In the wake of Jon R.'s fantastic twofer and synthesis of technetium, this is a bit of a sideshow. Carl's Jr. itself is in good shape for isotope synthesis even if the power supply still has odd issues (this time it's my new transformer--it needs different core material).
Europium appears to be very easy to activate. The activation target is a 5g plastic baggie of natural europium oxide, Eu2O3. Neutron irradiation took place for 10.2 min. in my flux trap about two weeks ago. As usual for me at the power level in use, the run ended because of a power supply failure (cracked trannie core). Conditions before that were 70 kV at 12 mA.
The baggie was immediately counted on my 2x2 NaI for 6000 sec. Background taken two days later, baggie still in place, was subtracted. The spectrum calibration is rather iffy...the only sources of calibration being Am-241 and some spectral features from Cs-137.
The induced gamma-emission activity at ~ 120 keV seems to be the 122 keV emission from Eu-152m1. The activity is definitely long-lived--I kept trying to take acceptable background counts commencing immediately after finishing the hot count, and found that the peak persisted noticably for more than a day. Eu-152m1 has a half-life of 9.3 hr., which is consistent. The other (but less-expected) possibility is that it is 46-min. Eu-154m which emits at 101 keV. The expected peak at 68 keV is not also present in strength, though, so I am inclined to dismiss this possibility. Realistically the big wide peak is probably a combination of both a large amount of Eu-152m1 and a little amount of Eu-154m. I consider this to be an unfinished experiment both because of the unwanted early shutdown and because Eu-152m1 also emits some high-energy gammas with better frequency than the 122 keV which I was not prepared to measure in this experiment.
Thermal neutron capture cross-sections also support this being (mainly) Eu-152m1:
Eu-151(n,g)Eu-152m1: 3300 b
Eu-153(n,g)Eu-154m: 330 b
Maybe the next time I nuke this bag, I should just airmail it to Jon for HPGe analysis? After all, the half-life is quite long.
-Carl
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2007-07-14 00:04 Activation of Europium 
(Carl Willis) [Latest: 2007-07-16 21:27]