αdecay and proton-neutron correlations

Abstract

We study the influence of proton-neutron (p-n) correlations on α-decay width. It is shown from the analysis of alpha Q values that the p-n correlations increase the penetration of the α particle through the Coulomb barrier in the treatment following Gamow's formalism, and enlarges the total α-decay width significantly. In particular, the isoscalar p-n interactions play an essential role in enlarging the α-decay width. The so-called "alpha-condensate" in Z ≥ 84 isotopes are related to the strong p-n correlations. PACS numbers: 23.60,+e, 21.60.Cs, The α decay has long been known as a typical decay phenomenon in nuclear physics [1]. Various microscopic approaches to estimating the formation amplitude of the α cluster have been proposed [2,3,4,5]. The calculations [6,7,8] showed that J = 0 proton-proton (pp) and neutron-neutron (n-n) pairing correlations cause substantial α-cluster formation on nuclear surface. This suggests that the BCS approach with a pairing force offers a promising tool to describe the α decay. Protonneutron (p-n) correlations are also significantly important for the α-decay process in a nucleus [9,10]. The effect of the p-n correlations on the α-formation amplitude was studied by a generalization of the BCS approach including the p-n interactions [11], though it was shown that the enhancement of the formation amplitude due to the p-n interactions is small. The authors of Ref. [12] pointed out that continuum part of nuclear spectra plays an important role in formation of α cluster. On the other hand, a shell model approach including α-cluster-model terms [13] gave a good agreement with the experimental decay width of the α particle from the nucleus 212 Po. It is also interesting to investigate the effect of deformation on the α-decay width. According to Ref. [12], the contribution of deformation improves theoretical values for deformed nuclei such as 244 Pu .The p-n interactions are expected to become strong in N ≈ Z nuclei because valence protons and neutrons in the same orbits have large overlaps of wavefunctions [14]. In fact, this can be seen in peculiar behavior of the binding energy at N = Z. The double differences of binding energies are good indicators to evaluate the p-n interactions [15,16]. We have recently studied [17] various aspects of the p-n interactions in terms of the double differences of binding energies, using the extended P + QQ force model [18]. The concrete evaluation confirmed that the p-n correlations become very strong in the N ≈ Z nuclei. It was shown in Ref. [19] that the isoscalar (T = 0) p-n pairing force persists over a wide range of N > Z nuclei. One of the double differences of binding energies was also discussed as a measure of α-particle superfluidity in nuclei [20,21]. (We abbreviate the α-like correlated four nucleons in a nucleus to "α-particle" in italic letters. The "α-particle" is not a free α particle but a correlated unit in a nucleus.) We expect that the p-n correlations must play an important role in the barrier penetration of the α decay.Experimenta...

Quantum time scales in alpha tunneling

“…In principle, the values of P full α depend on the details of the nuclear potentials which in turn affect the tunneling probabilities. The values of P full α found here should hence not be interpreted as a constraint on four-particle correlations [33] in microscopic nuclear structure models. A detailed study of the preformation factors for super heavy alpha emitters can be found in [35].…”

“…These values are close to those obtained in literature [19] with similar potentials. The interpreted as a constraint on four-particle correlations [33] in microscopic nuclear structure models. A detailed study of the preformation factors for super heavy alpha emitters can be found in [35].…”

“…The alphanucleus potential for the medium and super heavy nuclei is constructed using a double folding model with realistic nucleon-nucleon (NN)interactions as given in [30] and also used in some recent works [24,31]. An accurate estimate would however demand the latest available NN potentials [32] and considerations of the four-particle correlations in nuclei [33].…”

Local density approximation for proton-neutron pairing correlations: Formalism

“…The pn correlations are also expected to play some role in single-beta decay [29][30][31], double-beta decay [32][33][34][35][36][37][38], transfer reactions [39][40][41][42][43][44][45] (see, however, Ref. [16]), structure of lowlying collective states [46], alpha decay and alpha correlations [45,[47][48][49][50][51][52], structure of high spin states [14,20,, and in properties of low-density nuclear matter [80][81][82][83][84][85][86][87][88][89][90].…”

Systematic study of α decay for odd- A nuclei within a two-potential approach

“…Phenomenologically, by analyzing the data of α decay, it is founded that the α preformation probability takes local minimum for nuclei with nucleons number near to the magic numbers [9,10]. Moreover, other factors, e.g., the valence proton-neutron correlation, the α particle angular momentum effect and the deformation of nuclei, also play a role on the α preformation probability [24,27,28]. However, because the precise size of decaying nucleus is unknown, by adjusting the radius parameters and keeping the α preformation probability constant, good reproduces of experimental α decay width can also be obtained [29].…”