Decay chains disturbance

Other conditions being equal, the intermediate species with longer half-lives in a decay series have more opportunities to be fractionated from their parents. Hence, in the decay series of two nuclides °Th and Ra have a greater chance to be fractionated. In the decay series, Pa (half-life 32.8 has the greatest chance to be fractionated. In the Th decay series, all the intermediate species have short half-lives (the longest half-life of Intermediates is 5.75 3T for Ra (A, = 0.1205 3 ) and the disturbance of this decay system does not have much utility. That is, the U-series (including U and U series) disequilibrium is much more often applied. Some examples of disturbed decay chain (i.e., fractionation of the intermediate species) are given below ... 

An unfortunate footnote to this chapter in the history of the discovery of the heaviest elements is the revelation (Hofmann et al., 2002) that one of the decay chains reported by Hofmann et al. (1995a) for 269Ds was spuriously created, the result of human error or scientific misconduct. As disturbing as this finding is, it should not detract from the other correctly identified decay chains. 

It is an unfortunate fact that, within the natural decay chains, the nuclides most easily measured by gamma-ray spectrometry are in the later decay chain stages -beyond the point at which equilibrium might have been disturbed. 

Any disturbance from secular equilibrium decays back toward secular equilibrium through the decay of the shorter-lived supported chains. If the chains have significantly different decay rates, they are reasonably well decoupled and can be used to date processes comparable to the lifetimes of each chain (e.g., Condomines et al., 1988 Rubin et al., 1994 Thompson et al., 2003). As a useful rule of thumb, the time taken for a parent-daughter pair to return to approximate secular equilibrium, is about five half-lives of the shorter lived nuclide. In five half-lives, —97% of initial disequilibrium has decayed. Whether any detectable disequilibrium actually remains depends on the precision of measurements and degree of initial disequilibrium. 

The application of a properly timed rf pulse disturbs the net equilibrium magnetization aligned parallel to the magnetic field Hq. The return of nuclear magnetization to equilibrium for solid polymers depends on the chain mobility and is monitored by the FID. The crystalline phase content can be extracted by deconvoluting the decay curve into portions corresponding to crystalline and noncrystalline components. Crystallinity determination of various polyethylene samples by FID NMR based on two- and three-component approaches, as well as... 

A similar procedure was used to obtain spin-labelled TEE-HEP [49]. The presence of hexafluoropropylene (HFP) groups in this polymer leads to disturbance of the structural ordering typical of PTFE to more complex dynamics of their motion. After y-irradiation of powders and films of TFE-HFP copolymer in air, there are three types of stable peroxy macroradicals in the samples end radicals CF -CF O, secondary middle-chain radicals CF -CF(00 )-CF2, and tertiary middle-chain radicals CF2-C(CF3)(00 )-CF2. In contrast to PTFE, prolonged exposure (>100 hours) of these samples in a NO atmosphere at room temperature does not lead to the formation of aminoxyl macroradicals. However, two types of macroradicals are formed if TFE-HFP is heated with evacuation after the decay of radicals in a NO atmosphere. At 90 °C, the ESR spectrum demonstrates the presence of tertiary alkyl macroradicals CF2-C (CF3)-CF2 formed upon decay of the tertiary nitroso compounds [57]. On further increasing of the temperature up to 180 "C, the tertiary alkyl macroradicals... 

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