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It is possible to use a high energy electron accelerator to transmute
Mo-100 to Mo-99 via (e-, n) or (ɤ, n) as cited by Danon, Block and
Harvey:
The use of a gamma convertor is shown to provide a higher efficiency than
the 30 MeV electrons.
This TRIUMF paper by Thomas Ruth cites using high energy electron
cyclotrons to provide the gamma, and lower energy proton cyclotrons for (p, 2n)
for Mo-100 to Tc-99m.
So, I expect that the press release was correctly quoted for the high
energy electron case.
In the early 1990s I worked on the 10 MeV 50 kW electron IMPELA prototype
accelerator at Chalk River ( http://www.iotron.com/impela-technology/impela-accelerators/
). (100 mA beam current, 5% duty cycle).
After endurance tests we monitored the gamma spectrum from the SS beam stop
tank and found Mo-99 and Tc-99m (among other radionuclides). With other
supporting evidence our team nuclear physicist determined that the electrons
produced gamma, (ɤ, n) on iron provided neutrons that were thermalized in
the water filled beam stop and then captured by Mo-98 (24% natural abundance as
opposed to only 9.8% for Mo-100). Mo was not a listed in the recipe for the SS
so was present only in trace amounts. (The fields at the beam stop surface were
only a few mr/h when the accelerator was shut down.) So, it is possible to make
tiny amounts of these radionuclides without even trying.
Electron accelerators are a much more forgiving technology than proton
accelerators. Electron cyclotrons produce a “continuous” current with values up
to hundreds of microamps (the electrons are accelerated across the cyclotron D
gaps only in half of the rf phase). The centripetal acceleration of the
electrons leads to radiative losses.
Bryan
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