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The phenomenon of cold (neutronless) alpha ternary fission in spontaneous fission of {sup 252}Cf was experimentally observed by triple gamma coincidence technique with Gammasphere with 72 gamma-ray detectors. Correlated pairs of {sub 36}Kr-{sub 60}Nd, {sub 38}Sr-{sub 58}Ce, {sub 40}Zr-{sub 56}Ba, {sub 42}Mo-{sub 54}Xe, {sub 44}Ru-{sub 52}Te, and {sub 46}Pd-{sub 50}Sn were observed to be associated with {alpha} ternary fission of {sup 252}Cf. Yields of cold {alpha} ternary fission were extracted. {copyright} {ital 1998} {ital The American Physical Society}

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.

Ten new transitions in {sup 107}Mo have been observed and levels in {sup 109}Mo are identified for the first time in a {gamma}-{gamma}-{gamma} coincidence study from the spontaneous fission of {sup 252}Cf with 72 Compton suppressed Ge detectors in Gammasphere. Two sets of bands, each set intertwined by E1 transitions are observed in {sup 107}Mo and one such set in {sup 109}Mo. The observed level schemes are interpreted in terms of possible octupole deformation originating from the strong interaction of the h{sub 11/2} and d{sub 5/2} neutron shells. {copyright} {ital 1997} {ital The American Physical Society}

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.

From an experiment with Gammasphere and a 252 C spontaneous fission source, two bands with signatures -i and +i are identified in 153 Nd Also several new transitions in 149 Nd are observed for the first time. The band with signature -i in 153 Nd shows no back bending, similar to the one observed in 161 Er . The signature splitting observed in the ground band of 153 Nd is similar to the ones observed in N=93 isotones in this mass region. In 149 Nd the new transitions are placed into a band with a proposed configuration of [Formula: see text].

Independent yields of 139 individual secondary (appearing after neutron evaporation) fragment pairs of five different charge splits ${(Z}_{L}{/Z}_{H}=$46/52, 44/54, 42/56, 40/58, and 38/60) have been experimentally measured by detecting the coincidences between prompt $\ensuremath{\gamma}$ rays emitted in the spontaneous fission of ${}^{252}\mathrm{Cf}.$ Nuclear charge and mass distributions of fission fragments that follow from the measured yields of individual fragment pairs are consistent with similar previously known more integral data. Another type of data extracted from the yields of fragment pairs is the multiplicity distributions of prompt neutrons emitted in the five above charge divisions of ${}^{252}$Cf. For the measured charge splits, about 70% of the fission events where $g~7$ neutrons are evaporated from the fission fragments occur for the Mo-Ba split of ${}^{252}$Cf. Mass and excitation energy distributions of primary Ru-Xe, Mo-Ba, and Zr-Ce fragments were deduced from a least squares fit to the yield pattern of secondary fragment pairs. For the Ru-Xe and Zr-Ce splits, the experimental data are well fitted by assuming one fission mode with average total kinetic energy $〈\mathrm{TKE}〉$ values close to the value of $〈\mathrm{TKE}〉$ known for the ${}^{252}\mathrm{Cf}$ spontaneous fission. For the Mo-Ba split, a successful fit could be obtained only with the assumption that, in addition to this ``normal'' fission mode, a second mode with a remarkably lower value of $〈\mathrm{TKE}〉$ of 153 MeV contributes to this charge split. This is 36 MeV lower than for the normal mode. These data indicate that in mode two the barium nuclei are hyperdeformed (3:1 axis ratio) at scission. Mean angular momentum values of Mo-Ba fission fragments observed in pairs together with various partners have been deduced from the measured populations of different spin levels of the fragment nuclei. These angular momentum values are discussed in terms of their dependence on the primary fragment excitation energy and presence of two fission modes.

The {gamma} transitions in {sup 147}Ba, {sup 149}Ce, and {sup 151,153}Nd have been identified from {gamma}-{gamma}-{gamma}, {gamma}-{gamma}, {ital x}-{gamma}, and {ital x}-{gamma}-{gamma} coincidence studies of spontaneous fission of {sup 252}Cf. The yrast positive parity band in {sup 149}Ce is assigned to an {ital i}{sub 13/2}, neutron favored signature. The yrast negative parity band in {sup 149}Ce is assigned a {ital h}{sub 9/2} proton favored signature. The positive parity band in {sup 151}Nd corresponds to the positive parity band in {sup 149}Ce. The negative parity band in {sup 153}Nd corresponds to the negative parity bands of {sup 149}Ce and {sup 161}Er. The band observed in {sup 147}Ba is built on the {ital h}{sub 9/2} orbital. The plots for {ital J}{sub 1} in these isotopes are remarkably similar, supporting our assignments. {copyright} {ital 1996 The American Physical Society.}

From {gamma}-ray coincidence studies following spontaneous fission of {sup 252}Cf, direct measurements of yields and neutron multiplicities were made for Sr-Nd, Zr-Ce, Mo-Ba, Ru-Xe, and Pd-Te correlated pairs. A strong enhancement of the 7-10 neutron channels for Mo-Ba pairs is observed. A new fission mode associated with the enhanced neutron yields is identified. These data can be interpreted in terms of one or more of {sup 144,145,146}Ba being hyperdeformed at scission. Mean field calculations predict a hyperdeformed third minimum in {sup 252}Cf and an extremely deformed {sup 146}Ba fragment at scission. {copyright} {ital 1996 The American Physical Society.}

Coincidence \ensuremath{\gamma}-ray data from the spontaneous fission of $^{242}\mathrm{Pu}$ were collected at the Lawrence Berkeley Laboratory high purity Ge (HPGe) array, GAMMASPHERE. Data from several cold-fission (0 neutron emission) isotopic pairs were observed and are presented. An interesting trend in the fractional population of cold-fission events was observed and is discussed. Relative yields of Zr-Xe, Sr-Ba, and Mo-Te pairs were measured. The Zr-Xe system has the most complete data set. Some speculations on the trend in the number of neutrons emitted as a function of the mass of the Xe isotope populated are presented. Comparisons between the yields from the spontaneous fission of $^{242}\mathrm{Pu}$ and the yields from thermal-neutron-induced fission of $^{241}\mathrm{Pu}$ are also presented. \textcopyright{} 1996 The American Physical Society.

New insights into the fission process and the structure of neutron-rich nuclei have been gained by measuring γ-γ and γ-γ-γ coincidences of the prompt γ-rays following the spontaneous fission of 252Cf. The data were taken with the Compton Suppression Spectrometer System at HHIRF. New high spin levels were observed in 143,145,147Ba Only in 143Ba are intertwined bands observed with the characteristics of the octupole structure found only in 144Ba. New high spin states observed in the N = 84 136 Te, 138 Xe, 140 Ba nuclei exhibit a symmetry pattern suggestive of a pseudospin f - shell . For the first time in fission, the relative yields and neutron multiplicities were measured directly. Yields and multiplicities were measured directly for the ZrCe and MoBa correlated fragment pairs by observing the coincidences between the γ-rays in each fragment. Zero-neutron to ten-neutron emission yields were determined; the latter for the first time. The zero-neutron emission can be understood as a new example of cluster radioactivity. These results demonstrate that the use of the high resolution γ-γ-γ coincidence technique employed here for the first time opens up a new approach to the study of the fission process that will provide previously inaccessible details of the process.

With prompt \ensuremath{\gamma}-ray and x-ray spectroscopy on fission fragments, several new transitions in $^{109,111}\mathrm{Ru}$ have been identified. Angular correlation analysis of several of the new transitions yield evidence of a stretched E2 band structure. Qualitative Nilsson model arguments, systematics, and triaxial rotor+particle calculations support our hypothesis that the observed band is built on the unique parity \ensuremath{\nu}${\mathit{h}}_{11/2}$ orbital.

The levels in{sup 108,110,112}Ru have been investigated in the spontaneous fission of {sup 252}Cf using {gamma}-{gamma}-{gamma}-, {gamma}-{gamma}-, x-x-, x-{gamma}-, and x-{gamma}-{gamma}-coincidence techniques. The levels up to 16{sup +} and 9{sup +} in the yrast bands and {gamma}-vibrational bands have been identified with very little energy staggering in {sup 108,110,112}Ru. The ground bands in {sup 108,110}Ru have identical {gamma}-ray transition energies up to 8{sup +}. These are the lightest observed even-even nuclei with extended identical ground bands. Calculations in a collective model which includes rotations and vibrations reproduce the level energies and {gamma} band branching ratios above the 3{sup +} state rather well, while rigid triaxial rotor model calculations reproduce the branching ratios for the 2{sup +} and 3{sup +} states.

In this paper we illustrate that LEPS X-ray detectors operating in coincidence with γ-ray detectors yield additional data that are useful in prompt γ-ray spectroscopic studies of spontaneous fission fragments. Several X-X and X-γ gated spectra are presented as illustrations of spectroscopic techniques, and in support of new transitions in the level scheme of 147Ce.

High resolution [gamma]-[gamma] and [gamma]-[gamma]-[gamma] coincidences in the spontaneous fission of [sup 252]Cf were measured. Relative yields and neutron multiplicities from zero up to 10 were extracted directly for the first time in fission for the Zr-Ce and Mo-Ba correlated fragments pairs. The 0, 8, and the new 10 neutron emission yields for Mo-Ba are significantly larger than those reported previously for total [sup 252]Cf spontaneous fission. Our results demonstrate that the use of this high resolution [gamma]-[gamma]-[gamma] coincidence technique can provide important, previously inaccessible data on fission.

High spin excited states in neutron-rich nuclei [sup 112,114,116]Pd have been investigated by measuring prompt [gamma] rays emitted from a [sup 252]Cf spontaneous fission source. Two different measurements were performed. First, [gamma]-[gamma] coincidence data, necessary to determine the decay schemes, were obtained by using an array of 20 Compton-suppressed Ge detectors. Second, [ital Z] identification and the enhancement of a desired neutron channel were carried out using a [ital x]-[ital n]-[gamma] multiplicity spectrometer. Ground state bands have been extended to [ital J][sup [pi]]=10[sup +] for [sup 112]Pd, and [ital J][sup [pi]]=12[sup +] for [sup 114]Pd and [sup 116]Pd. Band crossings were observed in all three isotopes. It was found from cranked shell model calculations that these backbends are due to the alignment of two [ital g][sub 9/2] protons. The measured energy levels were also compared with predictions of the interacting boson model.

Excited states have been identified for the first time in the neutron-rich nuclide 136Te by observing prompt gamma -rays from 252Cf spontaneous fission fragments. The technique of triple gamma -ray coincidences was used for the first time in a spontaneous fission study to identify 136Te. In addition, new high-spin states in N=84 138Xe (12+) and 140Ba (8+) and N=86 140Xe (10+) have been observed. These provide the first high-spin yrast band systematics for the N=84 isotones.

From an experiment with Gammasphere and a ${}^{252}\mathrm{Cf}$ spontaneous fission source, a new negative-parity band in ${}^{154}\mathrm{Nd}$ and new negative-parity levels in ${}^{152}\mathrm{Nd}$ were identified and the yrast bands were extended to ${18}^{+}$ in ${}^{154}\mathrm{Nd}$ and ${20}^{+}$ in ${}^{152}\mathrm{Nd}$ in a triple gamma coincidence study. These new negative-parity bands are consistent with octupole vibrational mode. There is a constant difference as a function of spin between the ${J}_{1}$ values for the negative-parity band in ${}^{152}\mathrm{Nd}$ and ${J}_{1}$ for the similar negative-parity band in ${}^{154}\mathrm{Nd},$ however, their ${J}_{2}$ values are essentially identical. These bands indicate a new kind of identical band.

The yrast band was significantly extended to 14{sup +} and the {gamma} band to 5{sup +} in neutron-rich {sup 118}Pd by measuring the {gamma}-{gamma}-{gamma} coincidences emitted from the spontaneous fission of {sup 252}Cf with Gammasphere. The first band crossing was observed in the yrast band in {sup 118}Pd at a frequency of {Dirac_h}{omega}{approx}0.36 MeV at the starting point of the backbending, which is similar to that found in {sup 112-116}Pd. The first bandbending in the yrast cascade in {sup 118}Pd is interpreted to be built on a two h{sub 11/2} neutron configuration based on its similarity to the yrast bands in even-even {sup 112-116}Pd. Our result indicates {sup 118}Pd still maintains a prolate shape. The quasineutron Routhian calculations indicate a lower crossing frequency for the h{sub 11/2} level.

The decay of {sup 96}Tc{sup g} has been studied using low-temperature nuclear orientation. Multipole mixing ratios have been deduced for several transitions in the daughter nucleus {sup 96}Mo by measuring {gamma}-ray anisotropies following the decay of the oriented {sup 96}Tc nuclei. These new mixing ratios are compared with those determined from previous measurements in light of the possible presence of a low-energy 6{sup +} mixed-symmetry state in {sup 96}Mo. {copyright} {ital 1999} {ital The American Physical Society}

Prompt γ-γ-γ coincidence studies following spontaneous fission of 252Cf were carried out at Gammasphere first with 36 and later with 72 Ge detectors. Yields and neutron multiplicities were measured directly for Sr-Nd, Zr-Ce Mo-Ba, Ru-Xe, and Pd-Te correlated pairs. A new hot fission mode was discovered going via only 108Mo-144Ba, 107Mo-145Ba, and/or 106Mo-146Ba pairs where one or more of 144,145,146Ba are hyperdeformed at scission with 3:1 axis ratio. For the first time correlated pairs involved in cold ternary fission were observed with the third particle 4He, possibly 6He, and 10Be. The 142-146Ba data provide evidence for the predicted disappearance of stable octupole deformation at high spins. New level structures and isotopes include new octupole deformations, identical bands and other structures.

New insights into the fission process can be gained by better quantitative knowledge of how the energy released in fission is distributed between the kinetic energy of the two fragments, the excitation energy of the two fragments and the number of neutrons emitted. Studies of prompt gamma-rays emitted in spontaneous fission (SF) with large arrays of Compton suppressed Ge detector arrays are providing new quantitative answers to longstanding questions concerning fission as well as new insights into the structure of neutron-rich nuclei. For the first time the triple gamma coincidence technique was employed in spontaneous fission studies. Studies of SF of 252Cf and 242Pu have been carried out. These γ-γ-γ data provide powerful ways to identify uniquely gamma rays from a particular nucleus in the very complex gamma-ray spectra given off by the over 100 different nuclei produced. The emphasis of this paper is on the first quantitative measurements of the multiplicities of the neutrons emitted in SF and the energy levels populated in the fragments. Indeed, in the break up into Mo-Ba pairs, we have identified for the first time fragments associated with from zero up to ten neutrons emitted and observed the excited energy states populated in these nuclei. The zero neutron emission pairs like 104Mo - 148Ba, 106Mo - 146Ba and 104Zr - 148Ce observed in this work are particularly interesting because they represent a type of cold fission or a new mode of cluster radioactivity as proposed by Greiner, Sandulescu and co-workers1,2. These data provide new insights into the processes of cluster radioactivity and cold fission.