The Interpretation of theK42Radioactivity

Abstract

LETTERS TO THE EDITORentirely accounted for by the simple theory based on a Thomas precession u T = aXv/2c 2 ,proportional to the acceleration a and velocity v of a nucleon endowed with an intrinsic spin. [4][5][6] The analysis of the magnetic moments of the three-nucleon nuclei involves the graphic concept of exchange currents 7 representing the transport of charged mesons responsible for some of the inter-nucleon interactions. Certain types of mesons which may be responsible for nuclear forces (7r-mesons with spin 1) are carriers of spin as well as of charge, and one may anticipate on the basis of similar graphic concepts that the process of meson exchange which binds a circulating nucleon to the rest of the nucleus involves a predominantly centripetal acceleration of the meson momentarily associated with the circulating nucleon. This meson acceleration is expected to be much greater than the centripetal acceleration of the nucleon, since the exchange process may be expected in effect to take place many times per revolution. Although one does not have at hand a sufficiently complete analysis of the energetics of meson fields, it seems plausible to suppose that this large acceleration a of the meson, together with the tangential component of v which the meson would have in common with the circulating nucleon, should give rise to a Thomas precession of the meson spin much more rapid than that of the intrinsic nucleon spin previously derived from (1). Even if somewhat suppressed by a weighting factor representing the ephemeral association of the meson and nucleon (as enters, for example, in the interpretation of anomalous nucleon magnetic moments), 8 this might still give a spin-orbit coupling <r • COT much larger than that arising from precession of the nucleon spin alone. (A factor of ten or more seems to be needed by the empirical conjectures.) During the meson's fleeting association as part of the circulating nucleon, the meson spin has the direction of the nucleon spin of which it is a part (that is, a nucleon with spin up is part of the time a nucleon with spin down and a meson with spin up), and the directions of a and v are the same as before, so the sign of the coupling is the same as that arising from a Thomas precession of an intrinsic nucleon spin, which is satisfactory. From these graphic considerations, it seems more likely that a spin-orbit coupling belonging to each individual nucleon would arise from this second-order relativistic effect than from the second-order perturbation theory with a tensor interaction, as treated by Dancoff 6 in the simple case of He 5 with only one circulating nucleon. 1 M. G. Mayer, Phys. Rev. (to be published).A NUMBER of recent studies have been concerned with the occurrence of a characteristic forbidden type of energy distribution in several well-known beta-radioactive transitions. The necessary theoretical conditions 1 are (1) Gamow-Teller selection rules govern the beta-process, (2) the transition is first-forbidden, with AI = ±2 and a change in parity.For this situ...

Disintegration Scheme ofI131

“…18 The foregoing orbital assignments make the 812-kev spectrum a first-forbidden, a-type spectrum (Ay =2, yes), consistent with the observed value of log[(PF 0 2 -l)/o/]=9.9 or log/^8.5. 23 The abundance of this spectrum has been calculated on the assumption of an allowed shape, and if its spectrum is in fact of the a-shape, the abundance should be lowered somewhat from the value 0.7 percent shown in Table II. Since most of the 812-kev spectrum is obscured by more intense spectra of lower energy (Fig.…”

Constraints on the variations of the fundamental couplings

“…We will use f to calculate the energy dependence of the half-life for the allowed and first forbidden transitions. For unique first forbidden transitions (∆I = 2, ∆π = −), we will use the approximation f u ≈ (ǫ 2 0 − 1)f (see [29]). The calculated half-life is displayed in Figure 2 as a function of ∆Q/B for the isotopes of interest.…”

Small-Order Effects in Beta Spectra

“…The same method has been applied, with much more limited success, to the case of nuclei. [2][3][4] The magnitude of the second-order term (representing correlation effects) in the perturbation expansion of the total energy indicates that, in the case of typical nuclear interactions, the convergence is rather slow. The expansion has never been carried beyond the second order.…”

“…For the 2.0-Mev beta group of K 42 and the 2.4-Mev beta group of As 76 , which are presumably transitions with a spin change of zero and a parity change, [2][3][4][5][6] aZ/2R and Wo~ 1 are 7.3 mc 2 and 3.9 mc 2 , respectively, for K 42 and 10.6 mc 2 and 4.7 mc 2 , respectively, for As 76 . These two beta spectra are shown by the solid lines in the partial decay schemes shown in Figs.…”