In-beam Mossbauer spectroscopy

IN-BEAM MOSSBAUER SPECTROSCOPY USING A RADIOISOTOPE BEAM AND A NEUTRON CAPTURE REACTION... 

In-beam Mossbauer spectroscopy (IBMS) involves online measurement of Mossbauer -Y-radiation emitted from excited atoms produced by nuclear reactions, Coulomb excitation, and radioisotope (Rl) implantation. It provides useful information on local atomic and electronic configurations (i.e., site distributions, dynamic diffusion processes, and unusual chemical states) of extremely dilute atoms during the lifetime of the excited Mossbauer state. Physical and chemical transformations that occur in nonequilibrium and metastable states immediately after nuclear reactions and implantation can be observed in suitable materials. This chapter introduces past and current experimental techniques of in-beam Mossbauer spectroscopy and reviews some recent topics using Mn (T /2 = 85s) nuclei at RIKEN Rl Beam Factory (RIBF) and thermal neutron capture reaction. 

In this chapter, Mossbauer measurements performed in conjunction with (a)-(c) are referred to as in-beam Mossbauer spectroscopy. 

In-beam Mossbauer spectroscopy is a source experiment and, as such, has three distinct advantages over conventional absorption experiments. First, the concentration of Mossbauer probe atoms in a sample is typically several orders of magnitude lower than that in absorption experiments. This makes source experiments more sensitive than absorption experiments and leads to a preponderance of radioactive sources for dilute systems. A concentration in the range 10 10 atoms cm is generally sufficient to observe the Mossbauer effect. It has recendy become possible to measure a Fe Mossbauer spectrum using an implantation dose rate of I O particles s of Mn nuclei by using a... 

The remainder of this chapter is organized as follows. The next section describes some experimental and application investigations of in-beam Mossbauer spectroscopy using a Mn beam at the RIKEN RIBF. The system used for detecting Mossbauer 7-radiation in in-beam experiments is important. Nagatomo et al. [32] have recently developed a highly sensitive resonance counter based on parallel-plate avalanche and plastic scintillation counters. A new anticoincidence detection system is introduced. Finally, the experimental setup for online Mossbauer spectroscopy using the thermal neutron capture reaction, Fe (n, 7) Fe, and the results obtained are presented in the subsequent section. 

Weyer [50] developed a conversion electron detector based on a PPAC for Mossbauer spectroscopy. Conversion electrons are emitted from the surbce of a Mossbauer absorber after resonance absorption with a conversion coefficient a (a = 8.2 for 14.4 keV Fe). In principle, a conversion electron detector is very sensitive only for resonant Mossbauer 7-rays without interference of nonresonant 7-radiations. The PPAC is importantfor in-beam Mossbauer spectroscopy of implanted excited atoms and Rl nuclei in environments with high backgrounds. 

This chapter describes some past and current topics in in-beam Mossbauer spectroscopy. There have been a wide variety of application-related studies of in-beam Mossbauer spectroscopy in conjunction with nuclear reactions. Coulomb excitation, recoil implantation, and short-lived Rl beams. New in-beam measurement methods and the introduction of... 

In Chapters I and 2, an introduction is made to the synchrotron Mossbauer spectroscopy with examples. Examples include the/ns/tu Mossbauer spectroscopy with synchrotron radiation on thin films and the study of deep-earth minerals. Investigations of in-beam Mossbauer spectroscopy using a Mn beam at the RIKEN RIBF is presented in Chapter 3. This chapter demonstrates innovative experimental setup for online Mossbauer spectroscopy using the thermal neutron capture reaction, Fe (n, y) Fe. The Mossbauer spectroscopy of radionuclides is described in Chapters 4-7. Chapter 4 gives full description of the latest analysis results of lanthanides Eu and Gd) Mossbauer structure and powder X-ray diffraction (XRD) lattice parameter (oq) data of defect fluorite (DF) oxides with the new defect crystal chemistry (DCC) Oq model. Chapter 5 reviews the Np Mossbauer and magnetic study of neptunyl(+l) complexes, while Chapter 6 describes the Mossbauer spectroscopy of organic complexes of europium and dysprosium. Mossbauer spectroscopy is presented in Chapter 7. There are three chapters on spin-state switching/spin-crossover phenomena (Chapter 8-10). Examples in these chapters are mainly on iron compounds, such as iron(lll) porphyrins. The use of Mossbauer spectroscopy of physical properties of Sn(ll) is discussed in Chapter I I. 

New experiments on Fe in Si with the in-beam Mossbauer spectroscopy technique were performed at the Hahn-Meitner institute in Berlin. The technique is outlined in Sect. 6.3. The results of these Coulomb excitation recoil implantation studies [26] confirmed this picture and led to an unambiguous identification of... 

Fig. 6.16 The experimental set-up for in-beam Mossbauer spectroscopy at Hahn-Meitner Institute Berlin...

To overcome the above mentioned difficulties in the studies of the fast diffusion in metals, several research projects were designed and performed in 1980s for about 10 years using the in-beam Mossbauer spectroscopy technique combining... 

Y. Yoshida, Direct Observation of Substitutional and Interstitial Fe atoms in Si by high-temperature and In-beam Mossbauer Spectroscopy , in ALTECH 2003, ECS, Salt Lake City, US, 479-482 (2003). 

At this point, if we consider the Mossbauer parameters calculated in conventional Mossbauer spectroscopy, the isomer shift (IS) is not accessible from NFS spectra, because the latter only shows interference between radiation fields corresponding to different radiations. Isomer shifts will have to be measured relative to a second reference absorber that must be placed behind or in front of the sample along the y-ray beam. 

Conversion electron Mossbauer spectroscopy (CEMS) measurements with back scattering geometry have the merit that spectra can be obtained from a sample with much less isotope content compared with transmission measurements. Another merit is that a sample, deposited on a thick substrate, could be measured, and that because of the limited escape depth of the conversion electrons, depth-selective surface studies are possible. The CEMS technique was found to be best applicable to specimens of 10-100 pg Au cm, i.e., about two orders of magnitudes thinner than required for measurements in transmission mode [443]. This way (1) very thin films of gold alloys, as well as laser- and in beam-modified surfaces in the submicrometers range of depth [443], and (2) metallic gold precipitates in implanted MgO crystals [444] were investigated. 

Atoms are not rigidly bound to the lattice, but vibrate around their equilibrium positions. If we were able to look at the crystal with a very short observation time, we would see a slightly disordered lattice. Incident electrons see these deviations, and this, for example, is the reason that in LEED the spot intensities of diffracted beams depend on temperature at high temperatures the atoms deviate more from their equilibrium position than at low temperatures, and a considerable number of atoms are not at the equilibrium position necessary for diffraction. Thus, spot intensities are low and the diffuse background high. Similar considerations apply in other scattering techniques, as well as in EXAFS and in Mossbauer spectroscopy. 

Most often the transmission mode is found to be the most convenient in Mossbauer spectroscopy, i.e., the y radiation passes from the source through the absorber, and the attenuation of the primary beam is measured at the various Doppler velocities. However, there are a number of cases where a "scattering geometry may be advantageous (SO). The basis for this geometry lies in those processes that take place after resonant absorption of y radiation by the Mossbauer isotope. Specifically, after excitation the Mossbauer isotope may reemit the y ray, or it may decay by emission of internal conversion electrons and X rays [with the probability of internal conversion equal to a/(l + a)]. 

Vibrational (IR and Raman), UV-visible, photoelectron, NMR, and Mossbauer spectroscopy have all been reported for bis(bistrimethylsilyl-methyl)tin(II) and analogous tin(II) amides. Since an unusual tin-tin double bond has been proposed for the solid state of [Sn[CH(SiMe3)2]2]2 the Raman spectrum of this compound was of interest. Unfortunately, the compound decomposed in the laser beam however, an intense band at 300 cm-1 has been assigned as the Ge—Ge stretching frequency for the analogous germanium compound (68). 

The presence of the stable isotope Fe to an abundance of 2.2% in all natural compounds of iron makes it possible to study hemoglobin by the methods of Mossbauer spectroscopy (/). In such experiments one exposes a sample of hemoglobin to a beam of highly monochromatic... 

Pol] Poliak, H., Fleischmami, A., Luyckx, S.B., Koursaris, A., Investigation of the Phases Present in C-Fe-V Alloys by Mossbauer Spectroscopy and X-ray Diffraction , Nucl. Instrum. Methods Phys. Res., Sec. B., (Beam Interactions with Materials and Atoms), Netherlands, B76(l-4), 270-272 (1993) (Phase Relations, Experimental, 2)... 

The spin and valence states of iron in the lower-mantle minerals have been investigated bya number of synchrotron X-ray and optical laser spectroscopic techniques in a high-pressure diamond anvil cell (DAC). Mossbauer spectroscopy has been instrumental in our understanding of this topic because this method is specific to Fe-containing minerals and provides hyperfine QS and CS parameters [5,19-22]. Specifically, synchrotron Mossbauer spectroscopy (SMS) with a highly intense and focused beam coupled with the X-ray transparent DAC permits in situ observations of the Mossbauer spectra with reasonable data collection times at extreme P-T conditions [20-22]. 

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