Evaulation of the old prototype based on TL072

A project log for Gamma PIN - Semiconductor Radiation Detector

An attempt to design and deliver universal and accessible radiaton analyser to be used in nuclear spectroscopy

Marcin WachowiakMarcin Wachowiak 07/28/2018 at 15:160 Comments

The early stage prototype of the detector was designed to have an array of about 50 PIN diodes.
To distribute them equally I divided the array into 7 rows with 7 diodes each. Every single row had
it’s own sensing amplifier construced using TL072. This common and easily accesible solution was supposed to give me an insight to futher work with this kind of detectors. The design was preceded with simulations in LTspice to check what results may I expect.

LTspice Gamma PIN prototype simulations
Early stage TL072 design

This prototype was created in a wafer fashion to make it smaller and stackable. The power supply was based on common step-up inverters using LM2577. By changing the feedback resistor they may work up to 65V. TL072 worked at 18V and diodes were biased by 60V. These power modules were shielded to reduce the noise emitted by the coils.

Whole device
Board footprint

Unfortunatelly, in the final stage of the signal processing there have occurred an error stopping the grid detector from functioning properly. The pulse signal is negative and in the circuit there is diode added at the output of the TL072. It was supposed to prevent the signals from mixing if they were positive. This awful mistake is still present in the PCB files. If you wish to test your own detector make sure you have replaced the diodes with a proper solution that would stop the signals from interfering.

Schematic of the early design

I still managed to get use of the single row to measure some radiation. The first measurment was without any source. Even the background radiation managed to leave a trace, although the pulses were significantly smaller and happened less often.

Low energy pulse coming from the background radiation

Image of the collected pulses through short time with no source present

Then I placed a thoron mantle at the sensing area. Simultaneously the pulses were higher and more frequent. For a single singal trigger I didn’t have to wait even a second.

Detector with a thoron mantle placed upon it

High energy event - particle coming from thoron mantle

Pulses collected with the source present


On the whole, this prototype has allowed me to focus on a few problems that will need to be solved:

The early design was quite a crude one. The second one is going to be well thought over to provide reliable results.