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Recent developments associated with room temperature semiconductor detectors and inorganic scintillators suggest that these detectors may be viable alternatives for the primary detector in a Compton suppression spectrometer (CSS). The room temperature operation of these detectors allows removal of a substantial amount of material from between primary and secondary detector and, if properly designed should afford substantially better suppression factors than can be achieved by germanium-based spectrometers. We have chosen to study the optimum properties of a CSS with a LaX3:Ce scintillator (where X is chloride or bromide) as the primary gamma ray detector. A Monte Carlo photon transport model is used to determine the optimum geometric properties of this spectrometer. To validate the assumptions and basic design of the Monte Carlo simulations, the energy distribution of a 137Cs point source is measured and simulated for two experimental systems. Comparison of the suppression factors for the measured and simulated data validates the model accuracy. A range of CSS physical parameters are studied to determine optimal detector geometry and to maximize the Compton suppression factor. These physical parameters and their optimum values are discussed

A high-resolution, multi-stop, time-to-digital converter (TDC) was designed and developed to precisely measure the times-of-flight (TOF) of incident neutrons responsible for induced fission and capture reactions on actinide targets. The minimum time resolution is ±1 ns. The TDC design was implemented into a single, dual-wide CAMAC module. The CAMAC bus is used for command and control as well as an alternative data output. A high-speed ECL interface, compatible with LeCroy FERA modules, was also provided for the principle data output path. An Actel high-speed field programmable gate array (FPGA) chip was incorporated with an external oscillator and an internal multiple clock phasing system. This device implemented the majority of the high-speed register functions, the state machine for the FERA interface, and the high-speed counting circuit used for the TDC conversion. An external microcontroller was used to monitor and control system-level changes. In this work we discuss the performance of this TDC module as well as its application.

Room-temperature semiconductor CdZnTe (CZT) detectors are currently limited to total detector volumes of 1-2 cm/sup 3/, which is dictated by poor charge transport characteristics. Because of this size limitation, one of the problems in accurately determining isotope identification is the enormous background from Compton scattering events. Eliminating this background will not only increase the sensitivity and accuracy of measurements, but will also help to resolve peaks buried under the background and peaks in close vicinity to others. We are currently developing a fission products detection system based on Compton-suppressed CZT and LaCl/sub 3/ (Ce) detectors. In this application, the detection system is required to operate in a high radiation field. Therefore, a small 10 mm /spl times/10 mm/spl times/5 mm CZT and 13mm/spl times/15mm LaCl/sub 3/ detector are placed inside the center of a well-shielded 76 mm by 76 mm long NaI detector. So far, we have been able to successfully reduce Compton background by a factor of 3.7 to 4.0 for a /sup 137/Cs spectrum. In this work, we will discuss the performance of this detection system using both CZT and LaCl/sub 3/ detectors. The results are compared with MCNP calculations.

In this work, prompt gamma-rays emitted by thermal neutron-induced fission decay using fast coincidence techniques are used to identify both light and heavy fragments and obtain gamma-ray signatures and radiation multiplicity. The measurements were carried out with 235U and 239Pu targets using the Intense Pulsed Neutron Source (IPNS) at Argonne National Laboratory. This study reports the recent results of a preliminary analysis of experimental data collected from the induced fission of 235U and 239Pu. In this paper, we discuss how these results could be used to characterize an unknown sample of fissile material.

{\rtf1\ansi\ansicpg1250\deff0\deflang1038\deflangfe1038\deftab708{\fonttbl{\f0\froman\fprq2\fcharset238{\*\fname Times New Roman;}Times New Roman CE;}{\f1\froman\fprq2\fcharset161{\*\fname Times New Roman;}Times New Roman Greek;}} \viewkind4\uc1\pard\f0\fs24 Gamma-ray spectrometry measurements have been made of the fission yields of selected \f1\’e3\f0 -rays emitted by the spontaneously fissioning isotopes \super 252\nosupersub Cf and \super 244\nosupersub Cm. The measured \f1\’e3\f0 -rays were selected based on their relative abundance in the spectrum and their freedom from interference or, in a few instances, ease of interference correction. From these data and the cumulative and independent yield data of \scaps England\scaps0 and \scaps Rider\scaps0 , those \f1\’e3 \f0 -rays that are primarily produced by radioactive decay, as opposed to direct yield, were converted into the decays per spontaneous fission expressed in percent and compared to cumulative yield values of \scaps England\scaps0 and \scaps Rider\scaps0 . For those \f1\’e3 \f0 -rays whose production is dominated by direct (independent) yield, the ratio of \f1\’e3 \f0 -rays per spontaneous fission is reported. The \f1\’e3 \f0 -ray yield can be compared to the independent yield values of \scaps England\scaps0 and \scaps Rider\scaps0 when 100% of the direct feeding passes through the \f1\’e3 \f0 -ray. In those cases where both cumulative and independent yields contribute to the observed \f1\’e3 \f0 -ray emission rate, a direct comparison is not possible but a method to quantify the contribution from each is proposed. \par }

A pocket radiation detection system has been developed at the Idaho National Engineering and Environmental Laboratory for homeland security applications. It can detect both neutrons and gamma rays instantaneously. This sensor has been designed with an emphasis on compactness, recognizing the widespread need for a radiation detection instrument that could provide both neutron and gamma-ray detection in a single, portable unit. It is very small, extremely sensitive, versatile, and easy to operate. It can detect gamma rays and neutrons in a radiation field as low as 10 /spl mu/R/h above the ambient background, which makes it ideal for use in national security applications. The detection system is based on a technique of using a combination of two sensors made of lithium isotopes /sup 6/Li and /sup 7/Li. It operates on one rechargeable Li-ion battery and is small enough to be put in a pocket or clipped to a belt. In this paper, the detection technique used in developing this prototype sensor as well as its performance will be presented.

The rotational bands up to a spin of 16 in the neutron-rich 106Mo nucleus have been investigated by measuring high-fold prompt γ-ray coincidence events following spontaneous fission of 252Cf with a Gammasphere detector array. The ground-state band, the one-phonon and two-phonon γ-vibrational bands, as well as a quasi-particle band have been confirmed and expanded. The other four collective rotational bands, three proposed as two-quasi-particle bands and one proposed as a β-vibrational band, have been newly observed. The characteristics of these collective bands and the possible configurations for the quasi-particle bands are discussed.

Several new high-spin states are observed in the prompt $\ensuremath{\gamma}$-rays emitted from the neutron-rich, odd-$Z$ ${}^{145,147}\mathrm{La}$ fragments produced in the spontaneous fission of ${}^{252}\mathrm{Cf}.$ Alternating parity bands are extended up to spins 41/2 and 43/2 in ${}^{145,147}\mathrm{La},$ respectively. A new band completes the evidence for two sets of parity doublets expected for octupole correlations. Eight $B(E1)/B(E2)$ ratios (four new) between two bands in ${}^{145}\mathrm{La}$ are all essentially constant and somewhat larger than similar ratios in ${}^{143,144}\mathrm{Ba},$ where stable octupole deformation and/or correlations are reported. The new ratios out of the ${31/2}^{\ensuremath{-}}$ levels in both nuclei show a sharp spike compared to other states, presumably from a strong reduction in $E2$ strengths in this backbending region. In ${}^{145}\mathrm{La},$ collective bands show competition and coexistence between symmetric and asymmetric shapes. Band crossings occur in both nuclei around $\ensuremath{\Elzxh}\ensuremath{\omega}\ensuremath{\approx}0.26--0.30 \mathrm{MeV}.$ Their backbends are associated with the alignment of two ${i}_{13/2}$ neutrons according to cranked shell model calculations.

Several $\ensuremath{\gamma}$ transitions in ${}^{101--103}\mathrm{Nb},{ }^{98,100}\mathrm{Y},{ }^{146}\mathrm{La},$ and ${}^{149}\mathrm{Pr}$ are identified from spontaneous fission studies employing a ${}^{252}\mathrm{Cf}$ source and the Gammasphere detector array. In particular, the pairing-free bands in ${}^{100}\mathrm{Y}$ and ${}^{102}\mathrm{Nb}$ are extended, two rather highly deformed negative-parity bands feeding the 4.3-s $\ensuremath{\beta}$-decaying isomer of ${}^{102}\mathrm{Nb}$ are identified, and their possible bandhead configurations are discussed. In the case of ${}^{101,103}\mathrm{Nb},$ we have extended previously reported level schemes by over 20 transitions in each nuclide. For the fission partners ${}^{146}\mathrm{La}$ and ${}^{149}\mathrm{Pr}$ we have elucidated their previously unreported yrast level schemes.

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.

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}

Tensor moments t kq have been determined for the 6 Li ∗ (2.186 MeV, 3 + ) state produced in the 9 Be(p,α 1 ) 6 Li reaction at 40 MeV. Angular correlation measurements were made between α 1 and the α-particle or deuteron fragment from the breakup of 6 Li ∗ . Comparison of the t kq are made with the predictions of a model that includes direct and exchange processes. Angular distributions of the differential cross sections for the 9 Be(p,α) 6 Li reaction for the g.s. and first two excited states are presented.

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.

Level schemes for the neutron-rich 140,143Ba nuclei have been determined by study of prompt γ-rays in spontaneous fission of 252Cf. The level pattern and enhanced E1 transitions between π = + and π = - bands show reflection asymmetric shapes with simplex quantum number s = +1 in 140Ba and s = ±i in 143Ba, respectively. The octupole deformation stability with spin variation has been discussed.

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.

We have developed a new technique for the detection of neutrons in the presence of a high gamma-ray background. This was accomplished by using two lithium-loaded glass scintillators (/sup 6/Li//sup 7/Li) in combination. The neutron capture reaction in /sup 6/Li has a very high Q-value which means better discrimination against gamma-ray background. The /sup 7/Li detector, on the other hand, is neutron insensitive and was used to measure separately the gamma contribution in a mixed neutron-gamma field. By subtracting this gamma contribution from the /sup 6/Li data, which is sensitive to both gamma rays and neutrons, one can obtain the pure neutron counts.

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.

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.

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.

New, high spin band structures are established for the neutron-rich nuclei 142,143,145,147Ba, and 144Ce, and levels of 144,146Ba extended to higher spins from the study of γ-γ and γ-γ-γ coincidence studies in spontaneous fission. Alternating parity sequences connected by strong electric dipole transitions are identified in 142,143Ba and 144Ce but not in 145,147Ba to confirm theoretical predictions of stable octupole deformation for N = 86.

From gamma - gamma , X-X, X- gamma , and gamma - gamma - gamma coincidence studies of spontaneous fission of 252Cf, 160Sm levels were identified along with new high spin states in 156,158Sm. New bands, beginning at 5- in 156,158Sm are assigned a two-neutron configuration (5/2+(642) 5/2-(523))5-. The J1 and J2 values for the yrast bands increase smoothly with spin and neutron number and the differences in these values for corresponding transitions in neighbouring isotopes are reasonably constant.

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.

By using the triple gamma coincidence technique with 20 Ge detectors at the Holifield Laboratory in the spontaneous fission of 252Cf, neutronless fragmentations, like 104Mo-148Ba, 106Mo-146Ba, 108Mo-144Ba and 104Zr-148Ce, are experimentally observed directly for the first time. When zero neutron emission spontaneous fission occurs, essentially all the available energy goes into the total kinetic energy of the fragments (cold fission). This process is seen theoretically to be an extension of cluster radioactivity, which involves the emission of one light fragment like 14C, 20O, (24)Ne or 28Mg to nearly equal fragments. In the neutronless spontaneous fission reported here, double fine structures (i.e. decays to the excited states of both fragments) are observed experimentally in contrast to fine structure in only the heavy partner populated by the light partner in earlier cluster radioactivity work. Neutronless spontaneous fission is discussed in the framework of cluster radioactivity.

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.

Levels in the neutron-rich 104Mo nucleus have been investigated by observing prompt γ-rays from the spontaneous fission of 252Cf with the Gammasphere detector array. The ground-state band, the one-phone and the two-phone γ-vibrational bands as well as a quasiparticle band have been confirmed and expanded with spin up to 14. Other two side bands probably built on new quasiparticle states are identified. The possible configurations for the quasiparticle bands are discussed. Two of the quasiparticle bands show larger moments of inertia and may have pair-free characteristics. The levels of the ground-state band, the one-phonon γ-band and the two-phonon γ-band calculated from a general collective model are in close agreement with the experimental data. PACS: 21. 10. Re, 23. 20. Lv, 27. 60. +j, 25. 85. Ca

High spin states in neutron-rich odd-N 145Ba nucleus have been investigated from study of prompt γ-rays in spontaneous fission of 252Cf. The alternating parity bands are identified indicating octupole deformation with simplex quantum number s = -i. The ground state band shows signature splitting and inversion at low spin. These collective band structures exhibit the competition and co-existence between symmetric and asymmetric shapes.

Octupole deformation bands built on πh11/2 orbital in neutron-rich odd-Z 145,147La nuclei have been investigated by measuring the prompt γ-rays emitted from the 252Cf source. The alternating parity band structures and strong E1 transitions observed between negative- and positive-parity bands in both nuclei indicate the octupole deformation enhanced by the h11/2 single proton coupling. According to observed energy displacements the octupole deformation becomes stable at the intermediate spin states.

We have developed a multi-functional pocket radiation monitoring system capable of detecting and storing gamma ray and neutron data and then sending the data through a wireless connection to a remote central facility upon request. The device has programmable alarm trigger levels that can be modified for specific applications. The device could be used as a stand-alone device or in conjunction with an array to cover a small or large area. The data is stored with a date/time stamp. The device may be remotely configured. Data can be transferred and viewed on a PDA via direct connection or wirelessly. Functional/bench tests have been completed successfully. The device detects low-level neutron and gamma sources within a shielded container in a radiation field of 10 uR/hr above the ambient background level.

The levels in neutron-rich odd-A 107,109Ru nuclei have been investigated by using γ-γ- and γ-γ-γ-coincidence studies of the prompt γ-rays from the spontaneous fission of 252Cf. The ground state bands and the negative parity bands are identified and expanded in both nuclei. Triaxial rotor plus particle model calculations indicate the ground state bands originate from ν(d5/2 + g7/2) quasiparticle configurations and the negative parity bands are from νh11/2 orbital.

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.

In some environmental cleanup applications, there is a need for utilizing Si PIN diodes to detect electrons, x-rays, and low-energy gamma rays with very good energy resolution. The advantage of these detectors in such particular applications when compared with others is the ease of the operation at room temperature and at much lower bias voltages. We are currently investigating the feasibility of using silicon PIN photodiodes to detect the x-rays of radioisotopes such as Cs, Eu, La, U, Th, Am, and Pu for monitoring and characterizing topsoil contamination. The design and development of this Si PIN diode array will be discussed and the results of tests and its overall performance will be presented.

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.

Neutron-rich {sup 147,149,151}Pr nuclei, produced in the spontaneous fission of {sup 252}Cf, were studied using the Gammasphere array. Possible parity doublets in {sup 147}Pr with N=88 and {pi}h{sub 11/2} bands in {sup 149,151}Pr are proposed. These new data on the level structures of odd Pr isotopes suggest that octupole correlations may also be present in the neutron-rich {sub 59}{sup 147}Pr{sub 88} nucleus such as those observed in {sub 58}{sup 146}Ce{sub 88}, and also that the h{sub 11/2} bands in the {sup 149,151}Pr track in energy the yrast bands in {sup 148,150}Ce. The backbending related to the breaking of the neutron i{sub 13/2} pair is observed at {Dirac_h}{omega}{approx}0.27 (MeV) for the proton h{sub 11/2} band of {sup 149}Pr.

High-spin structures in the neutron-rich nuclei ${}^{145}\mathrm{Ce}$ and ${}^{147}\mathrm{Ce}$ produced in the spontaneous fission of ${}^{252}\mathrm{Cf}$ have been investigated by prompt $\ensuremath{\gamma}$-ray spectroscopy. A collective band structure in ${}^{145}\mathrm{Ce}$ is identified. Several sidebands along with the new high-spin states in ${}^{147}\mathrm{Ce}$ are also identified. Particle-plus-rotor model calculations indicate that the yrast bands in ${}^{145}\mathrm{Ce}$ and ${}^{147}\mathrm{Ce}$ most probably originate from coupling of the $\ensuremath{\nu}{i}_{13/2}$ orbital to the ground states of ${}^{144}\mathrm{Ce}$ and ${}^{146}\mathrm{Ce}.$ The ground state configurations of ${}^{145,147}\mathrm{Ce}$ are $(\ensuremath{\nu}{h}_{9/2}+\ensuremath{\nu}{f}_{7/2})$ and $\ensuremath{\nu}{h}_{9/2},$ respectively.

High spin states in neutron-rich odd-{ital Z} {sup 143,145}Ba nuclei have been investigated from the study of prompt {gamma} rays in the spontaneous fission of {sup 252}Cf by using {gamma}-{gamma}- and {gamma}-{gamma}-{gamma}- coincidence techniques. Alternating parity bands are identified for the first time in {sup 145}Ba and extended in {sup 143}Ba. A new side band, with equal, constant dynamic, and kinetic moments of inertia equal to the rigid body value, as found in superdeformed bands, is discovered in {sup 145}Ba. Enhanced E1 transitions between the negative- and positive-parity bands in these nuclei give evidence for strong octupole deformation in {sup 143}Ba and in {sup 145}Ba. These collective bands show competition and coexistence between symmetric and asymmetric shapes in {sup 145}Ba. Evidence is found for crossing M1 and E1 transitions between the s=+i and s={minus}i doublets in {sup 143}Ba. {copyright} {ital 1999} {ital The American Physical Society}

Yields of correlated fragment pairs were obtained in spontaneous fission of 242Pu. Charge, mass and neutron multiplicity distributions of fragment pairs were determined and compared to available data. The yield of cold fission without neutron emission was determined to about 10% for the set of observed correlated fragment pairs.

From γ-γ-γ coincidence measurements in spontaneous fission of 252Cf, level energies were established to spins 14+ to 20+ in many neutron-rich nuclei. New isotope 162Gd was identified. Yrast bands of 152,154,156Nd, 156,158,160Sm, and 160,162Gd exhibit near-identical transition energies and moments of inertia (MOI) 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 few cases of SIB for the most neutron-rich pairs around N=98–102 separated by 2n and 2p.

The data of Independent yields of secondary fission fragment pairs (emerging after prompt neutron emission from primary fragment pairs) obtained by detecting coincidences between γ rays following the spontaneous fission of 252Cf have been expanded. Our approach to estimate characteristics of the primary fragments pairs (mass and excitation energy distributions) by unfolding the yields of secondary fragment pairs is discussed. Mew model parameters were introduced and results are presented here. The new results confirmed our old assumption that in case of Mo-Ba charge split the two fission modes differing with average total kinetic energy 〈TKE〉 on ∼36 MeV are realized.