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High spin states of neutron-rich 146,147La have been reinvestigated by $\gamma$ - $\gamma$ - $ \gamma$ and $\gamma$ - $\gamma$ - $\gamma$ - $\gamma$ coincidence data from a 252Cf spontaneous fission experiment by using Gammasphere. Thirty-two new transitions in 146La are observed. Two new bands in 146La have been established. One of them is proposed to be the octupole parity partner of the previously known band. Twenty new transitions in 147La are observed. The ground state band of 147La has been established with a proposed $ 5/2^+$ band-head. Angular correlation of cascades has been used to study the spins and parities of the states. The B(E1)/B(E2) ratios and dipole moments of bands in 146, 147La have been measured.

The high spin states of neutron-rich 103Nb, 107Tc and 109Tc nuclei in A∼110 region have been investigated by measuring prompt γ-γ-γ coincident measurements populated with the spontaneous fission of 252Cf with the Gammasphere detector array. In 103Nb, one-phonon K = 9/2 and two-phonon K = 13/2 γ-vibrational bands have been identified. In 107Tc and 109Tc, one-phonon K = 11/2 and two-phonon K = 15/2 γ-vibrational bands, in which the zero-phonon bands are based on K=7/2 excited states, have also been identified. The two-phonon bands are first observed in odd-Z nuclei. The characteristics for these band structures have been discussed.

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.

High-spin states in neutron-rich 106Mo were investigated by detecting the prompt γ-rays in the spontaneous fission of 252Cf with Gammasphere. Several new bands are observed. Two sets of ΔI = 1 bands in 106Mo are found to have all the characteristics of a new class of chiral vibrational doublets. Tilted axis cranking calculations support the chiral assignment and indicate that the chirality is generated by neutron h11/2 particle and mixed d5/2, g7/2 hole coupled to the short and long axis, repectively.

Neutron-rich radioactive ion beams available from the HRIBF allow a variety of measurements around the 132Sn region, including Coulomb excitation and single-nucleon transfer. The B(E2;0+ → 2+) values for first 2+ excited states of even-even neutron-rich 132-136Te and 126-130Sn have been measured by Coulomb excitation in inverse kinematics. Neutron transfer onto a 134Te beam from 9Be and 13C targets, to populate single-particle states in 135Te, has also been studied. Gamma rays from the 13C(134Te, 12C) reaction were used to identify the νi13/2 state in 135Te, at an energy of 2109 keV. These and other results, and plans for future experiments with these neutron-rich beams, are presented.

For the first time, average angular momenta of the ternary fission fragments 100, 102Zr, 106Mo, 144, 146Ba and 138, 140, 142Xe from the α-accompanied fission of 252Cf were obtained from relative intensities of prompt γ-ray transitions with the use of the statistical model calculation. Average values of the angular momenta were compared with the corresponding values for the same fission fragments from the binary fission of 252Cf. Results indicate the presence of a decreasing trend in the average values of angular momenta induced in ternary fission fragments compared to the same binary fission fragments. On the average, the total angular momentum extracted for ternary fission fragments is ∼1.4 ℏ lower than in binary fission. Consequently, results indicate that the mechanism of the ternary α-particles emission may directly effect an induction of angular momenta of fission fragments, and possible scenarios of such mechanisms are discussed. Further, the dependence of the angular momenta of 106Mo and 140Xe on the number of emitted neutrons from correlated pairs of primary fragments was obtained also showing a decreasing dependence of average angular momenta with increasing number of emitted neutrons. Consequences are briefly discussed.

With new high statistic data, new isotopes and new high-spin structures are observed in neutron-rich nuclei populated in the spontaneous fission of 252Cf. The 135Te levels are extended, and many new levels in 139,141Ba observed. The coexistence of collective and single particle-hole states is found in 135Te. The N = 83 135Te and 139Ba show marked differences associated with differences in their particle and hole states. New levels in 141Ba complete evidence for two opposite-parity doublets characteristic of stable octupole deformation. In 114,116Pd a second backbend is observed for the first time in this mass region and the backbend in 118Pd occurs earlier than in 112-116Pd because of a reduction in pairing. Gamma-type vibrational bands are seen up to 13+ to 15+ in 104,106Mo, 108-112Ru, and 112-116Pd. Their behavior reflects prolate to triaxial shapes in these nuclei. The levels of 162,164Gd are observed for the first time. As N increases toward mid-shell at 104, the moments of inertia in N = 100 164Gd show an unexpected decrease compared to N = 98 162Gd. The levels in 162,164Gd form remarkable shifted identical bands with nuclei separated by 2n, 2p, α, and 2α.

The spontaneous fission of 252Cf has been studied via γ-γ-γ coincidence and γ-γ light charged particle coincidence with Gammasphere. The binary fission yields of correlated Mo−Ba pairs with 0–10 neutron emission have been remeasured. The existence of “hot” fission mode with 8–10 neutron emission seen previously in the Mo−Ba split is confirmed but with lower intensities. By gating on the light charged particles detected in ΔE-E detectors and a γ ray in one partner, the relative yields of correlated pairs in alpha ternary SF with zero to 6n emission are observed for the first time with the distribution peaked at 2.5n. New correlated pairs are identified in 10Be ternary SF. We observed essentially only cold, On 10Be and little, if any, hot, xn 10Be. New γ-γ-γ data with 2.3 times the total events show weak non-Doppler broadened high energy peaks in coincidence with transitions in correlated pairs in 10Be SF shifted by the same 6,1 to 26 keV from the 2-0 energy in 10Be as seen earlier.

Excited high spin states in 211At, 212Rn, 213Fr and 214Ra with N = 126 are reorganized and interpreted in terms of the stretched weak coupling of an octupole 3− phonon. Nearly identical sequences of levels with ΔI = 3 and the parity change are found, for the first time, up to 25− for 20 states of 214Ra, up to 35− for 36 states of 212Rn and up to 53/2+ for 16 states of 213Fr. The stretched weak coupling of an octupole phonon is extended up to the highest excitation energy of 11355 keV for 212Rn which has the largest experimental B(E3) value of 44.1(88) W.u. for the 11− → 82+ transition. The stretched weak coupling of an octupole 3− phonon needs to be considered when single particle configurations are assigned to high spin states. Average octupole excitation energies of 657(51) keV for 211At, 1101(28) keV for 212Rn, 667(25) keV for 213Fr, and 709(25) keV for 214Ra are obtained. The calculated level enegies are in a good agreement with the experimental level energies within the error limit of 4.3%.

From γ-γ-γ coincidence measurements in the spontaneous fission of252Cf, level energies were established for spins 14+ to 20+ in many neutron-rich nuclei. New isotopes160Sm and162Gd were identified. The yrast bands of152,154,156Nd,156,158,160Sm, and160,162Gd exhibit remarkably near-identical transition energies and moments of inertia which are shifted by the same constant amounts for every spin state from 2+ to 12+ or 14+ for nuclei differing by 2n, 4n, 2p, 4p, α, α+2p, and α+2n. These shifted identical bands (SIB) are a new phenomenon. Analysis of all known even-even proton- to neutron-rich nuclei from Ba (Z = 56) to Os (Z = 76) reveal no SIB for proton-rich nuclei and only a few additional cases of SIB for the most neutron-rich pairs aroundN = 98–102 separated by 2n and 2p. The levels in8107Mo were extended and levels in109Mo identified for the first time.

Experimental integral isotopic yields for the spontaneous cold (neutron-less) binary and α-ternary fission of252Cf were obtained by using triple γ-γ-γ coincidence technique at Gammasphere facility. For the first time10Be- and14C-ternary fission isotopic yields were also measured. The results are interpreted within simple cluster model with binary and ternary potential barriers generated by M3Y effective interaction and ground-state deformation.

The phenomenon of cold (neutronless) binary and ternary fission in spontaneous fission of252 Cf was experimentally observed by triple gamma coincidence technique with Gammasphere with 72 gamma-ray detectors. Many correlated pairs for both binary and ternary (4He,10Be) fission were observed in the spontaneous fission of252 Cf. Yields of cold ternary and cold binary fission were extracted. These results are compared with the theoretical calculations using M3Y nucleon-nucleon potential and WKB approximation for barrier penetration.

Spontaneous fission of252Cm was studied with 72 large Compton suppressed Ge detectors in Gammasphere. New isotopes160Sm and162Gd were identified. Through X-ray-γ and γ-γ-γ coincidence measurements, level energies were established to spins 14+ to 20+ in152, 154, 15660Nd92, 94, 96156, 158, 16062Sm94, 96, 98 and160, 16264Gd96, 98. These nuclei exhibit a remarkable variety of identical bands and bands where the energies and moments of inertia are shifted by the same constant amounts for every spin state from 2+ to 12+ for various combinations of nuclei differing by 2n, 4n, 2p, 4p and α.

The evolution of the πh 11/2 vh 11/2 and πh 11/2 vs 1/2 isomeric configurations was studied for the N = 77 isotones near the proton drip line. The decays of metastable levels in 140Eu, 142Tb, and 144Ho were measured by means of X-, gamma- and conversion electron spectroscopy at the Recoil Mass Spectrometer at Oak Ridge. The sequence of isomeric levels in 140Eu was experimentally determined. The half-life of the πh 11/2 vh 11/2 state in 142Tb was remeasured to be 25(1) µs. The spins and parities of 5− and 8+ for the πh 11/2 vs 1/2 and πh 11/2 vh 11/2 142Tb isomers, respectively, were established from measured multipolarities. No evidence for the expected 1+ ground state was found in the 144Ho decay data.

Excited high spin states in 136Xe, 137Cs, 138Ba, 140Ce and 142Nd with N = 82 are reorganized and interpreted in terms of the weak coupling mode of an octupole 3− phonon. Nearly identical sequences of levels with ΔI = 3 and Δπ = yes built on 17/2+ and 23/2− states are found, for the first time, up to 29/2+ and 35/2−, respectively, for 22 states of 137Cs . Also, nearly identical sequences of levels with ΔI = 3 and Δπ = yes built on the 6+ and 9− states are found, for the first time, up to 14+ and 17−, respectively, for 18 states of 136Xe, up to 14+ and 17−, respectively, for 24 states of 138Ba and up to 11+ and 14−, respectively, for 14 states of 140Ce. New spins and parities are assigned, tentatively, to the high spin states of these nuclei based on the weak coupling mode of an octupole 3− phonon. The weak coupling of an octupole 3− phonon needs to be considered when single particle configurations are assigned to high spin states. Neutron particle-hole states (νh 11/2 −1 f 7/2 +1 ) with weak coupling of an octupole 3− phonon are proposed, for the first time. The νh 11/2 −1 f 7/2 +1 excitation energies (E ext(1p1h)) are nearly constant with increasing of Z. One-phonon excited states in 136Xe, 137Cs, 138Ba and 140Ce have the stretched weak coupling configurations of ΔI = 3. But one-phonon excited states in 142Nd show the non-stretched weak coupling configurations of an octupole phonon with ΔI = 3 and 2.

Triple-γ coincidence data were used to study the γ-vibrational bands to 14+ in 104–106Mo, to 13+ in 108,110Ru and 17+ in 112Ru, and to 13+, 15+ in 112–116Pd. The even-odd spin energy level splittings show rapid variations with spin and neutron number in these nuclides. With one exception, the Sm-Pt nuclei show no such reversal and much smaller staggering.

An experiment was performed at the National Superconducting Cyclotron Laboratory at Michigan State University to investigate β decay of very neutron-rich cobalt isotopes. Beta-delayed neutron emission from 71–74Co has been observed for the first time. Preliminary results are reported.

By using different time-gated triple γ coincidence data, the half-lives (T1/2) of several short lived states in neutron-rich nuclei have been studied. The first excited states in the ground state bands often decay by delayed γ emission. By creating triple γ coincidence spectra with time windows of 8, 16, 20, 28, and 48 ns, we have studied states with half-lives below 10 ns. The estimated half-lives of 102Zr, 137Xe, and 143Ba are in reasonable agreement with previously reported values. We extract the first estimates of the half lives of the 2+ states in 104Zr and 152Ce.

New level schemes of 99,101Y and 101,105Nd are established based on the measurement of prompt γ-rays from the fission of 252Cf at Gammasphere. Triaxial-rotor-plus-particle model calculations and fitting suggest that in the A ≈ 100 neutron-rich nuclei triaxial shape is prevalent in the region with Z > 41.

Half-lives (T 1/2) of several states which decay by delayed γ transitions were determined from time-gated triple γ coincidence method. We determined, for the first time, the half-life of 330.6 + x state in 108Tc and the half-life of 19/2− state in 133Te based on the new level schemes. Five half-lives of 95,97Sr, 99Zr, 134Te and 137Xe are consistent with the previously reported ones. These results indicate that this new method is useful for measuring the half-lives.