Sciencemadness Discussion Board

Cheap calibration source for scintillation detector

MrFormula - 24-1-2025 at 09:05

Hello. A friend and I have been working on a DIY scintillation detector similar to the radio code. The basic idea is from a person on YouTube called spectrofreak who made a device called the "Gamma Freak". We have decided to improve on his design and add portable functionality using a RasberryPi so we can estimate received radiation and damage. I am currently looking for a cheap calibration source for our detector. We are using an R7400u PMT with a bialkali crystal at the top. I was thinking of using Cs-137 but it is a bit pricey and hard to find, at least for me. I was wondering if anyone has any alternatives. Would the americium from smoke detectors work, or would it be a problem with primarily alpha radiation? Thanks in advance.

[Edited on 1-24-25 by MrFormula]

pantone159 - 24-1-2025 at 10:19

United Nuclear sells disk sources sourced from Oak Ridge. I have bought one before and had it shipped to a residential address with no issues.
https://unitednuclear.com/radioactive-isotopes-c-2_5/

MrFormula - 24-1-2025 at 11:10

Quote: Originally posted by pantone159  

https://unitednuclear.com/radioactive-isotopes-c-2_5/
wow. That website is amazing. Thank you so much!!

Deathunter88 - 24-1-2025 at 13:33

Quote: Originally posted by MrFormula  
Hello. A friend and I have been working on a DIY scintillation detector similar to the radio code. The basic idea is from a person on YouTube called spectrofreak who made a device called the "Gamma Freak". We have decided to improve on his design and add portable functionality using a RasberryPi so we can estimate received radiation and damage. I am currently looking for a cheap calibration source for our detector. We are using an R7400u PMT with a bialkali crystal at the top. I was thinking of using Cs-137 but it is a bit pricey and hard to find, at least for me. I was wondering if anyone has any alternatives. Would the americium from smoke detectors work, or would it be a problem with primarily alpha radiation? Thanks in advance.

[Edited on 1-24-25 by MrFormula]


If you don't want to spend the money for a disk source you can use many common sources (I had this exact dilemma last month since I just got a gamma spectrometer). This forum discussion proved to be very helpful to me:

https://gammaspectacular.com/phpBB3/viewtopic.php?f=16&t...

Quoted:

"For simple energy calibration, a minimal set of disk sources would be none.
There's loads of options for natural, historic, or otherwise readily available radioactive material that have plenty of peaks to pin down an energy cal without splashing out on manufactured sources. Am-241 smoke detectors; K-40 in your background or enhanced with low sodium salt (KCl); Th-232 and daughters (lantern mantles, thoriated welding rods); Ra-226 and daughters (watch hands and aircraft dials) or more generally the full U-238/Ra-226 decay chain (fiestaware, uranium glass etc). Between a couple of these you have lines spanning 59keV at the low end, 186, plenty of intermediate peaks, and at the higher end 1460, 2614 and more.

If you're looking to have an efficiency calibration, you will want something with better known activity. From there, it depends how accurate you want to go. The nominal activity of the Spectrum Techniques disk sources is probably good enough for hobbyist purposes, but professionally it's usually worth paying the extra for a proper calibration traceable to national standards.

My recommendation for a minimal source would be a single Eu-152 disk - with lines from 122 to 1408 and plenty in between, you can pin down the majority of your efficiency curve with just the one source; and the 13 year half-life means it should last you a while.

Going further from there, it depends what you want to measure.

My work generally involves activation products, and having Co-60 and some of the other activation product peaks well calibrated is critical, so we usually get sources with Co-60 and activation nuclides to calibrate those exactly rather than interpolating from something else. There's a bunch of standard off-the-shelf mixed nuclide sources that provide most of what we need in one source.
For some things, though, it can be helpful to have a single line source. Cs-137 is usually a good readily available option for that, although I have had uses for others.
A beta+ source can be good for coincidence experiments with the opposite-direction annihilation photons, so something like Na-22 is a good choice."

Edit: Oh I would like to point out that Spectrum Techniques is very hobbyist friendly. Don't be afraid to contact them directly through their website and they will give you a quote (both with and without activity calibration) for any sources you want, even if it's clear you are just some guy interested in radiation and not a university or company.

[Edited on 24-1-2025 by Deathunter88]