Extensive investigation of0+states in rare earth region nuclei

Abstract

The nature of 0 + excitations, especially in transitional and deformed nuclei, has attracted new attention. Following a recent experiment studying 158 Gd, we investigated a large group of nuclei in the rare-earth region with the (p, t) pickup reaction using the Q3D magnetic spectrograph at the University of Munich MP tandem accelerator laboratory. Outgoing tritons were recorded at various lab angles, and their angular distributions are compared to those calculated using the distorted-wave Born approximation. Using the unique shape of the L = 0 angular distribution, more than double the number of 0 + states than were previously known are identified. The distribution of 0 + energies and cross sections is discussed in terms of collective and noncollective degrees of freedom, and the density of low-lying 0 + states is discussed as a corroboration of a characteristic feature of phase transition regions. The degree of level mixing, as extracted from Brody distribution fits to the energy spacings of adjacent 0 + levels, is also explored.

Lifetime measurements in Dy162

“…All indications are that this level is an excitation built on top of the K π = 2 + "γ" band. The level at 1666.27 keV has a spin and parity of 0 + and it was confirmed in the recent (p, t) measurement [36]. In this work, we report on the lifetime of the 2 + state at 1728…”

High-resolution study of excited0+states in200Hg and202Hg

“…Since the characteristic (p, t) angular distribution strongly peaks in the forward direction solely for L = 0 transfers [5], we use the ratio R(5/17.5) ≡ σ(5 Hg. We use a ratio R(5/17.5) > 3 as a safe lower limit for 0 + states assignments [7,9].…”

“…• data is used for the peak identification, but is not necessary for a clean separation of 0 + states from 2 + or 4 + states [5]. For each nucleus, the experimental runs were normalized to the integrated beam current measured in a Faraday cup behind the target.…”

“…This research has allowed a better understanding of the changes the nuclei undergo from the transitional Gd region -over the well-deformed Yb region -to the γ-soft Pt region and further towards the 208 Pb proton-neutron shell closure. The striking high number of low-lying 0 + excitations in the Gd region [4,5] was interpreted [10] as a new signature for shape-phase transitions [11] and large numbers of 0 + states throughout the rare earth region triggered many calculations reproducing the surprisingly high 0 + density [12][13][14][15]. The latest experiments on 192 Pt, 194 Pt [8], and 198 Hg [9] showed a rather smooth decline in 0 + state density towards the proton-neutron shell closure.…”

“…The (p, t) pickup transfer reaction has been studied in an extensive campaign in the rare earth region [4][5][6][7][8][9] from Gd to Hg. This research has allowed a better understanding of the changes the nuclei undergo from the transitional Gd region -over the well-deformed Yb region -to the γ-soft Pt region and further towards the 208 Pb proton-neutron shell closure.…”