ISO 15632-2021 pdf free download – Microbeam analysis — Selected instrumental performance parameters for the specification and checking of energy-dispersive X-ray spectrometers (EDS) for use with a scanning electron microscope (SEM) or an electron probe microanalyser (EPMA).
4 Requirements
4.1 General description
The manufacturer shall describe, using appropriate reference texts, the essential design elements of the spectrometer in order to permit the user to evaluate the performance of the spectrometer. Elements that are indispensable for the evaluation of the suitability of a spectrometer for a certain field of application shall be given explicitly. These are to include the type of EDS (Si-Li EDS, HpGe EDS, SDD EDS, etc.), the thickness of the sensor, the net active sensor area (excluding the window grid area and after collimation) and the type of the window (beryllium, thin film window or windowless). Parameters which may not be encompassed by this document, but that may influence detector performance, e.g. the construction principle of the cooling system, shall be explained in the reference text. Some detector systems are capable of very high count rates, but at high count rates other specifications like energy resolution may alter and artefacts may appear in the spectrum. All specifications should therefore be accompanied by a statement of the count rate at which they are measured and it should not be assumed that the specification will be the same at other count rates. NOTE In many cases the specific geometry of the EDS detector at a particular SEM/EPMA chamber can result in a reduction of the net active sensor area as expected after subtraction of shadowing area caused by the window grid. For example, a falsely mounted collimator, electron trap or shadowing by other parts in the SEM chamber can reduce additionally the illumination of the detector with X-rays. A practical procedure how to determine experimentally the effective area of an EDS detector and under which conditions is described in Reference [5].
4.2 Energy resolution The performance of an EDS depends on the pulse processing details. The energy resolution shall be specified as the FWHM of the manganese Kα peak and determined in accordance with Annex A. Spectrometers that claim detection of X-rays lower than 1 keV shall also be specified by the FWHM of the carbon K and the fluorine K-lines. The specified FWHM shall be an upper limit in that the resolution determined in accordance with Annex A is guaranteed to be no greater than the specified value. The resolution value shall be accompanied by a statement of count rate for which the specification is valid. For most detector systems the best energy resolution is attained at an ICR < 1 000 counts/s and the best energy resolution shall be specified. Where detector systems offer higher count rate capability, e.g. SDD EDS, the energy resolution shall also be specified at high ICR, e.g. 50 000 counts/s, 500 000 counts/s.
4.3 Dead time In order to evaluate the process time of the EDS, complementary to the energy resolution specified in 4.2, the corresponding dead-time fraction should be specified. The calculation of the dead-time fraction is given in 3.4. Dead time is a consequence of the electronics rejecting “bad” measurements in order to achieve high spectrum fidelity. In many systems, the rejection criterion is designed to ensure that the measurement time for each photon is identical. However, it is possible to reduce the dead-time fraction by relaxing the criterion for pulse rejection and allowing the measurement time per photon to vary according to the arrival time of photons (“adaptive filtering”). In this case, the process time is not defined, the peak shape and resolution will change with count rate and this could cause analytical results to vary with count rate. Therefore, any specification of dead-time fraction should include a description of the essential design elements of the electronics as per 4.1.
4.4 Peak-to-background ratio The peak-to-background ratio shall be derived at the point of manufacture of the spectrometer from an acquired spectrum of an 55 Fe source as a characteristic spectrometer parameter. The ratio shall be given by the peak height of the manganese Kα line divided by the background. The background shall be calculated as the mean number of counts per channel within the energy range from 0.9 keV to 1.1 keV. Sufficient counts shall be recorded in the spectrum to make the measure statistically significant (as per A.4) and the electronic threshold(s) shall be set up so that any energy cut-off occurs well below the specified range. NOTE 1 Beside other factors, the peak-to-background ratio depends on spectrometer resolution. Therefore, the ratio is only relevant for the comparison of spectrometers with similar resolution performance. NOTE 2 In an electron microscope, the bremsstrahlung from a manganese specimen can be considerably greater than the background component caused by degraded events. Therefore, a manganese specimen cannot be used to measure the peak-to-background ratio.ISO 15632 pdf download.