Cs 137 in the wild

[Jim Kovalchick]

A few weeks ago I visited the site of the Georgia Nuclear Aircraft Laboratory. It is a long shut research reactor facility that is now a public recreation area. There once was a small rail line from the reactor facility to a hot cell building. Along the path of that rail line, I found a piece of concrete that had slightly elevated counts above background. I counted it with a 2" NaI crystal this weekend and collected this spectrum. I believe there is a very tiny hint of Cs 137 in the marked peak. I double confirmed the calibration with a sealed Cs source and a sample of contaminated soil from the Fukushima accident. The peak does not appear in my background. The lump in the spectrum around 1.6 MeV is a mystery to me. I confirmed that it is not a miscalibrated K40 peak. The lump also does not appear in my background.

JK

[Sesselmann]

Jim,

How did you completely eliminate K40 ?

Perfect shielding or background subtraction....?

Steven

[Jim Kovalchick]

Steven,
To make sure that it wasn't K40, I put a K40 source in the same configuration and its peak came in with better resolution and where it should, slightly lower in energy. I also assume that if it is attenuated within the body of my sample that it would not appear to broaden to a higher energy.

I also own a ANSI 42.34 compliant RIID that uses a 2" NaI crystal that contains an intentional K40 contaminant for calibration purposes. When I counted my sample with that device, it shows the upper range peak as distinctly above the K40 calibration peak. The device software identifies the bulge in the spectrum as a peak but classifies it as unknown.

In both my spectroscopy setup and with the RIID, the peak does not show up in the background.,

I wonder if the peak is the result of more than one gamma, and self shielding within the sample is blurring them together.

Jim