MS Dual Detector

main idea and purpose

Mössbauer spectroscopy is an analytical technique to study any iron containing material in solid form to identify the local chemical and phase composition. The most common used experimental geometry is transmission. The main disadvantage is that transmission geometry requires sample which is transparent for 14.4 keV gamma photos. This limits the usage specifically on micro and nanomaterials. If bulk sample analysis is required, it is necessary to choose different approach. This is when Conversion Electron (CEMS) or X-ray geometries (CXMS) comes to play [1][2][3]. Conversion Electron measurement is sensitive on very thin surface layer, typically 100 - 300 nm. X-rays measurement is sensitive on thicker surface layer, typically 1 - 10 um, which practically represents the sample volume information. Common experimental procedure consists of 2 independent and time consuming analyses - one is CEMS and one is CXMS. Also typicall limitation is the applicability on small samples only.

The idea of the Dual Detector is to combine CEMS and CXMS detectors into single compact body and to be able to perform both analyses at the same time. Another significant advantage of the Dual Detector is that it designs allows to analyse samples with unlimited size. This detector may find its usage in studies of bulk materials and their aging (rusting), it can be used for thin layers investigation too and it is designed for usage not just in laboratory, but also on-site. Therefore it can be very useful tool to analyse steel constructions directly on-site.

Technical Description

Dual Detector main idea is shown on figure 1 bellow. The top left diagram shows the idea of the combination of both CEMS and CXMS detectors. Both detectors are designed as gas flow detection chambers. Both chambers are transparent for 14.4 keV gamma photons in vertical direction, thus the radiation goes from top, through both chambers, to the sample at the bottom. When the gamma photon is absorbed by sample, conversion electron or conversion X-rays photon is emitted. Conversion electrons are detected by CEMS detector, which is filled with Helium and Methane mixture. Conversion X-rays goes through CEM detector intact, until they reach CXMS detector where these photons are detected. CXMS detector is filled with Argon and Methane mixture.

The bottom left picture shows a 3D model of the Dual Detector, where gas inlets and outlets are visible (for both detection chambers). Also, anode is visible here, as the detector is designed to be simply placed directly on the surface of the sample (there is a special holder, if the sample is smaller.

The right picture shows an example of on-site application. The Dual Detector is attached to a velocity drive which is equipped with radioactive source. Then this device can be easily put on the surface of bulk sample.

Fig.1: Priciple diagram (top left), Dual Detector 3D model (bottom left), example of application (right).

Reference

[1] J. Frydrych, M. Mashlan, J. Pechousek, and D. Jancik, “Conversion Electron Detectors for 57Fe Mössbauer Measurements,” AIP Conf. Proc., vol. 1070, no. 1, pp. 170–184, Oct. 2008, doi: 10.1063/1.3030842.

[2] G. Klingelhöfer et al., “Athena MIMOS II Mössbauer spectrometer investigation,” J. Geophys. Res. Planets, vol. 108, no. E12, pp. 8067–8084, Dec. 2003, doi: 10.1029/2003JE002138.

[3] G. Longworth, “The use of Mössbauer spectroscopy in non-destructive testing,” NDT Int., vol. 10, no. 5, pp. 241–246, Oct. 1977, doi: 10.1016/0308-9126(77)90119-5.