# Ba-133 neutron capture

1. Feb 21, 2008

### GammaScanner

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.

2. Feb 22, 2008

### vanesch

Staff Emeritus
3. Feb 22, 2008

### GammaScanner

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

4. Feb 27, 2008

### vanesch

Staff Emeritus
Mmm, I would say that you still have the difference in nucleus densities:

You will reach equilibrium when you "burn" as much Ba-133 as you make, so you will reach equilibrium when:

flux x N(Ba-132) x 9 barn = flux x N(Ba-133) x 4 barn or

N(Ba-133) = 9/4 N(Ba-132)

In other words, unless you had the ambition to turn ALL of your Ba-132 into Ba-133, if you want just trace amounts, that should still be ok.

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.

5. Feb 27, 2008

### daveb

If you're specifically trying to make Ba-133, that may not be the way to go. From the Radiological Health Handbook, the primary method of Ba-133 production is a Cs133(p,n)Ba133 reaction. If you just want to make something in the reactor, use something with a large cross section.

6. Feb 27, 2008

### GammaScanner

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). And the cost of barium enriched in Ba-132 at$90 per mg was nothing to sneeze at either (not being a national lab). Doubling the amount of Ba-132 would cut the time in half (increasing Ba-132 cost from $9,000 to$18,000 though), but I had some volume constraints for the source size.

I can see why all the commercial isotope vendors seem to have 10mCi Ba-133 as an upper limit of activity. What's driving this is an industrial gaging application where I need a source of modest energy gammas. Cs-137 @ 662 KeV is way too high, Co-57 @ 122/136 KeV is fine, but the half life of 270 days is a nuisance in a machine that might be used for 20 years. Ba-133 with gammas ~ 300 KeV was a bit higher in energy than wanted, but the 10.5 year half life was useful.

Looks like I'll be sticking to Co-57, but it's interesting to look for other isotopes with low energy gammas, with a half life long enough to be useful, but short enough to get decent activity from a small volume.

For example, Rh-101 has 3.3 year half life and plentiful gammas @ 127 KeV and 198 KeV. But it doesn't look like it could be produced in a reactor (other than as a fission product). However, it might be made in an accelerator from Ru-100 + p -> Rh-101, but then Rh-101 + p -> Pd-102 which is stable + p -> Ag-103, etc. etc. and tables of proton capture seem not very comprehensive, for a reason I'm sure.

7. Feb 28, 2008

### vanesch

Staff Emeritus
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).

Did I make a stupid mistake somewhere ?

8. Feb 28, 2008

### GammaScanner

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

9. Feb 29, 2008

### vanesch

Staff Emeritus
Uh, yes, *9* barn. I took erroneously the *4* barn of Ba-133