Hahn decay

Radioactive, silvery metal of which only about 125 g exists worldwide, isolated from reactor material. Protactinium occurs in the decay series of 238U (K. Fajans) as 234Pa. It also occurs in that of 235U this isotope, 231Pa, was discovered by L. Meitner and 0. Hahn. The element is only of scientific interest. 

Fission of the nucleus, whereby it splits into two roughly equal halves, is accompanied by a huge release of energy. It was first observed by Hahn and Strassman (1939), who were bombarding uranium with neutrons. Many heavy elements are susceptible to induced fission, but spontaneous fission can occur in some of the heaviest elements, and is thought to be the principal mode of decay for the transuranic elements. 

It was first identified and named brevium, meaning brief, by Kasimir Fajans and O. H. Gohring in 1913 because of its extremely short half-life. In 1918 Otto Hahn (1879—1968) and Lise Meitner (1878-1968) independently discovered a new radioactive element that decayed from uranium into (actinium). Other researchers named it uranium X2. It was not until 1918 that researchers were able to identify independently more of the elements properties and declare it as the new element 91 that was then named protactinium. This is another case in which several researchers may have discovered the same element. Some references continue to give credit for protactinium s discovery to Frederich Soddy (1877—1956) and John A. Cranston (dates unknown), as well as to Hahn and Meitner. 

Fig. 3. The basic Hahn sequence for the measurement of the transverse relaxation time T2. Any precession motion characterized by the frequency v in the rotating frame is refocused. This precession may arise either from chemical shift or from Bq inhomogeneity (symbolized by the shaded area, which has been strongly reduced for visualization purposes owing to the fast decay of the fid, it should in fact extend to the whole circle).

Figure 3. Cross polarization magnetization for the PIP-cured epoxy under the SL (Hartmann-Hahn) condition. The cross polarization contact time is rcp. The decay corresponds to proton T,p relaxation.

Pa, protactinium, was first identified in 1913 in the decay products of U-238 as the Pa-234 isotope (6.7 h) by Kasimir Fajans and Otto H. Gohring. In 1916, two groups, Otto Hahn and Lisa Meitner, and Frederick Soddy and John A. Cranston, found Pa-231 (10 years) as a decay product of U-235. This isotope is the parent of Ac-227 in the U-235 decay series, hence it was named protactinium (before actinium). Isolation from U extraction sludges yielded over 100 g in 1960. 

Elliott. S.R.. A.A. Hahn, and K.M. Moe Direct Evidence for Two-Neutrino Double-Beta-Decay in Se," Physical Review Letters. 59, 18, pp. 2020-2023 (November 2, 1987). 

It was obvious that process 3 was the most normal - a resonance capture of slow neutrons to form 239U, a beta emitter which necessarily decays to element 93. If the Berlin team had been able to detect this element 93 and determine its chemical properties, they would have realized that processes 1 and 2 were incorrect. But they did not do it. In Berlin, as Hahn later wrote, they were not very interested because... 

In the Cohen-Addad-Sotta model [23, 25] the Hahn-echo decay is expressed without the assumption of dangling chains by the expression ... 

Figure 7.8 The shape of the Hahn-echo decay in cross-linked elastomers is given by the line of diamonds. In the short-time limit the curve can be approximated by a Gaussian (broken line) and in the long time limit it follows an exponential (solid line) [30]...

Figure 7.23 Applications of the NMR-MOUSE to elastomer materials (a) T2 values for a curing series of carbon-black filled NR. Comparison of values obtained at high homogeneous field (DMX 300) and with the NMR-MOUSE, (b) cross-link series of unfilled SBR with different sulfur content, (c) T2 versus glass-transition temperature Tg of unfilled SBR by the CPMG and the steady-state CPMG methods, (d) normalized Hahn-echo decay curves for poly(butadiene) latex samples. Different decay rates are obtained for small medium and large cross-link densities...

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