arXiv subjects

M. S. Martin

Publications and source records attributed to M. S. Martin.

6 recordsLinked to original sources

arXiv2026

Observation of a dominant $\boldsymbol{0f_{7/2}}$ neutron configuration in the $\boldsymbol{^{32}}$Si $\boldsymbol{J^{\pi}=5^-}$ isomeric state

An yrast, $J^{\pi}=5^-$, spin-trap isomer has been previously identified in $^{32}$Si. The isomeric state decays predominantly via a hindered $E3$ transition [B($E3$) = 0.0841(10)~W.u.], bypassing a nearby $E2$ decay path to the first excited $3^-$ level. The single-neutron aspects of these negative parity levels were investigated via the $^{31}$Si$(d$,$p)^{32}$Si reaction at 9.6~MeV/$u$ using HELIOS and the ATLAS in-flight facility. The $5^-$ state appears as a dominant $\ell=3$ transfer with a relatively large spectroscopic factor, confirming its single-particle $\nu0f_{7/2}$ character. The yrast $3^-$ level had a reduced $\ell=3$ spectroscopic factor of $\approx$ 0.44 compared to that of the $5^-_1$ level. This is similar to the situation observed in nearby $^{34}$S which by contrast has a measured B($E2, 5^-\rightarrow 3^-$) transition strength closer to 1~W.u.. It has been concluded that the hinderance of the $5^-_1\rightarrow 3^-_1$ transition in $^{32}$Si is not primarily due to the differing overlaps in the neutron structure. Instead, the lack of participation by both the protons and the neutrons in the transition is proposed as the transition-strength reduction mechanism.

nucl-ex↗

arXiv2026

The N=126 Factory: A New Multi-Nucleon Transfer Reaction Facility

Multi-nucleon transfer (MNT) reactions between two heavy ions offer an effective method of producing heavy, neutron-rich nuclei that cannot currently be accessed efficiently using traditional production techniques. These nuclei are important for understanding many astrophysical phenomena, such as the formation of the r-process $A\sim 195$ abundance peak. The N=126 Factory currently commissioning at Argonne National Laboratory's ATLAS facility will make use of these reactions to allow for the study of these nuclei. To convert MNT reaction products, which have a wide angular distribution, into a collimated, bunched beam suitable for experiments, a series of apparatus will be used. These start with a large-volume gas catcher for stopping the reaction products, which are then extracted through a radiofrequency quadrupole ion guide, undergo preliminary dipole magnetic separation, cooling and bunching in a Cooler-Buncher, and final separation using a multi-reflection time-of-flight mass separator, before final delivery to experimental systems.

physics.acc-ph↗

arXiv2025

Intruder structures in $^{32}$Si and $^{29}$Al

We have studied $^{32}$Si and $^{29}$Al using $^{12}$C($^{22}$Ne,2p) and $^{12}$C($^{22}$Ne,$α$p) fusion-evaporation reactions. In both cases, we observed significant population of high-spin structures distinct from the ground-state yrast bands. In $^{32}$Si, most of the high-energy states feed into a $J^π = 5^-$ nanosecond isomer. In $^{29}$Al, we identified a rotor-like negative-parity band with a $J^π = 7/2^-$ band-head. Doppler shift lifetime measurements were performed for all observed states. These results were compared to shell model calculations and interpreted in terms of proton and neutron cross-shell excitation.

nucl-ex↗

arXiv2024

Coulomb Excitation of $^{80}$Sr and the limits of the $N = Z = 40$ island of deformation

The region of $N\approx Z\approx 40$ has long been associated with strongly deformed nuclear configurations. The presence of this strong deformation was recently confirmed through lifetime measurements in $N\approx Z$ Sr and Zr nuclei. Theoretically, however, these nuclei present a challenge due to the vast valence space required to incorporate all deformation driving interactions. Recent state-of-the-art predictions indicate a near axial prolate deformation for $N=Z$ and $N=Z+2$ nuclei between $N=Z=36$ and $N=Z=40$. In this work we investigate the shores of this island of deformation through a sub-barrier Coulomb excitation study of the $N=Z+4$ nucleus, \textsuperscript{80}Sr. Extracting a spectroscopic quadrupole moment of $Q_s(2^+_1) = 0.45^{+0.83}_{-0.88}$~eb, we find that \textsuperscript{80}Sr is inconsistent with significant axial prolate deformation. This indicates that the predicted region of strong prolate deformation around $N=Z=40$ is tightly constrained to the quartet of nuclei: \textsuperscript{76,78}Sr and \textsuperscript{78,80}Zr.

nucl-ex↗

arXiv2023

Identifying the spin trapped character of the $^{32}$Si isomeric state

The properties of a nanosecond isomer in $^{32}$Si, disputed in previous studies, depend on the evolution of proton and neutron shell gaps near the `island of inversion'. We have placed the isomer at 5505.2(2) keV with $J^π = 5^-$, decaying primarily via an $E3$ transition to the $2^+_1$ state. The $E3$ strength of 0.0841(10) W.u. is unusually small and suggests that this isomer is dominated by the $(νd_{3/2})^{-1} \otimes (νf_{7/2})^{1}$ configuration, which is sensitive to the $N=20$ shell gap. A newly observed $4^+_1$ state is placed at 5881.4(13) keV; its energy is enhanced by the $Z=14$ subshell closure. This indicates that the isomer is located in a `yrast trap', a feature rarely seen at low mass numbers.

nucl-ex↗

arXiv2021

Testing isospin symmetry breaking in ab initio nuclear theory

In this work we present the first steps towards benchmarking isospin symmetry breaking in ab initio nuclear theory for calculations of superallowed Fermi $β$-decay. Using the valence-space in-medium similarity renormalization group, we calculate b and c coefficients of the isobaric multiplet mass equation, starting from two different Hamiltonians constructed from chiral effective field theory. We compare results to experimental measurements for all T=1 isobaric analogue triplets of relevance to superallowed $β$-decay for masses A=10 to A=74 and find an overall agreement within approximately 250 keV of experimental data for both b and c coefficients. A greater level of accuracy, however, is obtained by a phenomenological Skyrme interaction or a classical charged-sphere estimate. Finally, we show that evolution of the valence-space operator does not meaningfully improve the quality of the coefficients with respect to experimental data, which indicates that higher-order many-body effects are likely not responsible for the observed discrepancies.

nucl-th↗