arXiv subjects

P. C. Bender

Publications and source records attributed to P. C. Bender.

25 records · Page 2Linked to original sources

arXiv2019

Spectroscopy and lifetime measurements near the proton drip line: $^{26,27,28}$P

We report on the observation of excited states in the neutron-deficient phosphorus isotopes $^{26,27,28}$P via in-beam gamma-ray spectroscopy with both high-efficiency and high-resolution detector arrays. In $^{26}$P, a previously-unobserved level has been identified at 244(3) keV, two new measurements of the astrophysically-important 3/2$^+$ resonance in $^{27}$P have been performed, gamma decays have been assigned to the proton-unbound levels at 2216 keV and 2483 keV in $^{28}$P, and the gamma-ray lineshape method has been used to make the first determination of the lifetimes of the two lowest-lying excited states in $^{28}$P. The expected Thomas-Ehrman shifts were calculated and applied to levels in the mirror nuclei. The resulting level energies from this procedure were then compared with the energies of known states in $^{26,27,28}$P.

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arXiv2019

Is the structure of 42Si understood?

A more detailed test of the implementation of nuclear forces that drive shell evolution in the pivotal nucleus \nuc{42}{Si} -- going beyond earlier comparisons of excited-state energies -- is important. The two leading shell-model effective interactions, SDPF-MU and SDPF-U-Si, both of which reproduce the low-lying \nuc{42}{Si}($2^+_1$) energy, but whose predictions for other observables differ significantly, are interrogated by the population of states in neutron-rich \nuc{42}{Si} with a one-proton removal reaction from \nuc{43}{P} projectiles at 81~MeV/nucleon. The measured cross sections to the individual \nuc{42}{Si} final states are compared to calculations that combine eikonal reaction dynamics with these shell-model nuclear structure overlaps. The differences in the two shell-model descriptions are examined and linked to predicted low-lying excited $0^+$ states and shape coexistence. Based on the present data, which are in better agreement with the SDPF-MU calculations, the state observed at 2150(13)~keV in \nuc{42}{Si} is proposed to be the ($0^+_2$) level.

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arXiv2018

The structure of 70Fe: Single-particle and collective degrees of freedom

Excited states in the neutron-rich \nuc{70}{Fe} nucleus were populated in a one-proton removal reaction from \nuc{71}{Co} projectiles at 87~MeV/nucleon. A new transition was observed with the $γ$-ray tracking array GRETINA and shown to feed the previously assigned $4^+_1$ state. In comparison to reaction theory calculations with shell-model spectroscopic factors, it is argued that the new $γ$ ray possibly originates from the $6^+_1$ state. It is further shown that the Doppler-reconstructed $γ$-ray spectra are sensitive to the very different lifetimes of the $2^+$ and $4^+$ states, enabling their approximate measurement. The emerging structure of \nuc{70}{Fe} is discussed in comparison to LNPS-new large-scale shell-model calculations.

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arXiv2018

The GRIFFIN Facility for Decay-Spectroscopy Studies at TRIUMF-ISAC

Gamma-Ray Infrastructure For Fundamental Investigations of Nuclei, GRIFFIN, is a new high-efficiency $γ$-ray spectrometer designed for use in decay spectroscopy experiments with low-energy radioactive ion beams provided by TRIUMF's Isotope Separator and Accelerator (ISAC-I) facility. GRIFFIN is composed of sixteen Compton-suppressed large-volume clover-type high-purity germanium (HPGe) $γ$-ray detectors combined with a suite of ancillary detection systems and coupled to a custom digital data acquisition system. The infrastructure and detectors of the spectrometer as well as the performance characteristics and the analysis techniques applied to the experimental data are described.

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arXiv2018

High-resolution (p,t) reaction measurements as spectroscopic tests of {\it ab-initio} theory in the mid $pf$-shell

Detailed spectroscopic measurements of excited states in $^{50}$Cr and $^{62}$Zn were performed using 24~MeV (p,t) transfer reactions on $^{52}$Cr and $^{64}$Zn, respectively. In total, forty-five states in $^{50}$Cr and sixty-seven states in $^{62}$Zn were observed up to excitation energies of 5.5~MeV, including several previously unobserved states. These experimental results are compared to {\it ab-initio} shell-model calculations using chiral effective field theory ($χ$-EFT) with the valence-space in-medium similarity renormalization group (VS-IMSRG) method. This comparison demonstrates good agreement in the level orderings with these new theoretical methods, albeit with a slight over binding in the calculations. This work is part of a continued push to benchmark {\it ab-initio} theoretical techniques to nuclear structure data in $0^+\rightarrow0^+$ superallowed Fermi $β$ decay systems.

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arXiv2018

Shape Coexistence and Mixing of Low-Lying $0^+$ States in $^{96}$Sr

The low energy excited $0_{2,3}^+$ states in $^{96}$Sr are amongst the most prominent examples of shape coexistence across the nuclear landscape. In this work, the neutron $[2s_{1/2}]^2$ content of the $0_{1,2,3}^+$ states in $^{96}$Sr was determined by means of the d($^{95}$Sr,p) transfer reaction at the TRIUMF-ISAC2 facility using the SHARC and TIGRESS arrays. Spectroscopic factors of 0.19(3) and 0.22(3) were extracted for the $^{96}$Sr ground and 1229~keV $0^+$ states, respectively, by fitting the experimental angular distributions to DWBA reaction model calculations. A detailed analysis of the $γ$-decay of the isomeric $0_3^+$ state was used to determine a spectroscopic factor of 0.33(13). The experimental results are compared to shell model calculations, which predict negligible spectroscopic strength for the excited $0^+$ states in $^{96}$Sr. The strengths of the excited $0_{2,3}^+$ states were also analyzed within a two-level mixing model and are consistent with a mixing strength of $a^2$=0.40(14) and a difference in intrinsic deformations of $|Δβ|=0.31(3)$. These results suggest coexistence of three different configurations in $^{96}$Sr and strong shape mixing of the two excited $0^+$ states.

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arXiv2016

A Search for $0^+$ States in $^{50}$Cr: Implications for the Superallowed $β$-decay of $^{50}$Mn

A $^{52}$Cr$(p,t)$$^{50}$Cr two-neutron pickup reaction was performed using the Q3D magnetic spectrograph at the Maier-Leibnitz-Laboratorium in Garching, Germany. Excited states in $^{50}$Cr were observed up to an excitation energy of 5.3 MeV. Despite significantly increased sensitivity and resolution over previous work, no evidence of the previously assigned first excited $0^+$ state was found. As a result, the $0^+_2$ state is reassigned at an excitation energy of $E_x=3895.0(5)$ keV in $^{50}$Cr. This reassignment directly impacts direct searches for a non-analogue Fermi $β^+$ decay branch in $^{50}$Mn. These results also show better systematic agreement with the theoretical predictions for the $0^+$ state spectrum in $^{50}$Cr using the same formalism as the isospin-symmetry-breaking correction calculations for superallowed nuclei. The experimental data are also compared to $ab$-$initio$ shell-model predictions using the IM-SRG formalism based on $NN$ and $3N$ forces from chiral-EFT in the $pf$-shell for the first time.

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