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Too much fun - work to do

A project log for Gamma Ray Spectroscopy - small, cheap

The goal of this project is to design a light weight gamma ray scintillator in a 1u CubeSat frame

sparks.ronsparks.ron 12/06/2016 at 17:150 Comments

I realized I am, as usual getting distracted by the fun stuff and letting the "formal" planning slip. I know, but fun is fun. Last night I got to thinking about how the energy level of a pulse from the PMT could be measured. From the various data sources it looks like the pulses will be a few nanoseconds (up to maybe a microsecond) wide. I also saw some YouTube videos of people using DIY probes to measure calibrated sources.

From that it looked like the highest count rate any of the sources gave was around 400,000 cpm. That would work out to a pulse every 150 uS -- IF they were all evenly spaced. But they will not be. Obviously their distribution is the definition of a random Gaussian distribution. A nice discussion of pulse adjacency is covered in the paper I mentioned in my last entry.

But, back to the exploration at hand. How do you determine the output voltage level of each pulse? Some of the DIY systems use a fairly coarse (2 or 3 bit) discrete flash digitizer. But I wondered how much a very fast equivalent analog to digital (AD) chip would cost. Since this project is a one-off (up to a max of 10) a cost up to about US $10-15 would be acceptable.

I was pleasantly surprised - I found a couple of them in that price range that can do up to 80 MSP at 10 bits! Most likely that will be far more than I need, but it is a fun thought. That would give me a 10 bit sample as quickly as 125 nS.

Okay, now back to the project design spreadsheet to figure out when, or if, I need to go any further down that road.

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