Speaker
Description
The calcium ($Z = 20$) nuclides have long been considered as “textbook” shell-model nuclei, with established doubly magic isotopes at $N = 20,~28$ and proposed shell gaps emerging at $N = 32,~34$. Despite this, a growing body of evidence suggests that the shell model requires deeper investigation in this region. In $^{48}$Ca, a reduction of the $f_{7/2}$ strength across the $N = 28$ shell gap was observed from neutron-knockout reactions from the $f_{7/2}$ ground states of $^{48,~50}$Ca.
This is inconsistent with shell-model predictions using both phenomenological effective interaction Hamiltonians like $GXPF1$ and microscopically derived $NN + 3N$ interactions in the $pf$ model space. Furthermore, this result is also in disagreement with spectroscopic strengths determined from single-nucleon transfer reactions although the historical data here are sparse.
We will report on a first-of-its-kind simultaneous measurement of the $^{48}$Ca$(d,p)$ and $^{48}$Ca$(d,t)$ reactions with the Helical Orbit Spectrometer (HELIOS) at Argonne National Laboratory. For this experiment, HELIOS was equipped with dual Si-Arrays: the "standard" 6x4 HELIOS array positioned at $z = 900$ mm downstream to enable triton detection, and a "stub" 2x4 array at $z = 50$ mm upstream to detect protons. Additionally, a four quadrant $E\Delta E$ recoil detector with an attached ∼1-m-long blocker was positioned at $z = 750$ mm downstream. This ensured the acceptance of tritons while blocking scattered, multi-orbit protons and deuterons. Preliminary results from this experiment will be discussed and compared with shell-model calculations. The importance of demonstrating the capability of simultaneous reaction studies with solenoidal spectrometers including the SOLARIS device at FRIB, will be discussed.
This work is supported by the Australian Research Council Grant No. DP210101201, the International Technology Center Pacific (ITC-PAC) under Contract No. FA520919PA138, the Australian National University Major Equipment Committee, and the U. S. Department of Energy, Grant No. DE-SC0014552.
