This is a Bicron / Saint-Gobain 1.5M2.25/1.5L NaI(Tl) scintillation detector that I have personally refurbished.  It has a mu-metal shield for enhanced accuracy and I have added a high quality Amphenol BNC connector for reliable service.  The size of this crystal (38mm x 57mm) is very large while being in a relatively small enclosure, making it ideal for portable meters and an exceptional value.

The issue is that the instrument was originally used for high resolution isotope identification, and, as such, the probe was configured for low impedance, nominally 12M.  However, most hobbyists and radiation detectors need a high impedance, nominally 120M.

The conversion involves removing the cap using a heat gun and considerable effort, all the while keeping the crystal end cool.  Once the cap is removed it exposes the voltage divider circuit, consisting of SMDs (surface mounted devices) that need to be removed and replaced using higher impedance resistors. Working with SMDs requires a special soldering station and advanced soldering skills. After completing the conversion, installing the BNC connector, and testing the probe, I replace the cap and secure it with aluminum tape, making it easy to remove the cap in the future if further work is needed.

Here is a similar modification to a Scionix 38B57 probe.  The electronics are different but the technique is similar.  If is not for the faint of heart!  The photo of the inside of this probe for sale was taken before the mod and then after removing the components..

http://blog.kotarak.net/2023/05/modifying-scionix-holland-38b5715m-e1.html

My understanding is that this was pulled from a meter for routine maintenance.  It was in its original rubber boot and in perfect condition.  Who knows if it was actually used.  In my experience this probe is identical in size and performance to the Scionix 38B57/1.5M.  They both use the same Hamamatsu R980 Photomultiplier Tube. They were meant to be interchangeable.  My testing shows that they perform the same in terms of counting and gamma spectroscopy.  This can be seen by my Theremino/Gammaspectacular GS-USB-PRO scan of a Cs137 spark gap tube.

If you have any questions just send me a message.

Note that the Cs137 tube is not included.