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β-delayed two- and three-neutron emission is modeled with the effective density model and sequential neutron emission model based on the statistical level density of daughter nuclides. The results show a significant reduction in the delayed two- and three-neutron emission probability compared to other available calculations. Predictions for some selected isotopes, which may soon be available for experimental spectroscopic measurements, are presented. [ABSTRACT FROM AUTHOR]

The excited states of odd-odd 82As are studied in the β decay of 82Ge. An isotopically pure beam of 83Ga was produced at the Holifield Radioactive Ion Beam Facility using a resonance ionization laser ion source and high-resolution electromagnetic separation. The atoms of 82Ge are created after β-delayed neutron emission in the decay of 83Ga. The number of 82Ge atoms is found by normalization to the 1348-keV γ ray. Detailed analysis of the decay scheme is compared with shell-model calculations with several commonly used fpg shell interactions. [ABSTRACT FROM AUTHOR]

Beta decay of 86Ga was studied by means of β-neutron-γ spectroscopy. An isotopically pure 86Ga beam was produced at the Holifield Radioactive Ion Beam Facility using a resonance ionization laser ion source and high-resolution electromagnetic separation. The decay of 86Ga revealed a half-life of 43-15+21 ms and large β-delayed one-neutron and two-neutron branching ratios of P1n=60(10)% and P2n=20(10)%. The βγ decay of 86Ga populated a 527 keV transition that is interpreted as the deexcitation of the first 2+ state in the N=54 isotone 86Ge and suggests a quick onset of deformation in Ge isotopes beyond N=50. [ABSTRACT FROM AUTHOR]

Short-lived neutron-rich nuclei including 93Br, 93Kr, and 94Kr were produced in proton-induced fission of 238U at the Holifield Radioactive Ion Beam Facility in Oak Ridge. Their ß decay was studied by means of a high-resolution online mass separator and β-γ spectroscopy methods. The half-life of T1/2 = 152(8) ms and β-delayed branching ratio of Pn = 53' % measured for 93Br differs from the previously reported values of T1/2 = 102(10) ms and Pn = 68(7)%. At the same time the half-life of 94Kr Tlß = 227( 14) ms and both the half-life of T\ß = 1.298(54) s and β-delayed branching ratio of Pn = 1.9-0.2+0.6% of 93Kr are in very good agreement with literature values. The decay properties of 93Br include previously unreported γ transitions following β-delayed neutron emission. [ABSTRACT FROM AUTHOR]

The β+ decay of very neutron-deficient 43Cr was studied by means of an imaging time projection chamber that allowed recording tracks of charged particles. Events of β-delayed emission of one, two, and three protons were clearly identified. The absolute branching ratios for these channels were determined to be (81±4)%, (7.1±0.4)%, and (0.08±0.03)%, respectively. 43Cr is thus established as the second case in which the β-3p decay occurs. Although the feeding to the proton-bound states in 43V is expected to be negligible, the large branching ratio of (12±4)% for decays without proton emission is found. [ABSTRACT FROM AUTHOR]

Decay of 85Ga was studied by means of β-neutron-γ spectroscopy. A pure beam of 85Ga was produced at the Holifield Radioactive Ion Beam Facility using a resonance ionization laser ion source and a high-resolution electromagnetic separator. The β-delayed neutron emission probability was measured for the first time, yielding 70(5)%. An upper limit of 0.1% for β-delayed two-neutron emission was also experimentally established for the first time. A detailed decay scheme including absolute γ-ray intensities was obtained. Results are compared with theoretical β-delayed emission models. [ABSTRACT FROM AUTHOR]

β decay of neutron-rich nuclide 94Kr was reinvestigated by means of a high resolution on-line mass separator and β-γ spectroscopy. In total 22 γ-ray transitions were assigned to the decay of 94Kr, and a new isomeric state was identified. The new information allows us to build detailed levels systematics in a chain of odd-odd rubidium isotopes and draw conclusions on nuclear structure for some of the observed states. The discussed level structure affects the evolution of β-decay half-lives for neutron-rich selenium, krypton, and strontium isotopes. [ABSTRACT FROM AUTHOR]

The β -decay properties of very neutron rich nuclei 86Ge and 86As were measured at the Holifield Radioactive Ion Beam Facility at Oak Ridge National Laboratory. Spectroscopic information on new excited states in 86As and in 86Se was obtained and is interpreted within an advanced shell model approach. These calculations, previously explaining well the structure of 84Ge and 85Ge, are not able to reproduce all the experimentally determined features of the measured level schemes of 86As and 86Se. The Gamow-Teller decay of 86Ge and 86As is also investigated in a shell-model framework. The fission yield for 86Ge is discussed. [ABSTRACT FROM AUTHOR]

The β-decay properties of neutron-rich 87As produced in the proton-induced fission of 238U were studied at the Holifield Radioactive Ion Beam Facility at Oak Ridge National Laboratory. The low-energy excited states in N = 53 87Se and N = 52 86Se were identified through β-γ and β-delayed neutron-γ decay of 87As, respectively. The experimental systematics of low-energy levels of N = 53 isotones, Z = 34 87Se, and Z = 32 85Ge, and along with an analysis of shell-model calculations, allow us to discuss the main features of excited states expected for the next N = 53 isotone, 83Zn. [ABSTRACT FROM AUTHOR]

Irradiations of 239Pu and 240Pu targets with 48Ca beams aimed at the synthesis of Z=114 flerovium isotopes were performed at the Dubna Gas Filled Recoil Separator. A new spontaneously fissioning (SF) isotope 284Fl was produced for the first time in the 240Pu+48Ca (250 MeV) and 239Pu+48Ca (245 MeV) reactions. The cross section of the 239Pu(48Ca,3n)284Fl reaction channel was about 20 times lower than predicted by theoretical models and about 50 times lower than the maximum fusion-evaporation cross section for the 3n and 4n channels measured in the 244Pu+48Ca reaction. In the 240Pu+48Ca experiment, performed at 245 MeV in order to maximize the 3n-evaporation channel, three decay chains of 285Fl were detected. The α-decay energy of 285Fl was measured for the first time and decay properties of its descendants 281Cn, 277Ds, 273Hs, 269Sg, and 265Rf were determined with higher accuracy. The assignment of SF events observed during the irradiation of the 240Pu target with a 250 MeV 48Ca beam to 284Fl decay is presented and discussed. The cross sections at both 48Ca energies are similar and exceed that observed in the reaction with the lighter isotope 239Pu by a factor of 10. The decay properties of the synthesized nuclei and their production cross sections indicate a rapid decrease of stability of superheavy nuclei as the neutron number decreases from the predicted magic neutron number N=184. [ABSTRACT FROM AUTHOR]

The rare β-decay channel of 6He into the α + d continuum was investigated at the REX-ISOLDE facility. Bunches of postaccelerated He6 ions were implanted into the optical time projection chamber (OTPC), where the decays with emission of charged particles were recorded. This novel technique allowed us to extend the low-energy end of the spectrum down to 150 keV in α + d center of mass, corresponding to a deuteron energy of 100 keV. The branching ratio for this process amounts to [2.78±0.07(stat)±0.17(sys)]×10-6. The shape of the spectrum is found to be in a good agreement with a three-body model, while the total intensity is about 20% larger than the predicted one. [ABSTRACT FROM AUTHOR]

Results of decay spectroscopy on nuclei in the vicinity of the doubly magic 48Ni are presented. The measurements were performed with a time projection chamber with optical readout which records tracks of ions and protons in the gaseous volume. Six decays of 48Ni, including four events of two-proton ground-state radioactivity, were recorded. An advanced reconstruction procedure yielded the 2p decay energy for 48Ni of Q2p = 1.29(4) MeV. In addition, the energy spectra of β-delayed protons emitted in the decays of 44Cr and 46Fe, as well as half-lives and branching ratios, were determined. The results were found to be consistent with the previous measurements made with Si detectors. A new proton line in the decay of 44Cr corresponding to the decay energy of 760 keV is reported. The first evidence for the β2p decay of 46Fe, based on one clear event, is shown. [ABSTRACT FROM AUTHOR]

The β decay of 124,126Ag low- and high-spin isomers into levels in 124,126Cd was investigated. We have greatly expanded the decay schemes in these nuclei including the identification of the 02+ and 0+3 states among 63 new levels in 124Cd and the identification of the 22+ state among 30 new levels in 126Cd. Several states were identified in 124Cd, which based on energy are possible multiphonon states. Based on the decay of these states, we show that states in 124Cd behave similar to lighter Cd isotopes despite the higher intruder state energies. Our 124Cd data support the conclusion that the neutron-rich Cd nuclei are not described well by an anharmonic vibrator interpretation. [ABSTRACT FROM AUTHOR]

The β-decay properties of neutron-rich 85Ga produced in proton-induced fission of 238U were studied at the Holifield Radioactive Ion Beam Facility at Oak Ridge National Laboratory. Data consisted of β - γ and β - γ - γ coincidences were collected at the Low-energy Radioactive Ion Beam Spectroscopy Station after high-resolution on-line mass separation. For the first time, the excited states in the N = 53 isotone 85Ge were established from β-delayed γ decay of 85Ga. The level scheme of the N = 52 isotone 84Ge was improved and includes now 0+, 2+, (2)+, 4+, and (0)+ states populated in the β-delayed-neutron-γ decay of 85Ga. Advanced shell-model calculations were used to analyze experimental data on 85Ge and 84Ge. [ABSTRACT FROM AUTHOR]

Studies of superheavy nuclei produced in the 249Bk + 48Ca reaction were performed using the Dubna Gas Filled Recoil Separator. The cross section for the production of 293117 and 294117 isotopes was measured at five excitation energies of the 297117 compound nucleus ranging from 30 to 48 MeV and yielding maximum values of 1.1-0.6+1.2 pb for the 3n and 2.4-1.4+3.3pb for the 4n reaction channels. Alpha emission from 281Rg competing with spontaneous fission (ɑ/SF decay probability 1:9) was observed for the first time leading to the identification of the new isotope 277Mt (TSF ~ 5 ms). The measured decay properties are in good agreement with those expected based on the properties of neighboring even-Z and odd-Z nuclei. The ɑ energies and half-lives of odd-Z isotopes observed in the 293117 and 294117 decay chains together with results obtained for lower-Z superheavy nuclei demonstrate enhanced stability with increasing neutron number toward the predicted new magic number N = 184. [ABSTRACT FROM AUTHOR]

The β-decay properties of several neutron-rich germanium and arsenic isotopes were measured at the Holifield Radioactive Ion Beam Facility at Oak Ridge National Laboratory. The measurements of almost-pure radioactive sources were enabled by the combination of ion-source chemistry and two-stage mass separation. The half-life of 86Ge (226±21 ms) was determined for the first time, while those of 84,85Ge and 84-87As were remeasured. The results are compared to theoretical predictions of the gross theory of β decay, the finite-range droplet model, and the new calculations using the energy density functional DF3a with continuum quasiparticle random-phase approximation (CQRPA). We confirm the robustness and good predictive power of the latter model for nuclei near closed shells. These DF3a+CQRPA calculations were used recently to analyze r-process isobaric abundances. [ABSTRACT FROM AUTHOR]

Two years after the discovery of element 117, we undertook a second campaign using the 249Bk + 48Ca reaction for further investigations of the production and decay properties of the isotopes of element 117 on a larger number of events. The experiments were started in the end of April 2012 and are still under way. This Letter presents the results obtained in 1200 hours of an experimental run with the beam dose of 48Ca of about 1.5 X 1019 particles. The 249Bk target was irradiated at two energies of 48Ca that correspond to the maximum probability of the reaction channels with evaporation of three and four neutrons from the excited 297117. In this experiment, two decay chains of 294117 (3M) and five decay chains of 293117 (4M) were detected. In the course of the long-term work, 249Cf--the product of decay of 249Bk (330 d)--is being accumulated in the target. Consequently, in the present experiment, we also detected a single decay of the known isotope 294118 that was produced during 2002-2005 in the reaction 249Cf(48Ca, 3M)294118. The obtained results are compared with the data from previous experiments. The experiments are carried out in the Flerov Laboratory of Nuclear Reactions, Joint Institute for Nuclear Research, using the heavy-ion cyclotron U400. [ABSTRACT FROM AUTHOR]

The decay of the extremely neutron-deficient 48Ni was studied by means of an imaging time-projection chamber, which allowed the recording of tracks of charged particles. The decays of six atoms were observed. Four of them clearly correspond to two-proton radioactivity, providing the first direct evidence for this decay mode in 48Ni. Two decays represent β-delayed proton emission. The half-life of 48Ni is determined to be T1/2 = 2.1-0.4+1.4 ms. [ABSTRACT FROM AUTHOR]

We report the results of a β-decay study of fission products 86Br, 89Kr, 89Rb, 90gsRb, 90mRb, 90Kr, 92Rb, 139Xe, and 142Cs performed with the Modular Total Absorption Spectrometer (MTAS) and on-line mass-separated ion beams. These radioactivities were assessed by the Nuclear Energy Agency as having high priority for decay heat analysis during a nuclear fuel cycle. We observe a substantial increase in β feeding to high excited states in all daughter isotopes in comparison to earlier data. This increases the average γ-ray energy emitted by the decay of fission fragments during the first 10000 s after fission of 235U and 239Pu by approximately 2% and 1%, respectively, improving agreement between results of calculations and direct observations. New MTAS results reduce the reference reactor νe flux used to analyze reactor νe interaction with detector matter. The reduction determined by the ab initio method for the four nuclear fuel components, 235U, 238U, 239Pu, and 241Pu, amounts to 0.976, 0.986, 0.983, and 0.984, respectively. [ABSTRACT FROM AUTHOR]

Background: An assessment done under the auspices of the Nuclear Energy Agency in 2007 suggested that the β decays of abundant fission products in nuclear reactors may be incomplete. Many of the nuclei are potentially affected by the so called pandemonium effect and their β - γ decay heat should be restudied using the total absorption technique. The fission products 137I and 137Xe were assigned highest priority for restudy due to their large cumulative fission branching fractions. In addition, measuring β -delayed neutron emission probabilities is challenging and any new technique for measuring the β -neutron spectrum and the β -delayed neutron emission probabilities is an important addition to nuclear physics experimental techniques. Purpose: To obtain the complete β -decay pattern of 137I and 137Xe and determine their consequences for reactor decay heat and ¯ ν e emission. Complete β -decay feeding includes ground state to ground state β feeding with no associated γ rays, ground state to excited states β transitions followed by γ transitions to the daughter nucleus ground state, and β -delayed neutron emission from the daughter nucleus in the case of 137I. Method: We measured the complete β -decay intensities of 137I and 137Xe with the Modular Total Absorption Spectrometer at Oak Ridge National Laboratory. We describe a technique for measuring the β -delayed neutron energy spectrum, which also provides a measurement of the β -neutron branching ratio, Pn. Results: We validate the current Evaluated Nuclear Structure Data File (ENSDF) evaluation of 137Xe β decay. We find that major changes to the current ENSDF assessment of 137I β -decay intensity are required. The average γ energy per β decay for 137I β decay (γ decay heat) increases by 19%, from 1050-1250 keV, which increases the average γ energy per 235 U fission by 0.11%. We measure a β -delayed neutron branching fraction for 137I β decay of 7.9 ± 0.2 (fit) ± 0.4 (sys) % and we provide a β -neutron energy spectrum. Conclusions: The Modular Total Absorption Spectrometer measurements of 137I and 137Xe demonstrate the importance of revisiting and remeasuring complex β -decaying fission products with total absorption spectroscopy. We demonstrate the ability of the Modular Total Absorption Spectrometer to measure β -delayed neutron energy spectra. [ABSTRACT FROM AUTHOR]

The β-decay properties of the very neutron-rich nucleus 85Ge, produced in the proton-induced fission of 238U, were studied at the Holifield Radioactive Ion Beam Facility at Oak Ridge National Laboratory. The level scheme of 8533As52 populated in 85Ge βγ decay was reconstructed and compared to shell-model calculations. The investigation of the systematics of low-energy levels in N = 52 isotones together with shell-model analysis allowed us to provide an estimate of the low-energy structure of the more exotic N = 52 isotone 81Cu. [ABSTRACT FROM AUTHOR]

We report total absorption spectroscopy measurements of 92Rb, 96gsY, and 142Cs β decays, which are the most important contributors to the high energy νe spectral shape in nuclear reactors. These three β decays contribute 43% of the νe flux near 5.5 MeV emitted by nuclear reactors. This νe energy is particularly interesting due to spectral features recently observed in several experiments including the Daya Bay, Double Chooz, and RENO Collaborations. Measurements were conducted at Oak Ridge National Laboratory by means of proton-induced fission of 238U with on-line mass separation of fission fragments and the Modular Total Absorption Spectrometer. We observe a β-decay pattern that is similar to recent measurements of 92Rb, with a ground-state to ground-state β feeding of 91(3)%. We verify the 96gsY ground-state to ground-state β feeding of 95.5(20)%. Our measurements substantially modify the β-decay feedings of 142Cs, reducing the β feeding to 142Ba states below 2 MeV by 32% when compared with the latest evaluations. Our results increase the discrepancy between the observed and the expected reactor νe flux between 5 and 7 MeV, the maximum excess increases from ~10% to ~12%. [ABSTRACT FROM AUTHOR]

The β-delayed neutron emission of Ga83,84 isotopes was studied using the neutron time-of-flight technique. The measured neutron energy spectra showed emission from states at excitation energies high above the neutron separation energy and previously not observed in the β decay of midmass nuclei. The large decay strength deduced from the observed intense neutron emission is a signature of Gamow-Teller transformation. This observation was interpreted as evidence for allowed β decay to Ni78 core-excited states in Ge83,84 favored by shell effects. We developed shell model calculations in the proton fpg9/2 and neutron extended fpg9/2+d5/2 valence space using realistic interactions that were used to understand measured β-decay lifetimes. We conclude that enhanced, concentrated β-decay strength for neutron-unbound states may be common for very neutron-rich nuclei. This leads to intense β-delayed high-energy neutron and strong multineutron emission probabilities that in turn affect astrophysical nucleosynthesis models. [ABSTRACT FROM AUTHOR]

The β decay of 124Cd into levels in 124In was reinvestigated at the Holifield Radioactive Ion Beam Facility. Fifty-MeV protons were bombarded on uranium targets and the induced fission products were mass separated and deposited on a moving tape in the center of an array of γ detectors. The resulting γ-γ coincidences revealed appreciable disagreement with previous work and has resulted in a revised ordering of the low-energy states in 124In. The resulting partial decay scheme has four energy levels, three of which are new. [ABSTRACT FROM AUTHOR]

The β-decay properties of the very neutron-rich 84Ge nucleus were studied at the Holifield Radioactive Ion Beam Facility at Oak Ridge National Laboratory. Several new γ-transitions and levels were added to its decay scheme and the order of the two lowest-lying levels in the daughter 84As was corrected. For the first time γ radiation following β-delayed neutron emission was observed. The shell-model calculations and apparent β transition intensities were used to guide the spin assignment to the 84As levels, in particular for the low-energy part of the level scheme. The new spin-parity (2-) proposed for the ground state of 84As is supported also by the systematics of N=51 isotones. [ABSTRACT FROM AUTHOR]

A correction to the article "New half-life measurements of the most neutron-rich arsenic and germanium isotopes," by C. Mazzocchi and colleagues that was published in the 2013 issue is presented.

The β-delayed one- and two-neutron emission probabilities (P_{1n} and P_{2n}) of 20 neutron-rich nuclei with N≥82 have been measured at the RIBF facility of the RIKEN Nishina Center. P_{1n} of ^{130,131}Ag, ^{133,134}Cd, ^{135,136}In, and ^{138,139}Sn were determined for the first time, and stringent upper limits were placed on P_{2n} for nearly all cases. β-delayed two-neutron emission (β2n) was unambiguously identified in ^{133}Cd and ^{135,136}In, and their P_{2n} were measured. Weak β2n was also detected from ^{137,138}Sn. Our results highlight the effect of the N=82 and Z=50 shell closures on β-delayed neutron emission probability and provide stringent benchmarks for newly developed macroscopic-microscopic and self-consistent global models with the inclusion of a statistical treatment of neutron and γ emission. The impact of our measurements on r-process nucleosynthesis was studied in a neutron star merger scenario. Our P_{1n} and P_{2n} have a direct impact on the odd-even staggering of the final abundance, improving the agreement between calculated and observed Solar System abundances. The odd isotope fraction of Ba in r-process-enhanced (r-II) stars is also better reproduced using our new data.

We report the results of a β-decay study of fission products ^{86}Br, ^{89}Kr, ^{89}Rb, ^{90gs}Rb, ^{90m}Rb, ^{90}Kr, ^{92}Rb, ^{139}Xe, and ^{142}Cs performed with the Modular Total Absorption Spectrometer (MTAS) and on-line mass-separated ion beams. These radioactivities were assessed by the Nuclear Energy Agency as having high priority for decay heat analysis during a nuclear fuel cycle. We observe a substantial increase in β feeding to high excited states in all daughter isotopes in comparison to earlier data. This increases the average γ-ray energy emitted by the decay of fission fragments during the first 10 000 s after fission of ^{235}U and ^{239}Pu by approximately 2% and 1%, respectively, improving agreement between results of calculations and direct observations. New MTAS results reduce the reference reactor ν[over ¯]_{e} flux used to analyze reactor ν[over ¯]_{e} interaction with detector matter. The reduction determined by the ab initio method for the four nuclear fuel components, ^{235}U, ^{238}U, ^{239}Pu, and ^{241}Pu, amounts to 0.976, 0.986, 0.983, and 0.984, respectively.

The β-delayed neutron emission of ^{83,84}Ga isotopes was studied using the neutron time-of-flight technique. The measured neutron energy spectra showed emission from states at excitation energies high above the neutron separation energy and previously not observed in the β decay of midmass nuclei. The large decay strength deduced from the observed intense neutron emission is a signature of Gamow-Teller transformation. This observation was interpreted as evidence for allowed β decay to ^{78}Ni core-excited states in ^{83,84}Ge favored by shell effects. We developed shell model calculations in the proton fpg_{9/2} and neutron extended fpg_{9/2}+d_{5/2} valence space using realistic interactions that were used to understand measured β-decay lifetimes. We conclude that enhanced, concentrated β-decay strength for neutron-unbound states may be common for very neutron-rich nuclei. This leads to intense β-delayed high-energy neutron and strong multineutron emission probabilities that in turn affect astrophysical nucleosynthesis models.

We report total absorption spectroscopy measurements of ^{92}Rb, ^{96gs}Y, and ^{142}Cs β decays, which are the most important contributors to the high energy ν[over ¯]_{e} spectral shape in nuclear reactors. These three β decays contribute 43% of the ν[over ¯]_{e} flux near 5.5 MeV emitted by nuclear reactors. This ν[over ¯]_{e} energy is particularly interesting due to spectral features recently observed in several experiments including the Daya Bay, Double Chooz, and RENO Collaborations. Measurements were conducted at Oak Ridge National Laboratory by means of proton-induced fission of ^{238}U with on-line mass separation of fission fragments and the Modular Total Absorption Spectrometer. We observe a β-decay pattern that is similar to recent measurements of ^{92}Rb, with a ground-state to ground-state β feeding of 91(3)%. We verify the ^{96gs}Y ground-state to ground-state β feeding of 95.5(20)%. Our measurements substantially modify the β-decay feedings of ^{142}Cs, reducing the β feeding to ^{142}Ba states below 2 MeV by 32% when compared with the latest evaluations. Our results increase the discrepancy between the observed and the expected reactor ν[over ¯]_{e} flux between 5 and 7 MeV, the maximum excess increases from ∼10% to ∼12%.

The superheavy element with atomic number Z=117 was produced as an evaporation residue in the (48)Ca+(249)Bk fusion reaction at the gas-filled recoil separator TASCA at GSI Darmstadt, Germany. The radioactive decay of evaporation residues and their α-decay products was studied using a detection setup that allowed measuring decays of single atomic nuclei with half-lives between sub-μs and a few days. Two decay chains comprising seven α decays and a spontaneous fission each were identified and are assigned to the isotope (294)117 and its decay products. A hitherto unknown α-decay branch in (270)Db (Z = 105) was observed, which populated the new isotope (266)Lr (Z = 103). The identification of the long-lived (T(1/2) = 1.0(-0.4)(+1.9) h) α-emitter (270)Db marks an important step towards the observation of even more long-lived nuclei of superheavy elements located on an "island of stability."