1230 keV mystery peak from WWII era optical glass

[Lposter]

That really is the oddest thing......

[Lposter]

Maybe try measuring it a few cm away from the detector? If its some kind of true coincidence peak that should reduce it or eliminate it? If its still visible then it is not simply a sum peak....

[Bob-O-Rama]

Anticlimactic conclusion to the saga: severe calibration error. It kind of occurred to me that I should not be seeing the K-40 peak at all on the shielded background spectra, as 4" of lead should attenuate that 50:1. In comparing the counts in the same interval between shielded and unshielded - it did not change significantly. So whatever the 1480 peak was, it was unaffected by 4" of lead.

The peak that incidentally is at 1480, that I had assumed was K-40, is ... cosmic rays or something. I ran a pure KCl sample, and it all showed up at 1240. A stunning validation that I am an idiot prone to wild confabulation. Letting the KCl bake for a couple days, and adding that peak to the calibration curve. Anyway, thanks for everyone's help, I'm going to slink off to my shame cave and think on my metrological sins. I really need to invest in calibration sources to cover the higher energy.

[Rob Tayloe]

Co-60 (1.17 and 1.33 MeV) and Eu-152 (multiple with highest ~1.4 MeV) are available from Spectrum Techniques. You may wish to obtain some other sources, e.g., Cs-137, Na-22, Ba-133, etc. to fill in gaps in the calibration curve. It sounds like you have KCl (K-40 at 1.46 MeV). One could obtain lanthanum to get La-138 at 1.436 MeV. Otherwise one might need access to a nuclear reactor or accelerator.

The pdf file linked below gives some commonly observed gamma ray energies -
http://fizika.imfm.si/jazbinsek/FMF/Pra ... ergies.pdf

This pdf file also lists isotopes and gamma energies. The higher energy emitters have shorter half lives and thus need to be "created" somehow shortly before having the decay gamma rays measured.
https://web.physics.indiana.edu/courses ... _table.pdf

And yet another (somewhat more comprehensive) table of gamma emitting isotopes with half lives greater than 1 hr:
https://application.wiley-vch.de/books/ ... table2.pdf

For energies above 1.4 MeV there are not too many isotopes with sufficiently long half lives to be useful to the casual gamma spectroscopy hobbyist. Some with potential would appear to be listed below. I do not recall ever doing anything with V-50, Al-26, or Bi-208.

energy [keV] intensity isotope (half-life) associated gamma-rays
1553.768 8 83 50V(1.4×1017 y)
1808.65 7 99.76 4 26Al(7.17×105 y) - 1129.67, 2938
2614.533 13 100 208Bi(3.68×105 y)
2938 0.24 4 26Al(7.17×105 y) - 1808.65, 1129.67

Al-26 looks interesting, but might be somewhat difficult to obtain -
https://www.radiacode.com/isotope/al-26

In the USA the US NRC governs the exempt quantities of radioactive material that one may possess without having a license. Following is a list of the exempt quantity isotopes.
https://www.ecfr.gov/current/title-49/s ... on-173.436

Following is a presentation from 2009 about misperceptions regarding exempt quantities of radioactive material
https://www.radiationsafetyconsultants. ... 0Final.pdf

[Mike S]

Anticlimactic conclusion to the saga: severe calibration error. It kind of occurred to me that I should not be seeing the K-40 peak at all on the shielded background spectra, as 4" of lead should attenuate that 50:1. In comparing the counts in the same interval between shielded and unshielded - it did not change significantly. So whatever the 1480 peak was, it was unaffected by 4" of lead.

The peak that incidentally is at 1480, that I had assumed was K-40, is ... cosmic rays or something. I ran a pure KCl sample, and it all showed up at 1240. A stunning validation that I am an idiot prone to wild confabulation. Letting the KCl bake for a couple days, and adding that peak to the calibration curve. Anyway, thanks for everyone's help, I'm going to slink off to my shame cave and think on my metrological sins. I really need to invest in calibration sources to cover the higher energy.

No shame because we are all learning here and you shared the outcome so we could gain from your experience.

[Lposter]

Im a little dissappointed now...... good for you in pursuing it though!

[Rob Tayloe]

If one studies some of the lists of gamma emitting isotopes an interesting observation might be made. The radioisotope N-16 with a 7.2 second half life has gamma rays with energies of 6.1 and 7.1 MeV. Wow! how can I get some of that? And why or where is it significant?

The answer, in my experience, is with nuclear reactors. The water (H2O) goes through the reactor, picking up heat and some of the O-16 becomes N-16. The N-16 can be used to monitor the power level in the reactor as it is produced in proportion to the fast neutron flux (and power) of the reactor.

https://www.nuclear-power.com/nuclear-p ... onitoring/

In a Boiling Water Reactor the steam containing N-16 from the reactor goes to the turbine to produce electricity. The radiation from the decay of N-16 makes the turbine room a High Radiation Area. Thus, no one can be in the turbine room while the reactor is operating.

https://www.nrc.gov/docs/ML1117/ML111720212.pdf