UNRESTRICTED | ILLIMITÉ And I believeit should be “high energy protons”, not electrons, that are used to spallate neutrons from Mo-100. Good point about questioning the necessity to enrich the Mo, Jaro. As Bill said, I expect there must be a bunch of unwanted reactions . Side topic: Bill, thanks for getting the CANTEACH web site updated. Much nicer to work with. What a pile of CANDU documentation!! Morgan Brown, P.Eng., FCNS Research Engineer brownmj@aecl.ca From: cdn-nucl-l-admin@mailman1.cis.McMaster.CA [mailto:cdn-nucl-l-admin@mailman1.cis.McMaster.CA] On Behalf Of Garland, Bill [Internet] Jaro, Why does the Mo target have to be isotopically pure Mo-100 ? In the end it will be cost that decides, methinks, which is tied to yield among other things. A retired prof at McMaster (Dick Tomlinson) figured out how to irradiate a pure target in the Mac reactor to make Mo-99 directly and separate out the Mo-99 and recover the expensive target for reuse. The process worked and did an end run around the use of enriched U and fission product waste. I don't know the details of the process or whether the yield was sufficient for commercialization. Good idea though. Bill At 06:13 PM 21/02/2012, Brown, Morgan wrote: UNRESTRICTED | ILLIMITÉ There are several news articles this week describing the possibility of using cyclotrons for mass producing Mo-99 rather than the current reactor-based method (which generates Mo-99 as a fission product). I asked a colleague (a radiochemist) about the different processes; hopefully the following comments correctly reflect his comments. A cyclotron can be used to irradiate Mo-100 with high-energy electrons, which knock off (spallate) a neutron from the Mo-100 and leave radioactive Mo-99 behind. Mo-99 has a 2.75 day half-life, decaying to Tc-99m. It is the Tc-99m (“m” for meta-stable) which decays (6.0 hours half-life) and gives off a gamma useful for medical imaging. The resulting decay product Tc-99 is also radioactive, with a half-life of 213,000 years (Tc-99 decays to stable ruthenium-99). While Mo-100 is “a naturally occurring” isotope, it must be enriched from natural molybdenum (which is a mixture of seven stable or very-long-lived isotopes). Mo-100 represents 9.63% of natural Mo. and is the heaviest of the isotopes. Since there is a mass gap of 2 neutrons between Mo-100 and Mo-98 (the next isotope in naturally-occurring Mo), it makes it a bit easier to separate Mo-100 in a cyclotron (note that U-238 and U-235 are separated by a mass of 3 neutrons, and can be separated in a cyclotron, but the higher masses make the difference smaller on a fractional basis). Does anyone know if the Mo-100 will be (or can be) recycled into new targets after the Tc-99m is extracted? One only needs small amounts of Mo-99 to produce enough Tc-99m (according to Wikipedia, “a few micrograms of Mo-99 can potentially [be used to] diagnose ten thousand patients”). Thus there is no need to produce massive quantities of Mo-100, although there would be an optimum amount of irradiation of the Mo-100 targets. As the irradiation occurs, Mo-99 is produced and some will start to decay to Tc-99m. As irradiation continues, radioactive decay and spallation of the already-produced Mo-99+Tc-99m will then cause the loss of some of these nuclides (plus there are now fewer remaining target Mo-100 atoms). Anyone know the optimum fraction of Mo-100 to be consumed in a target before it is sent to processing? In a fission reactor (the current primary source), Mo-99 is primarily produced as a fission product of thermally-fissioned U-235. A Mo-99 atom is produced in 6.1% of all U-235 fissions (this is almost at the peak of one of the U-235 FP production peaks, and one of the Pu-239 FP peaks. See http://en.wikipedia.org/wiki/File:ThermalFissionYield.svg ). According to http://atom.kaeri.re.kr/ton/nuc5.html (type in Mo-99 in the “Nuclide” input box), Mo-99 is produced in 5.7 to 6.1% of fissions (thermal and fast) of U-235 and Pu-239, and in 6.2% of fast fissions of U-238. Strictly speaking, the above fission product yields are for the accumulated production of Mo-99 from all the 99 AMU (atomic mass unit) direct fission products that decay to Mo-99. Several 99 AMU nuclides are produced directly by fission, but they tend to have very short half-lives (ms to s) as they beta decay. Mo-99, with a much longer half-life (2.75 days) thus builds up in the radionuclide inventory from the very-short-half-life 99 AMU FPs. Again according to http://atom.kaeri.re.kr/ton/nuc5.html, the direct production of Mo-99 as an FP is 2 to 4 orders of magnitude less than the accumulated production (i.e., the summation of all the short-lived 99 AMU precursors that decay to Mo-99). High enrichment uranium targets are typically used for Mo-99 production in a reactor. This is so that reasonable amounts of Mo-99 can be produced prior to being lost to decay, and the concentration in the target matrix is high (i.e., relatively little waste). With lower enrichment or natural U targets, the Mo-99 concentration would be much lower than in highly enriched targets and more waste (3-4 times?) is produced. The proof of the proposed cyclotron process will be in the success of long-term Mo-99 production capability and cost of using cyclotrons. New finding may solve isotopes shortage National Post 21 February 2012 Margaret Munro Postmedia News Canadian scientists have shown they can make radioactive medicine without nuclear reactors, a new process that could go a long way toward solving the world's shortage of medical isotopes. The process uses hospital cyclotrons to make the compounds, bypassing the need for reactors. "It's essentially a win-win scenario for health care," Dr. Francois Benard of the B.C. Cancer Agency told a news conference Monday at the annual meeting of the American _______________________________________________ cdn-nucl-l mailing list cdn-nucl-l@mailman.McMaster.CA http://mailman.McMaster.CA/mailman/listinfo/cdn-nucl-l _______________________________________________ cdn-nucl-l mailing list cdn-nucl-l@mailman.McMaster.CA http://mailman.McMaster.CA/mailman/listinfo/cdn-nucl-l |
