PMT particle detection

AGFA ADC 5155 Photo Multiplier Tube (Part 4 of 4)

Teardown of the photomultiplier tube assembly (PMT) and its high voltage power supply. The high voltage power supply and PMT is reverse-engineering to use the PMT as a cosmic ray detector with a scintillation plastic crystal in front of the PMT.

Part 1 is the Teardown of a AGFA ADC 5155 x-ray image scanner / digitizer. Also known as Computerized Radiography (CR) it fulfills the job of scanning a x-ray exposed image plate with a laser beam and extract each pixel illumination with a photo multiplier tube setup.

This particular unit has a very interesting computer that runs on VME framework developed for the Motorola 68000 series CPUs. This can be seen in part 2.

The laser scanner and photomultiplier tube assembly made out a good chunk of the weight, a very heavy, on rubber mounts and sturdy unit built to minimize any kind of external vibrations. This is the teardown video of the laser scanning module, part 3.

To learn more about how photomultiplier tubes work, I did reverse engineering on a PMT module from a AGFA ADC Compact Plus and have some additional pinout information on circuit boards AG-IUP32-8 and AGFA-IUP16 which has square photomultiplier tubes.

Part 4 is about reverse engineering the photomultiplier tube assembly from this AGFA ADC 5155 solo machine. Getting the high voltage power supply unit to run without being controlled by the Motorola 68040 based computer and by reading the PMT output with a oscilloscope.

The tube assembly contains a Burle S83021E photomultiplier tube and a small circuit board with a V23100 reed relay output.

The high voltage power supply is a very nice unit from Heim Electronic GmbH. The type number SMP1.5N24/176 is most likely a custom version as the AFGA part numer F7.0486.1250.0 ans S.Nr. 98603-0343 is listed along with that information. It is a -1.5 kV / 6 mA output negative power supply, used to power the dynodes of the photomultiplier tube.

From the Burle S83012E datasheet it can be seen that a regular voltage for this tube is -1100 V, but the power supply only outputs -600 V, which is normal for a image acquisition tube, they are not driven that hard as there is plenty of light available from the laser scanner. However feeding it with a higher negative voltage like -1100 V would result in 20 times higher sensitivity which is needed when used with scintillation materials for radiation or particle detection.

The test setup used a cylindric piece of BC408 material that measures 50 mm in diameter and is 30 mm thick, this corresponds to a volume of 59 cm3. The detected particles gave raw output signals from the tube of up to -1000 mV amplitude, but most was detected in the range of -200 to -300 mV.

Mads Barnkob

Electrician, programmer, experimenter and amateur scientist with experience in industry automation, programming and all kinds of high voltage generating electronics. Administrator of and the high voltage community forum

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