# What is energy resolution

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

Staff Emeritus
Can someone explain the concept of energy resolution to me, especially in gamma cameras. Thanks.
Where did one find a reference to gamma cameras?

Nyasha
Where did one find a reference to gamma cameras?

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.

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

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Nyasha
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

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

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.

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.

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

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

It is related to gamma ray imaging.

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]

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Staff Emeritus