A value in a data sheet applies under stated conditions. Here is how to find the source of a figure, tell guaranteed limits from typical values and compare instruments on equal terms.
Scroll to follow one of the GEM40’s values.
| Relative efficiency | 40 % (minimum)1 |
|---|---|
| Energy resolution at 122 keV | ≤ 0.87 keV FWHM1 |
| Energy resolution at 1.33 MeV | ≤ 1.8 keV FWHM1 |
| Peak-to-Compton ratio | ≥ 64:11 |
| Peak shape FW.02M/FWHM | 2.6 (typical)1 |
Every technical value in the catalogue has a numbered source. The example is the ORTEC GEM40, an HPGe detector with at least 40 % relative efficiency.
The number leads to the manufacturer’s document – here p. 18 of the GEM series configuration guide, the table “Ordering Information and Warranted Specifications”. You can check the value there yourself.
In the table, ≤, ≥ and minimum are guaranteed limits. A typical value – such as the peak shape of 2.6 – is the normal outcome, not a guarantee. Resolution also applies at a stated energy, here 122 keV and 1.33 MeV.
The GMX40 also has at least 40 %, but at most 2.0 keV at 1.33 MeV against the GEM40’s 1.8 keV – and the GMX series measures from about 5 keV instead of about 40 keV. The comparison shows the differences straight away and can be downloaded as PDF or Excel, with the sources.
In NDEC’s catalogue every technical value has a numbered source. The number after the value refers to the source list further down the product page, where the manufacturer’s document is linked and the location of the value in it is given. For the GEM40, the relative efficiency of 40 % (minimum) is on p. 18 of ORTEC’s configuration guide for the GEM series – in the table Ordering Information and Warranted Specifications.
Manufacturers state values in different ways. A limit – a maximum (≤) or minimum (≥) – is a guarantee. A typical value is the normal outcome, but not a guarantee.
In ORTEC’s table for the GEM series, resolution and peak-to-Compton ratio are guaranteed limits: the GEM40 has ≤ 0.87 keV FWHM at 122 keV, ≤ 1.8 keV FWHM at 1.33 MeV and a peak-to-Compton ratio of ≥ 64:1. The same table gives the peak shape FW.02M/FWHM as a typical value: 2.6 (typical). In the catalogue the value keeps the manufacturer’s wording – minimum, maximum or typical.
A value applies at a stated energy, temperature or measurement geometry. For HPGe, resolution is given at 122 keV and 1,332 keV; for scintillators and CZT usually at 662 keV – so only compare values that apply at the same energy. Relative efficiency is a comparison number defined in IEEE Std 325 for a fixed geometry; read more in the guide Relative efficiency of HPGe detectors.
The GMX40 has the same relative efficiency as the GEM40, 40 % (minimum). Still they differ: the GMX40 has ≤ 2.0 keV FWHM at 1.33 MeV against the GEM40’s ≤ 1.8 keV FWHM, and the GMX series measures from about 5 keV while the GEM series is used from about 40 keV and up. Differences like these only show when the values sit side by side under the same conditions.
In the comparison you can put up to four products side by side, show only the differences and download the table as PDF or Excel – with the sources.
Unfamiliar term? Look it up in the glossary.
HPGe detectors for gamma spectroscopy
HPGe gamma detector
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