# What is energy resolution

1. Jun 13, 2012

### Nyasha

Can someone explain the concept of energy resolution to me, especially in gamma cameras. Thanks.

2. Jun 13, 2012

### Astronuc

Staff Emeritus
Where did one find a reference to gamma cameras?

3. Jun 13, 2012

### Nyasha

Well, l am reading a thesis on them and the author keeps on referring to energy resolution as a % FWHM. So l really don't understand what this means.

4. Jun 13, 2012

### billschnieder

Generally speaking, energy resolution refers to the degree of monochromaticity. So if we say the particles have an energy say e, actually they are not all the same energy rather they are spread in a gaussian distribution around e with e representing the mean. The smaller the sigma of the distribution, the higher the energy resolution and the bigger the sigma the lower the energy resolution. % FWHM (~2.35σ ) is often used instead of sigma to represent the resolution especially since the distribution is not always gaussian but can be lorentzian or a mixture.

http://en.wikipedia.org/wiki/Gamma_spectroscopy#Detector_resolution

Last edited: Jun 13, 2012
5. Jun 13, 2012

### Nyasha

So generally speaking, the lower the %FWHM the better the camera is ?

6. Jun 13, 2012

### Staff: Mentor

A smaller FWHM might come with some disadvantages elsewhere, but in general, a smaller value there gives a better energy resolution, which can help in the analysis.

7. Jun 13, 2012

### M Quack

FWHM means Full Width at Half Maximum. When talking about the resolution of a detector, this means that a beam of monochromatic=monoenergetic photons or particles will produce a Gaussian (or other) distribution of *detected* (or apparent) energies.

In spectroscopy this is significant, as it is sometimes necessary to distinguish gamma lines with close-by energies. If, roughly speaking, the resolution is worse than the energy difference, then the detector cannot tell the lines appart.

For many detectors, the resolution is related to the energy of the detected particle or photon. That is why the FWHM is given as percentage of the particle's energy.

8. Jun 13, 2012

### Astronuc

Staff Emeritus
Is this related to synchrotron radiation imaging or gamma ray imaging/tomography?

9. Jun 13, 2012

### Nyasha

It is related to gamma ray imaging.

10. Jun 15, 2012

### Bob S

In the attached sodium-iodide spectrum for cesium -137, the FWHM resolution is about 50 keV, or 7,5%. You can also see the Compton backscatter peak and the Compton edge. The energy resolution depends on the size and type of detector, and the gamma energy.

See http://en.wikipedia.org/wiki/File:Caesium-137_gamma_ray_NaI_scintillator_spectrum.jpg [Broken]

Last edited by a moderator: May 6, 2017
11. Jun 15, 2012

### ZapperZ

Staff Emeritus
In the future, you really should provide as much information, including exact citation to your sources, as possible, rather than giving annoying bits and pieces.

Zz.