WEMS2016

**On the Syntheses of ⁵⁷Mn Compounds for the Moessbauer Researches**

1 Jul 2016, 13:55

30m

Miscellaneous science

Speaker

Dr Sergey Dedushenko (-)

Description

⁵⁷Mn emission Moessbauer spectroscopy has been known since 1975, when Preston and Zabransky published the first paper [1]. They applied the nuclear reaction ⁵⁴Cr(α,p)⁵⁷Mn to synthesize the source of ⁵⁷Mn in Cr₂O₃ matrix. In 1992 Nakada et al. [2] used the same reaction to get the sources from metallic chromium, Cr₂O₃ and CrO₃. Later, the alternative approach for producing the ⁵⁷Mn sources by ion-implantation of ⁵⁷Mn into substance was developed in ISOLDE [3] and RIKEN [4].

The peculiarity of these two approaches is the complicated chemistry which accompanies the stabilization of ⁵⁷Mn ions after ⁵⁴Cr decay or the stabilization of ⁵⁷Mn ions braking in the target as well as the radiolysis of the substance. The half-life time of ⁵⁷Mn is quite short (85 s). Therefore, it is difficult to conduct the common chemical synthesis with it. However, such a synthesis could be realized using convincing chemical reactions.

The simplest way to involve manganese into chemical reaction is to heat-up the target. This approach was already applied for several matrices. But the spectra obtained are commonly quite complicated due to the presence of several forms of ⁵⁷Fe, magnetic effects being also observed. This is due to the nature of the matrices, in particular, their low chemical activity.

We believe that the use of chemically active matrices is a way to the synthesis of ⁵⁷Mn-doped compounds containing manganese in wide range of oxidation states. We would offer several reactions which were already used by us to synthesize the compounds of ⁵⁷Fe and ⁵⁷Co [5-9].

The first type of the reactions, which could be tested is the oxidation of ⁵⁷Mn in the matrix of alkali metals peroxides or superoxides (MO_x). These oxides contain active oxygen which allows one to oxidize manganese at moderate heating [5,6]. According to manganese chemistry such interactions lead to manganese(IV), (V) and (VI). To make such tests ⁵⁷Mn can be implanted into the powder or the melt of MO_x. Then, the short-time heating should be quickly done to transform manganese into MnO₄^n--ions, n=2,3,4. In spite of high chemical activity of the peroxides and superoxides, many of them are melted at high temperatures and stable when melting. The oxidation of the transition metal takes place locally. Thus, the reactions can be cyclically repeated with the same target.

The second type is the reactions with the mixture of alkali metal peroxides or superoxides and transition metals (metal powder, oxides, etc.) [3-5]. In this case, the chemical behavior of implanted ⁵⁷Mn is determined by the matrix of the synthesizing metallates (chromates, manganates, ferrates, cobaltates, etc.). But to repeat the synthesis one should use fresh mixture.

The above mentioned reactions are greatly exothermic. The interactions are self-sustaining and less sensitive to the temperature profile in the reaction zone. The irradiation by light can be effectively used to initiate the interactions. This should noticeably simplify the experimental set-up. In particular, it allows one to use different zones of one target sequentially for the implantation and the heating.

The formation of manganate-ions (⁵⁷MnO₄^n-) could be used for Moessbauer observation of Fe⁷⁺. Indeed, it is well-known that the proper acidification of the substrate containing MnO₄^n--ions leads to disproportionation of manganese:

5 MnO₄^n- + 8(n-1) H⁺ → (6-n) MnO₄^- + (n-1) Mn²⁺ + 4(n-1) H₂O

The respective study of ⁵⁷Co and ⁵⁷Fe with the dissolution in alkali media was already performed by us [10]. But instead of iron and cobalt reduced in acidic media, manganese can easily transform to septavalent state.

We consider also the third type of the reactions where ⁵⁷Mn could be implanted into a stable at high temperature easily melting but relatively inert substance of simple composition, e.g. into V₂O₅ [8,9]. In this case, any defects can be eliminated by melting. Then, the chemical behavior of manganese is determined by crystallizing melt. This synthesis can be also performed repeatedly with one target.

References:

1. R.S.Preston and B.J.Zabransky, Physics Lett. 1975, V.55A (3), p.179-180.

2. M.Nakada et al., Bull. Chem. Soc. Jpn. 1992, V.65, p.1-5.

3. V.N.Fedoseyev et al., Nucl. Instrum. Methods Phys. Res. B 1997, V.126, 88-91.

4. Y.Yoshida, Hyp. Int. 1998, V.113, p.183-198.

5. S.K.Dedushenko et al., J.Alloys Compd. 1997, V.262-263, p.78-80.

6. S.K.Dedushenko et al., Radiochemistry 1998, V.40 (5), p.416-419.

7. S.K.Dedushenko et al., Hyp. Int. 2008, V.185, p.197-202.

8. S.K.Dedushenko and Yu.D.Perfiliev, Bull. Rus. Acad. Sci. Physics 2001, V.65 (7), p.1125-1128.

9. S.K.Dedushenko et al., Radiochemistry 2014, V.56 (5), p.481-485.

10. L.A.Kulikov et al., J. Phys. Chem. Solids 1995, V.56 (8), p. 1089-1094.