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The $\ensuremath{\beta}$ decay of $^{125m,125}\mathrm{Ag}$ into levels in $^{125}\mathrm{Cd}$ was investigated at the Holifield Radioactive Ion Beam Facility (HRIBF). Uranium-238 targets were bombarded with 50-MeV protons with an intensity of $15\phantom{\rule{4pt}{0ex}}\ensuremath{\mu}$A, and the induced fission products were mass separated and deposited on a moving tape in the center of the VANDLE array consisting of $\ensuremath{\gamma}$ detectors and plastic scintillators. A partial decay scheme has been assigned for both $\ensuremath{\beta}$ decay of the (9/${2}^{+}$) ground state of $^{125}\mathrm{Ag}$ and its low-lying (1/${2}^{\ensuremath{-}}$) isomer, with the energy of the low-lying (11/${2}^{\ensuremath{-}}$) isomeric state in $^{125}\mathrm{Cd}$ assigned as 188.5 keV. In addition, $\ensuremath{\beta}$-delayed neutron emission probabilities were also determined to be 1.2(2)% for the (9/${2}^{+}$) $^{125}\mathrm{Ag}$ ground state and 4.6(10)% for the (1/${2}^{\ensuremath{-}}$) isomer, which are substantially lower than the previously reported value.

Decay protons from excited states in $^{21}\mathrm{Na}$ populated through a previously reported $^{24}\mathrm{Mg}(p,\ensuremath{\alpha})^{21}\mathrm{Na}$ transfer reaction [Cha et al., Phys. Rev. C 96, 025810 (2017)] were analyzed to extract the proton branching ratios of the energy levels. By utilizing 31-MeV proton beams from the Holifield Radioactive Ion Beam Facility of Oak Ridge National Laboratory and isotopically enriched $^{24}\mathrm{Mg}$ solid targets, the decay protons were detected in coincidence with $\ensuremath{\alpha}$ particles from the $(p,\ensuremath{\alpha})$ reaction using a silicon strip detector array. Proton decay branching ratios of several $^{21}\mathrm{Na}$ levels were deduced for the $p0$ and $p1$ decay channels to the ground and first excited states in $^{20}\mathrm{Ne}$, respectively.

New experimental data obtained from γ-ray tagged one-neutron and one-proton knockout from 55Co is presented. A candidate for the sought-after T = 1, T z = 0, Jπ = 6+ state in 54Co is proposed based on a comparison to the new data on 54Fe, the corresponding observables predicted by large-scale-shell-model (LSSM) calculations in the full fp-model space employing charge-dependent contributions, and isospin-symmetry arguments. Furthermore, possible isospin-symmetry breaking in the A = 54, T = 1 triplet is studied by calculating the experimental c coefficients of the isobaric mass multiplet equation (IMME) up to the maximum possible spin J = 6 expected for the (1f7/2)-2 two-hole configuration relative to the doubly-magic nucleus 56Ni. The experimental quantities are compared to the theoretically predicted c coefficients from LSSM calculations using two-body matrix elements obtained from a realistic chiral effective field theory potential at next-to-next-to-next-to leading order (N3LO).

We present a high-resolution in-beam γ-ray spectroscopy study of excited states in the mirror nuclei 55Co and 56Ni following one-nucleon knockout from a projectile beam of 56Ni. The newly determined partial cross sections and the γ-decay properties of excited states provide a test of state-of-the-art nuclear structure models and probe mirror symmetry in unique ways. The new experimental data are compared to large-scale shell-model calculations in the full pf space and including charge-dependent contributions. A mirror asymmetry for the partial cross sections leading to the two lowest 3/2− states in the A = 55 mirror pair was identified as well as a significant difference in the E1 decays from the 1/21+ state to the same two 3/2− states. The mirror asymmetry in the partial cross sections cannot be reconciled with the present shell-model picture or small mixing introduced in a two-state model. The observed mirror asymmetry in the E decay pattern, however, points at stronger mixing between the two lowest 3/2− states in 55Co than in its mirror 55Ni.

Half of the elements heavier than iron are believed to be produced through the rapid neutron-capture process ($r$ process). The astrophysical environment(s) where the $r$ process occurs remains an open question, even after recent observations of neutron-star mergers and the associated kilonova. Features in the abundance pattern of $r$-process ashes may provide critical insight for distinguishing contributions from different possible sites, including neutron-star mergers and core-collapse supernovae. In particular, the largely unknown neutron-capture reaction rates on neutron-rich unstable nuclei near $^{132}\mathrm{Sn}$ could have a significant impact on the final $r$-process abundances. To better determine these neutron-capture rates, the $(d,p)$ reaction has been measured in inverse kinematics using radioactive ion beams of $^{126}\mathrm{Sn}$ and $^{128}\mathrm{Sn}$ and a stable beam of $^{124}\mathrm{Sn}$ interacting with a ${({\mathrm{CD}}_{2})}_{n}$ target. An array of position-sensitive silicon strip detectors, including the Super Oak Ridge Rutgers University Barrel Array, was used to detect light reaction products. In addition to the present measurements, previous measurements of $^{130,132}\mathrm{Sn}(d,p)$ were reanalyzed using state-of-the-art reaction theory to extract a consistent set of spectroscopic factors for $(d,p)$ reactions on even tin nuclei between the heaviest stable isotope $^{124}\mathrm{Sn}$ and doubly magic $^{132}\mathrm{Sn}$. The spectroscopic information was used to calculate direct-semidirect $(n,\ensuremath{\gamma})$ cross sections, which will serve as important input for $r$-process abundance calculations.

The $^{15}$O($\alpha$,$\gamma$)$^{19}$Ne reaction is responsible for breakout from the hot CNO cycle in Type I x-ray bursts. Understanding the properties of resonances between $E_x = 4$ and 5 MeV in $^{19}$Ne is crucial in the calculation of this reaction rate. The spins and parities of these states are well known, with the exception of the 4.14- and 4.20-MeV states, which have adopted spin-parities of 9/2$^-$ and 7/2$^-$, respectively. Gamma-ray transitions from these states were studied using triton-$\gamma$-$\gamma$ coincidences from the $^{19}$F($^{3}$He,$t\gamma$)$^{19}$Ne reaction measured with GODDESS (Gammasphere ORRUBA Dual Detectors for Experimental Structure Studies) at Argonne National Laboratory. The observed transitions from the 4.14- and 4.20-MeV states provide strong evidence that the $J^\pi$ values are actually 7/2$^-$ and 9/2$^-$, respectively. These assignments are consistent with the values in the $^{19}$F mirror nucleus and in contrast to previously accepted assignments.

The $^{24}\mathrm{Mg}(p,\ensuremath{\alpha})^{21}\mathrm{Na}$ reaction was measured at the Holifield Radioactive Ion Beam Facility of the Oak Ridge National Laboratory to study the spectroscopy of the radionuclide $^{21}\mathrm{Na}$. A 31-MeV proton beam from the 25 MV tandem accelerator bombarded isotopically enriched $^{24}\mathrm{Mg}$ targets. Recoiling $^{4}\mathrm{He}$ particles were identified by an annular silicon strip detector array. Two energy levels at ${E}_{x}=6.594$ and 7.132 MeV were observed for the first time. By comparing the experimentally obtained angular distributions and distorted wave Born approximation calculations, the spins and parities of $^{21}\mathrm{Na}$ energy levels were constrained. The astrophysically-important $^{17}\mathrm{F}(\ensuremath{\alpha},p)^{20}\mathrm{Ne}$ reaction rate was also calculated for the first time using resonance parameters for 12 energy levels.

Comprehensive spectroscopy of the N = 29 nucleus 47Ar is presented, based on two complemen-tary direct reaction mechanisms: one-neutron pickup onto 46Ar projectiles and one-proton removal from the 1− ground state of 48K. The results are compared to shell-model calculations that use the state-of-the-art SDPF-U and SDPF-MU effective interactions. Also, from the 9Be(46Cl,45S+γ)X one-proton removal reaction, we report the first γ-ray transitions observed from 45S. Using compar-isons with shell-model calculations, and from the observed intensities and energy sums, we propose a first tentative level scheme for 45S.

Background: The study of excited states in mirror nuclei allows us to extract information on charge-dependent (i.e., isospin-nonconserving) interactions in nuclei. Purpose: To extend previous studies of mirror nuclei in the f7/2 region, investigating charge symmetry breaking of the strong nuclear force. Methods: γ-ray spectroscopy has been performed for the mirror (Tz= ±3/2) pair 53Ni and 53Mn, produced via mirrored one-nucleon knockout reactions. Results: Several new transitions have been identified in 53Ni from which a new level scheme has been constructed. Cross sections for knockout have been analyzed and compared with reaction model calculations where evidence is found for knockout from high-spin isomeric states. Mirror energy differences between isobaric analog states have been computed, compared to large scale shell-model calculations, and interpreted in terms of isospin-nonconserving effects. In addition, lifetimes for the long-lived J π = 5 /2 − 1 analog states in both 53Mn and 53Ni have been extracted through lineshape analysis, giving half-lives of t1/2 = 120 (14) ps and t1/2 = 198 (12) ps,respectively. Conclusions: The inclusion of a set of isovector isospin-nonconserving matrix elements to the shell-model calculations gave the best agreement with the experimental data.

The neutron-deficient nucleus Sn 107 has been studied by using the one-neutron knockout reaction. By measuring the decay γ rays and momentum distributions of reaction residues, the spins of the ground, 5/2 + , and first-excited, 7/2 + , states of Sn 107 have been assigned by comparisons to eikonal-model reaction calculations. Limits on the inclusive and exclusive cross sections have been measured and transitions due to neutron removals from below the N=50 closed shell have been observed. New excited states up to 5.5 MeV in Sn 107 have been identified.

The lifetimes of the yrast ${8}^{+}$ and ${9}^{+}$ states of $^{70}\mathrm{As}$ have been measured via the $\ensuremath{\gamma}$-ray lineshape method following population by the ${}^{9}\mathrm{Be}\phantom{\rule{0.16em}{0ex}}{(}^{78}\mathrm{Rb},{}^{70}\mathrm{As})$ reaction at 101.6 MeV/nucleon. The strength of the $E1\phantom{\rule{0.28em}{0ex}}{8}^{+}\ensuremath{\rightarrow}{7}^{\ensuremath{-}}$ transition is found to be $B(E1)=1.3(5)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}5} {e}^{2}\phantom{\rule{0.16em}{0ex}}{\text{fm}}^{2}$ or $1.2(4)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}5}$ Weisskopf units (W.u.) while the ${9}^{+}\ensuremath{\rightarrow}{8}^{+} M1$ transition is found to have a strength of $B(M1)=1.5(8) {\ensuremath{\mu}}_{N}^{2}$ or $0.85(42)$ W.u. The implications for the structure of these states is discussed and found to be consistent with an assignment to a $\ensuremath{\pi}{g}_{9/2}\ensuremath{\nu}{g}_{9/2}$ configuration.

The $^{240}\mathrm{Am}(n,f$) cross section has been measured for the first time above 4 MeV, using the surrogate-ratio method over the neutron energy range of 200 keV to 14 MeV. The reactions $^{243}\mathrm{Am}(p,tf$) and $^{238}\mathrm{U}(p,tf$), which proceed through the fissioning excited nuclei $^{241}\mathrm{Am}$* and $^{236}\mathrm{U}$*, were used as surrogates for the desired $^{240}\mathrm{Am}(n,f$) and $^{235}\mathrm{U}(n,f$) reactions. The experiment was fielded using the STARLiTeR detector system with a recently commissioned VME-based data acquisition system. The 38.4-MeV proton beam used in these measurements was provided by the K150 cyclotron at the Texas A Cyclotron Institute. The measured $^{240}\mathrm{Am}(n,f$) cross section disagrees with many of the most recent evaluations, and a reevaluation is recommended.

$\ensuremath{\gamma}$-ray transitions in ${}^{134}\text{Te}$, ${}^{135}\text{Te}$, and ${}^{136}\text{Te}$ were measured from ${}^{9}\text{Be}$-induced reactions with a radioactive ${}^{132}\text{Sn}$ beam at a sub-Coulomb barrier energy of 3 MeV per nucleon using particle-$\ensuremath{\gamma}$ coincidence spectroscopy. The transitions were selected by gating on alpha-like particles in a CsI detector following a combination of $({}^{9}\text{Be},\ensuremath{\alpha}1n)$, $({}^{9}\text{Be},\ensuremath{\alpha}2n)$, and $({}^{9}\text{Be},\ensuremath{\alpha}3n)$ incomplete fusion-evaporation reactions. Distorted-wave Born approximation calculations suggest little to no contribution from the $({}^{9}\text{Be},{}^{7}\text{He})$, $({}^{9}\text{Be},{}^{6}\text{He})$, and $({}^{9}\text{Be},{}^{5}\text{He})$ direct reactions.$\ensuremath{\gamma}$-ray transitions from previously known ${2}^{+}\ensuremath{\bigotimes}\ensuremath{\nu}\phantom{\rule{0.16em}{0ex}}2{f}_{7/2}$ and ${4}^{+}\ensuremath{\bigotimes}\ensuremath{\nu}\phantom{\rule{0.16em}{0ex}}2{f}_{7/2}$ multiplet members in ${}^{135}\text{Te}$ are observed. A new $\ensuremath{\gamma}$ ray is observed, assigned to the third-excited state in ${}^{135}\text{Te}$, and new ${2}^{+}\ensuremath{\bigotimes}\ensuremath{\nu}\phantom{\rule{0.16em}{0ex}}2{f}_{7/2}$ multiplet members are suggested. In addition, spin assignments are made by using recent one-neutron transfer data. The updated experimental data for ${}^{135}\text{Te}$ are compared to shell-model calculations for a relatively complete set of states up to the yrast ${15/2}^{\ensuremath{-}},{4}^{+}\ensuremath{\bigotimes}\ensuremath{\nu}\phantom{\rule{0.16em}{0ex}}2{f}_{7/2}$ multiplet member at 1505 keV.

The evolution of shell structure and the fragility of the benchmark magic numbers is a topic of major interest in nuclear-structure physics. The authors measured the structure-sensitive $g$ factors of states in unstable even-even strontium isotopes, following $\ensuremath{\alpha}$-pickup reactions by krypton beams from a carbon target. The results help elucidate how protons and neutrons contribute to the evolution of nuclear structure in this important mass region where rapid structural changes occur.

Excited states in C-16 were populated via the Be-9(N-17,C-16+gamma)X one-proton knockout reaction. The lifetime of the 2(1)(+) state in C-16 was measured using the recoil distance method. The extracted lifetime of tau(+)(21) = 11.4(-0.9)(+0.8)(stat) +/- 0.7(syst(B rho))(-1.5)(+0.0)(syst(feeding)) ps yields a deduced B(E2;2(1)(+) -> 0(1)(+)) = 4.21(-0.26)(+0.34)(stat)(-0.24)(+0.28)(syst(B rho))(-0.00)(+0.64)(syst(feeding)) e(2)fm(4) value in good agreement with a previous measurement. The one-proton knockout cross section is used to extract the proton amplitude of the C-16 2(1)(+) state, which confirms the neutron dominant character of this state. Gamma-ray branching ratios between the 2(2)(+) state and the 2(1)(+) and ground states were also determined. The results are compared with p-sd shell model and no-core shell model (with NN and NN + NNN) calculations. The inclusion of three-body forces are essential in order for the no-core shell model calculations to reproduce the experimental findings on the gamma-ray branching ratios.

The role of proton shell effects in the structure of the N=28 isotones 45Cl and 44S has been studied via one-proton knockout from 45Cl. We compare measured γ-ray intensities, inclusive and partial knockout cross sections, and the inclusive momentum distribution of outgoing 44S particles with shell-model and reaction-theory predictions. The strong population in this reaction of the recently identified 41+ state in 44S, identified through its subsequent γ-ray decay energy, makes a compelling case for a Jπ=3/2+ ground state in 45Cl.

Intermediate-energy Coulomb excitation measurements were performed on the neutron-rich isotopes ${}^{58,60,62}$Cr. The electric quadrupole excitation strengths, $B$($E$2; 0${}_{1}^{+}\ensuremath{\rightarrow}{2}_{1}^{+}$), of ${}^{60,62}$Cr are determined for the first time. The results quantify the trend of increasing quadrupole collectivity in the Cr isotopes approaching neutron number $N=40$. The results are confronted with large-scale shell-model calculations in the $fpgd$ shell using the state-of-the-art LNPS effective interaction. Different sets of effective charges are discussed that provide an improved and robust description of the $B(E2)$ values of the neutron-rich Fe and Cr isotopes in this region of rapid shell evolution. The ratio of the neutron and proton transition matrix elements, $|{M}_{n}/{M}_{p}|$, is proposed as an effective tool to discriminate between the various choices of effective charges.

Excited states in C-18 were populated by the one-proton knockout reaction of an intermediate energy radioactive N-19 beam. The lifetime of the first 2(+) state was measured with the Koln/NSCL plunger via the recoil distance method to be tau (2(1)(+)) = 22.4 +/- 0.9(stat)(-2.2)(+3.3)(syst) ps, which corresponds to a reduced quadrupole transition strength of B(E2; 2(1)(+) -> 0(1)(+)) = 3.64(-0.14)(+ 0.15)(stat)(-0.47)(+0.40)(syst) e(2)fm(4). In addition, an upper limit on the lifetime of a higher-lying state feeding the 2(1)(+) state was measured to be tau < 4.6 ps. The results are compared to large-scale ab initio no-core shell model calculations using two accurate nucleon-nucleon interactions and the importance-truncation scheme. The comparison provides strong evidence that the inclusion of three-body forces is needed to describe the low-lying excited-state properties of this A = 18 system.

The lifetimes of the first 2${}^{+}$ states in the neutron-deficient ${}^{76,78}$Sr isotopes were measured using a unique combination of the $\ensuremath{\gamma}$-ray line-shape method and two-step nucleon exchange reactions at intermediate energies. The transition rates for the 2${}^{+}$ states were determined to be $B(\mathrm{E}2;{2}^{+}\ensuremath{\rightarrow}{0}^{+})=2220(270)$ ${e}^{2}$fm${}^{4}$ for ${}^{76}$Sr and 1800(250) ${e}^{2}$fm${}^{4}$ for ${}^{78}$Sr, corresponding to large deformation of ${\ensuremath{\beta}}_{2}$ $=$ 0.45(3) for ${}^{76}$Sr and 0.40(3) for ${}^{78}$Sr. The present data provide experimental evidence for mutually enhanced collectivity that occurs at $N$ $=$ $Z$ $=$ 38. The systematic behavior of the excitation energies and $B(\mathrm{E}2)$ values indicates a signature of shape coexistence in ${}^{76}$Sr, characterizing ${}^{76}$Sr as one of most deformed nuclei with an unusually reduced $E$(4${}^{+}$)$/E$(2${}^{+}$) ratio.

The neutron-rich $N=28$ nucleus $^{44}\mathrm{S}$ was studied using the two-proton knockout reaction from $^{46}\mathrm{Ar}$ at intermediate beam energy. We report the observation of four new excited states, one of which is a strongly prolate deformed 4${}^{+}$ state, as indicated by a shell-model calculation. Its deformation originates in a neutron configuration which is fundamentally different from the ``intruder'' configuration responsible for the ground-state deformation. Consequently, we do not have three coexisting shapes in $^{44}\mathrm{S}$, but three coexisting configurations, corresponding to zero-, one-, and two-neutron particle-hole excitations.

The neutron-rich $N=50$ isotones $^{82}\mathrm{Ge}$ and $^{84}\mathrm{Se}$ were investigated using intermediate-energy Coulomb excitation on a $^{197}\mathrm{Au}$ target and inelastic scattering on $^{9}\mathrm{Be}$. As typical for intermediate-energy Coulomb excitation with projectile energies exceeding 70 MeV/nucleon, only the first ${2}^{+}$ states were excited in $^{82}\mathrm{Ge}$ and $^{84}\mathrm{Se}$. However, in the inelastic scattering on a $^{9}\mathrm{Be}$ target, a strong population of the first ${4}^{+}$ state was observed for $^{84}\mathrm{Se}$, while there is no indication of a similarly strong excitation of the corresponding state in the neighboring even-even isotone $^{82}\mathrm{Ge}$. The results are discussed in the framework of systematics and shell-model calculations using three different effective interactions.

$^{9}\mathrm{Be}$-induced inelastic scattering of $^{62,64,66}\mathrm{Fe}$ and $^{60,62,64}\mathrm{Cr}$ was performed at intermediate beam energies. Excited states in $^{64}\mathrm{Cr}$ were measured for the first time. Energies and population patterns of excited states in these neutron-rich Fe and Cr nuclei are compared and interpreted in the framework of large-scale shell-model calculations in different model spaces. Evidence for increased collectivity and for distinct structural changes between the neighboring Fe and Cr isotopic chains near $N=40$ is presented.

gamma-ray decays from excited states in {sup 30}Ne and inclusive and exclusive cross sections were measured in the {sup 9}Be({sup 32}Mg,{sup 30}Ne+gamma)X two-proton knockout reaction at incident beam energies of 99.7 and 86.7 MeV/nucleon. The measured cross section is suppressed compared to calculations and is indicative of a reduced overlap of initial and final state wave functions in {sup 32}Mg and {sup 30}Ne. We interpret this reduction as due to large 4p4h amplitudes present in the {sup 30}Ne ground state wave function, but not {sup 32}Mg. Such large intruder components are predicted to help stabilize the heavier fluorine isotopes against neutron emission.

We report on the first measurement of the absolute transition strength $B(E2;{0}_{1}^{+}\ensuremath{\rightarrow}{2}_{1}^{+})$ in the self-conjugate nucleus $^{68}\mathrm{Se}$. It is found that the ${0}_{1}^{+}\ensuremath{\rightarrow}{2}_{1}^{+}$ transition displays a strength similar to that for the triaxial $^{64}\mathrm{Ge}$ nucleus, in sharp contrast to the much stronger collectivity observed for the oblate $^{72}\mathrm{Kr}$ nucleus. Shape evolution along the $N=Z$ line from zinc to strontium is analyzed through beyond-mean-field calculations using the D1S force. Over this narrow mass region the nuclear structure shows clear-cut transition from prolate to oblate and back to prolate, with $^{68}\mathrm{Se}$ standing as pivotal between triaxial and oblate deformations.