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Decay studies of very neutron-deficient nuclei 43Cr and 48Ni with the application of a time projection chamber with optical readout are presented. [ABSTRACT FROM AUTHOR]

Neutron transfer (d, p) reactions have been measured with neutron-rich fission fragment beams of 130,132Sn and 134Te populating l = 1 and l = 3 excitations above the N = 82 shell gap. Preliminary results and future prospects are discussed. [ABSTRACT FROM AUTHOR]

Neutron transfer reactions were performed in inverse kinematics using radioactive ion beams of 132Sn, 130Sn, and 134Te and deuterated polyethylene targets. Preliminary results are presented. The Q-value spectra for 133Sn, 131Sn and 135Te reveal a number of previously unobserved peaks. The angular distributions are compatible with the expected lf7/2 nature of the ground state of 133Sn, and 2p3/2 for the 3.4 MeV state in 131Sn. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

The discovery potential for new proton-emitting isotopes of elements with atomic numbers 35100Sn. Fusion-evaporation reactions studied by means of the Recoil Mass Separator at the Holifield Radioactive Ion Beam Facility (HRIBF) at Oak Ridge National Laboratory are compared to heavy-ion fragmentation based studies at the National Superconducting Cyclotron Laboratory using the A1900 separator. The l = 4 proton emitters 93Ag and 89Rh are identified as primary candidates to be discovered. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Fine structure in proton emission from the deformed states 141g.s.Ho (T1/2 = 4.1 ms) and 141mHo (T1/2 = 7.4 μs) has been discovered at Oak Ridge by detecting fusion evaporation residues with the Recoil Mass Spectrometer, Si-detectors and digital signal processing electronics. The branching ratios to the first 2+ excited state in 140Dy were measured to be Ipg.s.(2+) = 0.9±0.1% and Ipm(2+) = 1.7±0.5%. A comparison of the available calculations to the experimental values calls for further development of the theoretical models. [ABSTRACT FROM AUTHOR]

In an experiment performed at the NSCL/MSU A1900 separator the decay of 45Fe was investigated in detail. Two-proton radioactivity channel was clearly identified and for the first time the correlations between two protons emitted from the nuclear ground state were determined. The comparison with a theoretical model indicates the genuine three-body character of this decay and sheds light on the shell structure of this exotic nucleus. The β decay channels of 45Fe, followed by one-, two-, and three-proton emission, were also identified. The β3p decay channel was observed for the first time. The half-life of 45Fe was found to be 2.6±0.2 ms and the 2p decay branching ratio is 70±4%. In the experiment a new type of gaseous detector has been applied in which a technique of digital imaging was used to record tracks of charged particles. [ABSTRACT FROM AUTHOR]

The abBA collaboration is developing a new type of field-expansion spectrometer to measure neutron beta decay angular parameters, a, b, B, and A, to the 0.1% precision level. This precision will be achieved by combining three new technical approaches; a pulsed cold neutron beam, a 3He neutron spin filter, and segmented large-area thin-dead layer silicon detectors. Both the electron and proton resulting from the decay will be guided by electric and magnetic fields and detected in coincidence by two 2π solid-angle silicon detectors. For the neutron polarization-dependent observables A and B, a novel precision neutron polarimetry technique has been developed. The parameters a and b will be obtained from the proton time-of-flight and the measured electron energy spectrum. Measurement of the four parameters in the same apparatus provides a redundant determination of parameter λ=gA/gV, providing a test of the standard electroweak interaction. © 2005 American Institute of Physics [ABSTRACT FROM AUTHOR]

An experiment was performed at the National Superconducting Cyclotron Laboratory at Michigan State University to investigate β- and isomer decay properties of several isotopes in the vicinity of 78Ni. The identification of an (8+) isomer in 76Ni was confirmed and its deexcitation cascade identified; the β-decay of 71–73Co was reinvestigated and that of 74Co studied for the first time. First evidence of β-delayed neutron emission in neutron-rich cobalt isotopes was also obtained. Preliminary results are reported. © 2005 American Institute of Physics [ABSTRACT FROM AUTHOR]

Decay studies on rare earth nuclei around the proton drip line have been performed by means of the Recoil Mass Spectrometer at the Holifield Radioactive Ion Beam Facility in Oak Ridge. The proton emission from the odd-odd N=77 isotone 146Tm was reinvestigated, resulting in the assignment of the 1.01 MeV proton line to the decay of a short-lived 146Tm state. A new proton radioactivity of 144Tm was identified. The decays of isomeric levels in the N=77 isotones, 140Eu, 142Tb and 144Ho were remeasured using γ and electron detectors. The analysis of the structure of studied nuclei, which accounts for the coupling between the protons and neutrons and for core excitations, is presented. © 2005 American Institute of Physics [ABSTRACT FROM AUTHOR]

The mass A = 140 products of the 54Fe (315 MeV) + 92Mo reaction were selected by a recoil mass spectrometer and studied in a recoil - delayed γ-γ coincidence experiment. A new 7 μs isomer was identified in the drip line nucleus 140Dy. Five cascading γ transitions were assigned to the decay of the Iπ = 8- {v9/2-[514] x v7/2+[404]} K isomer via the ground state band transitions. The established structure of 140Dy is discussed with reference to the fine structure in proton decay of 141Ho. © 2003 American Institute of Physics [ABSTRACT FROM AUTHOR]

Two observations of fine structure in proton emission are reported : 3-μs 145Tm and 4-ms 141Ho. These experiments were performed using the Recoil Mass Separator (RMS) at the Holifield Radioactive Ion Beam Facility at Oak Ridge. The signals from the RMS detectors were digitally processed using Digital Gamma Finder modules. The fine structure branching ratios, 9.6±1.5% and 0.70±0.15%, and measured energies of the 2+ excited levels in daughter nuclei, 330 and 202 keV, respectively, helped us to determine the deformations and wave functions of proton-emitting states. © 2003 American Institute of Physics [ABSTRACT FROM AUTHOR]

In an experiment performed at the GSI Fragment Separator the decay of 45Fe has been investigated. Five 45Fe atoms were implanted in a silicon telescope mounted inside a high-efficiency NaI detector. The implantation events were correlated with radioactive decay signals. One of them was consistent with the β decay of 45Fe accompanied by the emission of a 10 MeV proton. In each of the four other decay events, a signal corresponding to the emission of 1.1 ± 0.1 MeV particle(s) was recorded with no coincident signals in the NaI detector. This observation represents the first evidence for the two-proton ground state decay of 45Fe. The time distribution of the observed decay events corresponds to a half-life of 3.2[sub -1.0][sup +2.6] ms. © 2003 American Institute of Physics [ABSTRACT FROM AUTHOR]

According to most mass models, several of the best candidates for two-proton radioactivity lie in the A = 50 mass region, at the proton drip-line. Recent experiments using the fragmentation of a 58Ni beam allowed us to reach this region and observe some of these candidates, like 45Fe and 48Ni. During an experiment at the GANIL / LISE3 facility helded in 2000, we could identify 22 events of implantation of 45Fe nuclei. The energy distribution of the corresponding decay events shows a clear peak at (1.14 ± 0.04) MeV that could be assigned to the direct 2-proton emission from the ground state. This energy is in very good agreement with several theoretical predictions, and no coincident β particle has been observed experimentally. A half-life of (4.7[sub -1.4][sup +3.4]) ms has been measured for the decay of 45Fe. © 2003 American Institute of Physics [ABSTRACT FROM AUTHOR]

A series of experiments were performed to establish excited states in proton emitters 151Lu, 109I and 113Cs. These experiments used (HI, p2n) reactions to populate the proton emitters and employed the recoil decay tagging technique to identify gamma rays in the corresponding proton-unbound nucleus. Gamma-decay sequences were established in these nuclei and their configurations were tentatively assigned based on systematic trends. This paper reviews the three experimental studies and discusses the data in comparison with those of their neighboring nuclei. © 2003 American Institute of Physics [ABSTRACT FROM AUTHOR]

An experiment was performed at GANIL to observe isomeric- and beta-delayed gamma rays from very neutronrich nuclei around [sup 74]Ni. Fragmentation products of the [sup 86]Kr beam at 58 AMeV were studied using new devices: the LISE 2000 spectrometer and detectors from the EXOGAM germanium array. The primary aim of the experiment was to find the 8[sup +] microsecond isomer in [sup 76]Ni and to perform beta decay spectroscopy of Co nuclei. We have successfully measured the beta delayed gammas from the decay of [sup 72]Co to [sup 72]Ni. The energies for the lowest excited states in [sup 72]Ni are proposed, with the first 2[sup +] state at 1096 keV. These findings suggest a solution of the problem of the disappearance of the 8[sup +] isomer in [sup 72]Ni. We also measured beta decay of other neutron-rich Co isotopes including [sup 70]Co. First evidence was found for a new short lived isomer, most likely the I[sup π]=8[sup +] state, in [sup 76]Ni. [ABSTRACT FROM AUTHOR]

The observation of fine structure in proton emission allows one to measure the composition of the parent state's wavefunction and the deformation of the daughter state. A systematic study of proton-unbound nuclei in the rare earth region is ongoing at the HRIBF. Newly discovered fine structure in the decays of [sup 145]Tm and [sup 141]Ho are discussed, as well as advances in our experimental equipment. [ABSTRACT FROM AUTHOR]

In experiments at the FRS of GSI and at the SISSI-LISE3 facility of GANIL, the decay of the proton drip-line nucleus [sup 45]Fe has been studied after projectile fragmentation of a [sup 58]Ni primary beam. Fragment-implantation events have been correlated with radioactive decay events in silicon telescopes on an event-by-event basis. The decay-energy spectrum of [sup 45]Fe implants shows a distinct peak consistent with a two-proton ground-state decay of [sup 45]Fe. None of the events in the peak were found to be in coincidence with γ radiation or with β particles which were searched for in the telescope-surrounding detectors. The decay energy for [sup 45]Fe agrees nicely with several theoretical predictions for two-proton emission. These predictions strongly support the observed decay to be a simultaneous two-proton ground-state decay. [ABSTRACT FROM AUTHOR]

We report on the first application of the TDPAD method to measure the g factor of neutron-rich isomeric states, produced and aligned in a projectile fragmentation reaction. The feasibility of similar measurement opens up a new, unexplored region of the nuclear chart for studies of the magnetic moments of microsecond isomers. Nuclei around [sup 68]Ni were produced following the fragmentation of 61.6 MeV/u [sup 76]Ge on a 145 mg/cm² Be target. The isotopes of interest were selected using the LISE spectrometer at GANIL, Caen, France, and were implanted in a high purity Cu foil fixed between the poles of an electromagnet. Two Ge Clover detectors, positioned in a plane perpendicular to the holding magnetic field, were used to observe the rotation of the nuclear spin ensemble and to derive the experimental R(t) function. The experimental result for the isomer in [sup 67]Ni (Jπ = 9/2[sup +], T[sub ½] = 13.3 µs, E[sub x] = 1007 keV), g = 0.125(6), is presented herein and is also compared to the theoretical expectations. [ABSTRACT FROM AUTHOR]

Deformations and wave functions of proton-radioactive nuclei are studied using measured tine structure properties of proton emission and microscopic theoretical models. The experimental data are available for [SUP131]Eu and [SUP145]Tm decays, as well as for [SUP141gs]Ho, where an observation of line structure in proton emission is reported for the first time. [ABSTRACT FROM AUTHOR]

The status of experimental approach to [sup 100]Sn and [sup 78]Ni is reviewed. Revised single particle energies for neutrons are deduced for the N=Z=50 shell closure and evidence for low lying I[sup π]=2[sup +] and 3[sup -] states is presented. Moderate E2 polarization charges of 0.1 e and 0.6 e are found to reproduce the experimental data when core excitation of [sup 100]Sn is properly accounted for in the shell model. For the neutron rich Ni region no conclusive evidence for an N=40 subshell is found, whereas firm evidence for the persistence of the N=50 shell at [sup 78]Ni is inferred from the existence of seniority isomers. The disappearance of this isomerism in the mid vg[sub 9]/2 shell is discussed. The spectroscopy of [sup 216]Th disproves the existence of a Z=92 shell gap as predicted by some recent mean field calculations. Inversion of the πh[sub 9/2] and f[sub 7/2] orbitals at Z=90 is ascribed to the coupling of the f[sub 7/2] (and i[sub 13/2]) protons to the low-lying 3[sup -] state (...ω[sub 3]=1.69 MeV). [ABSTRACT FROM AUTHOR]

The doubly magic nucleus [sup48]Ni has been observed for the first time at GANIL. The experiment was performed using a high intensity [sup58]Ni beam at 74.5 MeV/A on a nickel target. This T[subZ] = −4 nucleus is the most proton-rich nucleus ever observed, and is a good candidate for two-proton radioactivity. In this experiment, we also implanted around 280 [sup42]Cr, 50 [sup45]Fe and 100 [sup49]Ni isotopes, for which no experimental information about the decay is available [ABSTRACT FROM AUTHOR]

We studied the proton emission from [sup146][sub69]Tm[sub77] and observed three new transitions. New transition at 0.89 and 0.93 MeV have half-lives similar to that of the previously observed transition at 1.19 MeV, while a new transition at 1.02 MeV has a half-life similar to that of the previously observed transition at 1.12 MeV. These new transitions indicate the population of excited neutron single-particle states in [sup145][sub68]Er[sub77] [ABSTRACT FROM AUTHOR]

Proton radioactivity studies performed at the Holifield Radioactive Ion Beam Facility (HRIBF) within the last few years are reviewed. The discovery of five new proton radioactivities [sup140]Ho,[sup141m]Ho, [sup145]Tm, [sup150m]Lu and [sup151m]Lu is presented together with a recent observation of fine structure in proton emission from [sup146gs,m]Tm. These proton emitters were produced by means of fusion-evaporation reactions and studied with the HRIBF Recoil Mass Separator and detection system based on a Double-sided Silicon Strip Detector. For [sup113]Cs and [sup151]Lu, the studies of level structure were extended beyond the proton-emitting states via the measurements with a clover array CLARION using Recoil Decay Tagging [ABSTRACT FROM AUTHOR]

Great progress has been made in the last 20 years in the study of proton emission from unstable nuclei, but the prospects for additional strides in the next several years are bright. The present main limitations on the study of proton radioactivity are related to the inability to produce copious quantities of nuclides beyond the proton drip line, and the difficulty of measuring proton radioactivity of a mass-separated nucleus in the first few microseconds of its existence. At the Holifield Facility we will attack the second of these limitations by using new signal processing CAMAC modules DGF-4C. Digitizing of the preamplifier signals should enable the analysis of a proton decay occurring at times even less than 1 microsecond after an implant in a strip detector. In the same process, the threshold energy at which we can make measurements will be lowered. These two things will hopefully enable the measurement of lower-energy, but faster decays of isotopes in the [sup100]Sn region and below. For the latter region, the proton decays crucial for a rp-process scenario are of particular interest (e.g. [sup69]Br decay). Secondly, for very short-lived species, we plan to make measurements (without residue separation) at points much closer to the target, thus reducing the flight time between the target and detector. As more intense radioactive beams become available, eg. [sup56]Ni, we will utilize these to produce more neutron-deficient nuclides by use of colder reactions than is possible with stable beams. In some cases where delayed proton emitters are present in the same isobaric chain, the use of the cold reactions with radioactive beams can provide purer samples of the isotope of interest, with a reduction in background from the delayed proton emitters in the same mass chain [ABSTRACT FROM AUTHOR]