New neutron-rich nucleiZr103,104and theA∼100 region of deformation

Abstract

Partial decay schemes in the neutron-rich nuclei '^^Zr and '"^Zr have been measured for the first time and rotational bands in '^-'022r have been extended to spins of up to 10h by observing prompt / rays from the spontaneous fission of ^"^^Cm. These nuclei are among the most deformed known at low spin and excitation energy. The level structures in the odd-A nuclei show that the hwn intruder orbital plays an important role in stabilizing the deformation in this region. PACS numbers: 21.10.Re, 23.20.Lv, 25.85.Ca, 27.60.+jThe region of deformation among neutron-rich nuclei with ^ -100 exhibits many interesting features including (1) an abrupt transition from nearly spherical to highly deformed ground states (j32'-0.4) in the Zr and Sr isotopic chains' at A^=60; (2) evidence for coexistence of spherical and deformed shapes^ near the shape transition; and (3) moments of inertia approaching the rigid-body value, suggesting that the pairing forces are relatively weak in these nuclei. Accounting for these features has proved to be a challenge to theories of nuclear structure. The properties of the Zr isotopes have been discussed^'* in terms of the spherical shell model, the emphasis being on the importance of the isovector neutron-proton interactions between nucleons occupying spin-orbit partner states (g9/2 protons and ^7/2 neutrons) in establishing a stable deformation. These studies suggest that the h\\/2 intruder orbital is not important at the onset of deformation. On the other hand, calculations using deformed mean fields ^'^ indicate that states derived from the neutron h\\/2 orbital lie well below the Fermi level for large deformations near A^=60. Hence, the relative importance of the vh\\/2 and vg'j/2 states in stabilizing the large ground-state deformations in this region is not clear. Further insight into this problem can be gained in two ways: First, by extending, to higher excitation energy and spin, decay schemes in those neutron-rich nuclei for which only data on low-lying levels are available; second, by examining hitherto unobserved isotopes with large neutron excess in which the occupation probabilities of the important single-particle levels are changed.At present the neutron-rich nuclei in the ^4 -100 region can only be produced for experimental study through fission, and most existing data on them have come from j3 "-decay studies of mass-separated fission

Evidence for a Smooth Onset of Deformation in the Neutron-Rich Kr Isotopes

“…Quantum phase transitions occur in atomic nuclei as a function of the number of protons or neutrons and describe changes of the ground-state shapes [2]. The so-called A % 100 mass region of the nuclear chart around 100 Zr is one of the most popular regions for the study of this phenomenon since the zirconium (Z ¼ 40) and strontium (Z ¼ 38) isotopes undergo a shape transition from almost spherical to strongly deformed shapes when going from neutron number N ¼ 58 to N ¼ 60 [3][4][5][6][7]. This PRL 108, 062701 (2012) P…”

Neutron configurations inPd113

“…the Nilsson diagram in Ref. [28]). This orbital is a natural candidate for the ground-state configuration of 113 Pd.…”

Spectroscopy of neutron rich nuclei using cold neutron induced fission of actinide targets at the ILL: the EXILL campaign

“…In this regime, the neutrons bring just enough energy into the system to produce fission, which preserves the neutron-richness of the fragments. The average spin generated in this reaction is 6-7ħ [1] and states with spins as high as 20ħ can be observed. Of particular interest in this context is the use of 235 U and 241 Pu fissile targets which give access to nuclei that are too weakly produced using spontaneous fission sources or another production mean to perform their prompt spectroscopy.…”