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Re: Photonuclear reactions
I once discovered unexpected activation in a cyclotron target room where an electron
beam experiment had been running. The cause turned out to be photoneutrons from hi
energy bremsstrahlung.
The opinions expressed are strictly mine.
It's not about dose, it's about trust.
Bill Lipton
liptonw@dteenergy.com
Jacques.Read@eh.doe.gov wrote:
> 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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