landau, Pergamon Press, Oxford 1965,
         p. 586-588

L.D. Landau, I.Ya. Pomeranchuk
         Electron-cascade processes at ultra-high energies (In Russian)
          Dokl. Akad. Nauk SSSR 92, 735-738 (1953)
          Collected papers of L.D. Landau, Pergamon Press, Oxford 1965,
          p. 589-593

A.B. Migdal
          Bremsstrahlung and pair production in condensed media at high
          Phys. Rev. 103, 1811 (1956)

A.B. Migdal
          Bremsstrahlung and pair production at high energies in condensed
          Zh. Exp. Teor. Fiz. SSSR 32, 633-646 (1957)
          Sov. Phys. JETP 5, 527-536 (1957)

        Giuseppe Battistoni

On 07/09/2013 01:17 AM, Maruyama, Takashi wrote:
> We have large angle pair production data from 5.5 GeV brems photons, where pairs are detected at more than 20 mrad, and we are comparing data and simulation. In pair production, four variables, typically Energy(e+), Theta(e+), Theta(e-), and Phi, are necessary to specify the final state. Since it is not trivial to sample from a four-variable function and photoproduction takes place at a very small angle, various approximations are used. Both EGS5 and Geant4 assume Phi=180 deg. Geant4 assumes Theta(e+)=Theta(e-), while EGS5 treats Theta(e+) and Theta(e-) independently. Both EGS5 and Geant4 assume no correlation between Energy and angle. The double rate, where both e+ and e- are scattered more than 20 mrad, is very sensitive to the approximation used in simulation. Fluka seems to yield best agreement with data. I am looking for the function that Fluka uses to simulate pair production, and any approximations used. I cannot find Physics Reference Manual in Fluka web site.
> Takashi Maruyama
Received on Wed Jul 10 2013 - 11:08:07 CEST

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