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Re: [cdn-nucl-l] New finding may solve isotopes shortage
Why does the Mo target have to be isotopically pure Mo-100 ?
....in the end, it's the Tc-99m that is separated chemically, so it shouldn't matter how much Mo it's separated from, and whether it's pure Mo-99 or not, right ?
On Wednesday, February 22, 2012, Bill Garland wrote:
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.
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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
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
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
21 February 2012
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