β-decay half-lives and β-delayed neutron emission probabilities for neutron rich nuclei close to the $N=82r$-process path

β-delayed neutron emission branchings (or upper limits) for neutron rich ${}^{116-120}\mathrm{Rh}$, ${}^{120-122}\mathrm{Pd}$, and ${}^{124}\mathrm{Ag}$ have been measured. These branching ratios serve as direct inputs to astrophysical rapid neutron capture process models and affect the final abundances calculated in these models. In addition, half-lives for neutron rich ${}^{114-115}\mathrm{Tc}$, ${}^{114-118}\mathrm{Ru}$, ${}^{116-121}\mathrm{Rh}$, and ${}^{119-124}\mathrm{Pd}$ near the proposed path of the r-process have also been measured. The results agree with theoretical quasiparticle random-phase approximation calculations within model uncertainties; the only exception is the delayed neutron branching in the decay of ${}^{120}\mathrm{Rh}$, which is found to be much smaller than predicted.

Figure 1

${}^{110}\mathrm{Zr}$ to ${}^{133}\mathrm{Sn}$ mass region showing the region of interest. Isotopes with previously known half-lives are shown to the left of the dashed line. Half-lives measured in this work are colored in gray. In addition, white circles indicate nuclei where a $P_n$ value (or upper limit) was also measured. The r-process waiting points predicted with the ETFSI-Q mass model in the classical r-process model [19] are framed with thick black lines.

Figure 2

Energy loss in the first Si PIN detector vs TOF of implanted nuclei in the DSSD. Inset shows the total kinetic energy of nuclei inside the circled area. Shaded area is an additional gate used to identify ${}^{119}\mathrm{Rh}$.

Figure 3

Histogram of the time differences between observed β decays and subsequent neutron detections considered as β-neutron coincidences.

Figure 4

Fitted decay curves of rhodium isotopes. Contributions from the parent, daughter, granddaughter, and background are shown.

Figure 5

Same as Fig. 4, but for palladium isotopes.

Figure 6

Same as Fig. 4, but for silver isotopes.

Figure 7

Experimental half-lives from this work and from literature for (a) technetium, (b) ruthenium, (c) rhodium, and (d) palladium isotopes compared with QRPA calculations using mass extrapolations and the FRDM and ETFSI-Q ground state deformation predictions.

Figure 8

Theoretical ${}^{119}\mathrm{pd}$ half-life calculated as a function of quadrupole deformation ${\epsilon }_2$ with ${\epsilon }_4=0$ using a QRPA model. Shaded region corresponds to the experimental $T_{1/2}$ obtained in this work.

Figure 9

Experimental half-lives from this work and from literature compared with QRPA calculations using FRDM and ETFSI-Q ground state deformation, $Q_{\beta }$ value and $S_n$ predictions.

Figure 10

Experimental β-delayed neutron emission probabilities from this work and from literature compared with QRPA calculations using mass extrapolations and the FRDM and ETFSI-Q ground state deformation predictions.

Figure 11

Theoretical ${}^{120}\mathrm{Rh}$ $T_{1/2}$ and $P_n$ values calculated as a function of quadrupole deformation ${\epsilon }_2$ with ${\epsilon }_4=0$ using a QRPA model. The two lines correspond to the upper and lower limits of the $Q_{\beta }$ input value in the QRPA calculation. Shaded region corresponds to the experimental $T_{1/2}$ or $P_n$ obtained in this work.