Mossbauer spectroscopy blocking temperature

In studies of superparamagnetic relaxation the blocking temperature is defined as the temperature at which the relaxation time equals the time scale of the experimental technique. Thus, the blocking temperature is not uniquely defined, but depends on the experimental technique that is used for the study of superparamagnetic relaxation. In Mossbauer spectroscopy studies of samples with a broad distribution of relaxation times, the average blocking temperature is commonly defined as the temperature where half of the spectral area is in a sextet and half of it is in a singlet or a doublet form. 

This temperature is determined by Fe Mossbauer spectroscopy. The blocking temperature, the spectral superparamagnetic transition temperature, is the temperature at which doublet and sextet signals have equal integrated intensities. The doublet arises from small particles and the sextet from larger particles. 

The smaller diameter of the iron cores of ferritin in brain compared to that in liver tissues fits well with the blocking temperatures measured by Mossbauer spectroscopy. The blocking temperature determined by MS for SN is about I5 K [20] compared to about 35-40 K for human liver [21 ]. Figure 16.4 presents the Mossbauer spectra obtained from SN at 20 K, I OK, and 4.1 K, from which the blocking temperature was estimated. 

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