DIY Plastic Scintillator

Inspired by the work made by Lukas and published by him into this post LINK, I’ve tried to replicate his experiment. I’ve choosed to change some ingredients like epoxy and wavelength shifter. He uses E45 epoxy but I’ve preferred E30 because is more clear with better optical properties. He also uses cumarine-102 but cumarine-1 matches better the PPO 2,5-Diphenyloxazole emission spectra.

 

“Standard mixture” to make a 32gr plastic scintillator sample I use:

  • Epoxy E30 part A (base) 20gr
  • Epoxy E30 part B (hardener) 12gr
  • PPO scintillator 0.32gr
  • Cumarin-1 0.032gr

The procedure:

  • Heat part A at 80⁰
  • Dissolve PPO + cumarin-1 into part A
  • Re-heat again solution to 80⁰
  • Add part B heating when stirring for 5 minutes
  • Pour into a suitable mould like HDPE plastic or silicon
  • Put the mould with epoxy over a 3D printed heath bed setted at 80⁰C and let it stay for 2h aprox. This way the 3D printed heath bed acts as an heather helping the epoxy catalisys.
  • I use hot air gun for soldering SMD to heath part A at the start of the procedure simply carefully blowing hot air over the epoxy and stirring to dissolve PPO + cumarin-1

Results show that this kind of epoxy-based scintillator is sensible with alpha beta and gamma rays but especially sensible to beta radiation.

I’ve also made a test to demostrate the effectiveness of cumarin-1 as wavelenght shifter. I’ve made a scintillator without it and… it doesn’t scintillate. Actually it scintillate into UV so I cannot se it!

On the left a standard mixture on the right without cumarin-1.

 

Standard mixture glows bright even in daylight if excited with enought UV from an UV lamp.

The effect is even more drammatic at night.

Stilbene

Stilbene is an organic solid scintillator material used for fast neutron detection.

Characteristics:

  • Direct detection of fast neutrons
    • Stilbene is highly sensitive to fast neutrons, hence they do not need to be moderated to lower energies to be detected
    • Stilbene takes advantage of the low background of fast neutrons for low-noise measurements
    • Detection of unmoderated neutrons preserves information about neutron trajectories and energies

 

  • Excellent discrimination between neutrons and gamma rays
    • Facilitates counting fast neutrons without false positives from gamma rays
    • Permits use of lower energy thresholds than liquid scintillators

 

  • Safe and Easy to Handle and Transport
    • Solid, non-hygroscopic, not flammable, not hazardous
    • Unpackaged stilbene is stable
    • Avoids the transportation, storage, and handling concerns of many liquid organic scintillators

Po210 + Be Neutron source

Neutrons are cool. Them are the key ingredient of any nuclear chain reaction, the trigger wich split the atom, the “biliard ball” that striking other atoms turns them in radioactive isotopes. Bothe and Becker in 1930 made them for first by “bombing” Beryllium with alpha rays emitted from Polonium 210. Why not try to replicate?

Po210 is not simple to be aquired in Italy expecially into high quantity needed to make a measurable ammount of neutrons. Actually the ony way that I’ve find  to get some was to buy a Staticmaster brush cartridge from Adorama – USA – and pay it twice it’s price because of customs and shipping fees. The cartrige contains 2x 250uCi of Po210 enclosed into a safe metallo/ceramic alloy golden covered ribbon. Such quantity in Italy is completly illegal and Po210 is 20000 times more poisonous than cyanide. This product it’s otherwise completly safe if you don’t dismantle the source frm it’s location and respects only the USA regulations in matter of exempt quantity of radioactive isotopes. Beware!

Po210 half life is 138 days. Mine was made in Juy 2020 and I’m writing this post in March 2021. In total 243 days. My sample in a month will be 125uCi.

An interesting thing to do with it is also see how alpha’s can trigger luminescenze into a  ZnS(Ag) scintillation screen. To do that I’ve very carefully removed the sources from the staticmaster brush and glued over an alluminium sheet for handling.

It’s quiet impressive! It glows strongly than appares on picture. I’ve noticed by moving the scintillation screen that departing it from the source of just 3-5mm is enought to stop the effect. This means probably that just 3-5mm oof air are enought to stp the apha emitted by the Po210 source. Interesting.

Now let’s go back to the main topic. I’ve the Po210 now I need a beryllium target. This is quiet easy and legal to source. Just buy a smal sheet of pure beryllium from eBay. It’s commonly sold there in rods and sheets.

Now that I’ve the Po210 and the Be target how to measure the effective generation of neutrons? Luckly I’ve bought some time ago a Stilbene crystal scintillator. Stilbene is an organic solid scintillator material used for fast neutron detection. It’s quiet efficent indeed!

This crystal coupled with a photomultplier tube was my neutron detection scintillation probe. I’ve used it with an Eberline ESP1 scaler/rate meter.

I’ve take a series of 3 measures:

  1. Background without source
  2. Po210 no Be target
  3. Po210+Be

The experiment was repeated 10 times. The difference between readings will show us what Stilbene is detecting. As example take a look at following pictures

Background

 

Only Po210

 

Po210+Be

 

As you can see I’ve got:

  1. 4740 pulses background
  2. 6340 pulses background + xray generated by alpha hitting the aluminium of the detector
  3. 7300 pulses background + xray + something else… NEUTRONS!!! I’ve got it!

Considering uniform the background I can assume that I’ve generated 7300 – 6340 = 960 neutrons in 8 minutes that’s the time setted into ESP1 for counting. 2N/sec. My Po210 +Be source generated 2N/sec when it was at almost full strenght. My Stilbene crystal is small and probably many neutrons escaped counting but… yes I confirm, it works.

Sadly to try neutron activation of materials I need a stronger source of neutrons.