No abstract

The transition probabilities W{E2,y) are known only for the 2 +/ -* 0 transitions; therefore, it is necessary to use the theoretical ratio (1) to deter mine the relative transition probabilities for use in (2). The relation M(2 ;2 -2 )EE ^ » ' ^= a " a2> W(£2,y;2 -2 ) where a 2 is the theoretical E2 conversion coefficient, gives the desired ratio of transition probabilities. The monopole transition probability W(E0, e"; 2+' -2 + ) was determined in turn from (1) and the experimental B(E2;2+' -+0) d values. The nuclear monopole strength parameter, p, is defined by W(E0,e')=Qp 2 ,where £2, the electronic factor, is given graphically. 2 Reiner 3 has treated the problem of monopole enhancement for deformed nuclei and has derived a formula for the ratio of the EO to E2 transition probabilities from )3 -vibrational states. For Th 232 his formula leads to M(2 + '; 2 + ' -2 + ) = 3.8, a value which is intermediate between the experimental values obtained by Methods A and B. For U 238 , however, Reiner's formula gives ju(2 + ';2 + -*2 + ) = 1.4 which is a factor of ten larger than the value obtained experimentally. The explanation of the Since the early works on the alpha disintegration problem, the barrier for the alpha emission has traditionally been taken to be purely Coulomb-Ian with an abrupt cutoff at the nuclear boundary defined by some appropriate A ys law. Alpha decay was first considered 1 by the present author by assuming that the potential barrier is not purely Coulombian and should be taken as 2(Z -2)e 2 /r -V, where V is defined as the short-range interaction between the emitted alpha particle and the residual nucleus. Subsequently, the form of the interaction, V, which is superposed on the discrepancy is not apparent in terms of the simple vibrational model used by Reiner, since Th 232 and U 238 have similar atomic numbers, equilibrium deformations, and vibrational energies which are the only parameters entering into the calculation. The values obtained for the nuclear strength parameter p are close to the approximate value of £ predicted by Church and Weneser for 0 + -0 + transitions from vibrational states in spheroidal nuclei, 2 Again, however, it is not clear why the value of p should differ by a factor of two between Th 232 and U 238 . Perhaps one sees in these discrepancies the influence of the different ground-state configurations. tThis work was supported in part by the U. S. Atomic Energy Commission, (private communcation, 1960), and to be published. 5 F. E. Durham, D. H. Rester, and C. M. Class, Bull. Am. Phys. Soc. j5, 110 (1960). 6 De-excitation of the 788-kev state through the 4 + rotational state was ignored, in line with the interpretation of the 788-kev state as y-vibrational. 7 F. K. McGowan and P. H. Stelson, report to International Congress of Nuclear Physics, Paris, 1958 (unpublished).Coulomb field, has been taken differently by different authors 2 " 5 in their calculations of the barrier penetrability.It is, however, worth while to note that in the above calculations of the penetrabilit...

2014 La méthode pour calculer les taux de décroissance 03B1 en prenant pour barrière le potentiel coulombien et un potentiel non local alpha-noyau avec terme d'échange est appliquée aux isotopes 149,151Tb, 149Tbm et 153Dy. Ce calcul montre que l'intensité relative mesurée, 03BB1/03BB0, peut en grande partie être reproduite par les rapports des pénétrabilités, ce qui permet de calculer les largeurs partielles 03B421. Des calculs similaires utilisant un potentiel alpha-noyau statique donnent 03B42l ~ 03B420, en contradiction avec l'analyse des amplitudes spectroscopiques qui donne 03B421 > 03B420. Il est remarquable que cette méthode corrige dans une large mesure ce désaccord, donnant un rapport 03B421/03B420 de l'ordre de 1,1 à 2,2. On peut en conclure que les valeurs de 03B421 obtenues avec un potentiel statique sont trop faibles et que celles données dans le tableau II peuvent être utilisées, dans des limites raisonnables, pour des études de structure nucléaire. Abstract. 2014 The method of calculating alpha-decay intensities taking the barrier to be the usual Coulomb potential superposed by a non-local alpha-nucleus potential with exchange term is applied here to the fine structures of the rare-earth isotopes 149,151Tb, 149Tbm and 153 Dy. The present calculations consistently show that the measured relative intensities, 03BB1/03BB0, are largely accounted for in terms of the non-local penetrability ratios and hence the values of the reduced widths 03B421, are calculated. Similar calculations using static alpha-nucleus potential give 03B421 ~ 03B420 which is contrary to the finding, viz., 03B421 > 03B420 obtained from other sources, for example, from the studies of alpha-spectroscopic amplitudes. It is remarkable that the present method largely makes up this discrepancy giving 03B421/03B420 in the range of 1.1 to 2.2, and it is concluded that the values of 03B421 from static potential are too low and those given in table II are within reasonable limits for use in studying nuclear structures.

No abstract

In the present paper, the penetrability factor for alpha emission has been calculated from the following standpoint. The barrier for alpha emission is the usual Coulomb field assumed here to be superposed by a nonlocal alpha-nucleus interaction. The static part of the barrier is taken to be the Igo potential and its nonlocal part is assumed to be represented by an approximate delta function.Calculations for the ground-state transitions of all the even-even nuclei have been completed. The results show that the current values of penetrability are too low, and that the inclusion of the nonlocal correction factor increases these local values by more than 50%.