Heavy cluster emission

It was relatively recently that heavy cluster emission was observed at a level enormously lower than these estimates. Even so, an additional twist in the process was discovered when the radiation from a 223Ra source was measured directly in a silicon surface barrier telescope. The emission of 14C was observed at the rate of 10-9 times the a-emission rate, and 12C was not observed. Thus, the very large neutron excess of the heavy elements favors the emission of neutron-rich light products. The fact that the emission probability is so much smaller than the simple barrier penetration estimate can be attributed to the very small probability... 

The existence of cluster substructure in nuclei is supported also by the observation of cluster decay. Besides a particles, the heavy nuclei can emit Ne, Mg, Si clusters, too. The partial half-lives for these decays depend on the penetrability of the Coulomb barrier in a way very similar to a decay (Mikheev and Tretyakova 1990 see Geiger-NuttaU-type relations in O Sect. 2.4.1.1). The heavy cluster decay is a very rare phenomenon. For example, in the decay of Ra there were 65 x 10 a particles observed, while only 14 cluster emissions during the same time (Rose and Jones 1984). For the detection of rare clusters solid state track detectors are very suitable. 

Since the intracluster medium will become polluted by heavy elements because of the explosion of massive stars in the member galaxies, the amount of heavy elements in the cluster gas is a clue to the efficiency of this process, and an indirect clue to the heating mechanism. Recent observations with ROSAT and ASCA suggest that many observed clusters have lower than solar iron abundance, suggesting that chemical pollution by supernovae is not so important. However, spatially resolved X-ray spectra of galaxy cluster emission by ROSAT show that the central... 

L.) collected by beekeepers in apparently polluted and nonpolluted environments was performed by using inductively coupled plasma atomic emission spectrometry (ICP-AES) to measure significant concentrations of Ag, Ca, Cr, Co, Cu, Fe, Li, Mg, Mn, Mo, P, S, Zn, Al, Cd, Hg, Ni, and Pb. Fortunately, Cd, Hg, Ni, and Pb were not detected in the analyzed samples. Conversely, Ag, Cu, Al, Zn, and S were found in some samples located near industrial areas. Because a high variability was found in the concentration profiles, correspondence factor analysis was used to rationalize the data and provide a typology of the honeys based on the concentration of these different elements in the honeys. The results were confirmed by means of principal component analysis and hierarchical cluster analysis. Finally, the usefulness of the acacia honey as a bioindicator of heavy metal contamination is discussed. 

Nonequilibrium phenomena are distinguished by two principal features. First, they occur on a time scale much shorter than the typical equilibration time for statistical decay of a compound nucleus (t 10 s). Second, they produce multiparticle final states that are subsequently followed by statistical decay of the excited heavy product. In normal kinematics (Ap < At), the energetic light particles or clusters are forward-peaked and form a distinct exponential tail (area B in Fig. 3.41) on the Maxwellian spectra produced in later evaporation stages (area A in O Fig. 3.41). The preequilibrium component for the nucleon channels is as in by early stage emissions of the multistep compound model, as in by the FKK model for example. At the extreme of nonequilibrium emissions are the discrete peaks (labeled C), which correspond to direct reactions, or the first step in a multistep compound model. 

For bombarding energies well above the barrier, one also observes the preequilibrium emission of intermediate-mass fragments (2 < Z < 20, or IMFs) in reactions on heavy nuclei. The reaction observables for IMF emission strongly resemble those for light particles and presumably occur on a comparable short time scale. Models based upon a coalescence concept (Bond et al. 1977) have met with some success for light clusters, but encounter more difficulties for IMFs. 

A number of uncommon decay modes exist which are of little direct relevance to gamma spectrometrists and I will content myself with just listing them delayed neutron emission, delayed proton emission, double beta decay (the simultaneous emission of two 3 particles), two proton decay and the emission of heavy ions or clusters , such as and Ne. Some detail can be found in the more recent general texts in the Further Reading section, such as the one by Ehmann and Vance (1991). 

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