Geiger (or other ionizing ray) Probe for Vacuum Conditions

[consuli]

I am planning a physical experiement under vacuum conditions. In this experiement, I want to detect ionizing rays, especially as broad band as possible, for instance including alpha radiation.

Typically geiger tubes are filled with a certain gas, that gets ionized by the radiation to measure. In the case of alpha-radiation detecting probes, tube containing the gas is just closed with a thin metal foil, to let helium ions (alpha-radiation) pass into tube. Under vacuum conditions most probably the gas will be sucked out of the tube by the vacuum.

What kind of geiger probe or other broadband ionizing ray probe could I use under vacuum conditions?

 

[gleem]

I want to detect ionizing rays, especially as broad band as possible, for instance including alpha radiation.

Can you better explain what you mean by "Broad Band"?

G-M typically are not used or alpha radiation since the window typically are too thick. Alphas can be stopped entirely by as little a 5mg/cm² thickness i.e. about 5cm of air.

The pressure in a G_M is typically significantly less that atmospheric. about 0.1 atmospheres.

Anyway there are trade offs for detecting different types of radiations with various detectors.

 

[consuli]

Can you better explain what you mean by "Broad Band"?

Broad band means, I want to detect as many accelerated particles as possible. Alpha radiation, beta radiation, gamma radiation, even fast protons and neutrons if possible.

 

[gleem]

The next question is what is the goal of this project since this will also have bearing on the choice of detector?

 

[gleem]

So this is your dissertation project? Each detector (system) has its strengths and weakness depending on the object of the project. I'm trying to be as helpful as possible.

Let me make some quick general comments about a couple of common detectors systems. There is no system that will adequately detect all forms of radiation. The G-M counter is OK for gamma, high energy beta and maybe high energy alphas but it require a very thin window. It is simple with minimal electronics. G-M counters have a wide efficiency variability for gamma of different energies which you should be aware of.. G-M counter cannot discriminate the different particles so you detect the radiation but you do not know what it was. Actually all detector suffer from this problem is some way.

To determine what radiation you are detecting one generally tries to inhibit the occurrence of the other types of radiation or have some way of determining the energy deposited in the detector.so as to get a clue of identify the radiation. These systems like scintillation detectors or solid state detectors require additional electronics to analyze the signals but are much more sensitive and thus good for low fluence sources. The analysis of the signals from a scintillation detector is more complex especially if you are trying to determine the number of particular radiation particles.

Neutrons are difficult to detect because they are neutral and do not produce ions directly. They can be detected by elastic scattering off of protons in the gas but this is not efficient. However if you introduce some material into a G-M type tube that has a high cross section for interaction with neutrons like B¹⁰ then the decay product being an alpha particle produce the required ionization. But these types of systems are more complex.

High energy protons or muons have minimal energy deposition per unit length in air so they are not easy to detect and a gas type detector has a low . efficiency.

If you are interested in just the net ionization being produced by the radiation then an ion chamber is the best detector but requires a large volume for a good signal at low radiation fluences.

This was just a quick and dirty survey. If you have more specific questions I will be glad to try and help.

 

[consuli]

Thanks gleem.
For me it is a (joined) master thesis project. Due to the graduation rules of my uni I am not allowed to discuss and especially to gain advice to central parts of my work or the general setup of the experiment (plagiation concerns).

 

[consuli]

Let me make some quick general comments about a couple of common detectors systems. There is no system that will adequately detect all forms of radiation. The G-M counter is OK for gamma, high energy beta and maybe high energy alphas but it require a very thin window.

Could I use a Geiger tube with a beryllium window to detect alpha-radiation? Or spoken the other way round is there a gas that gets easiliy ionized (thus being ideal for a Geiger tube), which does not pass through beryllium?

 

[berkeman]

Thanks gleem.
For me it is a (joined) master thesis project. Due to the graduation rules of my uni I am not allowed to discuss and especially to gain advice to central parts of my work or the general setup of the experiment (plagiation concerns).

Wait, what? You are not allowed to get outside assistance on this schoolwork project, but you are asking for detailed help here at the PF? Please send me a PM to clarify this -- thread is locked temporarily...