Where are the beta particles?

In summary: Make sure you calibrate the equipment so that you are comparing the same things. If you are getting an out of range signal, it could be due to a defective phototube, bad coupling of the scintillator to the phototubes, or a dirty and poorly illuminated scintillator.
  • #1
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This may be a pretty basic question ,but i'll through it out any way. As a project i built a muon detector from 2 matched PMTs and 2 4x6x1 plastic PVT scintillators. And pulse processing NIM modules. I was getting pretty good coincidence reading,some what less than predicted.ie ( 1 count/sqcm/min) However ,when I wanted to calibrate by using a small sample on strontium 90 (.5Mev beta ) i get no signal anywhere. I made sure there was no obstruction between it and the scintillator. Now from what i understand the average muon
energy at Earth surface is around 2Gev. I am assuming the beta fully is stopped by the scintillator. I am not sure the bethe bloch formula is valid for the speed of the beta, So where should i be looking for this signal?
Should the gain be turned way down to see the beta? I am trying to get an idea of where the strontium signal is compared to the muons. Thanks j
 
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  • #2
Hmm, it's interesting. At 0.5 MeV of kinetic energy the electron will stop within the material. Remember that 0.5 MeV is the maximum kinetic energy for the electron, but the energy spectrum is continuous and the most probable energy is less.

If you have a cosmic ray background with an average energy of 2-3 GeV, the beta signal can be very low in comparison; or not, I don't know what fraction of its energy will deposit the cosmic ray inside your detector, maybe you should compute the stopping powers for both and compare (will the cosmic ray lose more than 0.5 MeV?). Anyway, don't forget to put the high voltage of the PMT in the region of the plateau.

Then, you can measure the background due to environmental radiation (including cosmic rays) to characterize it; next, place the source near the detector and start measuring. You must remove the background to extract the signal from the beta.

To get good statistics, you must take measures for a long time both to measure the background and the signal.
 
  • #3
Thanks. Well ,on my multichannel analyzer,I saw no spikes,but I do register the muons. Also I used a single channel analyzer with a discriminator,to weed out the dark counts and saw nothing over that level. My Geiger counter shows I’ve got plenty of activity from the strontium, way over the dark count rate from the tubes. I adjusted the gains on both tubes so that they both drop off the dark counts at the same voltage on my amplifier chain. From what I can gather,the velocity of the beta is an order of magnitude lower than the muons. Next I’ll try dropping below the nominal voltage of the tubes to see if it shows up. Any other ideas? Thanks
 
  • #4
Hard to say without actually looking at your equipment, but here's a few possibilities. How is the scintillator coupled to the phototubes? You have scintillator that is 4x6x1. How do you match it to the shape of the phototube so that you are collecting all of the light? Is the scintillator well polished and everything very light tight? Your betas could be under the background.
 

1. Where are beta particles found in nature?

Beta particles can be found in various naturally occurring radioactive elements, such as uranium, thorium, and radium. They are also often produced in nuclear reactions and can be found in radioactive waste.

2. How are beta particles detected?

Beta particles can be detected using a Geiger counter, which measures the ionization caused by the particles as they pass through a gas-filled chamber. Other methods include scintillation detectors and cloud chambers.

3. Can beta particles be harmful to humans?

Yes, beta particles can be harmful to humans if they are ingested or inhaled, as they can damage cells and potentially lead to cancer. However, they can also be used in medical treatments when carefully controlled.

4. Do beta particles have a charge?

Yes, beta particles have a negative charge. They are essentially electrons that are emitted from the nucleus during radioactive decay.

5. How do beta particles differ from alpha particles?

Beta particles are smaller and have a lower mass than alpha particles. They also have a longer range and can penetrate further into materials. Additionally, beta particles have a negative charge while alpha particles have a positive charge.

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