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GammaScanner
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Anybody have good values and a source for thermal neutron capture cross section for Ba-133, both ground and excited states? CRC Handbook gives 4 barns, but wanted to verify it. Thanks.
vanesch said:Looks like it is about 4 at 0.025 eV:
http://www.nndc.bnl.gov/sigma/index.jsp?as=133&lib=endfb7.0&nsub=10
GammaScanner said:Thanks! Good table. Cross sections for all the energies is a plus. Was looking at making some 100 mCi Ba-133 sources from enriched Ba-132 in reactor. But with Ba-132 at about 9 barns you don't make much, and with Ba-133 not much smaller at 4 barns, you lose a lot of the Ba-133 you do make. Takes a LOT of neutrons. Thanks again. - Ed
vanesch said:Or still in other words, if there are many more Ba-132 around than Ba-133, the probability for a neutron to be captured by the Ba-132 is still way higher than the probability for it to destroy a Ba-133, so you should win by neutron irradiation.
GammaScanner said:That's the thing I love about this stuff - scientific notation. The equilibrium ratio 9 to 4, is way more to us, but when we're talking 1.2 10E20 atoms of Ba-132 (in 100 mg Barium carbonate enriched to 40%, natural Barium has only .1% atoms of Ba-132) that gets us to 2.7 10E20 which just doesn't seem to be way more with all those zeros.
The folks at MURR (Missouri U Research Reactor) estimated it would take 5 weeks of irradiation in their hi flux neutron nook (4 10E14 n/s/cmE2) to get 100 mCi of Ba-133 from our 100 mg starting sample, at a cost on the order of $100,000 (if we could get the time, doubtful).
vanesch said:Mmm. I have slightly different numbers:
100 mg Ba with 40% of Ba-132 gives me 1.8E20 Ba-132 atoms
An activity of 100 mCi (3.7E9 Bq) of Ba-133 with a half-life of 10.52 years (3.32E8 seconds) gives me 1.77E18 atoms of Ba-133 that you want to obtain.
Now, irradiating 1.8E20 atoms of Ba-132 at a cross section of 4 barn with a flux of 4E14, will give me a needed time (not including capture by Ba-133):
time = 1.8E18 / {4E14 x 1.8E20 x 4E-24}= 6.1E6 seconds, or 71 days.
So how did they get to 5 weeks ? I find 10 weeks (sundays included).
GammaScanner said:Raw material is barium carbonate, BaCO3, 196g/mole hence the 1.2E20 atoms of Ba-132, which makes it even longer. 1.77E18 of Ba-133 is what I had.
Cross section for Ba-132 is 9 barns which would give the 5 weeks (they run 6.5 days a week from what I understand), not counting the conversion of Ba-133 to Ba-134 which I'd think would be significant
The neutron capture cross section of an element is a measure of its ability to capture neutrons and form new isotopes. In the case of Ba-133, its cross section is important for understanding the behavior of this isotope in nuclear reactors and other nuclear applications.
The thermal state refers to the energy level of the neutrons being absorbed, which is typically around 0.025 eV. Excited states, on the other hand, refer to higher energy levels where neutrons may have energies of 1 eV or more. The cross section for neutron capture in these excited states may be different from the thermal cross section.
The cross section is determined through experimental measurements using neutron sources and detectors. These experiments involve bombarding Ba-133 with neutrons of different energies and measuring the resulting neutron capture rate. The data is then analyzed to determine the cross section at various energy levels.
The cross section can be influenced by factors such as temperature, energy of the neutrons, and the presence of other elements or isotopes. Additionally, the nuclear structure of Ba-133 can also play a role in determining the cross section.
The cross section of Ba-133 is important for understanding the behavior of this isotope in nuclear reactors and other nuclear applications. It can affect the stability and efficiency of nuclear reactions, as well as the production of other isotopes through neutron capture. Therefore, a thorough understanding of the Ba-133 cross section is crucial for safe and efficient operation of nuclear systems.