[fluka-discuss]: Photofission cross section of Uranium

From: Felix Ernst Horst <felix.ernst.horst_at_kmub.thm.de>
Date: Thu, 05 Mar 2015 15:31:48 +0100

Dear FLUKA experts,

We carried out an experiment where we irradiated uranium samples
(natural isotope composition) with bremsstrahlung photons from a
clinical 18 MeV electron accelerator. We have then determined the
fission yield by quantitative gamma spectrometry (actually we measured
I-131 and calculated from its activity to the integral fission yield).

We have modelled that accelerator in FLUKA. Its output is expressed in
monitor units and due to an additional simulation of the monitor
ionization chamber calibration situation with a water phantom we are
able to convert the FLUKA results normalized per primary electron into
results normalized per monitor unit.

When i fold the photon spectrum obtained by USRTRACK with the
photofission cross section of U-238 (from "A. V. Varlamov et al., Atlas
of Giant Dipole Resonances (1999)") i come very close to the
experimentally determined fission yield value (fissions per gramm
uranium per monitor unit) while the fission yield i scored with RESNUCLE
is about a sixth of the measured value. I checked my normalization to
the volume and density and could not find any errors there.

Is such a large underestimation by FLUKA possible or could there be
another explanation?

And can i trust the cross sections for other photonuclear reactions such
as neutron disintigration from lead or tungsten?

Thank you and regards!


Felix Horst, B.Sc.
Institut für Medizinische Physik und Strahlenschutz (IMPS)
Technische Hochschule Mittelhessen
Wiesenstr. 14, 35390 Gießen
Raum D10.12a
Telefon: 0641 309 2642
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Received on Thu Mar 05 2015 - 17:10:23 CET

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