Re: Photonuclear reactions

[Jacques.Read@eh.doe.gov]

Somebody cited:

 "Denbo said some metals that have been recently X-rayed can
  also set off the detectors."

The binding energy of a nucleon in a nucleus is of the order of  8 MeV, so a
several MeV gamma ray can create a radionuclide by (gamma,n) reactions.  In
addition, a few dozen common stable isotopes have low-lying metastable states
that can be formed by photon bombardment, which either decay back to the stable
ground state,  re-emitting the photon that formed them via IT, or beta-decaying.
The existence of these metastable states is the basis for the X-ray lasers that
the air force is doing research on.   I don't have any ready access to
cross-section data for looking up possible candidates, but bear in mind that the
physical properties that cause metastable states to have half-lives long enough
to meet Denbo's description involve a spin such that transition to the ground
state is "forbidden."  In general that means that the X-ray capable of creating
a long-lived metastable state must have an energy of at least many tens of kev.
Again, I don't have any knowledge of what X-ray machines are used for
sterilization or baggage-inspection, but I would doubt that any used energies
vastly above the K-shell of the major elements in common materials.

Examples are:
Osmium-190m, 10 minute half-life, 190 kev
Silver-107m, 44 sec.,93 kev
Silver-109m, 41 sec., 88 kev
Rhodium-103m, 57 min.,40 kev
Selenium-77m, 19 sec, 162 kev






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