Gamma ray spectroscopy: Germanium detector efficiency calibration.

In summary, the group is trying to create a plot of efficiency against energy for a planar germanium detector. They have spectra for different sources at a fixed distance from the detector and are wondering how to calculate efficiency. The equation for full energy peak efficiency is provided, but they are unsure how to calculate the probability. They are also seeking help with radioactive isotope decay levels and branching ratios. X-ray attenuation coefficients and solid angle calculations may not be necessary for their experiment.
  • #1
quantumlolz
8
0
Hi all,

Got a bit of a problem with a lab experiment at uni (I'm not sure if this is the right place to post this, mods feel free to move it if necessary!)

Anyway: We're trying to get a plot of efficiency against energy for a planar germanium detector. We've got spectra for different sources at a fixed distance from the detector.

The main question really is: how do we calculate efficiency? I've got Gilmore's "Practical Gamma Ray Spectroscopy" book in front of me opened at the efficiency calibration section. The only one that seems to mention that the source-detector distance is important (they specify in the lab script that we get spectra at a particular source/detector distance...) is absolute full energy peak efficiency. The equation given for this is:

efficiency = full energy peak count rate/(source strength x probabiltiy of emission of the particular gamma ray being measured)

(I think this is the one we're meant to be using - but how does one then calculate the probability??)

I'll be massively massively grateful to anyone that can help, because I'm really pretty confused...
 
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  • #2
Last edited by a moderator:
  • #3
The first two lines of Bob S's #2 are basically the answer you need.

@Bob S: I don't think they need the x-ray attenuation coefficients for germanium, since they're trying to measure efficiency empirically, not predict it theoretically. They also don't need to calculate solid angle (assuming they have the source at the actual distance from the detector where it'll be in the actual experiment). Scattering materials nearby shouldn't actually matter, since they're measuring the photopeak efficiency; if it's scattered the Ge won't get a photopeak event, it'll get some lower (Compton-scattered) energy.
 

1. What is gamma ray spectroscopy?

Gamma ray spectroscopy is a technique used to measure the energy levels of gamma rays emitted from radioactive materials. It involves using a detector, such as a germanium detector, to measure the energy and intensity of gamma rays in a sample.

2. What is a germanium detector?

A germanium detector is a type of semiconductor detector that is commonly used in gamma ray spectroscopy. It is made of high-purity germanium crystals and is highly sensitive to gamma rays, making it ideal for measuring their energy levels.

3. Why is efficiency calibration important in gamma ray spectroscopy using a germanium detector?

Efficiency calibration is important because it allows for accurate measurements of the energy and intensity of gamma rays. The detector's efficiency can vary based on factors such as temperature and voltage, so calibration is necessary to ensure reliable results.

4. How is efficiency calibration performed in gamma ray spectroscopy using a germanium detector?

Efficiency calibration is typically done by measuring the gamma ray emissions from a known radioactive source with a known energy level. The results are compared to the expected values, and adjustments can be made to the detector's settings if necessary.

5. What factors can affect the efficiency calibration of a germanium detector in gamma ray spectroscopy?

Some factors that can affect the efficiency calibration of a germanium detector include temperature, voltage, and the type and energy of the gamma rays being measured. Improper handling or damage to the detector can also impact its efficiency and calibration.

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