Decay and Electron Capture

The decay energies for P decay and electron capture, i.e., Qp and Qg, were also evaluated by Wapstra and Audi [22]. They calculated these data according to Qp or Qg = Am —Amy, where Am denotes the mass excess (in keV) and the indices x and y refer to the decaying nucleus and the daughter nucleus, respectively. Note also, that —Qp y, i e., for the 

In Fig. 1-7, p. 16, the dependence of the partial half-life for p decay on the decay energy is shown, in the upper part of the figure the values for the elements with odd proton number Z and in the lower part those for elements with an even Z are given, in both cases a general trend is clearly visible however, the scatter is quite large. The shaded areas show the half-lives calculated with a microscopic model [51]. The spread in the areas is due to different plausible assumptions used in the calculations. Klapdor etal. Gmeiin Handbook References p. 28 

The uncertainties given in brackets refer always to the last digits. The values marked by were obtained from systematic trends [24]. The Qg values for the reverse decay mode, for instance Rhs Ru, are obtained by changing the sign of the given value for Qp- of Rui .Rh. 

For neutron-deficient nuclides both modes of decay, i.e., emission and electron capture, are possible if the Qg value is higher than 1.02 MeV. Calculated ratios for the probabilities of the two modes of decay are published in [48, 49]. The dependence of these ratios on the maximum energy for allowed transitions (Al = 0 or 1, no parity change) and first forbidden nonunique transitions (Al = 0 or 1, parity change) is shown in Fig. 1-9, p. 17. 

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Ans. (a) 16C, /G-decay (b) 18Ne, both fJ4--decay and electron capture are possibilities on the basis of the given data. 

Beta decay is a general term applied to radioactive decay processes that result in the mass number A remaining constant while the atomic number Z changes. There are three types of beta decay beta-minus (/3 ) decay, positron (/3+) decay, and electron capture decay. It should be mentioned that (3 decay is often referred to as just beta decay, which is not strictly correct, because it is only one type of beta decay. 

H. Behrens, J. Janecke, Numerical Tables for Beta Decay and Electron Capture, Landolt-Bdrnstein, New Series, Vol. 1/4, Springer, Berlin, 1964... 

The calculated jS-decay and electron-capture half-lives in Fig. 4 c decrease from 1 y for nuclei along the iimer contour to 10 y (about 3 sec) for nuclei at the outer contour. The total half-lives in Fig. 4d are obtained by taking into account all three decay modes. The longest total half-life of 10 years is found for the nucleus 2 4110. A three-dimensional plot of these results (35) is given in Fig. 5, where the island character of this region of relative stability is beautifully demonstrated. 

Fig. 3. The Fermi and GT resonances observed through / -decay and electron capture between nuclei (N,Z) and (N-1,Z+1) (taken from [6])...

Although beta decay and electron captures on stellar core nuclei do not produce energy in major ways they nevertheless play a crucial role in shifting the pathways of nuclear and thermodynamic evolution in the core conditions. These ultimately determine the mass of the core and its entropy structure which finally collapses in a supernova explosion. 

X-radiation is a product of radioactive decay of certain isotopes. The term gamma ray is often used for an X-ray resulting from such a decay process. Alpha and beta decay and electron capture processes can result in the release of gamma rays. Table 8.4 lists some common radioisotopes used as XRF sources. 

The primary decay products are neodymium and samarium isotopes. Promethium-146 decays to neodymium and samarium ( " Nd and "" Sm), the lighter isotopes generally to neodymium via positron decay and electron capture, and the heavier isotopes to samarium via beta decay. Exceptions are °Pm and Pm which give rise to Pr ( Pr and respectively) via positron emission. The isotope Pm decays to both Nd and Pr via positron emission, although the majority leads to Nd (Oliveira 2011). 

In addition to the radioactivity of Fr, 0.02% of naturally occurring K consists of which decays according to scheme 11.2. The overall half-life for both the P-decay and electron capture is 1.25 x 10 yr. 

FUNDAMENTAL INTERACTIONS) in Which an unstable atomic nucleus changes into a nucleus of the same nucleon number (A) but different proton number (Z). There are three types of beta decay negative beta decay, positive beta decay, and electron capture. Negative beta decay ... 

The ratio of count rates in the two ionization chambers at a known rotational speed of the wheel (800-1,400 rpm) allowed to calculate the half-life of the spontaneously fissioning nuclides. The value obtained was 0.02 s - about lo times shorter than expected for a normal spontaneously fissioning nuclide of this fissility parameter (see O Fig. 4.4). (The shortest-lived normal spontaneously fissioning nuclide that could be considered is pm formed in the reaction ( 0,2n) Fm. Its fissility parameter would be Z /A = 39.7. The half-life extrapolated from the systematics (O Fig. 4.4) would be of the order of 10 -10 s. The species observed here was later identified to be a shape isomer of Am (fissility parameter of 37.3). The ground state of Am decays by P decay and electron capture with a half-life of 16 h.)... 

The stability valley of nudei. The vertical projection of the bottom of the valley on the Z x A plane follows the line of stable nuclei (cf. Fig. 2.7 in Chap. 2) at an "altitude" expressed by the ratio of the nudidic mass (M) and the mass number (A). The horizontal projection of the bottom of the valley onto the (M/A) x A plane is essentially the same as the graph labeled "experimental" in Fig. 2.3 in Chap. 2, except that it is upside down. The isobaric cross sections of the valley are parabolic as a consequence of the Weizsacker formula (2.3) in Chap. 2. (See also the legend of Fig. 7.2 in this chapter, as well as Fig. 14.5 in Chap. 14, Vol. 2.) The local dips marked are related to magic numbers (Ca N=20 Fe-Ni A/=28, Z= 28 Y A(=50 Ba Af=82). Beta decay occurs all along the valley. On the near side of the valley decay is predominant, on the far side decay and electron capture (EC) compete with each other as indicated on the parabola. Alpha decay occurs for A > 60 mainly on the far side of the valley... 

For neutron deficient nuclides with a potential decay energy somewhat above the 1022 keV threshold, both positron decay and electron capture decay will occur, in a proportion statistically determined by the different decay energies of the two processes. Figure 1.11 shows the major components of the decay scheme of Na, where both... 

The overall half-life for both the p-decay and electron capture is 1.25 x lO yr. 

Two other modes of radioactive decay are positron decay and electron capture. A positron is an electron with a positive charge and is symbolized +ie or p+. Positron decay is, in a sense, the opposite of beta decay—instead of a neutron turning into a proton, a proton turns into a neutron. The result is to decrease the atomic number by one unit, again without changing the mass number. This time, therefore, the daughter isotope is located one space to the left of the parent, instead of one space to the right. 

Positive P decay and electron capture are competing processes, with the probability of electron capture increasing as Z increases. With few exceptions, unstable neutron-deficient nuclei with values of Z below 30 undergo positron decay, whereas such nuclei with Z values above 30 decay most often by electron capture. Both processes are observed for 30 < Z < 80. 

Fig. 1-10. Dependence of the partial half-life for p+ decay and electron capture on the decay energy Qg. The filled symbols refer to the decay of the ground state whereas the corresponding open symbols denote the values for the decay of the metastable state. The shaded areas show the trends expected according to microscopic theory using different...

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