Mossbauer decay scheme

In the following sections, we discuss the decay schemes for all Mossbauer-active transition metal nuclides other than iron. For the sake of completeness, the decay scheme for Fe (see Fig. 7.1) is inserted here. The relevant nuclear data,... 

There are two iridium isotopes, ir and Ir, suitable for Mossbauer spectroscopy. Each of them possesses two nuclear transitions with which nuclear resonance absorption has been observed. Figure 7.58 (from [266]) shows the (simplified) nuclear decay schemes for both iridium Mossbauer isotopes the Mossbauer transitions are marked therein with bold arrows. The relevant nuclear data known to date for the four Mossbauer transitions are collected in Table 7.1 at the end of the book. 

Fig. 7.58 Simplified decay scheme leading to the population of the four nuclear Mossbauer transitions of lr and Ir (from [266])...

There are two y-transitions in Pt amenable to the Mossbauer effect - the 130 keV transition between the 5/2 excited state and the 1/2 ground state and the 99 keV transition between the first excited 3/2 state and the ground state. Figure 7.70 shows the simplified decay scheme of Pt. The relevant nuclear data may be taken from Table 7.1 (at the end of the book). 

Fig. 7.70 Simplified decay scheme of The two Mossbauer transitions have energies of 98.86 keV and 129.74 keV (from [1])...

Figure 1. Simplified decay schemes of the Mossbauer source nuclides.

Fig. 3.40 The decay scheme of for Mossbauer spectroscopy with Fe. (Reprinted with permission from ref. 13. Copyright 1974 Pion Limited, London.)...

Fig. 2.7 The decay scheme of Kr showing how the 9-3-keV Mossbauer level is populated by I.T., and E.C. decay. The levels are not drawn to scale, and the details are taken from ref. 47.

The first excited state of I can be populated by decay of 33-day Te or 70-minute Te. Both parents are conveniently produced by the Te(n, y) reaction. The decay scheme (shown in simplified form in Fig. 15.17a) is very complex, and there is some divergence of opinion regarding the details. We have adapted the recent work of Berzins et al. [69]. Early I measurements were made using inaccurate values for some of the relevant nuclear constants. The currently accepted value for the I MOssbauer y-ray energy is = 27-72(6) keV [70]. The excited-state lifetime is = 16-8(2) ns, giving a natural width of 0-59 mm s" [70]. The y-ray has nearly pure Ml multipolarity, and the nuclear spin states are and /g =... 

The 134-24-keV resonance of Re was reported in 1960 [56]. In addition to the inherent disadvantages of a high y-ray energy, the excited-state lifetime is also shorter than usual, although this parameter was unknown until determined from the Mossbauer resonance. A tungsten source (see simplified decay scheme in Fig. 16.18) and rhenium absorber were used at 20 K, and... 

Fig. 2. Decay scheme of Co(57).TheMl decay from the 14.41 keV level is the Mossbauer active decay...

Fig. 4. Source decay-scheme and energy transitions at a Fe and b Ni Mossbauer isotopes...

The source decay-scheme and the energy transitions for detection of Te Mossbauer isotopes are simple if we start from the popular parent (EC 60 d) or from sb (EC2.7y) [7]. 

Using two detectors simultaneously, one has to detect the 122 keV y quanta coming from the Mossbauer source as a start signal. This actually marks the birth of the 14.4 keV Mossbauer excited level (see the decay scheme inO Fig. 25.7). Then, with the other detector, the 14.4 keV y quantum is detected, and the elapsed time measured (stop signal). With this method, Mossbauer spectra can be recorded in any time interval after the nuclear decay of Co. Recording characteristic X-rays following the electron capture, part of the aftereffect events can be filtered off. Due to the coincidence technique, very low activities can only be used, and therefore these measurements are rather time consuming (several weeks or months). 

As a typical example. Figure 6 shows the decay scheme of Co which populates the 14.4 keV Mossbauer level of Fe with a lifetime of T=140ns. The isotope Co can be produced in a cyclotron by the nuclear reaction Fe(d,n) Co. The decay of Co occurs essentially by electron capture (99.8 %) from the K-shell leaving a hole in this shell which is tilled from higher shells under emission of a 6.4 keV X ray. Sources of Co are usually prepared by electrochemically depositing the carrier-free isotope on metallic supports and then diffusing it into the metal at high temperatures. 

FIGURE 5. Decay schemes of ""Sn and Co. The nuclear transitions associated with Mossbauer spectroscopy measurements are shown by the heavy arrows. Also indicated are the transition lifetimes, Ti/2, for the states involved. Internal conversion processes have not been included. Energies are given in keV. E.C. refers to electron capture. (Adapted from Ref. 2a.)... 

The most common type of source for Fe Mossbauer spectroscopy consists of elemental Co incorporated into a host metal lattice such as rhodium or copper. In the case of Sn measurements, " Sn-enriched CaSnOa or BaSnOa is used as a source. Schematic diagrams of the radioactive decay schemes for these two isotopes are shown in Figure 5. In addition to these transitions, internal conversion processes may give rise to emission of radiation of other energies. For example, in the case of Fe, the / = state may decay via the ejection of a X-shell 7.3-keV electron, and the hole created be filled by an L-shell electron, leading to the emission of either a 6.4-keV electron (Auger process) or X-ray in order to conserve energy. 

---