Search

The nature of the 1 − and 2 − excited states in Be 10 is studied using the Be 11 ( p , d ) transfer reaction in inverse kinematics at 10A MeV at TRIUMF ISAC-II, in particular to assess whether either of them can be considered as an excited halo state. The angular distributions for both states are extracted using deuteron- γ coincidences and analyzed using a transfer model taking into account one-step and two-step processes. A good fit of the angular distributions is obtained considering only the one-step process, whereby an inner p 3 / 2 neutron of Be 11 is removed, leaving the halo neutron intact. Higher-order processes however cannot be rejected. The small spectroscopic factors extracted suggest that the structure of both states is not uniquely halo-like, but rather display a more complex configuration mixing cluster and halo structures. Further insights are limited, as this experiment specifically probed the halo-like (but not cluster-like) Be 11 ( 1 / 2 + ) ⊗ ( ν p 3 / 2 ) − 1 configuration in both states.

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.

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.

The $\beta^-$ decay of $^{47}$K to $^{47}$Ca is an appropriate mechanism for benchmarking interactions spanning the $sd$ and $pf$ shells, but current knowledge of the $\beta^-$-decay scheme is limited. We have performed a high-resolution, high-efficiency study of the $\beta^-$-decay of $^{47}$K with the GRIFFIN spectrometer at TRIUMF-ISAC. The study revealed 48 new transitions, a more precise value for the $^{47}$K half-life (17.38(3)~s), and new spin and parity assignments for eight excited states. Levels placed for the first time here raise the highest state observed in $\beta^-$ decay to within 568(3) keV of the $Q$-value and confirm the previously measured large $\beta^-$-decay branching ratios to the low-lying states. Previously unobserved $\beta^-$-feeding to 3/2$^+$ states between 4.5 and 6.1~MeV excitation energy was identified with a total $\beta^-$-feeding intensity of 1.29(2)\%. The sum of the $B(GT)$ values for these states indicates that the $1s_{1/2}$ proton hole strength near this excitation energy is comparable to the previously known $1s_{1/2}$ proton and neutron hole strengths near 2.6 MeV.

Background: Neutron-rich nuclei in the mass region around A=160 have been and will continue to be of interest for the study of nuclear structure because of the rapid onset of deformation between 88 and 90 neutrons. The observation of detailed changes in nuclear structures within this mass region has provided and will continue to provide insight into the nuclear force. Purpose: Investigations of γ rays emitted following Eu163 β-decay to Gd163 have been performed for evaluation of the nuclear structure of Gd163. Method: Data were collected at the LeRIBSS station of the Holifield Radioactive Ion Beam Facility at Oak Ridge National Laboratory with an array of four Clover HPGe detectors for γ-rays and two plastic scintillators for β detection. The γ rays were identified as belonging to Gd163 via mass selection and γ-γ-β, x-ray-γ, or γ-γ coincidences. Results: In total 107 new γ-ray transitions were observed in Gd163 from 53 newly identified levels. Conclusions: The structure of Gd163 has been identified for the first time. This structure has been evaluated in comparison to projected shell model, and potential energy surface calculations with good agreement.

We report on high-statistics data from the $\beta^-$ decay of the $^{46}$K $J^{\pi}$ = 2$^-$ ground state taken with the GRIFFIN spectrometer located at the TRIUMF-ISAC facility. In total, 199 $\gamma$ rays and 42 excited states were placed in the level scheme, and from the observed $\beta$ feeding and angular correlations of pairs of cascading $\gamma$ rays, it was possible to assign spins and parities to excited states and determine mixing ratios for selected $\gamma$ rays. The level structure of $^{46}$Ca is compared to theoretical predictions from a microscopic valence-space Hamiltonian derived from two- (NN) and three-nucleon (3N) forces. These calculations are in reasonable agreement with the experimental data and indicate that the protons in this region are not as inert as would be expected for semi-magic nuclei.

The Versatile Array of Neutron Detectors at Low Energy (VANDLE) is a new, highly efficient plastic-scintillator array constructed for decay and transfer reaction experimental setups that require neutron detection. The versatile and modular design allows for customizable experimental setups including beta-delayed neutron spectroscopy and (d,n) transfer reactions in normal and inverse kinematics. The neutron energy and prompt-photon discrimination is determined through the time of flight technique. Fully digital data acquisition electronics and integrated triggering logic enables some VANDLE modules to achieve an intrinsic efficiency over 70% for 300-keV neutrons, measured through two different methods. A custom Geant4 simulation models aspects of the detector array and the experimental setups to determine efficiency and detector response. A low detection threshold, due to the trigger logic and digitizing data acquisition, allowed us to measure the light-yield response curve from elastically scattered carbon nuclei inside the scintillating plastic from incident neutrons with kinetic energies below 2 MeV.

Background: Nucleosynthesis of mid-mass elements is thought to occur under hot and explosive astrophysical conditions. Radiative α capture on S34 has been shown to impact nucleosynthesis in several such conditions, including core and shell oxygen burning, explosive oxygen burning, and type Ia supernovae. Purpose: Broad uncertainties exist in the literature for the strengths of three resonances within the astrophysically relevant energy range (ECM=1.94-3.42MeV at T=2.2GK). Further, there are several states in Ar38 within this energy range which have not been previously measured. This work aimed to remeasure the resonance strengths of states for which broad uncertainty existed as well as to measure the resonance strengths and energies of previously unmeasured states. Methods: Resonance strengths and energies of eight narrow resonances (five of which had not been previously studied) were measured in inverse kinematics with the DRAGON facility at TRIUMF by impinging an isotopically pure beam of S34 ions on a windowless He4 gas target. Prompt γ emissions of de-exciting Ar38 recoils were detected in an array of bismuth germanate scintillators in coincidence with recoil nuclei, which were separated from unreacted beam ions by an electromagnetic mass separator and detected by a time-of-flight system and a multianode ionization chamber. Results: The present measurements agree with previous results. Broad uncertainty in the resonance strength of the ECM=2709keV resonance persists. Resonance strengths and energies were determined for five low-energy resonances which had not been studied previously, and their strengths were determined to be significantly weaker than those of previously measured resonances. Conclusions: The five previously unmeasured resonances were found not to contribute significantly to the total thermonuclear reaction rate. A median total thermonuclear reaction rate calculated using data from the present work along with existing literature values using the STARLIB rate calculator agrees with the NON-SMOKER statistical model calculation as well as the REACLIB and STARLIB library rates at explosive and nonexplosive oxygen-burning temperatures (T=3-4GK and T=1.5-2.7GK, respectively).

Gamma-Ray Infrastructure For Fundamental Investigations of Nuclei (GRIFFIN) is a new high-efficiency $\gamma$-ray spectrometer for decay spectroscopy research with low-energy (20-60 keV) stopped radioactive beams from the Isotope Separator and Accelerator (ISAC) facility at TRIUMF in Vancouver, Canada. GRIFFIN is comprised of 16 HPGe clover detectors and hosts a suite of auxiliary detection systems for tagging $\beta$ particles, neutrons, and internal conversion electrons in coincidence with $\gamma$ rays. GRIFFIN is a powerful new tool for studying the nuclear structure of exotic short-lived isotopes far from stability, and for measuring weak $\gamma$-ray branches that are important in tests of fundamental symmetries and nuclear astrophysics. In this work, first results from the GRIFFIN physics program will be discussed, including a recent measurement of the half-lives of the neutron-rich $^{128-130}$Cd and $^{131}$In isotopes.

The $\ensuremath{\beta}$-decay half-lives of $^{128--130}\mathrm{Cd}$ have been measured with the newly commissioned GRIFFIN $\ensuremath{\gamma}$-ray spectrometer at the TRIUMF-ISAC facility. The time structures of the most intense $\ensuremath{\gamma}$ rays emitted following the $\ensuremath{\beta}$ decay were used to determine the half-lives of $^{128}\mathrm{Cd}$ and $^{130}\mathrm{Cd}$ to be ${T}_{1/2}=246.2\phantom{\rule{0.16em}{0ex}}(21)$ ms and ${T}_{1/2}=126\phantom{\rule{0.16em}{0ex}}(4)$ ms, respectively. The half-lives of the $3/{2}^{+}$ and $11/{2}^{\ensuremath{-}}$ states of $^{129}\mathrm{Cd}$ were measured to be ${T}_{1/2}(3/{2}^{+})=157\phantom{\rule{0.16em}{0ex}}(8)$ ms and ${T}_{1/2}(11/{2}^{\ensuremath{-}})=147\phantom{\rule{0.16em}{0ex}}(3)$ ms. The half-lives of the Cd isotopes around the $N=82$ shell closure are an important ingredient in astrophysical simulations to derive the magnitude of the second $r$-process abundance peak in the $A\ensuremath{\sim}130$ region. Our new results are compared with recent literature values and theoretical calculations.

Decays of neutron-rich nuclei $^{82,83}\mathrm{Zn}$ and $^{82,83}\mathrm{Ga}$ produced in proton-induced fission of $^{238}\mathrm{U}$ were studied at the Holifield Radioactive Ion Beam Facility using on-line mass separation and $\ensuremath{\beta}\text{\ensuremath{-}}\ensuremath{\gamma}$ spectroscopy techniques. New $\ensuremath{\gamma}$-ray transitions were identified and level schemes, which include states at high excitation energies in the range between 3--7 MeV were constructed. These high-energy levels were identified to be populated through allowed Gamow-Teller $\ensuremath{\beta}$ transitions, and their structure was interpreted with new shell-model calculations. A $\ensuremath{\beta}$-delayed neutron branching ratio of $69\ifmmode\pm\else\textpm\fi{}7%$ was deduced for $^{82}\mathrm{Zn}$ and revised $\ensuremath{\beta}$-decay half-life values of $^{82}\mathrm{Zn}$ [155(17)(20) ms] and $^{83}\mathrm{Zn}$ [122(28) ms] were determined.

The β-delayed neutron emission of ^{83,84}Ga isotopes was studied using the neutron time-of-flight technique. The measured neutron energy spectra showed emission from states at excitation energies high above the neutron separation energy and previously not observed in the β decay of midmass nuclei. The large decay strength deduced from the observed intense neutron emission is a signature of Gamow-Teller transformation. This observation was interpreted as evidence for allowed β decay to ^{78}Ni core-excited states in ^{83,84}Ge favored by shell effects. We developed shell model calculations in the proton fpg_{9/2} and neutron extended fpg_{9/2}+d_{5/2} valence space using realistic interactions that were used to understand measured β-decay lifetimes. We conclude that enhanced, concentrated β-decay strength for neutron-unbound states may be common for very neutron-rich nuclei. This leads to intense β-delayed high-energy neutron and strong multineutron emission probabilities that in turn affect astrophysical nucleosynthesis models.

The β-decay half lives of nuclei near the r-process path are critical information required for abundance calculations, especially those near neutron number N = 82. Specifically, the nuclei below doubly-magic 132Sn are key, and play an important role in the formation and shape of the second r-process abundance peak. The half lives in this region are challenging to measure due to the significant β-delayed neutron decay branches and the population of isomeric states with half lives comparable to the ground states. However, by measuring the time distribution of γ rays, these complications can be eliminated. This requires, however, a very effcient γ-ray spectrometer since the production of isotopes in this region is very limited. The new GRIFFIN array at TRIUMF-ISAC provides the high effciency required for these measurements. Recent improvements in the quality of the beams produced at TRIUMF, employing the IG-LIS device, are outlined, as well as the current status of the ARIEL facility. The GRIFFIN spectrometer and its use are briefly described. The experiment to measure the half lives of 128-130Cd is outlined and the results given, and some examples of the power of GRIFFIN to expand decay schemes, specifically for the decay of 128Cd to 128In, are given.

The α-decay chain 109Xe → 105Te → 101Sn was identified at the Holifield Radioactive Ion Beam Facility. Advances in digital electronics have made possible the identification of both alpha emitters in the same experiment despite the disparate half-lives of 13 ±2 ms and 620 ±70 ns for 109Xe and 105Te, respectively. Two α-decay transitions were observed from 109Xe with Qα values of 4067 ±10 and 4217 ±8 keV. One transition between the ground states of 105Te and 101Sn was observed with a Qα value of 4889 ±6 keV. Using the measured half-lives, branching ratios, and Qα values the reduced α-decay widths, δ2, were determined. Comparison of the δ2 value for 105Te with 213Po indicates a “superallowed" character in the α emission of 105Te.

Near shell closures, the presence of unexpected states at low energies provides a critical test of our understanding of the atomic nucleus. New measurements for the $N=42$ isotones $_{27}^{69}\mathrm{Co}$ and $_{29}^{71}\mathrm{Cu}$, along with recent data and calculations in the Ni isotopes, establish a full set of complementary, deformed, intruder states astride the closed-shell $_{28}\mathrm{Ni}$ isotopes. Nuclei with a one-proton hole or one-proton particle adjacent to $Z=28$ were populated in $\ensuremath{\beta}$-decay experiments and in multinucleon transfer reactions. A $\ensuremath{\beta}$-decaying isomer, with a 750(250)-ms half-life, has been identified in $_{27}^{69}\mathrm{Co}_{42}$. It likely has low spin and accompanies the previously established $7/{2}^{\ensuremath{-}}$ state. Complementary data for the levels of isotonic $_{29}^{71}\mathrm{Cu}_{42}$ support the presence of a deformed, $\mathrm{\ensuremath{\Delta}}J=1$ band built on the proton intruder $7/{2}^{\ensuremath{-}}$ level at 981 keV. These data, together with recent studies of lower-mass Co and Cu isotopes and extensive work near $^{68}\mathrm{Ni}$, support the view that intruder states based on particle-hole excitations accompany all closed proton shells with $Z\ensuremath{\ge}28$.

1 Oak Ridge Associated Universities, Oak Ridge, TN 37830, USA. 2 Dept. of Physics & Astronomy, University of Tennessee, Knoxville, TN 37996, USA 3 Physics Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831, USA 4 Dept. of Physics & Astronomy, Rutgers University, New Brunswick, NJ 08903, USA 5 Dept. of Physics, Colorado School of Mines, Golden, CO 80401, USA 6 Dept. of Physics & Astronomy, Louisiana St. University, Baton Rouge, LA 70803, USA

Short lived neutron rich nuclei including 93 Br, 93 Kr and 94 Kr were produced in proton induced fission of 238 U at the HRIBF in Oak Ridge. Their beta decay was studied by means of a high resolution on line mass separator and beta gamma spectroscopy methods. The half life of 93Br T1/2 = 152(8) ms and delayed branching ratio of Pn = 53-8+11 may be compared to the previously reported values of T1/2 = 102(10) ms and Pn = 68(7)%. At the same time the half life of 94Kr T1/2 = 227(14) ms and B delayed branching ratio of Pn = 1.9+0.6 0.2 % of 93Kr are in very good agreement with literature values. The decay properties of 93Br include four new gamma transitions following beta delayed neutron emission.

Background: The nuclei in the region around ${}^{68}$Ni display an apparent rapid development of collectivity as protons are removed from the ${f}_{7/2}$ single-particle state along the $N=40$ isotonic chain. Proton and neutron excitations across the $Z=28$ and $N=40$ gaps are observed in odd-A ${}_{27}$Co and ${}_{26}$Fe isotopes. Little spectroscopic information beyond the excited 2${}^{+}$ and 4${}^{+}$ is available in the even-even ${}_{26}^{66,68}\mathrm{Fe}$ nuclei to compare with shell model calculations.Purpose: Our goal is to determine the low-energy level schemes of ${}^{66,68}$Fe and compare the observed excitations with shell model calculations to identify states wherein a contribution from excitations across $Z=28$ and $N=40$ are present.Method: The low-energy states of ${}^{66,68}$Fe were populated through the beta decay of ${}^{66,68}$Mn produced at the National Superconducting Cyclotron Laboratory. Beta-delayed gamma-ray transitions were detected and correlated to the respective parent isotope to construct a low-energy level scheme.Results: The low-energy level schemes of ${}^{66,68}$Fe were constructed from observed gamma-ray coincidences and absolute gamma-ray intensities. Tentative spin and parity assignments were assigned based on comparisons with shell model calculations and systematics. The two lowest 0${}^{+}$ and 2${}^{+}$ states were characterized in terms of the number of protons and neutrons excited across the respective shell gaps.Conclusion: The removal of two protons from ${}^{68}$Ni to ${}^{66}$Fe results in an inversion of the normal configuration and the one characterized by significant excitation across the $Z=28$ and $N=40$ gaps. Approximately, one proton and two neutrons are excited across their respective single-particle gaps in the ground state of ${}^{66}$Fe.

The {beta} decays of neutron-rich nuclei near the doubly magic {sup 78}Ni were studied at the Holifield Radioactive Ion Beam Facility using an electromagnetic isobar separator. The half-lives of {sup 82}Zn (228 {+-} 10 ms), {sup 83}Zn (117 {+-} 20 ms), and {sup 85}Ga (93 {+-} 7 ms) were determined for the first time. These half-lives were found to be very different from the predictions of the global model used in astrophysical simulations. A new calculation was developed using the density functional model, which properly reproduced the new experimental values. The robustness of the new model in the {sup 78}Ni region allowed us to extrapolate data for more neutron-rich isotopes. The revised analysis of the rapid neutron capture process in low entropy environments with our new set of measured and calculated half-lives shows a significant redistribution of predicted isobaric abundances strengthening the yield of A > 140 nuclei.

The$\ensuremath{\beta}$-decay properties of neutron-rich Cu isotopes produced in proton-induced fission of ${}^{238}$U were studied at the Holifield Radioactive Ion Beam Facility at Oak Ridge National Laboratory. The data were collected using high-resolution online mass separation, reacceleration, and digital $\ensuremath{\beta}\text{\ensuremath{-}}\ensuremath{\gamma}$ spectroscopy methods. An improved decay scheme of $N=49$ ${}^{78}$Cu and the first observation of $N=50$ ${}^{79}$Cu $\ensuremath{\beta}$-delayed neutron decay followed by a gamma transition are reported. Spin and parity (5${}^{\ensuremath{-}}$) are deduced for ${}^{78gs}$Cu. The $\ensuremath{\beta}$-delayed neutron branching ratios (${P}_{\ensuremath{\beta}n}$) for the ${}^{77}$Cu and ${}^{79}$Cu precursors are analyzed with the help of nuclear structure models.

The low-energy level structures for the neutron-rich Co isotopes at N = 39 and N = 41 are constructed following the beta decay of the respective even-even Fe isotopes. Spin and parity assignments of the lowest energy populated state in {sup 66}Co and {sup 68}Co are consistent with a 1{sup +} spin and parity assignment and attributed to the coupling of the deformed proton configurations identified in {sup 67}Co and deformed neutron configurations inferred from neighboring Fe isotones. Comparisons along the N = 39 and N = 41 isotonic chains reveal a similarity in the structures of the Co and Mn isotopes.

The low-energy level structures of 64 25Mn39 and 66 25Mn41 were investigated through both the decay of Mn metastable states and the population of levels following the decay of 64Cr and 66Cr. The deduced level schemes and tentatively assigned spins and parities suggest the coexistence of spherical and deformed configurations above and below N = 40 for the odd-odd Mn isotopes. The low-energy deformed configurations are attributed to the coupling between a proton in a K = 1/2 level with neutrons in either the K = 1/2 or K = 3/2+ levels originating from the p3/2, p1/2, and g9/2 single-particle states, respectively.

The $\ensuremath{\beta}$ decay of $^{75}\mathrm{Cu}$ [${t}_{1/2}=1.222(8)$s] to levels in $^{75}\mathrm{Zn}$ was studied at the Holifield Radioactive Ion Beam Facility of Oak Ridge National Laboratory. The $\ensuremath{\gamma}\ensuremath{\gamma}$ and $\ensuremath{\beta}\ensuremath{\gamma}$ data were collected at the Low-energy Radioactive Ion Beam Spectroscopy Station using the high-resolution isobar separator to obtain a purified $^{75}\mathrm{Cu}$ beam with a rate of over 2000 ions per second. The excited states in $^{75}\mathrm{Zn}$ have been identified for the first time. A total of 120 $\ensuremath{\gamma}$-ray transitions were placed in a level scheme containing 59 levels including two states above the neutron separation energy and a previously unknown $1/{2}^{\ensuremath{-}}$ isomeric state at 127 keV. Spins and parities of several states were deduced and interpreted based on the observed $\ensuremath{\beta}$ feeding and $\ensuremath{\gamma}$-decay pattern.

The $\ensuremath{\beta}$ decay of the $N=51$ nucleus $^{81}\mathrm{Zn}$ was studied by means of $\ensuremath{\beta}$-$\ensuremath{\gamma}$ spectroscopy and from isotopically pure beams produced at the Holifield Radioactive Ion Beam Facility (HRIBF). We observe several competing $\ensuremath{\beta}$ transitions populating $^{81}\mathrm{Ga}$ that are interpreted as allowed Gamow-Teller decays to positive parity, core excited states, and first-forbidden decays to negative parity states. The measured $\ensuremath{\beta}$-decay pattern suggests an assignment of ${I}^{\ensuremath{\pi}}=5/{2}^{+}$ for the $^{81}\mathrm{Zn}$ ground state. The systematics of core excited states in $N=50$ isotones indicate a strengthening of the $N=40$ subshell gap near $^{78}\mathrm{Ni}$.

The structure of neutron-rich nuclei beyond $^{78}\mathrm{Ni}$ was studied using postaccelerated radioactive beams of $^{83,84,85}\mathrm{Ga}$ utilizing $\ensuremath{\beta} \ensuremath{\gamma}$ and $\ensuremath{\beta}\ensuremath{-}n \ensuremath{\gamma}$ spectroscopy. Our data, when combined with energy level systematics, suggests a possible new spherical subshell closure at $N=58$ is created by the nearly degenerated $\ensuremath{\nu}3{s}_{1/2}$ and $\ensuremath{\nu}2{d}_{5/2}$ orbitals being well separated from other orbitals above $N=50$. The near degeneracy of these states could be evidenced by isomerism in this region. The energies of the ${2}_{1}^{+}$ and proposed ${4}_{1}^{+}$ states observed in $N=52$ $^{84}\mathrm{Ge}$ are interpreted as an indication of a possible weakening of the doubly magic $^{78}\mathrm{Ni}$ core for nuclei beyond $N=50$. The experimental evidence is supported by spherical HFB calculations using the ${\mathrm{SkO}}_{T}$ functional involving the tensor term in the nucleon-nucleon interaction.

Isobarically purified beams of {sup 77}Cu with energies of 225 and 0.2 MeV were used at the Holifield Radioactive Ion Beam Facility of Oak Ridge National Laboratory to study {beta} decay into states in {sup 77}Zn. Data taken at 225 MeV allowed the determination of absolute branching ratios relative to the decay of {sup 77}Cu for this {beta} decay as well as its daughters. From these we obtained a refined {beta}-delayed neutron emission probability of 30.3(22)% and a probability that the decay proceeds through {sup 77}Zn{sup g} of 49.1(26)%. A total of 64 {gamma} rays were placed in a level scheme for {sup 77}Zn containing 35 excited states including one state above the neutron separation energy, whereas two {gamma} rays were observed for the {beta}n branch to states in {sup 76}Zn. The growth and decay curves of some prominent {gamma} rays indicate a single {beta}-decaying state with a half-life of 480(9) ms. The decay pattern for {sup 77}Cu, with observed feeding of 8(3)% to 7/2{sup +} {sup 77}Zn{sup g} and 6(3)% to 1/2{sup -} {sup 77}Zn{sup m}, in contrast to the large feeding observed for decay of {pi}p{sub 3/2} {sup 73}Cu{sup g} to 1/2{sup -} {sup 73}Zn{sup g}, strongly suggestsmore » a {pi}f{sub 5/2} ground state for the studied {sup 77}Cu activity.« less

The $\ensuremath{\beta}$-delayed neutron branching ratios (${P}_{\ensuremath{\beta}n}$) for nuclei near doubly magic $^{78}\mathrm{Ni}$ have been directly measured using a new method combining high-resolution mass separation, reacceleration, and digital $\ensuremath{\beta}\mathrm{\text{\ensuremath{-}}}\ensuremath{\gamma}$ spectroscopy of $^{238}\mathrm{U}$ fission products. The ${P}_{\ensuremath{\beta}n}$ values for the very neutron-rich isotopes $^{76--78}\mathrm{Cu}$ and $^{83}\mathrm{Ga}$ were found to be much higher than previously reported and predicted. Revised calculations of the $\ensuremath{\beta}n$ process, accounting for new mass measurements and an inversion of the $\ensuremath{\pi}2{p}_{3/2}$ and $\ensuremath{\pi}1{f}_{5/2}$ orbitals, are in better agreement with these new experimental results.

The beta-delayed neutron branching ratios (P{betan}) for nuclei near doubly magic 78Ni have been directly measured using a new method combining high-resolution mass separation, reacceleration, and digital beta-gamma spectroscopy of 238U fission products. The P{betan} values for the very neutron-rich isotopes ;{76-78}Cu and 83Ga were found to be much higher than previously reported and predicted. Revised calculations of the betan process, accounting for new mass measurements and an inversion of the pi2p{3/2} and pi1f{5/2} orbitals, are in better agreement with these new experimental results.

Production of nuclei above $^{100}\mathrm{Sn}$ in fusion-evaporation reactions between $^{58}\mathrm{Ni}$ and $^{54}\mathrm{Fe}$ ions was studied at Oak Ridge National Laboratory by means of the recoil mass spectrometer and charged particle detection. The beam energy was varied to optimize the yields for the two-, three- and four-particle evaporation channels. Experimental results verified the predictions of the statistical model code HIVAP. The optimum energy for the $^{54}\mathrm{Fe}$($^{58}\mathrm{Ni}$,$4n$)$^{108}\mathrm{Xe}$ reaction channel that allows one to study the $^{108}\mathrm{Xe}$-$^{104}\mathrm{Te}$-$^{100}\mathrm{Sn}$ \ensuremath{\alpha} decay chain is deduced as 240 MeV.

An alpha-decay branch of (1.4+/-0.4) x 10(-4) has been discovered in the decay of 109I, which predominantly decays via proton emission. The measured Q(alpha) value of 3918+/-21 keV allows the indirect determination of the Q value for proton emission from 105Sb of 356+/-22 keV, which is approximately of 130 keV more bound than previously reported. This result is relevant for the astrophysical rapid proton-capture process, which would terminate in the 105Sn(p,gamma)106Sb(p,gamma)107Te(alpha decay)103Sn cycle at the densities expected in explosive hydrogen burning scenarios, unless unusually strong pairing effects result in a 103Sn(p,gamma)104Sb(p,gamma)105Te(alpha decay)101Sn) cycle.

In an experiment at the Recoil Mass Spectrometer at the Holifield Radioactive Ion Beam Facility, the very small α‐decay branch of 109I, bα = (1.4±0.4)⋅10−4, has been measured. The Qα‐value for this transition allowed for the determination of Qp(105Sb) = 356±22 keV, about 130 keV lower than previously claimed. This difference increases the partial half‐life for proton decay by several orders of magnitude, making the probability of observing direct proton decay of 105Sb very small, much below any previous experimental limit. The results and consequences for the astrophysical rp‐process are discussed.

Production of nuclei above 100Sn in fusion‐evaporation reactions between 58Ni beam and 54Fe target was investigated. Reaction products were studied at Oak Ridge by means of the Recoil Mass Spectrometer and charged particle detection. The yields for the 2n, pn, 3n, p2n, 2pn, p3n and 2p2n fusion‐evaporation channels were measured. These experimental results were used to verify the predictions of the statistical model code HIVAP. The optimum energy for the 54Fe(58Ni,4n)108Xe reaction allowing detection of the 108Xe‐104Te‐100Sn alpha decay chain is deduced as 240 MeV.

The 8 pi spectrometer, installed at the TRIUMF-ISAC facility, was the world's most sensitive gamma-ray spectrometer dedicated to beta-decay studies. A description is given of the 8 pi spectrometer and its auxiliary detectors including the plastic scintillator array SCEPTAR used for beta-particle tagging and the Si(Li) array PACES for conversion electron measurements, its moving tape collector, and its data acquisition system. The recent investigation of the decay of Cs-124 to study the nuclear structure of Xe-124, and how the beta-decay measurements complemented previous Coulomb excitation studies, is highlighted, including the extraction of the deformation parameters for the excited 0(+) bands in Xe-124. As a by-product, the decay scheme of the (7(+)) Cs-124 isomeric state, for which the data from the PACES detectors were vital, was studied. Finally, a description of the new GRIFFIN spectrometer, which uses the same auxiliary detectors as the 8 pi spectrometer, is given.

Two new $\ensuremath{\alpha}$ emitters $^{109}\mathrm{Xe}$ and $^{105}\mathrm{Te}$ were identified through the observation of the $^{109}\mathrm{Xe}\ensuremath{\rightarrow}^{105}\mathrm{Te}\ensuremath{\rightarrow}^{101}\mathrm{Sn}$ $\ensuremath{\alpha}$-decay chain. The $^{109}\mathrm{Xe}$ nuclei were produced in the fusion-evaporation reaction $^{54}\mathrm{Fe}(^{58}\mathrm{Ni},3n)^{109}\mathrm{Xe}$ and studied using the Recoil Mass Spectrometer at the Holifield Radioactive Ion Beam Facility. Two transitions at ${E}_{\ensuremath{\alpha}}=4062\ifmmode\pm\else\textpm\fi{}7\text{ }\text{ }\mathrm{keV}$ and ${E}_{\ensuremath{\alpha}}=3918\ifmmode\pm\else\textpm\fi{}9\text{ }\text{ }\mathrm{keV}$ were interpreted as the $l=2$ and $l=0$ transitions from the $7/{2}^{+}$ ground state in $^{109}\mathrm{Xe}$ (${T}_{1/2}=13\ifmmode\pm\else\textpm\fi{}2\text{ }\text{ }\mathrm{ms}$) to the $5/{2}^{+}$ ground state and a $7/{2}^{+}$ excited state, located at $150\ifmmode\pm\else\textpm\fi{}13\text{ }\text{ }\mathrm{keV}$ in $^{105}\mathrm{Te}$. The observation of the subsequent decay of $^{105}\mathrm{Te}$ marks the discovery of the lightest known $\ensuremath{\alpha}$-decaying nucleus. The measured transition energy ${E}_{\ensuremath{\alpha}}=4703\ifmmode\pm\else\textpm\fi{}5\text{ }\text{ }\mathrm{keV}$ and half-life ${T}_{1/2}=620\ifmmode\pm\else\textpm\fi{}70\text{ }\text{ }\mathrm{ns}$ were used to determine the reduced $\ensuremath{\alpha}$-decay width ${\ensuremath{\delta}}^{2}$. The ratio ${\ensuremath{\delta}}_{^{105}\mathrm{Te}}^{2}/{\ensuremath{\delta}}_{^{213}\mathrm{Po}}^{2}$ of $\ensuremath{\sim}3$ indicates a superallowed character of the $\ensuremath{\alpha}$ emission from $^{105}\mathrm{Te}$.

A new excited state at 2164 keV has been identified in 72Ni with tentative spin and parity of 4+ based on comparison to shell model calculations. This level is suggested to be populated via the ?-decay of an isomeric state in 72Co, and is postulated to be one of the key states that play a role in the disappearance of isomers in Ni. The known low-energy levels in 72Ni are compared with results of shell model calculations using the NR78 interaction to follow the seniority of the observed states. In addition, the half-life of the 8+ isomer in 76Ni has been measured as 630(90) ns and the full cascade of transitions from this isomer has been verified experimentally in this work.