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We performed a Penning trap mass measurement of $^{61}{\rm Zn}$ at the National Superconducting Cyclotron Laboratory and NuShellX calculations of the $^{61}{\rm Zn}$ and $^{62}{\rm Ga}$ structure using the GXPF1A Hamiltonian to obtain improved estimates of the $^{61}{\rm Zn}(p,\gamma)^{62}{\rm Ga}$ and $^{60}{\rm Cu}(p,\gamma)^{61}{\rm Zn}$ reaction rates. Surveying astrophysical conditions for type-I X-ray bursts with the code MESA, implementing our improved reaction rates, and taking into account updated nuclear masses for $^{61}{\rm V}$ and $^{61}{\rm Cr}$ from the recent literature, we refine the neutrino luminosity from the important mass number $A=61$ urca cooling source in accreted neutron star crusts. This improves our understanding of the thermal barrier between deep heating in the crust and the shallow depths where extra heat is needed to explain X-ray superbursts, as well as the expected signature of crust urca neutrino emission in light curves of cooling transients., Comment: Submitted

Protons and neutrons in the atomic nucleus move in shells analogous to the electronic shell structures of atoms. The nuclear shell structure varies as a result of changes in the nuclear mean field with the number of neutrons N and protons Z, and these variations can be probed by measuring the mass differences between nuclei. The N = Z = 40 self-conjugate nucleus 80Zr is of particular interest, as its proton and neutron shell structures are expected to be very similar, and its ground state is highly deformed. Here we provide evidence for the existence of a deformed double-shell closure in 80Zr through high-precision Penning trap mass measurements of 80–83Zr. Our mass values show that 80Zr is substantially lighter, and thus more strongly bound than predicted. This can be attributed to the deformed shell closure at N = Z = 40 and the large Wigner energy. A statistical Bayesian-model mixing analysis employing several global nuclear mass models demonstrates difficulties with reproducing the observed mass anomaly using current theory. High-precision mass measurements of exotic zirconium nuclei are reported, and reveal a double-shell closure for the deformed nucleus 80Zr, which is more strongly bound than previously thought.

We report high-precision mass measurements of $^{50--55}\mathrm{Sc}$ isotopes performed at the LEBIT facility at NSCL and at the TITAN facility at TRIUMF. Our results provide a substantial reduction of their uncertainties and indicate significant deviations, up to 0.7 MeV, from the previously recommended mass values for $^{53--55}\mathrm{Sc}$. The results of this work provide an important update to the description of emerging closed-shell phenomena at neutron numbers $N=32$ and $N=34$ above proton-magic $Z=20$. In particular, they finally enable a complete and precise characterization of the trends in ground state binding energies along the $N=32$ isotone, confirming that the empirical neutron shell gap energies peak at the doubly magic $^{52}\mathrm{Ca}$. Moreover, our data, combined with other recent measurements, do not support the existence of a closed neutron shell in $^{55}\mathrm{Sc}$ at $N=34$. The results were compared to predictions from both ab initio and phenomenological nuclear theories, which all had success describing $N=32$ neutron shell gap energies but were highly disparate in the description of the $N=34$ isotone.

Background: The quadratic isobaric multiplet mass equation (IMME) has been very successful at predicting the masses of isobaric analog states in the same multiplet, while its coefficients are known to follow specific trends as functions of mass number. The Atomic Mass Evaluation 2016 [Chin. Phys. C 41, 030003 (2017)] $^{44}\mathrm{V}$ mass value results in an anomalous negative $c$ coefficient for the IMME quadratic term; a consequence of large uncertainty and an unresolved isomeric state. The $b$ and $c$ coefficients can provide useful constraints for construction of the isospin-nonconserving Hamiltonians for the $pf$ shell. In addition, the excitation energy of the ${0}^{+},T=2$ level in $^{44}\mathrm{V}$ is currently unknown. This state can be used to constrain the mass of the more exotic $^{44}\mathrm{Cr}$.Purpose: The aim of the experimental campaign was to perform high-precision mass measurements to resolve the difference between $^{44}\mathrm{V}$ isomeric and ground states, to test the IMME using the new ground state mass value and to provide necessary ingredients for the future identification of the ${0}^{+}$, $T=2$ state in $^{44}\mathrm{V}$.Method: High-precision Penning trap mass spectrometry was performed at LEBIT, located at the National Superconducting Cyclotron Laboratory, to measure the cyclotron frequency ratios of [${^{44g,m}\mathrm{VO}]}^{+}$ versus [${^{32}\mathrm{SCO}]}^{+}$, a well-known reference mass, to extract both the isomeric and ground state masses of $^{44}\mathrm{V}$.Results: The mass excess of the ground and isomeric states in $^{44}\mathrm{V}$ were measured to be $\ensuremath{-}23\phantom{\rule{4pt}{0ex}}804.9(80)$ keV/${c}^{2}$ and $\ensuremath{-}23\phantom{\rule{4pt}{0ex}}537.0(55)$ keV/${c}^{2}$, respectively. This yielded a new proton separation energy of ${S}_{p}=1\phantom{\rule{4pt}{0ex}}773(10)$ keV.Conclusion: The new values of the ground state and isomeric state masses of $^{44}\mathrm{V}$ have been used to deduce the IMME $b$ and $c$ coefficients of the lowest ${2}^{+}$ and ${6}^{+}$ triplets in $A=44$. The ${2}^{+}\phantom{\rule{4pt}{0ex}}c$ coefficient is now verified with the IMME trend for lowest multiplets and is in good agreement with the shell-model predictions using charge-dependent Hamiltonians. The mirror energy differences were determined between $^{44}\mathrm{V}$ and $^{44}\mathrm{Sc}$, in line with isospin-symmetry for this multiplet. The new value of the proton separation energy determined, to an uncertainty of 10 keV, will be important for the determination of the ${0}^{+}$, $T=2$ state in $^{44}\mathrm{V}$ and, consequently, for prediction of the mass excess of $^{44}\mathrm{Cr}$.

We report high-precision mass measurements of ^{50-55}Sc isotopes performed at the LEBIT facility at NSCL and at the TITAN facility at TRIUMF. Our results provide a substantial reduction of their uncertainties and indicate significant deviations, up to 0.7 MeV, from the previously recommended mass values for ^{53-55}Sc. The results of this work provide an important update to the description of emerging closed-shell phenomena at neutron numbers N=32 and N=34 above proton-magic Z=20. In particular, they finally enable a complete and precise characterization of the trends in ground state binding energies along the N=32 isotone, confirming that the empirical neutron shell gap energies peak at the doubly magic ^{52}Ca. Moreover, our data, combined with other recent measurements, do not support the existence of a closed neutron shell in ^{55}Sc at N=34. The results were compared to predictions from both ab initio and phenomenological nuclear theories, which all had success describing N=32 neutron shell gap energies but were highly disparate in the description of the N=34 isotone.

Background: Isobaric quintets provide the best test of the isobaric multiplet mass equation (IMME) and can uniquely identify higher order corrections suggestive of isospin symmetry breaking effects in the nuclear Hamiltonian. The generalized IMME (GIMME) is a novel microscopic interaction theory that predicts an extension to the quadratic form of the IMME. Only the $A=20,32$ $T=2$ quintets have the exotic ${T}_{z}=\ensuremath{-}2$ member ground state mass determined to high precision by Penning trap mass spectrometry.Purpose: We aim to establish $A=36$ as the third $T=2$ isobaric quintet with the ${T}_{z}=\ensuremath{-}2$ member ground state mass measured by Penning trap mass spectrometry and provide the first test of the predictive power of the GIMME.Method: A radioactive beam of neutron-deficient $^{36}\mathrm{Ca}$ was produced by projectile fragmentation at the National Superconducting Cyclotron Laboratory. The beam was thermalized and the masses of $^{36}\mathrm{Ca}^{+}$ and $^{36}\mathrm{Ca}^{2+}$ were measured by the time-of-flight ion cyclotron resonance method in the LEBIT 9.4 T Penning trap.Results: We measure the mass excess of $^{36}\mathrm{Ca}$ to be $\mathrm{ME}=\ensuremath{-}6483.6(56)$ keV, an improvement in precision by a factor of 6 over the literature value. The new datum is considered together with evaluated nuclear data on the $A=36$, $T=2$ quintet. We find agreement with the quadratic form of the IMME given by isospin symmetry, but only coarse qualitative agreement with predictions of the GIMME.Conclusion: A total of three isobaric quintets have their most exotic members measured by Penning trap mass spectrometry. The GIMME predictions in the $T=2$ quintet appear to break down for $A=32$ and greater.

Background: Ultralow $Q$-value $\ensuremath{\beta}$ decays are interesting processes to study with potential applications to nuclear $\ensuremath{\beta}$-decay theory and neutrino physics. While a number of potential ultralow $Q$-value $\ensuremath{\beta}$-decay candidates exist, improved mass measurements are necessary to determine which of these are energetically allowed.Purpose: To perform precise atomic mass measurements of $^{89}\mathrm{Y}$ and $^{139}\mathrm{La}$. Use these new measurements along with the precisely known atomic masses of $^{89}\mathrm{Sr}$ and $^{139}\mathrm{Ba}$ and nuclear energy level data for $^{89}\mathrm{Y}$ and $^{139}\mathrm{La}$ to determine if there could be an ultralow $Q$-value decay branch in the $\ensuremath{\beta}$ decay of $^{89}\mathrm{Sr}\phantom{\rule{4pt}{0ex}}\ensuremath{\rightarrow}\phantom{\rule{4pt}{0ex}}^{89}\mathrm{Y}$ or $^{139}\mathrm{Ba}\phantom{\rule{4pt}{0ex}}\ensuremath{\rightarrow}\phantom{\rule{4pt}{0ex}}^{139}\mathrm{La}$.Method: High-precision Penning trap mass spectrometry was used to determine the atomic mass of $^{89}\mathrm{Y}$ and $^{139}\mathrm{La}$, from which $\ensuremath{\beta}$-decay $Q$ values for $^{89}\mathrm{Sr}$ and $^{139}\mathrm{Ba}$ were obtained.Results: The $^{89}\mathrm{Sr}\phantom{\rule{4pt}{0ex}}\ensuremath{\rightarrow}\phantom{\rule{4pt}{0ex}}^{89}\mathrm{Y}$ and $^{139}\mathrm{Ba}\phantom{\rule{4pt}{0ex}}\ensuremath{\rightarrow}\phantom{\rule{4pt}{0ex}}^{139}\mathrm{La}\phantom{\rule{4pt}{0ex}}\ensuremath{\beta}$-decay $Q$ values were measured to be ${Q}_{\mathrm{Sr}}=1502.20(0.35)$ keV and ${Q}_{\mathrm{Ba}}=2308.37(0.68)$ keV. These results were compared to energies of excited states in $^{89}\mathrm{Y}$ at 1507.4(0.1) keV, and in $^{139}\mathrm{La}$ at 2310(19) keV and 2313(1) keV to determine $Q$ values of $\ensuremath{-}5.20(0.37)$ keV for the potential ultralow $\ensuremath{\beta}$-decay branch of $^{89}\mathrm{Sr}$ and $\ensuremath{-}1.6(19.0)$ keV and $\ensuremath{-}4.6(1.2)$ keV for those of $^{139}\mathrm{Ba}$.Conclusion: The potential ultralow $Q$-value decay branch of $^{89}\mathrm{Sr}$ to the $^{89}\mathrm{Y}$ ($3/{2}^{\ensuremath{-}}$, 1507.4 keV) state is energetically forbidden and has been ruled out. The potential ultralow $Q$-value decay branch of $^{139}\mathrm{Ba}$ to the 2313 keV state in $^{139}\mathrm{La}$ with unknown ${J}^{\ensuremath{\pi}}$ has also been ruled out at the $4\ensuremath{\sigma}$ level, while more precise energy level data is needed for the $^{139}\mathrm{La}$ ($1/{2}^{+}$, 2310 keV) state to determine if an ultralow $Q$-value $\ensuremath{\beta}$-decay branch to this state is energetically allowed.

Background: The understanding and description of forbidden decays provides interesting challenges for nuclear theory. These calculations could help to test underlying nuclear models and interpret experimental data.Purpose: Compare a direct measurement of the $^{138}\mathrm{La}\phantom{\rule{4pt}{0ex}}\ensuremath{\beta}$-decay $Q$ value with the $\ensuremath{\beta}$-decay spectrum end-point energy measured by Quarati et al. using ${\mathrm{LaBr}}_{3}$ detectors [Appl. Radiat. Isot. 108, 30 (2016)]. Use new precise measurements of the $^{138}\mathrm{La}\phantom{\rule{4pt}{0ex}}\ensuremath{\beta}$-decay and electron capture (EC) $Q$ values to improve theoretical calculations of the $\ensuremath{\beta}$-decay spectrum and EC probabilities.Method: High-precision Penning trap mass spectrometry was used to measure cyclotron frequency ratios of $^{138}\mathrm{La}$, $^{138}\mathrm{Ce}$, and $^{138}\mathrm{Ba}$ ions from which $\ensuremath{\beta}$-decay and EC $Q$ values for $^{138}\mathrm{La}$ were obtained.Results: The $^{138}\mathrm{La}\phantom{\rule{4pt}{0ex}}\ensuremath{\beta}$-decay and EC $Q$ values were measured to be ${Q}_{\ensuremath{\beta}}=1052.42(41)$ keV and ${Q}_{\mathrm{EC}}=1748.41(34)$ keV, improving the precision compared to the values obtained in the most recent atomic mass evaluation [Wang et al., Chin. Phys. C 41, 030003 (2017)] by an order of magnitude. These results are used for improved calculations of the $^{138}\mathrm{La}\phantom{\rule{4pt}{0ex}}\ensuremath{\beta}$-decay shape factor and EC probabilities. New determinations for the $^{138}\mathrm{Ce}$ 2EC $Q$ value and the atomic masses of $^{138}\mathrm{La}$, $^{138}\mathrm{Ce}$, and $^{138}\mathrm{Ba}$ are also reported.Conclusion: The $^{138}\mathrm{La}\phantom{\rule{4pt}{0ex}}\ensuremath{\beta}$-decay $Q$ value measured by Quarati et al. is in excellent agreement with our new result, which is an order of magnitude more precise. Uncertainties in the shape factor calculations for $^{138}\mathrm{La}\phantom{\rule{4pt}{0ex}}\ensuremath{\beta}$ decay using our new $Q$ value are reduced by an order of magnitude. Uncertainties in the EC probability ratios are also reduced and show improved agreement with experimental data.

Nuclear structure and astrophysics studies rely heavily on precision mass measurements of rare isotopes. However, many of these isotopes far from the valley of stability can only be produced at very low rates, which are incompatible with the destructive measurement techniques used by rare isotope Penning trap mass spectrometry facilities. To this end, the Low Energy Beam and Ion Trap facility at the National Superconducting Laboratory is in the process of commissioning a single ion Penning trap (SIPT) mass spectrometer that relies on the non-destructive narrowband Fourier Transform ion cyclotron resonance technique. SIPT is the first Penning trap designed to perform mass measurements of rare isotopes produced via projectile fragmentation at rates on the order of one ion per day. The system details and cryogenic detection design, as well as results from the room and cryogenic temperature commissioning, are discussed at length.

Background: The $^{51}\mathrm{Fe}(p,\ensuremath{\gamma})^{52}\mathrm{Co}$ reaction lies along the main rp-process path leading up to the $^{56}\mathrm{Ni}$ waiting point. The uncertainty in the reaction $Q$ value, which determines the equilibrium between the forward proton-capture and reverse photodisintegration $^{52}\mathrm{Co}(\ensuremath{\gamma},p)^{51}\mathrm{Fe}$ reaction, contributes to considerable uncertainty in the reaction rate in the temperature range of interest for Type I x-ray bursts and thus to an $\ensuremath{\approx}10%$ uncertainty in burst ashes lighter than $A=56$.Purpose: With a recent Penning trap mass measurement of $^{52}\mathrm{Co}$ reducing the uncertainty on its mass to 6.6 keV [Nesterenko et al., J. Phys. G 44, 065103 (2017)], the dominant source of uncertainty in the reaction $Q$ value is now the mass of $^{51}\mathrm{Fe}$, reported in the 2016 atomic mass evaluation to a precision of 9 keV [Wang et al., Chin. Phys. C 41, 030003 (2017)]. A new, high-precision Penning trap mass measurement of $^{51}\mathrm{Fe}$ was performed to allow the determination of an improved precision $Q$ value and thus new reaction rates.Method: $^{51}\mathrm{Fe}$ was produced using projectile fragmentation at the Coupled Cyclotron Facility at the National Superconducting Cyclotron Laboratory, and separated using the A1900 fragment separator. The resulting secondary beam was then thermalized in the beam stopping area before a mass measurement was performed using the LEBIT 9.4T Penning trap mass spectrometer.Results: The new mass excess, $\mathrm{ME}=\ensuremath{-}40189.2(1.6)$ keV, is sixfold more precise than the current AME value, and $1.6\ensuremath{\sigma}$ less negative. This value was used to calculate a new proton separation energy for $^{52}\mathrm{Co}$ of 1431(7) keV. New excitation levels were then calculated for $^{52}\mathrm{Co}$ using the nushellx code with the GXPF1A interaction, and a new reaction rate and burst ash composition was calculated.Conclusions: With a new measured $Q$ value, the uncertainty on the $^{51}\mathrm{Fe}(p,\ensuremath{\gamma})$ reaction rate is dominated by the poorly measured $^{52}\mathrm{Co}$ level structure. Reducing this uncertainty would allow a more precise rate calculation and a better determination of the mass abundances in the burst ashes.

International audience; We discuss the motivation and technique of Penning trap mass spectrometry applied to radioactive$^{44}$V and$^{44}^{m}$V, using the LEBIT 9.4 T Penning trap mass spectrometer at the National Superconducting Cyclotron Laboratory (NSCL) at Michigan State University. A complementary measurement of these nuclides, performed at the CSRe in Lanzhou, China, was recently published, but with errors several times larger than obtainable for a short-lived radionuclide in a Penning trap. Interpretation of the higher precision results is ongoing and a full accounting of this measurement is anticipated in the coming months.

We report the mass measurement of $^{56}\mathrm{Cu}$, using the LEBIT 9.4 T Penning trap mass spectrometer at the National Superconducting Cyclotron Laboratory at Michigan State University. The mass of $^{56}\mathrm{Cu}$ is critical for constraining the reaction rates of the $^{55}\mathrm{Ni}(p,\ensuremath{\gamma})$ $^{56}\mathrm{Cu}(p,\ensuremath{\gamma})$ $^{57}\mathrm{Zn}({\ensuremath{\beta}}^{+})$ $^{57}\mathrm{Cu}$ bypass around the $^{56}\mathrm{Ni}$ waiting point. Previous recommended mass excess values have disagreed by several hundred keV. Our new value, $\mathrm{ME}=\ensuremath{-}38626.7(7.1)\text{ }\text{ }\mathrm{keV}$, is a factor of 30 more precise than the extrapolated value suggested in the 2012 atomic mass evaluation [Chin. Phys. C 36, 1603 (2012)], and more than a factor of 12 more precise than values calculated using local mass extrapolations, while agreeing with the newest 2016 atomic mass evaluation value [Chin. Phys. C 41, 030003 (2017)]. The new experimental average, using our new mass and the value from AME2016, is used to calculate the astrophysical $^{55}\mathrm{Ni}(p,\ensuremath{\gamma})$ and $^{56}\mathrm{Cu}(p,\ensuremath{\gamma})$ forward and reverse rates and perform reaction network calculations of the $rp$ process. These show that the $rp$-process flow redirects around the $^{56}\mathrm{Ni}$ waiting point through the $^{55}\mathrm{Ni}(p,\ensuremath{\gamma})$ route, allowing it to proceed to higher masses more quickly and resulting in a reduction in ashes around this waiting point and an enhancement to higher-mass ashes.

We report the mass measurement of ^{56}Cu, using the LEBIT 9.4 T Penning trap mass spectrometer at the National Superconducting Cyclotron Laboratory at Michigan State University. The mass of ^{56}Cu is critical for constraining the reaction rates of the ^{55}Ni(p,γ) ^{56}Cu(p,γ) ^{57}Zn(β^{+}) ^{57}Cu bypass around the ^{56}Ni waiting point. Previous recommended mass excess values have disagreed by several hundred keV. Our new value, ME=-38626.7(7.1) keV, is a factor of 30 more precise than the extrapolated value suggested in the 2012 atomic mass evaluation [Chin. Phys. C 36, 1603 (2012)CPCHCQ1674-113710.1088/1674-1137/36/12/003], and more than a factor of 12 more precise than values calculated using local mass extrapolations, while agreeing with the newest 2016 atomic mass evaluation value [Chin. Phys. C 41, 030003 (2017)CPCHCQ1674-113710.1088/1674-1137/41/3/030003]. The new experimental average, using our new mass and the value from AME2016, is used to calculate the astrophysical ^{55}Ni(p,γ) and ^{56}Cu(p,γ) forward and reverse rates and perform reaction network calculations of the rp process. These show that the rp-process flow redirects around the ^{56}Ni waiting point through the ^{55}Ni(p,γ) route, allowing it to proceed to higher masses more quickly and resulting in a reduction in ashes around this waiting point and an enhancement to higher-mass ashes.