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Several MCA8000A versions are showing up on eBay.?

It should be understood that these are not complete MCAs, like a Spectrum Techniques UCS-20/30 or an URSA2.

The sections lacking are the front end electronics and HV bias supply, namely the sensor preamplifier and the shaping amplifier, and HV generator. The input to the MCA8000 is a trapezoid, not a sharp pulse such as from a PMT and the level is TTL (I think), definitely not low milliVolts.

The MCA8000 is designed to work with a power supply/ shaping amplifier unit between it and the sensor/preamp package, such as the PX2 series.

So a typical setup is an XR-100 detector box containing just the sensor and preamp, then the PX2, the version specified for the type of sensor in the XR-100 (i.e.Si-PIN, CZT, CdTe etc), then the MCA8000.

In this lineup the PXT provides the HV Bias to the sensor and all the various low Voltages that are required by the preamplifier module inside the XR-100 head. In the PX2 these are not programmed by a computer, but rather by a technician, indeed the PX2 does not have a computer port on it, that is only on the MCA8000.?

Notice that the MCA8000 does not supply HV or any other support to the sensor box, .

AMPTEK does make a version of the MCA8000 that is set up for PMT based systems, but it has the several expensive additions, and in my opinion is not too practical, although one would be great if the price were not so high.

Si-PIN PX2 power supply/shaper amplifiers can provide only 110V HV. The PX-2T can provide up to 500V and is the one to use for CZT/CdTe, although they actually require 600V and above, so again, not ideal.

What I'm still looking for is a comprehensive list of sensor model numbers that tells what's actually inside there. Until we have that, we don't always really know what is being offered on eBay etc. by sellers who obviously know way less than we do about the subject.
Geo

A picture showing some different AMPTEK sensors.

Bottom is the Si-PIN we use, the latest and greatest technology, married with the DP5-PC5.

Top left- older original tech CdTe
Top right- older Si-PIN.

Always demand to see a picture of the end of the sensor when considering a purchase. Many of the items on eBay have been demilitarized or DE_MILLED, which is to say intentionally destroyed before disposal. If the window in not flat and smooth, suspect damage. Also some of the AMPTEK boxes are empty- for example the MINI-X-Ray on eBay now has all of the electronics removed, contains just the bare tube.

Remember most folks are buying this stuff with no way of testing it and simply putting them on the shelf for "later", so we are not hearing from them or seeing results posted, one way or the other.

Geo

Geo

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Pictures of the interior of a typical sensor.

The sensor+FET itself is on a ceramic substrate while the Peltier cooler is located directly on the base over the mounting stud.

Coupling the two are tall, heavy, thick rectangular slugs of some heat and electrical conductor, soldered to the matching PCB contact arrays. Obviously the arrangement is really fragile and top-heavy, so I can imagine physical shock can dislodge one or more of those over-levered connections. Pics are of a broken one I bought intentionally as a mechanical model for making the GEO-1-2-3 boxes (all of its coupling rectangles were detached).

Notice on my units there are rubber feet on all boxes, this is for heat flow on the bottom of course but primarily to dissipate shock waves occurring anywhere on the work surface.

The tech involved is not that advanced really, 1-Peltier, 1-photocell, 1-FET, 1-1N914- they get $4000 for the sensor because they can make it and we can't.

Geo

now the pics