Well Developed Deformation inSi42

Abstract

Excited states in 38,40,42 Si nuclei have been studied via in-beam γ-ray spectroscopy with multinucleon removal reactions. Intense radioactive beams of 40 S and 44 S provided at the new facility of the RIKEN Radioactive Isotope Beam Factory enabled γ-γ coincidence measurements. A prominent γ line observed with an energy of 742 (8) 23.20.Lv, 27.40.+z, 29.38.Db Shell closures and collectivity are important properties that characterize the atomic nucleus. Interchange of their dominance along isotopic or isotonic chains has attracted much attention. The recent extension of the research frontier to nuclei far away from the valley of stability has revealed several new phenomena for neutronor proton-number dependent nuclear structure. For example, a weakening or even disappearance of shell closures occur in several neutron-rich nuclei at N = 8 [1][2][3] and N = 20 [4][5][6]. A well known example in the case of N = 20 is the so-called 'island of inversion ' [7] located around the neutron-rich nucleus 32 Mg. The low excitation energy of the first 2 + state E x (2 + 1 ) and large E2 transition probability [4][5][6] clearly indicate shell quenching in 32 Mg despite the fact that N = 20 is traditionally a magic number. The next magic number, N = 28, which appears due to the f 7/2 -f 5/2 spin-orbit splitting, has also been explored [8][9][10][11][12][13]. Weakening of the shell closure is seen by the decrease of the 2 With proton number Z = 14 and neutron number N = 28, the nuclear structure of 42 Si is of special interest. A simple but important question that arises is whether the weakening of the N = 28 shell closure continues, causing an enhancement of nuclear collectivity, or if shell stability is restored owing to a possible doubly magic structure. A study on 42 Si was made by a two-proton removal reaction experiment with radioactive 44 S beams at the NSCL [15]. The small two-proton removal cross sec-

Investigating nuclear shell structure in the vicinity ofNi78: Low-lying excited states in the neutron-rich isotopesZn80,82<

“…The main constituents of the secondary radioactive isotope (RI) beam were 82 Ge and 83 As, both with purities of ∼20%. The RI beam was delivered to a secondary 9 Be target with a thickness of 1.89 g/cm 2 , located at the eighth focal plane of BigRIPS. The typical midtarget energy of the RI projectiles was about 250 MeV/nucleon.…”

“…In the present work, the BigRIPS and ZeroDegree spectrometers were optimized for transmission of 79 Cu and 78 Ni, respectively. The γ -ray detector array DALI2 [34], which surrounded the secondary 9 Be reaction target, was employed to measure γ rays emitted from nuclear excited states populated by the reactions. DALI2 consisted of 186 NaI(Tl) detectors covering angles of ∼18…”

“…This value was adopted as part of the systematic uncertainty in the γ -ray relative intensity measurements. Figure 2 displays Doppler-shift-corrected γ -ray energy spectra deduced from the 9 Be( 80 Zn , 80 Zn +γ ) and 9 Be( 81 Ga , 80 Zn +γ ) reactions. A coincidence timing window between particle and γ -ray detection of 10 ns was adopted.…”

“…Indeed, recent developments in accelerator technology and isotope separators have made it possible to explore unreached regions of the Segrè chart, yielding many new, exotic phenomena that cannot be explained in the framework of the standard shell model. Several highlights include the weakening of the traditional magic numbers N = 8 [3][4][5], 20 [6], and 28 [7][8][9], while new magic numbers at N = 16 [10,11], 32 [12][13][14][15][16][17][18][19][20], and 34 [21] have been reported. The next conventional neutron magic number, N = 50, has also attracted much attention recently, and investigations into the robustness of this magic number in neutron-rich systems have been encouraged.…”

Ground-state configuration of neutron-rich Al35 via Coulomb breakup

“…That large deformation was explained by considering intruder effects which suggest a clear vanishing of the shell gap between the sd and pf shells around N = 20 [4]. Later, in many neutron-rich nuclei around N ∼ 20 and 28, large deviations in the nuclear structure from conventional shell models were observed [5][6][7][8][9][10][11]. These observation have been explained by considering tensor interactions, three-body interaction, etc.…”