Re: Photonuclear reactions

[Tad Blanchard <Tad.M.Blanchard.1@gsfc.nasa.gov>]

Just to clarify something in the article.  Marshall Space Flight Center (MSFC) only uses standard industrial xray techniques for metals inspection (ie, 250 KvP).  The metals "Denbo" was referring to evidently didn't come from MSFC.

Also, the vacuum gage (sometimes referred to as an "Alphatron") that almost got away contained Radium-226 (~500 micrograms) and was not regulated by the NRC.  We used to possess some of these at Goddard Space Flight Center and they were all replaced with electronic vacuum detection devices.  The alphatron gages are easily detected.  I seem to recall 40 Mr/hr on contact with them.



At 09:46 AM 8/18/00 -0500, you wrote:
>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
>
>
************************** /^\   /^\ ***********************************
Tad Blanchard             /___\ /___\   NASA-Goddard Space Flight Center
Ass't Rad Safety Officer       O         Code 205.9, Greenbelt, MD 20771
Parallax, Inc                 / \                    Phone: 301-286-9157
A Member of the OHI Team     /___\                   Fax:   301-286-1618
               mailto:tmblanch@pop200.gsfc.nasa.gov
************************************************************************ ************************************************************************ The RADSAFE Frequently Asked Questions list, archives and subscription information can be accessed at http://www.ehs.uiuc.edu/~rad/radsafe.html