RE accelerator question

["Ryder, Roy" <R.Ryder@dl.ac.uk>]

These reactions occur as a secondary process in the
electromagnetic cascade from high energy electrons.
Photons are first produced by repeated bremmstrahlung,
pair production, positron annihilation etc.

The excitation function of all photonuclear reactions
shows a series of three resonance peaks.

The lowest occurs at photon energies of 25 MeV for light
nucleii and14-15 MeV for heavy. This peak is large and is
often known as the 'giant resonce'. The emitted neutrons have
 energies from about 1 to 12 MeV. This is a prolific reaction
emitting about 1 neutron per three incident electrons.

The next peak is the pseudo-deuteron reaction  for electrons
between 80 and 300 MeV. In this model, it is assumed that the
photon is absorbed by a deuteron (proton-neutron pair) in
the nucleus and that the deuteron then disintegrates. The
emitted neutrons have energies about 30 MeV depending
on the atomic number of the nucleus. The neutron production rate
is about 1000 times lower than the giant resonance reactions.

The third peak occurs above the meson production threshold
of 200 MeV and is known as the photopion reaction. In the high
enegry limit the cross section has been calculated and
verified by measurement to be about 120 +/- 40 mb. The
 production rate is about one neutron ( of energy from 100 MeV
to the energy of the incident electron) per 100 electrons. This
reaction dominates accelerator shielding calculations because
of the penetrating neutrons (which can initiate the hadron cascade)

For a good reference use Induced Radioactivity by M Barbier
or contact me by e-mail for further details.

Roy Ryder


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From: radsafe
To: Multiple recipients of list
Subject: Accelerator Question
Date:  11 October 1994 08:18

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          In reading a report on accelerator health physics, I have
          come across a term that I can not find in any of my
          references.  They refer to the pseudodeuteron process at
          electron accelerators in the 30 to 150 Mev range.  Can
          anyone define this for me or give me an example?  Thanks in
          advance.