Shell model and octupole states in148Gd from in-beam experiments

1121The so-called "two-octupole-phonon states" in 146. 148 Gd are theoretically analyzed by using the Dyson boson mapping method. In our analyses, the free ground state of 146Gd is treated as doubly closed shell since Z=64 is rather good subshell closure. The starting collective multi-phonon space that we take consists of collective octupole phonons and collective monopole pairing phonons for 146Gd. Additionally correlated particle-pair modes with J ' *' 0 are included in the multi-phonon space for 148Gd. The effective Hamiltonian used is constituted by a W oods-Saxon-type single-particle potential, an octupole-octupole force for particle-hole modes and a surface-delta interaction for particle-pair and hole-pair modes. The numerical calculation can considerably well reproduce the octupole collectivity shown by experiments for 146. 148 Gd. It is shown that the Dyson boson mapping method is useful for such a complicated system as 148Gd. § 1. IntroductionThe octupole correlation is, as known well, quite strong and very important in medium-heavy nuclei. Particularly, most magic number nuclei have low-lying 3-states, which have been considered as one-phonon states of elementary vibrational mode of octupole character. A typical example is the nucleus 208Pb, whose first excited state is a strongly collective 3-state. In our previous paperl) (referred to as I hereafter), we analyzed the so-called two-octupole-phonon states in 208Pb using the Dyson boson mapping method, and we had deep understanding of the low-lying collective states in 20BPb. It is interesting to see how the collective octupole excitations occur in different regions of nuclei and how the same method as that used for 208Pb works there. The nucleus 208Pb is a very simple system; i.e., a doubly-closed shell one. We can therefore perform a microscopic analysis by using the Dyson boson mapping method as shown in I. If there exist additional nucleons on top of doubly-closed shell, then microscopic analyses would become more difficult. It is interesting to see whether microscopic analyses are possible or not for such complicated nuclei by using the Dyson boson mapping method.Kleinheinz and Piiparinen et a1. 2 )-7) have long investigated the octupole vibration states in Gd region nuclei, and they have recently published detailed experimental results on the two-phonon E3 transition strength in 148Gd. This region seems to be a good battlefield to study the collectivity of octupole correlation and to test the applicability of the Dyson boson mapping method for study on collective states in more complicated nuclei.The first excited (1.579 MeV) state of 146Gd is a strongly collective 3-state (B(E3; 3t--->Ot)~37 Bw). This seems quite similar to the case of 208Pb. In fact, as seen later, 146Gd can be treated as a doubly-magic nucleus, since Z=64 is considered as a rather good closed-subshell. If this 3-state can, roughly speaking, be considered as a one-octupole-boson (or one-I-boson) state, it is natural to expect "two-boson"

show abstract

“…This supports the results obtained by the empirical particle-phonon coupling model of Piiparinen et al 4 …”

Section: O~------------------------~o+~supporting

confidence: 82%

“…The last two, 3-and 9-, modes are included as a main source of the dynamical coupling effect as suggested in Ref. 4). A possible 12+ neutron-particle pair mode seems also important for the stretch-coupling sequence of our present interest, but we cannot help neglecting this because of difficulty of numerical calculations.…”

mentioning

confidence: 99%

Two-Octupole-Phonon States in 146,148Gd

Takada

Shimizu

1996

Progress of Theoretical Physics

View full text Add to dashboard Cite

show abstract

“…It is worth pointing out that the negative-parity states shown in Fig. 3(b) have the same behavior (relative energies of evenand odd-I states and deexcitation modes) as those identified in 148 Gd [21]. On the other hand, the two groups of even-I negativeparity states, as well as the two groups of odd-I positiveparity states [see the filled circles in Figs.…”

Section: Prl 104 042701 (2010) P H Y S I C a L R E V I E W L E T T Ementioning

confidence: 92%

Do alpha particles cluster inside heavy nuclei?

Carpenter¹

2010

Physics

View full text Add to dashboard Cite

Excited states in212 Po were populated by transfer using the 208 Pbð 18 O; 14 CÞ reaction, and their deexcitation rays were studied with the Euroball array. Several levels were found to decay by a unique E1 transition (E < 1 MeV) populating the yrast state with the same spin value. Their lifetimes were measured by the Doppler-shift attenuation method. The values, found in the range 0.1-1.4 ps, lead to very enhanced transitions, BðE1Þ ¼ 2 Â 10 À2 -1 Â 10 À3 W:u: These results are discussed in terms of an -cluster structure which gives rise to states with non-natural-parity values, provided that the composite system cannot rotate collectively, as expected in the '' þ 208 Pb'' case. Such states due to the oscillatory motion of the -core distance are observed for the first time. DOI: 10.1103/PhysRevLett.104.042701 PACS numbers: 25.70.Hi, 21.60.Gx, 23.20.Àg, 27.80.+w In the early days of the development of nuclear theory, the particle was considered as the basic building block of any nucleus, providing a simple explanation for the emission of s by heavy nuclei or the fact that all of the light nuclei with A ¼ 4n have higher binding energies per particle than any of their neighbors. But many arguments [1] were rapidly developed against this picture, which was almost completely abandoned to the benefit of singleparticle description of nuclei based on the hypothesis of a common mean field for all nucleons.A strong revival of the -cluster model occurred in the 1960s when both experimental and theoretical studies revealed that the concept of clustering is essential for the understanding of the structure of light nuclei. The states based on particles (and other bound substructures) are not so much found in the ground states but rather observed as excited states close to the decay thresholds into clusters, as suggested by Ikeda [2]. In particular, the Hoyle state, i.e., the 0 þ 2 state at 7.65 MeV in 12 C which has recently been interpreted as an -particle condensate [3], and other similar states in heavier n nuclei, have attracted much renewed attention (see, e.g., [4]). Also, so-called nuclear molecules, such as the -core system rotating about its center of mass, have lately been studied intensely and with great success (for a review, see [5]).The persistence of clustering in heavy nuclei is much less documented. This is even the case of 212 Po, a typical nucleus with two protons and two neutrons outside the doubly magic core, 208 Pb. Up to now, there was no clearcut evidence of its cluster structure. Shell model (SM) configurations involving a few orbits account reasonably well for the excitation energies of its low-lying yrast states [6]. Nevertheless, the width of its ground state is predicted more than 1 order of magnitude smaller than the experimental value. This has called for a hybrid model comprising both shell and cluster configurations [7]. Then the -decay energy and the half-life are well reproduced and a large amount of clustering is found (30%). Such a result suggests that the low-lying yrast spectrum of ...

show abstract

“…So far, two1oooo phonon octupole excitations were observed only in the 146Gd region, where due to the dominating single particle content (n d5/2 -I hl12) of the mode large devi5oo0 ations from harmonicity were found [3]. Recently Wollersheim et al y W-coincidences have been measured with the OSIRIS spectrometer (11 Compton suppressed Ge-detectors) together with multiplicity and sum energy from the 48 element BGO ball.…”

mentioning

confidence: 97%

On the origin of the 2485 keV?-ray observed in near-barrier collisions of various heavy ions with208Pb

Schramm

Grawe

Heese

et al. 1992

Z. Physik A - Hadrons and Nuclei

Self Cite

View full text Add to dashboard Cite

In collisions of 64Ni and 82Se projectiles with a thick 208Pb target at energies around 10% above the static Coulomb barrier a 2485 keV y-ray is observed, which is in conspicuous agreement with the recently reported y-ray deexeiting the two-phonon octupole state in 208Pb [1]. The y-ray observed in the present toDo experiments is not in coincidence with any known 208Pb y-rays, but belongs likely to207Pb.

show abstract

Shell model and octupole states in148Gd from in-beam experiments

Cited by 20 publications

References 35 publications

Two-Octupole-Phonon States in 146,148Gd

Two-Octupole-Phonon States in 146,148Gd

Do alpha particles cluster inside heavy nuclei?

On the origin of the 2485 keV?-ray observed in near-barrier collisions of various heavy ions with208Pb

Contact Info

Product

Resources

About