Re: Photonuclear reactions

["Jim Hardeman" <Jim_Hardeman@mail.dnr.state.ga.us>]

Perhaps "Denbo" might have been using the term "X-ray" to include such activities as industrial radiography, which would, in fact, utilize gamma energies sufficient to lead to (gamma, n) reactions, if the information below is correct. I can't imagine, however, how recently radiographed metal would make it into the scrap metal stream in a short enough time to observe the short-lived radionuclides that might have been formed. More likely sources in scrap metal would be (a) accumulation of NORM inside piping, pumps, etc., or (b) electrostatic deposition of radon daughters.

Jim Hardeman
Jim_Hardeman@mail.dnr.state.ga.us

>>> Jacques.Read@eh.doe.gov 8/17/2000 7:05:44 >>>


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






************************************************************************
The RADSAFE Frequently Asked Questions list, archives and subscription
information can be accessed at http://www.ehs.uiuc.edu/~rad/radsafe.html

************************************************************************
The RADSAFE Frequently Asked Questions list, archives and subscription
information can be accessed at http://www.ehs.uiuc.edu/~rad/radsafe.html