A. Korgul,1 K. P. Rykaczewski,2 R. K. Grzywacz,3,2 C. R. Bingham,3,2 N. T. Brewer,2,4,5 C. J. Gross,2 A. A. Ciemny,1 C. Jost,3 M. Karny,1,6 M. Madurga,3 C. Mazzocchi,1 A. J. Mendez II,2 K. Miernik,1,2 D. Miller,3 S. Padgett,3 S. V. Paulauskas,3 M. Piersa,1 D. W. Stracener,2 M. Stryjczyk,1 M. Wolińska-Cichocka,2,5,7 and E. F. Zganjar8 1Faculty of Physics, University of Warsaw, PL 02-093 Warsaw, Poland 2Physics Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USA 3Department of Physics and Astronomy, University of Tennessee, Knoxville, Tennessee 37996, USA 4Department of Physics and Astronomy, Vanderbilt University, Nashville, Tennessee 37235, USA 5Joint Institute for Nuclear Physics and Applications, Tennessee 37831, USA 6Oak Ridge Associated Universities, Oak Ridge, Tennessee 37831, USA 7Heavy Ion Laboratory, University of Warsaw, PL 02-093 Warsaw, Poland 8Department of Physics and Astronomy, Louisiana State University, Baton Rouge, Louisiana 70803, USA (Received 7 April 2016; published 28 June 2016)

Production of nuclei above Sn-100 in fusion-evaporation reactions between Ni-58 and Fe-54 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 Fe-54(Ni-58, 4n)Xe-108 reaction channel that allows one to study the Xe-108-Te-104-Sn-100 alpha decay chain is deduced as 240 MeV.

The alpha decay chain 109Xe→105Te→101Sn was first identified at the Holifield Radioactive Ion Beam Facility. Recent developments in digital electronics enabled the detection of both alpha decays despite the short half‐life of 105Te. The development of the software algorithm responsible for extracting the double‐alpha events from the experimental data is ongoing. The possibility of using the derivative of the double‐alpha pulse to selectively identify double alpha pulses shows promise and is being developed.

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.

Capture-fission cross sections were measured for the near symmetric reaction between the massive nuclei Sn-124 and Zr-96 for center of mass energies from 195 to 265 MeV. Coincident fission fragments were detected and separated from elastic and deep inelastic scattering products by angle/energy/mass conditions. The measured capture cross sections agree quite well with calculations using the dinuclear system (DNS) model. The DNS model also predicts the fusion cross section for this reaction with a fusion barrier height of 208.0 MeV. The deduced extra push energy, corresponding to this barrier height, differs from that deduced from evaporation residue measurements.

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

In the fusion-evaporation reaction $^{40}\mathrm{Ca}+^{24}\mathrm{Mg}$ at $104\phantom{\rule{0.3em}{0ex}}\text{MeV}$ beam energy, excited states have been observed for the first time in the isotope ${^{31}_{61}\mathrm{Ga}}_{30}$. The experimental setup comprised the Ge array CLARION, a recoil mass spectrometer and, in its focal plane, an ionization chamber. Five transitions in $^{61}\mathrm{Ga}$ are identified, out of which a cascade of three transitions has been established by means of recoil-$\ensuremath{\gamma}\ensuremath{\gamma}$ coincidences. The strong transitions at $271\phantom{\rule{0.3em}{0ex}}\text{keV}$ in $^{61}\mathrm{Ga}$ and $124\phantom{\rule{0.3em}{0ex}}\text{keV}$ in $^{61}\mathrm{Zn}$ are viewed as the ``mirror'' $5/{2}^{\ensuremath{-}}\ensuremath{\rightarrow}3/{2}^{\ensuremath{-}}$ ground-state transitions. The rather large energy difference of $150\phantom{\rule{0.3em}{0ex}}\text{keV}$ is suggested to arise from Coulomb monopole contributions. Shell-model calculations support this interpretation.

In the fusion-evaporation reaction Ca-40+Mg-24 at 104 MeV beam energy, excited states have been observed for the first time in the isotope Ga-31(61)30. The experimental setup comprised the Ge array CLARION, a recoil mass spectrometer and, in its focal plane, an ionization chamber. Five transitions in Ga-61 are identified, out of which a cascade of three transitions has been established by means of recoil-gammagamma coincidences. The strong transitions at 271 keV in Ga-61 and 124 keV in Zn-61 are viewed as the "mirror" 5/2(-)-->3/2(-) ground-state transitions. The rather large energy difference of 150 keV is suggested to arise from Coulomb monopole contributions. Shell-model calculations support this interpretation.

The first (d,p) neutron transfer reaction on a neutron-rich r-process nucleus has been measured at the Holifield Radioactive Ion Beam Facility. The {sup 2}H({sup 82}Ge,p){sup 83}Ge reaction was studied by bombarding a 430-{mu}g/cm{sup 2} (CD{sub 2}){sub n} target with a 330-MeV beam of radioactive {sup 82}Ge. The reaction Q value (Q=1.47{+-}0.02 stat. {+-}0.07 sys. MeV) has been measured leading to the first determination of the mass of the N=51 nucleus {sup 83}Ge. Excitation energies, angular distributions, and spectroscopic factors for the first two states of {sup 83}Ge have also been determined.

The degree to which the (p,gamma) and (p,alpha) reactions destroy 18F at temperatures 1-4x10^8 K is important for understanding the synthesis of nuclei in nova explosions and for using the long-lived radionuclide 18F, a target of gamma-ray astronomy, as a diagnostic of nova mechanisms. The reactions are dominated by low-lying proton resonances near the 18F+p threshold (E_x=6.411 MeV in 19Ne). To gain further information about these resonances, we have used a radioactive 18F beam from the Holifield Radioactive Ion Beam Facility to selectively populate corresponding mirror states in 19F via the inverse d(18F,p)19F neutron transfer reaction. Neutron spectroscopic factors were measured for states in 19F in the excitation energy range 0-9 MeV. Widths for corresponding proton resonances in 19Ne were calculated using a Woods-Saxon potential. The results imply significantly lower 18F(p,gamma)19Ne and 18F(p,alpha)15O reaction rates than reported previously, thereby increasing the prospect of observing the 511-keV annihilation radiation associated with the decay of 18F in the ashes ejected from novae.

The first (d,p) neutron transfer reaction on a neutron-rich r-process nucleus has been measured at the Holifield Radioactive Ion Beam Facility. The H-2(Ge-82,p)Ge-83 reaction was studied by bombarding a 430-mug/cm(2) (CD2)(n) target with a 330-MeV beam of radioactive Ge-82. The reaction Q value (Q=1.47+/-0.02 stat. +/-0.07 sys. MeV) has been measured leading to the first determination of the mass of the N=51 nucleus Ge-83. Excitation energies, angular distributions, and spectroscopic factors for the first two states of Ge-83 have also been determined.

New data, obtained from beta(-) decay of Sb-132 radioactive beam at HRIBF, has led to a significantly revised gamma-decay scheme for Te-132. The changes to the level scheme include a number of new, likely 2(+), states below 2.5 MeV, which allows a test of very recent quasiparticle random phase approximation calculations with a density-dependent pairing force, and the removal of a 3(-) state at 2281 keV, which resolves an incompatibility with the shell model and leads to a simple interpretation of the low-lying negative parity states.

We have measured the B(E2;0(+) --> 2(+)) for the first excited 2(+) states in the double-closed shell nucleus Sn-132 and the two-neutron nucleus Sn-134. The results, based on a preliminary analysis are shown in Fig. 1 along with measurements on the stable Sn isotopes, and earlier results on Sn-126,Sn-128,Sn-130 [1]. The experimental setup developed for the Sn-132,Sn-134 measurements was also employed in a successful measurement of B(E2;0(+) --> 2(+)) for the closed-neutron-shell nucleus Ge-82.

A new generation of pulse processing electronics was successfully tested on-line and applied for the first time in particle and gamma-ray spectroscopy experiments. It is based on a Digital Signal Processing (DSP) technology.

Over 240 transitions and three new rotational bands have been observed in the well-deformed, odd-odd Pr-128(59)69 nucleus. The high-spin states were populated in two experiments using the Mo-92(Ca-40,3pn) reaction at beam energies of 170 and 184 MeV. Several structures were confirmed in the former experiment using the Clarion and HyBall arrays with the recoil mass spectrometer at Oak Ridge National Laboratory. Gammasphere, in conjunction with the Microball, were employed in the latter experiment at Argonne National Laboratory to extend the sequences to very high spins. Rotational structures in Pr-126 were also identified in the alphapn channel of the same reaction. The recent discrepancies of spin assignments for the yrast bands in Pr-126,Pr-128 and the interpretation of the lowest crossing in the pih(11/2) band in Pr-127 are discussed. An adiabatic crossing of the intruder i(13/2) neutron with one of the normal-deformed bands in Pr-128 is observed at high rotational frequency. Experimental trends in the signature inversion phenomenon of the pih(11/2)nuh(11/2) bands in the Aapproximate to130 region are defined and prove to be surprisingly irregular with respect to those found in the pih(11/2)nui(13/2) bands of the Aapproximate to160 region.