Decay energies

The effects of a rather distinct deformed shell at = 152 were clearly seen as early as 1954 in the alpha-decay energies of isotopes of californium, einsteinium, and fermium. In fact, a number of authors have suggested that the entire transuranium region is stabilized by shell effects with an influence that increases markedly with atomic number. Thus the effects of shell substmcture lead to an increase in spontaneous fission half-Hves of up to about 15 orders of magnitude for the heavy transuranium elements, the heaviest of which would otherwise have half-Hves of the order of those for a compound nucleus (lO " s or less) and not of milliseconds or longer, as found experimentally. This gives hope for the synthesis and identification of several elements beyond the present heaviest (element 109) and suggest that the peninsula of nuclei with measurable half-Hves may extend up to the island of stabiHty at Z = 114 andA = 184. 

Values are for decay to a Z = 60 daughter nucHde and a decay energy of 500 keV and are estimated from data in Ref. 3. 

Parent Daughter P-Decay energy, keV Mode Half-life PP-Decay energy, keV... 

PP2- However, there is an alternative theoretical mechanism by which the two Ps could be emitted without any neutriao, denoted PPq- The experimental methods that are used to look for the double P decay mode are often more sensitive to one of these decay modes than the other. The difference ia the expected energy distribution of the electrons is clear from the fact that ia the first case the total decay energy is divided between four particles, including the two antineutfinos that caimot be observed ia the second, it is only divided between the two electrons. As more exotic modes of decay are measured and even larger limits are placed on some of the half-fives, the constraints on theory become even stronger. 

Calorimeter. The P-decay energy of tritium is very precisely known (9). The thermal energy generated by the decay can thus be used with a specially designed calorimeter to measure the quantity of tritium in a system of known heat capacity. 

C22-0090. Neutrons decay into protons. What is the other product of this decay If all of the decay energy is converted into kinetic energy of this other product, how much kinetic energy does it have ... 

Beyond the Boson peak, the reduced DOS reveals for all studied glasses a temperature-independent precisely exponential behavior, g(E)/E exp( / o) with the decay energies Eo correlating with the energies E of the Boson peak. This finding additionally supports the view that the low-energy dynamics of the glasses are indeed delocalized collective motions because local and quasilocal vibrations would be described in terms of a power law or a log-normal behavior [102]. 

Isotope Half-life years Mode of formation3) Specific activity Ci/g Principal mode of decay Energy, MeV Maximum15) permissible body burden liC i... 

The functions of the solvent are to keep the scintillator or solute in solution, and to absorb the decay energy of the radioisotope for subsequent transfer to the solute. Solvents fall broadly into three categories ... 

If the available decay energy (mass difference between decaying and produced nuclides) exceeds 1.02 MeV, one positron and one electron may be annihilated reciprocally, with the emission of two y photons of energy corresponding to the masses of the annihilated particles—i.e.. 

Electron capture is a particular form of )3 decay, described for the first time by Alvarez (1938) and practically equivalent to positron emission. When the decay energy of the nuclide is not sufficient to attain the reaction... 

The low decay energy prevents accurate determinations of half-life by direct counting. Reported half-lives range from 3 to 6.6 X 10 ° a. The most recent direct determination (Lindner et al., 1989) assigns a half-life of (4.23 0.13)Xl0 °a to the decay process of equation 11.117, which is fairly consistent with the indirect estimates of Hirt et al. (1963) [(4.3 0.5) X 10 ° a]. The isochron equation is normalized to the °Os abundance ... 

The only isotope of Es available in at least multimicrogram quantities is Es, whose half-life is 20.5 days. Considering the 6.6-MeV a-particles it emits at the rate of about 6 x 10 min /ig S the a-decay energy alone amounts to some 1.5 x 10 kJ mol min". This explains why there have been very few attempts to prepare Es metal ... 

The values In parentheses are the decay energies for the beta particles. 

Table 6.1. Biochemically important radioisotopes. Half-life, )3-decay energy, and specific radioactivity...

Mass number Half-life Mode of decay < energy (mev)... 

Kinetic energy of fission fragments 165 Radioactive-decay energy 23... 

In many situations, the experimenter will prefer to buy labeled compounds from commercial suppliers rather than attempt to synthesize them. The radiochemical purity of such purchased compounds cannot be assumed. Radiation-induced selfdecomposition (radiolysis) can result in the formation of a variety of labeled degradation products, which must be removed before experimental use of the compounds. The extent of radiolysis depends on the nature of the labeled compound, how long it has been stored, and the manner of storage. Radiolysis is most significant with low-energy (3 emitters (especially tritium) since the decay energy is dissipated almost entirely with the compound itself. Furthermore, impurities involving other radionuclides may be present. 

---