Conversion electron spectroscopy at the fragment mass analyzer focal plane: Studies of isomeric decays near the proton drip line

Abstract

The decays of seniority isomers in the N =82 nuclei ' Er and ' Yb and in their respective N =81 isotopes Er and ' 'Yb were studied following mass separation by the Argonne Fragment Mass Analyzer. Conversion electrons were detected with Si p-i-n diodes operated at room temperature. The low-energy isomeric transitions in ' " Yb have been observed for the first time in the electron spectra. Multipolarity assignments were made for many of the decay y rays of the four nuclei.

Fine structure in the α decay of high-spin isomers in Lu155 and Hf156

“…Figure 5(b) shows the projection of γ rays in coincidence with 6274-keV α particles (as well as those of 5942 keV to be discussed in the next section). These appear on the Q[ 156 Hf (8 + ) → 152 Yb(0 + )] line and the 2 + 1 state in 152 Yb has previously been identified 1531 keV above the 0 + ground state [9,10,23]. The coincidences are therefore proposed to derive from the α decay of 156 Hf (8 + ) to the 2 + 1 state in 152 Yb.…”

“…A cascade of five γ rays was used to identify levels from the π (h 11/2 ) 6 , s = 2, multiplet sequence, as well as the three negative-parity states. A further investigation was carried out detecting γ rays and conversion electrons emitted following the decay of the isomer in 152 Yb [9]. From this work, the multipolarities of all the transitions were determined, allowing for a firm assignment of all energies, spins, and parities of the levels.…”

“…3(e), shows them to be consistent; implying they could be produced by the decay of 156 Hf (8 + ). If these counts are assumed to be associated with the α decay that populates the 3 − state in 152 Yb at 1890 keV [9,10,23], which decay via a cascade of 359and 1531-keV transitions, then the total Q value would be 7989(15) keV for the decay. This is consistent with the value of 7980(5) keV for the α decay to the ground state.…”

“…The establishment of 146 64 Gd 82 as a semi-doubly-magic nucleus [1][2][3] has meant that the neighboring nuclei are excellent cases in which to test the nuclear shell model for systems with small numbers of valence nucleons. Notable successes of the shell model in this region have been the excellent reproduction of observed level energies, as well as B(E2) values from decaying seniority isomers in the N = 82 isotones 148 Dy, 149 Ho, 150 Er, 151 Tm, 152 Yb, 153 Lu, and 154 Hf above Z = 64 [4][5][6][7][8][9][10][11][12]. Here, low-lying levels are largely determined by valence protons in the h 11/2 , s 1/2 , and d 3/2 shells.…”

Blurring the Boundaries: Decays of Multiparticle Isomers at the Proton Drip Line

“…The excitation energies, spins, and parities of yrast states that could be populated by proton emission from the new isomer in 158 Ta and the multiparticle isomers in 157 Ta and 153;154;155 Lu are known [16,[30][31][32][33]. Partial half-lives for proton-decay branches from the multiparticle isomers in 155 Lu and 157;158 Ta estimated by using a simple formula that reproduces measured proton-decay half-lives [34] are presented in Fig.…”