Branching decay

Parent Original name Half-hfe Decay Branching, % Daughter... 

However, as shown in figure 11.16, also decays into " °Ca (jS = 89.5%). The " °K-to-" °Ar decay branch is dominated by electron capture, although a limited amount of positron emission of low energy is observed (about 0.001%). 

This method of analysis is called absolute activation analysis and is done rarely. The reasons for this are the need for detailed knowledge of the flux and energy of the bombarding particles in the sample, the compounding of the uncertainties of our knowledge of cross sections, decay branching ratios, and the like in the final results. A simpler technique is to irradiate and count a known amount of pure X under the same conditions used for the mixture of X inY. Then... 

The external dose to an inadvertent intruder who is assumed to be exposed to uncovered waste for a period of 1,000 h at the time of facility closure can be estimated as follows. For a 137Cs source assumed to be uniformly distributed in surface soil with its decay product 137mBa in activity equilibrium, and taking into account the decay branching fraction of 0.946 (Kocher, 1981), the external dose rate per unit concentration is 2.9 X 10 11 Sv s 1 per Bq g 1 (Eckerman and Ryman, 1993). Multiplying this external dose coefficient by the assumed concentration of 137Cs (4.8 Bqg ) and exposure time (1,000 h) gives a total dose for the assumed scenario of 5 X 10 4 Sv. 

By studying the a decay of mass-separated nuclei in the region around Z=82 we have extended the knowledge of shell-model intruder states. The allowed a-decay branches of the odd-odd Bi nuclei connect across the Z=82 shell closure initial and final states of the same single-particle character. 

With rn( only the total decay rate or, equivalently, the total level width of an inner-shell hole-state has been considered so far. In general, the system has different decay branches. In many cases these branches can be classified as radiative (fluorescence) or non-radiative (Auger or autoionizing) transitions, and even further, by specifying within each group individual decay branches to different final ionic states. (Combinations of radiative and non-radiative transitions are also possible in which a photon is emitted and simultaneously an electron is excited/ ejected. These processes are termed radiative Auger decay (see [Abe75]).) As a result, the total transition rate Pnr and, hence, the total level width is composed of sums over partial values ... 

Before these partial quantities are discussed further, an important comment has to be made unlike the partial transition rates, the partial level widths have no direct physical meaning, because even for a selected decay branch it is always the total level width which determines the natural energy broadening. The partial level width is only a measure of the partial transition rate. Both aspects can be inferred from the Lorentzian distribution attached to a selected decay branch, e.g., Auger decay, which is given by... 

The dominant decay branches which result from Is ionization in neon are shown in Fig. 2.5. The fluorescence decay concerns the dipole transitions 2p - Is, shown in the upper row. In the X-ray nomenclature they are called K-L2 3 transitions where the dash is used to separate the initial and final hole-states. These transitions are also called Ka, 2 transitions (see Fig. 2.2). As can be seen in the experimental fluorescence spectrum shown in Fig. 2.6, in addition to these K-L2 3 main transitions there are other lines called satellites. These satellites result from KL-L2 and even KL2-L3 transitions where the dash again separates initial and final hole-states, e.g., KL-L2 radiative transitions start with two holes, one in the K-shell, and one in the L-shell, and they end with two holes in the L-shell. 

Summarizing the individual decay branches of the 4d5/2 -> 6p resonance, one finds that all final ionic states can also be reached by outer-shell photoionization, in (a) and (b) by main processes, and in (c)-(i) by discrete and continuous satellite processes. The effect of the resonance decay will then be a modification of these otherwise undisturbed direct outer-shell photoionization processes which turns out to be an enhancement in the present case. Therefore, these outer-shell satellites are called resonantly enhanced satellites. In this context it is important to note that outer-shell photoionization also populates other satellites, attached, for example, to electron configurations 5s25p4ns and 5s25p4nd. However, the parity of these satellites is even, while the decay branches (c)-(/) lead to odd parity. Therefore, both groups of final ionic states can be treated independently of each other (if configuration interaction in the continuum is neglected). 

Motivated by the observed decay rate discrepancy between QED theory and experiment for At, numerous searches have been performed for forbidden, small or exotic decay modes. An exotic decay branch, besides o-Ps —> 37, with roughly 10-3 branching ratio could be causing the higher decay rate and is given by A 0bs = + A exotic- Many candidate decay branches have been proposed in... 

The primary conclusion is that there is no evidence for the existence of any exotic decay branch from o-Ps, which, in turn, could be causing the o-Ps decay rate discrepancy. The statistical significance of the negative results is, in most cases, overwhelming. On the other hand, o-Ps exotic decays cannot be conclusively ruled out as the cause of the decay rate discrepancy. Certain mass... 

On-line gas chemical studies of dubnium have been mostly performed with Db. This nuclide can be produced in the reaction Bk( 0,5n) at a beam energy of about 100 MeV. It has a half-life of 34 5 s and decays with 67 % by emission of two sequential a particles via 258Lr (T1/2=4.4 s) to the long-lived 254Md (Ti/2=28m). In addition, 262Db has a spontaneous fission decay branch of 33%. Hence, identification of each separated labeled molecule is based on either detection of two characteristic a-particles and their lifetimes or on the detection of a spontaneous fission decay. 

The prior presence of " Pu, the only transura-nic nuclide known to have been present in the early solar system, can be inferred from its spontaneous-fission decay branch, through production of fission tracks and, more diagnostically, by production of fission xenon and krypton. The identification of " Pu as the fissioning nuclide present in meteorites is unambiguous, since the meteoritic fission spectrum is distinct from that of but consistent with that of artificial " Pu (Alexander et al, 1971). The demonstration of the existence of " Pu in the solar system reinforced the requirement (from the presence of I) of a relatively short time between stellar nucleosynthesis and solar-system formation and made it incontrovertible, since while it might be possible to make in some models of early solar system development, the rapid capture of multiple neutrons (the r-process) needed to synthesize Pu could not plausibly be supposed to have happened in the solar system. 

Many candidate decay branches have been proposed in... 

Abbreviations are y, year d, day m, minute and second. Less prevalent decay branches are shown in blue. 

Many measurements of B decays involve admixtures of B hadrons. Previously we arbitrarily included such admixtures in the B section, but because of their importance we have created two new sections "B /B Admixture for T(4S) results and 6 /6 /6°/b-baryon Admixture for results at higher energies. Most inclusive decay branching fractions are found in the Admixture sections. B -B mixing data are found in the 6 section, while B -B mixing data and B-B mixing data for a B /B admixture are found in the 6° section. CP-violation data are found in the section, b-baryons are found near the end of the Baryon section. 

Elements 85 and 87 fall into the region covered by the natural decay series and could therefore be expected to be fed by rare decay branches. As early as 1914, a particles were observed in carefully purified Ac (Z = 89), which implied the formation of element 87 (Meyer et al. 1914). However, the work of Marguerite Perey in 1939 is credited with the discovery of element 87 - the last discovery of a new element in nature (Perey 1939a, b). She proved that a 21 min P emitter ( 87) growing from Ac had chemical properties akin to cesium, and named the element francium (Fr). Element 85, astatine (At), the heaviest known halogen, was first produced artificially in 1940 as 85 (Ty2 = 7 h) by (a,2n) reaction on ° Bi (Corson et al. 1940a, b) before short-lived isotopes were found also in rare branches of the decay series. 

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