Development of a Reference Database for Beta-Delayed Neutron Emission
P. Dimitriou, I. Dillmann, B. Singh, V. Piksaikin, K. P. Rykaczewski, J. L. Tain, A. Algora, K. Banerjee, I. N. Borzov, D. Cano-Ott, S. Chiba, M. Fallot, D. Fol… 展开作者
P. Dimitriou, I. Dillmann, B. Singh, V. Piksaikin, K. P. Rykaczewski, J. L. Tain, A. Algora, K. Banerjee, I. N. Borzov, D. Cano-Ott, S. Chiba, M. Fallot, D. Foligno, R. Grzywacz, X. Huang, T. Marketin, F. Minato, G. Mukherjee, B. C. Rasco, A. Sonzogni, M. Verpelli, A. Egorov, M. Estienne, L. Giot, D. Gremyachkin, M. Madurga, E. A. McCutchan, E. Mendoza, K. V. Mitrofanov, M. Narbonne, P. Romojaro, A. Sanchez-Caballero, N. D. Scielzo
Beta-delayed neutron emission is important for nuclear structure and astrophysics as well as for reactor applications. Significant advances in nuclear experimental techniques in the past two decades have led to a wealth of new measurements that remain to be incorporated in the databases. We report on a coordinated effort to compile and evaluate all the available beta-delayed neutron emission data. The different measurement techniques have been assessed and the data have been compared with semi-microscopic and microscopic-macroscopic models. The new microscopic database has been tested against aggregate total delayed neutron yields, time-dependent group parameters in 6-and 8-group re-presentation, and aggregate delayed neutron spectra. New recommendations of macroscopic delayed-neutron data for fissile materials of interest to applications are also presented. The new Reference Database for Beta-Delayed Neutron Emission Data is available online at: http://www-nds.iaea.org/beta-delayed-neutron/database.html.
We have observed beta+-delayed alpha and p-alpha emission from the proton-rich nucleus 21Mg produced at the ISOLDE facility at CERN. The assignments were cross-checked with a time distribution analysis. This is the third identified case of beta-p-alpha emission. We discuss the systematic of beta-delayed particle emission decays, show that our observed decays fit naturally into the existing pattern, and argue that the patterns are to a large extent caused by odd-even effects.
The neutron long counter NERO was built at the National Superconducting Cyclotron Laboratory (NSCL), Michigan State University, for measuring beta-delayed neutron-emission probabilities. The detector was designed to work in conjunction with a beta-decay implantation station, so that beta decays and beta-delayed neutrons emitted from implanted nuclei can be measured simultaneously. The high efficiency of about 40%, for the range of energies of interest, along with the small background, are crucial for measuring beta-delayed neutron emission branchings for neutron-rich r-process nuclei produced …
Measurements of beta-delayed gamma-ray spectra following 14-MeV neutron-induced fissions of 232Th, 237Np, and 238U were conducted at Lawrence Berkeley National Laboratory's 88-Inch Cyclotron. Spectra were collected for times ranging from 1 minute to 14 hours after irradiation. Intensity ratios of gamma-ray lines were extracted from the data that allow identification of the fissioning isotope.
A measurement of the 20Na beta-delayed alpha spectrum with a high-granularity set-up has allowed the decay scheme to be revised on several points. Three new transitions of low intensity are found at low alpha-particle energy. An R-matrix fit of the complete spectrum gives an improved description of the decay and indicates feeding to the broad 2^+ alpha-cluster state close to 9 MeV.
Beta-delayed proton emission from $^{21}$Mg has been measured at ISOLDE, CERN, with a detection setup including particle identification capabilities. $β$-delayed protons with center of mass energies between 0.39$\,$MeV and 7.2$\,$MeV were measured and used to determine the half life of $^{21}$Mg as $118.6\pm 0.5\,$ms. From a line shape fit of the $βp$ branches we extract spectroscopic information about the resonances of $^{21}$Na. Finally an improved interpretation of the decay scheme in accordance with the results obtained in reaction studies is presented.
Excited states in 17C were investigated through the measurement of beta?-delayed neutrons and gamma rays emitted in the ? decay of 17B. In the measurement, three negative-parity states and two inconclusive states, were identified in 17C above the neutron threshold energy, and seven gamma-lines were identified in a beta?-delayed multiple neutron emission of the 17B ? decay. From these transitions, the beta?-decay scheme of 17B was determined. In the present work, the fibeta-NMR technique is combined with the ?-delayed particle measurements using a fragmentation-induced spin-polarized 17B beam. …
While the 12C(a,g)16O reaction plays a central role in nuclear astrophysics, the cross section at energies relevant to hydrostatic helium burning is too small to be directly measured in the laboratory. The beta-delayed alpha spectrum of 16N can be used to constrain the extrapolation of the E1 component of the S-factor; however, with this approach the resulting S-factor becomes strongly correlated with the assumed beta-alpha branching ratio. We have remeasured the beta-alpha branching ratio by implanting 16N ions in a segmented Si detector and counting the number of beta-alpha decays relative t…
The $^{11}$Be neutron halo nucleus appears to decay into $^{10}$Be with a rate that exceeds expectations. Neutron disappearance into dark matter, beta decay of a halo neutron, or beta-delayed proton decay have been offered as explanations. In this work we study the latter option; we carry out shell model calculations and sequential decay analysis examining the beta-delayed proton decay going through a resonance in $^{11}$B. The narrow energy window, lack of states with sufficient spectroscopic strength, overwhelming alpha decay branch, all make reconciling the observed rate with beta-delayed p…
The beta-delayed alpha-decay of 16N has been used to restrict the E1 fraction of the ground state gamma-transition in the astrophysically important 12C(alpha,gamma)16O reaction in several experiments including those performed at TRIUMF and several other laboratories. A review of the published measurements is given, and GEANT4 simulations and R-Matrix calculations are presented to further clarify the observed alpha spectra. A clear response-function, in the form of a low-energy tail from the scattering of alpha-particles in the catcher foil is observed in these simulations for any foil thicknes…
Beta-delayed proton emission from nuclides in the neighborhood of 100Sn was studied at the National Superconducting Cyclotron Laboratory. The nuclei were produced by fragmentation of a 120 MeV/nucleon 112Sn primary beam on a Be target. Beam purification was provided by the A1900 Fragment Separator and the Radio Frequency Fragment Separator. The fragments of interest were identified and their decay was studied with the NSCL Beta Counting System (BCS) in conjunction with the Segmented Germanium Array (SeGA). The nuclei 96Cd, 98Ing, 98Inm and 99In were identified as beta-delayed proton emitters, …
We report on an attempt to reproduce the observation of $β^-$-delayed proton emission from $^{11}$Be through detection of the final state nucleus $^{10}$Be with accelerator mass spectrometry. Twelve samples were collected at the ISOLDE facility at CERN at different separator settings, allowing tests of different sources of contamination to be carried out. The observed amounts of $^{10}$Be per collected $^{11}$Be rule out several contamination sources, but do not agree internally. Formation of BeH molecular ions in the ion source may explain our data, in which case an upper limit of the $β$p br…
The beta+ decay of very neutron deficient 43Cr has been studied by means of an imaging time projection chamber which allowed recording tracks of charged particles. Events of beta-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(4)%, and 0.08(3)%, respectively. The 43Cr is thus established as the second case in which the beta-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 …
The results of a study of the beta decays of three proton-rich nuclei with $T_z=\text{-}2$, namely $^{48}$Fe, $^{52}$Ni and $^{56}$Zn, produced in an experiment carried out at GANIL, are reported. In all three cases we have extracted the half-lives and the total $β$-delayed proton emission branching ratios. We have measured the individual $β$-delayed protons and $β$-delayed $γ$ rays and the branching ratios of the corresponding levels. Decay schemes have been determined for the three nuclei, and new energy levels are identified in the daughter nuclei. Competition between $β$-delayed protons an…
Beta-delayed neutron emission and $β$-delayed fission ($β$df) probabilities were calculated for heavy, neutron-rich nuclei using the Los Alamos coupled Quasi-Particle Random Phase Approximation plus Hauser-Feshbach (QRPA+HF) approach. In this model, the compound nucleus is initially populated by $β$-decay and is followed through subsequent statistical decays taking into account competition between neutrons, $γ$-rays and fission. The primary output of these calculations includes branching ratios along with neutron and $γ$-ray spectra. We find a relatively large region of heavy nuclides where th…
Background: The process of beta-delayed fission (bDF) provides a versatile tool to study low-energy fission in nuclei far away from the beta-stability line, especially for nuclei which do not fission spontaneously. Purpose: The aim of this paper is to investigate systematic trends in bDF partial half-lives. Method: A semi-phenomenological framework was developed to systematically account for the behavior of bDF partial half-lives. Results: The bDF partial half-life appears to exponentially depend on the difference between the Q value for beta decay of the parent nucleus and the fission-barrier…
Background: Measurements of $β$ decay provide important nuclear structure information that can be used to probe isospin asymmetries and inform nuclear astrophysics studies. Purpose: To measure the $β$-delayed $γ$ decay of $^{26}$P and compare the results with previous experimental results and shell-model calculations. Method: A $^{26}$P fast beam produced using nuclear fragmentation was implanted into a planar germanium detector. Its $β$-delayed $γ$-ray emission was measured with an array of 16 high-purity germanium detectors. Positrons emitted in the decay were detected in coincidence to redu…
We investigate the decay of 87Br, 88Br and 94Rb using total absorption gamma-ray spectroscopy. These important fission products are beta-delayed neutron emitters. Our data show considerable gamma-intensity, so far unobserved in high-resolution gamma-ray spectroscopy, from states at high excitation energy. We also find significant differences with the beta intensity that can be deduced from existing measurements of the beta spectrum. We evaluate the impact of the present data on reactor decay heat using summation calculations. Although the effect is relatively small it helps to reduce the discr…
The beta decay of 31Ar, produced by fragmentation of a 36Ar beam at 880 MeV/nucleon, was investigated. Identified ions of 31Ar were stopped in a gaseous time projection chamber with optical readout allowing to record decay events with emission of protons. In addition to \b{eta}-delayed emission of one and two protons we have clearly observed the beta-delayed three-proton branch. The branching ratio for this channel in 31Ar is found to be 0.07(2)%.
Beta-delayed-neutron ($β$n) spectroscopy was performed using the Beta-decay Paul Trap and an array of radiation detectors. The $β$n branching ratios and energy spectra for $^{135,136}$Sb and $^{140}$I were obtained by measuring the time of flight of recoil ions emerging from the trapped ion cloud. These nuclei are located at the edge of an isotopic region identified as having $β$n branching ratios that impact the r-process abundance pattern around the A~130 peak. For $^{135,136}$Sb and $^{140}$I, $β$n branching ratios of 14.6(11)%, 17.6(28)%, and 7.6(28)% were determined, respectively. The $β$…
$β$ decay of $^{26}$P was used to populate the astrophysically important $E_x=$5929.4(8) keV $J^π=3{^+}$ state of $^{26}$Si. Both $β$-delayed proton at 418(8) keV and gamma ray at 1742(2) keV emitted from this state were measured simultaneously for the first time with corresponding absolute intensities of 11.1(12)\% and 0.59(44)\%, respectively. Besides, shell model calculations with weakly bound effects were performed to investigate the decay properties of other resonant states and a spin-parity of $4^+$ rather than $0^+$ was favored for the $E_x=$5945.9(40) keV state. Combining the experimen…
The neutron-rich $^{11}$Li halo nucleus is unique among nuclei with known separation energies by its ability to emit a proton and a neutron in a $β$ decay process. The branching ratio towards this rare decay mode is evaluated within a three-body model for the initial bound state and with Coulomb three-body final scattering states. The branching ratio should be comprised between two extreme cases, i.e.\ a lower bound $6 \times 10^{-12}$ obtained with a pure Coulomb wave and an upper bound $5 \times 10^{-10}$ obtained with a plane wave. A simple model with modified Coulomb waves provides plausib…
The beta-strength in beta-delayed particle decays has up to now been defined in a somewhat ad hoc manner that depends on the decay mechanism. A simple, consistent definition is presented that fulfils the beta strength sum rules. Special consideration is given to the modifications needed when employing R-matrix fits to data. As an example the 11Be(beta-p) decay is investigated through simple models.
Status of delayed-neutron precursor data: Half-lives and neutron emission probabilities
本文介绍了裂变产物区（27 <= Z <= 57）的缓发中子前兆实验数据，即β衰变半衰期（T_1/2）和中子发射几率（P_n）的现状。这些数据进行了比较，两个模型的预测有很大的不同的复杂性：（一）经验Kratz-Herrmann公式（KHF）的更新，和（ii）一个统一的宏观微观模型内的准粒子随机相位近似（QRPA）。这两个模型也被用来计算迄今未知的T_1/2和P_n值，直到Z=63。建议在微观计算中进行一些可能的改进，以进一步提高这些数据在反应堆和天体物理应用中的核物理基础。
Beta delayed neutron emission of $N=84$ $^{132}$Cd
University of Tennessee（田纳西大学）；Obsidian Research（黑曜石研究公司）；University of Notre Dame（圣母大学）；Los Alamos National Laboratory（洛斯阿拉莫斯国家实验室）；University of York（约克大学）；INFN, Sezione di Milano（意大利国家核物理研究所米兰分部）；CERN（欧洲核子研究中心）；“Horia Hulubei” National Institute of Physics and Nuclear Engineering（霍里亚·胡卢贝伊国家物理与核工程研究所）；Institute for Nuclear Research and Nuclear Energy, BAS（保加利亚科学院核研究与核能研究所）；K.U. Leuven（荷语鲁汶大学）；Universidad Complutense de Madrid（马德里康普顿斯大学）
A multi-hit capacity setup was used to study the decay of the dripline nucleus 31Ar, produced at the ISOLDE facility at CERN. A spectroscopic analysis of the beta-delayed three-proton decay of 31Ar is presented for the first time together with a quantitative analysis of the beta-delayed two-proton-gamma-decay. A new method for determination of the spin of low-lying levels in the beta-proton-daughter 30S using proton-proton angular correlations is presented and used for the level at 5.2 MeV, which is found to be either a 3+ or 4+ level, with the data pointing towards the 3+. The half-life of 31…
We have observed beta-delayed proton emission from the neutron-rich nucleus 11Be by analysing a sample collected at the ISOLDE facility at CERN with accelerator mass spectrometry (AMS). With a branching ratio of (8.4 +- 0.6) 10^{-6} the strength of this decay mode, as measured by the B(GT)-value, is unexpectedly high. The result is discussed within a simple single-particle model and could be interpreted as a quasi-free decay of the 11Be halo neutron into a single-proton state.
In $β$-decay studies the determination of the decay probability to the ground state of the daughter nucleus often suffers from large systematic errors. The difficulty of the measurement is related to the absence of associated delayed $γ$-ray emission. In this work we revisit the $4πγ-β$ method proposed by Greenwood and collaborators in the 1990s, which has the potential to overcome some of the experimental difficulties. Our interest is driven by the need to determine accurately the $β$-intensity distributions of fission products that contribute significantly to the reactor decay heat and to th…
We report here the results of a study of the $β$ decay of the proton-rich Ge isotopes, $^{60}$Ge and $^{62}$Ge, produced in an experiment at the RIKEN Nishina Center. We have improved our knowledge of the half-lives of $^{62}$Ge (73.5(1) ms), $^{60}$Ge (25.0(3) ms) and its daughter nucleus, $^{60}$Ga (69.4(2) ms). We measured individual $β$-delayed proton and $γ$ emissions and their related branching ratios. Decay schemes and absolute Fermi and Gamow-Teller transition strengths have been determined. The mass excesses of the nuclei under study have been deduced. A total $β$-delayed proton-emiss…
Impact of newly measured $β$\nobreakdash-delayed neutron emitters around \myisoSimp{78}{Ni} on light element nucleosynthesis in the neutrino-wind following a neutron star merger
We study for the first time the internal structure of 140Te through the beta-delayed gamma-ray spectroscopy of 140Sb. The very neutron-rich 140Sb, Z = 51 and N = 89, ions were produced by the in-flight fission of 238U beam on a 9Be target at 345 MeV per nucleon at the Radioactive Ion Beam Factory, RIKEN. The half-life and spin-parity of 140Sb are reported as 124(30) ms and (4-), respectively. In addition to the excited states of 140Te produced by the beta-decay branch, the beta-delayed one-neutron and two-neutron emission branches were also established. By identifying the first 2+ and 4+ excit…
In this review we will present the results of recent beta-decay studies using the total absorption technique that cover topics of interest for applications, nuclear structure and astrophysics. The decays studied were selected primarily because they have a large impact on the prediction of a) the decay heat in reactors, important for the safety of present and future reactors and b) the reactor electron antineutrino spectrum, of interest for particle/nuclear physics and reactor monitoring. For these studies the total absorption technique was chosen, since it is the only method that allows one to…
A role of β-delayed neutron emission and fission in r-process nucleosynthesis attracts a high interest. Although the number of study on them covering r-process nuclei is increasing recently, uncertainties of β-delayed neutron and fission are still large for r-process simulations. Our purpose is to make a new database on β-delayed neutron emission and fission rates. To this end, the data that are not investigated experimentally have to be predicted. Microscopic theoretical approaches based on a nuclear energy density functional and statistical models are one of the competent tools for the predi…
Beta-delayed proton emission from the neutron halo ground state of $^{11}$Be raised much attention due to the unusually high decay rate. It was argued that this may be due to the existence of a resonance just above the proton decay threshold. In this Letter, we use the lenses of real-energy continuum shell model to describe several observables including the Gamow-Teller rates for the $β^-$-delayed $α$ and proton decays, and argue that, within our model, the large $β^-{\rm p}$ branching ratio cannot be reconciled with other data.
We argue that conclusions of [PRL 123, 082501 (2019)] are incorrect. The authors present the direct observation of beta-delayed proton emission in the beta decay of 11Be. From the determined branching ratio for this process and from the energy spectrum of emitted protons the existence of a so far unobserved narrow resonance in 11Be was deduced. The given beta strength for the transition to this state is however wrong. In addition, we show that the combination of peak position and branching ratio is in strong disagreement with models considered by the authors. Furthermore, we identify several d…
In this work, the large-scale shell-model calculations for $β$-decay properties have been done. The $β$-delayed $γ$-ray spectroscopy has been performed recently at ILL, Grenoble [M. Si \textit{et al.}, Phys. Rev. C {\bf 106}, 014302 (2022)] to study $β$-decay properties corresponding to $^{137}$Te (($7/2^-))$ $\rightarrow$ $^{137}$I ($J_f$) transitions. We have done a systematic shell-model study for nuclear structure properties and compared the obtained results with the experimental data. Finally, the $β$-decay properties such as the $\log ft$ values and average shape factors have been report…
We calculate the rate of the rare decay $^{11}\text{Be}$ into $^{10}\text{Be} + p +e^- + \barν_e$ using Halo effective field theory, thereby describing the process of beta-delayed proton emission. We assume a shallow $1/2^+$ resonance in the $^{10}\text{Be}-p$ system with an energy consistent with a recent experiment by Ayyad et al. and obtain $b_p = 4.9_{-2.9}^{+5.6}\text{(exp.)}_{-0.8}^{+4.0}\text{(theo.)} \times 10^{-6}$ for the branching ratio of this decay, predicting a resonance width of $Γ_R = (9.0^{+4.8}_{-3.3}\text{(exp.)}^{+5.3}_{-2.2}\text{(theo.)})~\text{keV}$. Our calculation show…
We analyze within a nuclear database framework the shoulder observed in the antineutrino spectra in current reactor experiments. We find that the ENDF/B-VII.1 database predicts that the antineutrino shoulder arises from an analogous shoulder in the aggregate fission beta spectra. In contrast, the JEFF-3.1.1 database does not predict a shoulder for two out of three of the modern reactor neutrino experiments, and the shoulder that is predicted by JEFF-3.1.1 arises from $^{238}$U. We consider several possible origins of the shoulder, and find possible explanations. For example, there could be a p…
The Indian Scintillator Matrix for Reactor Anti-Neutrino detection - ISMRAN experiment aims to detect electron anti-neutrinos ($\barν_e$) emitted from a reactor via inverse beta decay reaction (IBD). The setup, consisting of 1 ton segmented Gadolinium foil wrapped plastic scintillator array, is planned for remote reactor monitoring and sterile neutrino search. The detection of prompt positron and delayed neutron from IBD will provide the signature of $\barν_e$ event in ISMRAN. The number of segments with energy deposit ($\mathrm{N_{bars}}$) and sum total of these deposited energies are used as…
Beta-delayed proton emission may occur at very low rates in the decays of the light nuclei $^{11}$Be and $^8$B. This paper explores the potential physical significance of such decays, estimates their rates and reports on first attempts to detect them: an experiment at ISOLDE/CERN gives a branching ratio for $^{11}$Be of $(2.5 \pm 2.5) \cdot 10^{-6}$ and an experiment at JYFL a 95% confidence upper limit of $2.6 \cdot 10^{-5}$ for $^8$B.
