Speaker
Description
About half of the elements heavier than iron are synthesized through the slow neutron capture process, in which the neutron-capture timescales of the nuclei involved are typically longer than their $\beta$-decay lifetimes. In the modeling of this process, significant uncertainties arise from the competition between neutron capture and $\beta$-decay in certain isotopes called “branching points”. $^{85}$Kr is one of the most important branching points of the s-process, influencing both the $^{86}$Kr/$^{82}$Kr ratio measured from presolar grains and the abundances of heavy Sr isotopes, which are also produced by the r-process.
A precise description of this branching point requires a well-constrained $^{85}$Kr(n,$\gamma$) cross section. However, a direct measurement of this cross section is extremely challenging due to the radioactivity of the sample (T$_{1/2}$ = 10.7 yr). An alternative approach is to use $^{85}$Kr as a beam to perform the (d,p$\gamma$) reaction, which has been demonstrated to be a reliable indirect probe of the (n,$\gamma$) cross section.
The $^{85}$Kr(d,p$\gamma$)$^{86}$Kr reaction was performed at 10 MeV/u in inverse kinematics at Argonne National Laboratory using the HELIOS spectrometer coupled with the Apollo array. Neutron excitations around and above S$_n$ in $^{86}$Kr were populated, achieving a Q-value resolution of about 150 keV. The coupling of Apollo with HELIOS enables the coincident detection of $\gamma$-rays and protons, allowing the determination of $\gamma$-ray emission probabilities as a function of excitation energy [P$_{p\gamma}$(E$_{ex}$)].
The $2^+ \to 0^+$ and $4^+ \to 2^+$ $\gamma$-rays were clearly observed, showing the characteristic constant behavior of P$_{p\gamma}$ below S$_n$ and a decrease above S$_n$. These results are used to extract the cross sections of the $^{85}$Kr(n,$\gamma$) reaction and demonstrate the strong potential of this approach for future indirect studies of the (n,$\gamma$) reaction.
| Contribution category | Experiment |
|---|---|
| Presenter status | Postdoc |