Gamma Scintillation Detectors

When it comes to gamma spectrometry the detector is the most important component. Modern electronics and software outperform all available detector materials, so if you have a limited budget it would be wise to spend the money on the best detector you can afford.

The two main determining factors are resolution and efficiency, and in rare cases speed may also be a factor.

Resolution is the ability of a crystal to output light in proportion to the captured gamma ray. This may sound simple enough, but in reality most scintillation materials don't do it very well. Whilst they may well capture all the energy of the gamma ray, not all of it is emitted at the exact energy, some energy is simply lost to longer wavelength photons and not captured by the photomultiplier tube (PMT) and some energy may be absorbed by thermal motion inside the crystal which results in a gaussian distribution of energy around the main photo peak.

The most common scintillation crystal is Thallium doped Sodium Iodide or NaI(Tl) scintillation detector which typically has a pulse height resolution of around 7% at 662 keV. The 662 keV gamma from Cs137 is the industry standard for measuring detector resolution.

Pulse height resolution is the photo peaks full width at half maximum (FWHM) divided by the actual peak energy. For example if the FWHM of the 662 keV. photo peak is 66.2 keV. then the resolution would be 10%.

The popularity of Sodium Iodide scintillators is due to the relatively low cost with acceptable resolution, but there are both cheaper and more expensive materials available. The resolution of gamma detectors can range from more than 20% to less than 1% for Germanium detectors which require cryogenic cooling in order to work.

Plastic scintillation materials like BC412 are relatively inexpensive, but have poor resolution, BC412 is therefore unsuitable for gamma spectrometry, however it's extremely short decay time of the light output, only 3.3 ns makes this material perfect for fast gamma counting.

For applications where high resolution is desired, there are several exotic scintillation materials like CeBr3, LaBr3 which can give a nice 2.5% resolution at room temperature, but these materials come at a high cost. Considering how a small LaBr detector often gives better information than a large NaI(Tl) Scintillation detector the cost difference is not as extreme as it looks. Detectors like the GS-1010-LABR are only slightly more than a 2" NaI(tl) detector, so it is worth consideration.

Gammaspectacular source the best quality scintillation crystals and PMT's (Photomultiplier tubes) from around the world, and assemble the components professionally in our own workshop. Each unit is thoroughly tested before shipping and comes with a 12 months guarantee. Please see our individual detector specifications for specific resolution guarantee.