The Mossbauer Spectrometer

Mossbauer spectra are usually recorded in transmission geometry, whereby the sample, representing the absorber, contains the stable Mossbauer isotope, i.e., it is not radioactive. A scheme of a typical spectrometer setup is depicted in Fig. 3.1. The radioactive Mossbauer source is attached to the electro-mechanical velocity transducer, or Mossbauer drive, which is moved in a controlled manner for the modulation of the emitted y-radiation by the Doppler effect. The Mossbauer drive is powered by the electronic drive control unit according to a reference voltage (Fr), provided by the digital function generator. Most Mossbauer spectrometers are operated in constant-acceleration mode, in which the drive velocity is linearly swept up and down, either in a saw-tooth or in a triangular mode. In either case. 

Giitlich et al., Mossbauer Spectroscopy and Transition Metal Chemistry, 

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The Mossbauer spectrometer will typically divide the velocity scale into 256 channels. For a 0.93 GBq source (25 mCi), the total count rate of photons arriving at the detector and having the proper pulse-height is usually about C = 20,000 counts s Only about 85% of these will be 14.4 keV radiation the others are... 

Fig. 3.14 Left. NASA Mars-Exploration-Rover (artist view courtesy NASA, JPL, Cornell). On the front side of the Rover the robotic arm carrying the Mossbauer spectrometer and other instruments can be seen in stowed position. Right, robotic arm before placement on soil target at Victoria crater rim, Meridian Planum, Mars. The Mossbauer instrument MIMOS II with its circular contact plate can be seen, pointing towards the rover camera. See also Sect. 8.3...

Fig. 8.27 NASA Mars-Exploration-Rover artist view (courtesy NASA, JPL, Cornell). On the front side of the Rover, the robotic arm (IDD) carrying the Mossbauer spectrometer and other instruments can be seen...

Thermal Emission Spectrometer) instrument indicated the metallic nature of the rock [340]. Observations made with the panoramic camera and the microscopic image revealed that the surface of the rock is covered with pits interpreted as regmaglypts and indicate the presence of a coating on the surface. The a-Particle-X-ray spectrometer (APXS) and the Mossbauer spectrometer were used to investigate the undisturbed and the brushed surface of the rock. Based on the Ni and Ge... 

The miniaturized Mossbauer spectrometer MIMOS II has been used already in several terrestrial applications which would not have been possible before. A number of other possible terrestrial applications, for example, in the field, in industry, and fundamental research, are under consideration. With the new generation of the Mossbauer spectrometer MIMOS 11, the method itself can be applied to numerous new fields in research, environmental science, planetary science, and many other fields. Because of this reason, Mossbauer spectroscopy may become a more widely used method than it is today. 

Morris, R.V. et al. 2004. Mineralogy at Gusev Crater from the Mossbauer Spectrometer on the Spirit Rover. Science, 305, 833-836. 

Fig. 2.44. Mossbauer spectroscopy (a) nuclear transitions giving rise to the Mossbauer effect in Fe (b) principles involved in the Mossbauer spectrometer (c) Mdssbauer resonant absorption of iron in different crystal environments and the resulting spectral types. (After Vaughan and Craig, 1978 reproduced with the publisher s permission).

Although the Mossbauer spectrometer will not appear in the clinical laboratory for some time, if ever, it is conceivable that the very specific information it provides may become useful as diagnostic procedures become more refined. 

The Mossbauer spectrometer was equipped with a 10 mC 57Co/Rh source maintained at room temperature, A Northern NS-900 multichannel analyser was used for taking the spectra. The Mttssbauer parameters were determined by least square computer programme. The isomer shift (5) was calculated with reference to a-Fe, The characteristics of iron in various iron molybdates and iron antimonate are given in table I. 

The velocity calibration of the Mossbauer spectrometer is performed either by measuring the Mossbauer spectrum of standard materials or by a calibrator instrument measuring the absolute velocity of the source relative to the absorber. The latter can be achieved by counting the fringes from a Michelson interferometer with a laser source connected to the multichannel analyzer, and thus the velocity for each channel can be obtained. 

The possible experimental setup to perform in situ high-temperature transmission Mossbauer spectra is shown in Fig. 18.31. A powdered sample is uniformly spread on quartz wool and put into a quartz tube. The tube is then inserted into the special furnace (see Fig. 18.31). The furnace was placed between source and detector of the Mossbauer spectrometer. The temperature inside the furnace was regulated accurately by PID (Proportional-Integral-Derivative)... 

The furnace for in situ Mossbauer spectroscopy put between 7-rays source and detector of the Mossbauer spectrometer. 

The Mossbauer spectrometers which are in use nowadays generate the spectrum by the velocity-sweep method. The drive sy.stem moves the source (or absorber) repeatedly over a range of velocities, while simultaneously counting the y-quanta behind the absorber into synchronized channels. 

Andreeva MA, Belozerski GN, Grishin OV, Irkaev SM, Nikolaev VI and Semenov VG (1993) Mossbauer total external reflection A new method for surface layers analysis. I. Design and developing of the Mossbauer spectrometer. Nuclear Instruments and Methods B74 545-553. 

The theoretical spectrum of the 129 keV y-ray of Tr absorbed by an atom in iridium metal is shown in Figure 1. The Mossbauer spectrometer is sensitive only to the narrow, recoil-free line at zero energy... 

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