Search

We present two results of a search for MeV-scale neutrino and anti-neutrino events correlated with gravitational wave events/candidates and large solar flares with KamLAND. The KamLAND detector is a large-volume neutrino detector using liquid scintillator, which is located at 1 km underground under the top of Mt. Ikenoyama in Kamioka, Japan. KamLAND has multiple reaction channels to detect neutrinos. Electron antineutrino can be detected via inverse-beta decay with 1.8 MeV neutrino energy threshold. All flavors of neutrinos can be detected via neutrino-electron scattering without neutrino energy threshold. KamLAND has continued the neutrino observation since 2002 March. We use the data set of 60 gravitational waves provided by the LIGO/Virgo collaboration during their second and third observing runs and search for coincident electron antineutrino events in KamLAND. We find no significant coincident signals within a ±500 s timing window from each gravitational wave and present 90% C.L. upper limits on the electron antineutrino fluence between 108–1013 cm−2 for neutrino energies of 1.8–111 MeV. For a solar-flare neutrino search at KamLAND, we determine the timing window using the solar X-ray data set provided by the GOES satellite series from 2002 to 2019 and search for the excess of coincident event rate on the all-flavor neutrinos. We find no significant event rate excess in the flare time windows and get 90% C.L. upper limits on the fluence of neutrinos of all flavors (electron anti-neutrinos) between 1010–1013 cm−2 (108–1013 cm−2) for neutrino energies in the energy range of 0.4–35 MeV.

The low-lying dipole strength of the deformed nucleus 156Gd was investigated in the energy region from 3.1 MeV to 6.2 MeV using the method of nuclear resonance fluorescence (NRF). The NRF experiments were performed at the Darmstadt High Intensity Photon Setup (DHIPS) at Technische Universitat Darmstadt using unpolarized continuous-energy bremsstrahlung and at the High-Intensity γ-ray Source (HIγS) at Duke University using quasi-monoenergetic and linearly-polarized photon beams. The combination of both experiments allows to separate electric and magnetic contributions and to determine absolute transition strengths for individual excited states as well as averaged quantities over narrow excitation energy regions. The investigated energy regions cover the region of the scissors mode as well as the low-energy part of the Pygmy Dipole Resonance. This is the first experiment where both of these excitation modes as well as the region in between has been successfully studied in a deformed heavy nucleus using the NRF method.

For the first time the de-excitation cross section of the isomeric-state nuclide 180 m Ta has been measured with mono-energetic photon beams in the 1.56 MeV to 3.70 MeV energy range. The measurement of this inelastic scattering cross section on nature’s rarest isotope was performed at eight energies at the High-Intensity Gamma-Ray Source Facility with natural tantalum targets. After irradiation for typically 20 h with photon fluxes ranging from 0 . 3 × 1 0 7 γ /( cm 2 × s) to 3 . 2 × 1 0 7 γ /( cm 2 × s), the 180 m Ta de-excitation cross section was obtained from the yield of the K α 1 and K α 2 X rays of 180 m Hf at 55.79 keV and 54.61 keV, respectively, produced after electron capture on the unstable 180 m Ta ground state. The cross-section values found vary between ( 2 . 0 ± 0 . 7 ) mb and ( 4 . 7 ± 1 . 5 ) mb, providing a very large cross section for the de-excitation of 180 m Ta. Extensive tests were performed to check on the reliability of the present data. The effect of bremsstrahlung photons of higher energy than the mono-energetic beam was carefully studied and corrected for. It was found that even a very small contamination of the mono-energetic photon beam by bremsstrahlung photons with E γ > 7 . 6 MeV can provide a sizable yield of 180 m Hf X rays via the reaction 181 Ta ( γ , n ) 180 Ta, if a natural tantalum target is used, which contain four orders of magnitude more 181 Ta nuclei than 180 m Ta nuclei available for the 180 m Ta ( γ , γ ′ ) 180 Ta reaction of interest.

Most theoretical approaches used in nuclear astrophysics to model the nucleosynthesis of heavy elements incorporate the so-called statistical model in order to describe the excitation and decay properties of atomic nuclei. One of the basic assumptions of this model is the validity of the Brink–Axel hypothesis and the related concept of so-called photon strength functions to describe γ-ray transition probabilities. We present a novel experimental approach that allows for the first time to experimentally determine the photon strength function simultaneously in two independent ways by a unique combination of quasi-monochromatic photon beams and a newly implemented γ–γ coincidence setup. This technique does not assume a priori the validity of the Brink–Axel hypothesis and sets a benchmark in terms of the detection sensitivity for measuring decay properties of photo-excited states below the neutron separation energy. The data for the spherical off-shell nucleus $^{128}$Te were obtained for γ-ray beam-energy settings between 3 MeV and 9 MeV in steps of 130 keV for the lower beam energies and in steps of up to 280 keV for the highest beam settings. We present a quantitative analysis on the consistency of the derived photon strength function with the Brink–Axel hypothesis. The data clearly demonstrate a discrepancy of up to a factor of two between the photon strength functions extracted from the photoabsorption and photon emission process, respectively. In addition, we observe that the photon strength functions are not independent of the excitation energy, as usually assumed. Thus, we conclude, that the Brink–Axel hypothesis is not strictly fulfilled in the excitation-energy region below the neutron separation threshold (Sn=8.78MeV) for the studied case of $^{128}$Te.

The $E2/M1$ multipole mixing ratio of the ${1}_{\text{sc}}^{+}\ensuremath{\rightarrow}{2}_{1}^{+}\phantom{\rule{4pt}{0ex}}\ensuremath{\gamma}$-ray transition and therefore the $F$-vector $E2$ decay of the scissors mode of the shape-phase transitional nucleus $^{152}\mathrm{Sm}$ have been measured with the nuclear resonance fluorescence method at the High-Intensity $\ensuremath{\gamma}$-ray Source ($\mathrm{HI}\ensuremath{\gamma}\mathrm{S}$). Furthermore, parity quantum numbers of several dipole-excited states have been remeasured, making use of the polarized $\ensuremath{\gamma}$-ray beam at $\mathrm{HI}\ensuremath{\gamma}\mathrm{S}$, and partially reassigned. The new data enable an unambiguous determination of the proton and neutron effective boson quadrupole charges within the proton-neutron interacting boson model. With the well-constrained parameter set, a new mixed-symmetry state is predicted.

Gamma-ray production cross-section data have been obtained for the inelastic neutron scattering reactions $^{126,128,130}\mathrm{Te}(n,{n}^{\ensuremath{'}}\ensuremath{\gamma})$ at five neutron energies between 3.6 and 10 MeV. We report data for the $\ensuremath{\gamma}$-ray energy region relevant to $0\ensuremath{\nu}\ensuremath{\beta}\ensuremath{\beta}$ decay of $^{130}\mathrm{Te}$ with a ${Q}_{\ensuremath{\beta}\ensuremath{\beta}}$ value of 2527.515 keV, assuming natural-abundance tellurium, as used at CUORE and $\mathrm{SNO}+$. The natural abundance of $^{130}\mathrm{Te}$, $^{128}\mathrm{Te}$, and $^{126}\mathrm{Te}$ is 34%, 32%, and 19%, respectively. For CUORE the $\ensuremath{\gamma}$-ray cascades from the excited state in $^{130}\mathrm{Te}$ at 2527.06 keV and in $^{126}\mathrm{Te}$ at 2533.85 keV are of concern. For $\mathrm{SNO}+$, accounting for its inferior energy resolution, an additional four levels are important in $^{130}\mathrm{Te}$, an additional nine levels in $^{128}\mathrm{Te}$, and an additional eight levels in $^{126}\mathrm{Te}$. Of these, we report neutron-induced $\ensuremath{\gamma}$-ray production cross sections for the strongest transitions: the 2581.15 keV level in $^{130}\mathrm{Te}$, the 2494.20, 2508.06, and 2630.14 keV levels in $^{128}\mathrm{Te}$, and the 2496.83 and 2585.46 keV level in $^{126}\mathrm{Te}$. The largest cross-section values were found for cascade $\ensuremath{\gamma}$-ray transitions to the ground state, while direct transitions to the ground state are very weak and were not observed in the present work. Both the CUORE and $\mathrm{SNO}+$ detectors, however, may not be able to distinguish between cascade transitions and direct transitions to the ground state, making the neutron-induced excitation of the 2527.06 keV state of $^{130}\mathrm{Te}$ in particular a potential problem for $0\ensuremath{\nu}\ensuremath{\beta}\ensuremath{\beta}$ decay searches of $^{130}\mathrm{Te}$, because it matches its ${Q}_{\ensuremath{\beta}\ensuremath{\beta}}$ value.

Background: Numerous studies of the ground-state decay of the pygmy dipole resonance (PDR) have been carried out in the past. However, data on the decay of the PDR to low-lying excited states is still very scarce due to limitations of the sensitivity to weak branching transitions of experimental setups.Purpose: We present a detailed examination of the low-energy dipole response of $^{128}\mathrm{Te}$ and $^{130}\mathrm{Te}$ below their neutron separation thresholds of 8.8 and 8.5 MeV, respectively.Methods: Photonuclear reactions with the subsequent $\ensuremath{\gamma}$-ray spectroscopy of the decay channel with continuous-energy bremsstrahlung at varying endpoint energies and linearly polarized quasimonochromatic $\ensuremath{\gamma}$-ray beams with energies ranging from 2.7 to 8.9 MeV in steps of roughly 250 keV were used for probing the decay behavior of the low-energy dipole response in $^{128}\mathrm{Te}$ and $^{130}\mathrm{Te}$. In addition, $(\stackrel{P\vec}{\ensuremath{\gamma}},{\ensuremath{\gamma}}^{\ensuremath{'}}{\ensuremath{\gamma}}^{\ensuremath{'}\ensuremath{'}})$ reactions were used to study the population of low-lying states of $^{128}\mathrm{Te}$.Results: Spin-parity quantum numbers and reduced transition probabilities are determined for individual photo-excited states. The analysis of average decay properties for nuclear levels in narrow excitation-energy bins enable the extraction of photoabsorption cross sections, average branching ratios to the ${2}_{1}^{+}$ state, and the distinction between $E1$ and $M1$ transitions to the ground state and to the ${2}_{1}^{+}$ state accounting for resolved and unresolved transitions.Conclusions: Above 5 MeV, the experimental data are in reasonable agreement to calculations within the quasiparticle phonon model. The major fraction of the ground-state decay channel is due to $E1$ transitions, while less than $5--10$% stem from $M1$ transitions. Furthermore, first direct experimental evidence is provided that the population of the ${2}_{1}^{+}$ state of $^{128}\mathrm{Te}$ via primary $\ensuremath{\gamma}$-ray transitions from excited states in the PDR region from 5 to 9 MeV is dominated by $E1$ transitions of ${1}^{\ensuremath{-}}$ states.

The KamLAND-Zen 800 experiment is searching for the neutrinoless double-beta decay of $^{136}$Xe by using $^{136}$Xe-loaded liquid scintillator. The liquid scintillator is enclosed inside a balloon made of thin, transparent, low-radioactivity film that we call Inner Balloon (IB). The IB, apart from guaranteeing the liquid containment, also allows to minimize the background from cosmogenic muon-spallation products and $^{8}$B solar neutrinos. Indeed these events could contribute to the total counts in the region of interest around the Q-value of the double-beta decay of $^{136}$Xe. In this paper, we present an overview of the IB and describe the various steps of its commissioning minimizing the radioactive contaminations, from the material selection, to the fabrication of the balloon and its installation inside the KamLAND detector. Finally, we show the impact of the IB on the KamLAND background as measured by the KamLAND detector itself., 23 pages, 16 figures, to be submitted to JINST

The $^{169}\mathrm{Tm}(n,2n)^{168}\mathrm{Tm}$ and $^{169}\mathrm{Tm}(n,3n)^{167}\mathrm{Tm}$ cross sections have been measured in the neutron energy range between 15 and 21 MeV using the $^{3}\mathrm{H}(d,n)^{4}\mathrm{He}$ neutron source reaction. The $^{169}\mathrm{Tm}(n,3n)^{167}\mathrm{Tm}$ data are intended to provide an accurate database for interpreting so-called reaction-in-flight neutron yields, which provide a sensitive tool for studying properties of the deuterium-tritium plasma created in inertial confinement fusion laser shots at the National Ignition Facility at Lawrence Livermore National Laboratory. The data are compared to previous data and evaluations for the reaction studied and are found to be in good agreement with the ENDF/B-VIII.0 evaluation, although small adjustments are necessary for the $^{169}\mathrm{Tm}(n,3n)^{167}\mathrm{Tm}$ reaction. For the first time in any $(n,2n)$ cross-section measurements to date, a comprehensive data set ranging from threshold to 21 MeV has been obtained by the same group.

Isomeric fission products, such as ${}^{134m}\mathrm{Te}$ (${T}_{1/2}=164$ ns) and ${}^{136m}\mathrm{Xe}$ (${T}_{1/2}=2.95\phantom{\rule{0.2em}{0ex}}\ensuremath{\mu}\mathrm{s}$), are proposed as a signature of special nuclear materials in active interrogation applications. To test this conjecture, monoenergetic 9, 11, and 13 MeV photons from the $\mathrm{HI}\ensuremath{\gamma}\mathrm{S}$ facility are used to induce fission of ${}^{235}\mathrm{U}$, ${}^{238}\mathrm{U}$, and ${}^{239}\mathrm{Pu}$ targets. The de-excitation $\ensuremath{\gamma}$ rays of the isomers are measured using time-gated spectroscopy with high-purity germanium detectors. The ${}^{134m}\mathrm{Te}$ and ${}^{136m}\mathrm{Xe}$ isomers are detected and identified by the energy and decay half-life of their characteristic $\ensuremath{\gamma}$-ray transitions. The ratio of yields for these two signature $\ensuremath{\gamma}$ rays, corresponding to ${}^{134m}\mathrm{Te}/{(}^{136m}\mathrm{Xe}{+}^{136}\mathrm{I})$, is found to be strongly correlated with the identity of the fissioning nuclei. These results show that fission-product isomers may be used in active interrogation to detect and identify special nuclear materials, even providing information on the isotopic enrichment. The feasibility of an active interrogation scenario using a bremsstrahlung beam is discussed.

The dipole strength of the $N=28$ closed-shell nuclide $^{54}\mathrm{Fe}$ was studied in photon-scattering experiments using bremsstrahlung produced with electron beams of kinetic energies of 7.5 and 13.9 MeV at the $\ensuremath{\gamma}\mathrm{ELBE}$ facility as well as using quasimonoenergetic and linearly polarized photon beams of 26 different energies within the range from 5.5 to 11.4 MeV at the $\mathrm{HI}\ensuremath{\gamma}\mathrm{S}$ facility. About 100 $J=1$ states were newly identified, out of them 19 with ${1}^{+}$ and 30 with ${1}^{\ensuremath{-}}$ assignments. The quasicontinuum of unresolved transitions was included in the analysis of the spectra and the intensities of branching transitions were estimated on the basis of simulations of statistical $\ensuremath{\gamma}$-ray cascades. As a result, the photoabsorption cross section up to the neutron-separation energy was determined and compared with predictions of the statistical reaction model. The experimental $M1$ strengths from resolved ${1}^{+}$ states are compared with results of large-scale shell-model calculations.

Background: Little data is available for the pygmy dipole resonance (PDR) in axially deformed nuclei. Photon-scattering experiments are complicated by high level densities in the PDR region and the small energy difference of transitions to the ground state and to excited states.Purpose: We report on an experimental study of the low-energy dipole strength distribution of the well-deformed nucleus $^{164}\mathrm{Dy}$ between 4.0--7.7 MeV.Methods: The low-lying photoresponse of $^{164}\mathrm{Dy}$ has been investigated using the method of nuclear resonance fluorescence using a quasimonochromatic linearly polarized $\ensuremath{\gamma}$-ray beam in the energy range of 4.0--7.7 MeV in steps of 0.2 MeV.Results: For excitation energies between 4 MeV and 5 MeV, sufficiently low level densities allow for the identification of individual states, including level energies, reduced transition widths and branching ratios. Energy-averaged mean decay branching ratios, mean population ratios and partial absorption cross sections were determined above 5 MeV up to the neutron-separation threshold at 7.7 MeV. A Lorentzian-shaped enhancement of the partial photo absorption cross section followed by decays back to the ground-state band is found at 6.10(5) MeV with a width of 0.77(23) MeV. A comparison with results from complementary measurements is performed using the framework of the statistical model.Conclusions: The experimental results for the mean population ratios deviate systematically from the statistical model simulation by 30(6)%. However, they are in agreement within one standard deviation of the simulation.

The size of a $\mathrm{\ensuremath{\Delta}}K=0$ $M1$ excitation strength has been determined for the first time in a predominantly axially deformed even-even nucleus. It has been obtained from the observation of a rare $K$-mixing situation between two close-lying ${J}^{\ensuremath{\pi}}={1}^{+}$ states of the nucleus $^{164}\mathrm{Dy}$ with components characterized by intrinsic projection quantum numbers $K=0$ and $K=1$. Nuclear resonance fluorescence induced by quasimonochromatic linearly polarized $\ensuremath{\gamma}$-ray beams provided evidence for $K$ mixing of the ${1}^{+}$ states at 3159.1(3) and 3173.6(3) keV in excitation energy from their $\ensuremath{\gamma}$-decay branching ratios into the ground-state band. The $\mathrm{\ensuremath{\Delta}}K=0$ transition strength of $B(M1;{0}_{1}^{+}\ensuremath{\rightarrow}{1}_{K=0}^{+})=0.008(1){\ensuremath{\mu}}_{N}^{2}$ was inferred from a mixing analysis of their $M1$ transition rates into the ground-state band. It is in agreement with predictions from the quasiparticle phonon nuclear model. This determination represents first experimental information on the $M1$ excitation strength of a nuclear quantum state with a negative $\mathcal{R}$-symmetry quantum number.

The European physical journal / A 56(4), 105 (2020). doi:10.1140/epja/s10050-020-00118-8, Published by Springer, Heidelberg

New measurements of the neutron-neutron quasifree scattering cross section in neutron-deuteron breakup at an incident neutron energy of 10.0 MeV are reported. The experiment setup was optimized to evaluate the technique for determining the integrated beam-target luminosity in neutron-neutron coincidence cross-section measurements in neutron-deuteron breakup. The measurements were carried out with a systematic uncertainty of $\pm 5.6 \%$. Our data are in agreement with theoretical calculations performed using the CD-Bonn nucleon-nucleon potential in the Faddeev formalism. The measured integrated cross section over the quasifree peak is $20.5 \pm 0.5 \text{(stat)} \pm 1.1 \text{(sys)}$ mb/sr$^2$ in comparison with the theory prediction of 20.1 mb/sr$^{2}$. These results validate our technique for determining the beam-target luminosity in neutron-deuteron breakup measurements., 23 pages, 12 figures, published in Physical Review C

Experiments are underway at the Triangle Universities Nuclear Laboratory (TUNL) that provide data for evaluating calculations based on low-energy QCD theories, e.g., effective field theory formulations of two-nucleon and three-nucleon interactions, chiral-perturbation theory, and Lattice QCD. Few-nucleon reaction measurements are carried out using the monoenergetic polarized gamma-ray beam at the High Intensity Gamma-ray Source (HI\(\gamma \)S) and the neutron beams at the tandem laboratory. Experiments in nucleon structure are performed at HI\(\gamma \)S. In this paper we present the status of recent few-nucleon experiments that measure the cross sections for neutron-neutron quasifree scattering in neutron-deuteron breakup and for photodisintegration of \(^3\)He.

Fission product yields (FPY) are one of the most fundamental quantities that can be measured for a fissioning nucleus and are important for basic and applied nuclear physics. Recent measurements using mono-energetic and pulsed neutron beams generated using Triangle Universities Nuclear Laboratory’s tandem accelerator and employing a dual fission chamber setup have produced self-consistent, high-precision data critical for testing fission models for the neutron-induced fission of 235,238U and 239Pu between neutron energies of 0.5 to 15.0 MeV. These data have elucidated a low-energy dependence of FPY for several fission products using irradiations of varying lengths and neutron energies. This paper will discuss new measurements just beginning utilizing a RApid Belt-driven Irradiated Target Transfer System (RABITTS) to measure shorterlived fission products and the time dependence of fission yields, expanding the measurements from cumulative towards independent fission yields. The uniqueness of these FPY data and the impact on the development of fission theory will be discussed.

The Bohr hypothesis, one of the most fundamental assumptions in nuclear fission theory, states that the decay of a compound nucleus with a given excitation energy, spin and parity is independent of its formation. Using fission product yields (FPYs) as a sensitive probe, we have performed new high precision test of the combined effects of the entrance channel, spin and parity on the fission process. Two different reactions were used in a self-consistent manner to produce a compound 240Pu nucleus with the same excitation energy: neutron induced fission of 239Pu at En = 4.6 MeV and photon-induced fission of 240Pu at Eγ = 11.2 MeV. The FPYs from these two reactions were measured using quasimonoenergetic neutron beams from the TUNL's FN tandem Van de Graaff accelerator and quasimonenergetic photon beams from the High Intensity γ-ray Source (HlγS) facility. The first results comparing the FPYs from these two reactions will be presented. Implications for validating the Bohr hypothesis will be discussed.

Fission product yields (FPYs) are a uniquely sensitive probe of the fission process, with well established dependence on the species of nucleus undergoing fission, its excitation energy and spin. Thus FPYs are well suited for testing Bohr’s hypothesis in the context of nuclear fission, which states that the decay of a compound nucleus with a given excitation energy, spin and parity is independent of its formation. Using FPYs, we have performed a new highprecision test of the combined effects of the entrance channel, spin and parity on the fission process from two of the most commonly used particles to induce fission neutrons and photons. The 239 Pu(n,f) reaction at En = 4.6 MeV and the 240 Pu(γ,f) reaction at Eγ = 11.2 MeV were used to produce a 240 Pu∗ compound nucleus with the same excitation energy. The FPYs from these two reactions were measured using quasimonoenergetic neutron beams from the TUNL’s FN tandem Van de Graaff accelerator and quasimonenergetic photon beams from the High Intensity γ-ray Source (HIγS) facility. The FPYs from these two reactions are compared quantitatively for the first time.

Journal of physics / G 49(1), 010502 (2022). doi:10.1088/1361-6471/ac2827, Published by IOP Publ., Bristol

International audience; The nature of the high-lying final levels of the 96Ygsβ decay, one of the three most important contributors to the high-energy reactor antineutrino spectrum, has been investigated in high-resolution γ-ray spectroscopy following the β decay as well as in a campaign of inelastic photon scattering experiments. The comprehensive approach establishes 1− levels associated with the Pygmy Dipole Resonance as high-lying final levels in the β decay. Branching ratios extracted from β decay complement photon scattering and allow the absolute E1 excitation strength to be determined for levels populated in both reactions. The combined data represents a comprehensive approach to the wavefunction of the 1− levels below the Qβ value, which are investigated in the Quasiparticle Phonon Model. The calculations reveal that the components populated in β decay contribute only with small amplitudes to the complex wavefunction of these 1− levels. A comparison of the β decay results to data from total absorption γ-ray spectroscopy demonstrates a good agreement between both measurements.

A high-resolution study of the electromagnetic response of 206Pb below the neutron separation energy is performed using a γ→,γ′) experiment at the HIγ→S facility. Nuclear resonance fluorescence with 100% linearly polarized photon beams is used to measure spins, parities, branching ratios, and decay widths of excited states in 206Pb from 4.9 to 8.1 MeV. The extracted ΣB(E1)↑ and ΣB(M1)↑ values for the total electric and magnetic dipole strength below the neutron separation energy are 0.9±0.2 e2fm2 and 8.3±2.0μN 2, respectively. These measurements are found to be in very good agreement with the predictions from an energy-density functional (EDF) plus quasiparticle phonon model (QPM). Such a detailed theoretical analysis allows to separate the pygmy dipole resonance from both the tail of the giant dipole resonance and multi-phonon excitations. Combined with earlier photonuclear experiments above the neutron separation energy, one extracts a value for the electric dipole polarizability of 206Pb of αD=122±10 mb/MeV. When compared to predictions from both the EDF+QPM and accurately calibrated relativistic EDFs, one deduces a range for the neutron-skin thickness of Rskin 206=0.12–0.19 fm and a corresponding range for the slope of the symmetry energy of L=48–60 MeV. This newly obtained information is also used to estimate the Maxwellian-averaged radiative cross section Pb205(n,γ)Pb206 at 30 keV to be σ=130±25 mb. The astrophysical impact of this measurement—on both the s-process in stellar nucleosynthesis and on the equation of state of neutron-rich matter—is discussed., SCOPUS: ar.j, info:eu-repo/semantics/published

Photofission cross-section ratios of 235U and 238 U have been measured using monoenergetic photon beams at the HI γS facility of TUNL. These measurements have been performed in small energy steps between 9.0 and 16.6 MeV using a dual-fission ionization chamber . Measured cross-section ratios are compared with the previous experimental data as well as with the recent evaluated nuclear data library ENDF.

The excitation of atomic nuclei via magnetic dipole transitions is closely related to the inelastic neutral-current neutrino-nucleus (NC-$\ensuremath{\nu}\mathrm{A}$) scattering process due to the similarity of the transition operators. NC-$\ensuremath{\nu}\mathrm{A}$-scattering serves for the detection of supernova neutrinos and poses a significant source of background in modern liquid-argon based high-energy neutrino detection experiments. To enable tests of the reliability of predictions for neutrino-nucleus scattering, the magnetic dipole response of $^{40}\mathrm{Ar}$ below 7.7 MeV was characterized in a nuclear resonance fluorescence experiment using quasimonoenergetic $\ensuremath{\gamma}$-ray beams. The linear polarization of the beams allowed for assignments of electric or magnetic character to previously known dipole excitations. A total magnetic dipole strength of $0.{36}_{\ensuremath{-}0.05}^{+0.04}\phantom{\rule{4pt}{0ex}}{\ensuremath{\mu}}_{N}^{2}$ was identified in the energy range of the present experiment. Combined with data from previous measurements, the full magnetic dipole strength of $^{40}\mathrm{Ar}$ below the neutron separation threshold was investigated. Due to the low background in the energy range within the bandwidth of the $\ensuremath{\gamma}$-ray beams, the previous sensitivity limit was improved. A large-scale nuclear shell model calculation in the $sd\text{\ensuremath{-}}fp$ space satisfactorily agrees with the data in terms of excitation energies and strengths of the observed ${1}^{+}$ states.

Background: The low-lying electric dipole strength provides insights into the parameters of the nuclear equation of state via its connection with the pygmy dipole resonance and nuclear neutron skin thickness.Purpose: The aim was to complement the systematic of the pygmy dipole resonance and first study its behavior across the $N=28$ neutron shell closure.Methods: Photon-scattering cross sections of states of $^{50,54}\mathrm{Cr}$ were measured up to an excitation energy of 9.7 MeV via the nuclear resonance fluorescence method using $\ensuremath{\gamma}$-ray beams from bremsstrahlung and Compton backscattering.Results: Transitions strengths, spin and parity quantum number, and average branching ratios for 55 excited states, 44 of which were observed for the first time, were determined. The comparison between the total observed strengths of the isotopes $^{50,52,54}\mathrm{Cr}$ shows a significant increase above the shell closure.Conclusions: The evolution of the pygmy dipole resonance is heavily influenced by the shell structure.

We present a precision analysis of the ^{136}Xe two-neutrino ββ electron spectrum above 0.8 MeV, based on high-statistics data obtained with the KamLAND-Zen experiment. An improved formalism for the two-neutrino ββ rate allows us to measure the ratio of the leading and subleading 2νββ nuclear matrix elements (NMEs), ξ_{31}^{2ν}=-0.26_{-0.25}^{+0.31}. Theoretical predictions from the nuclear shell model and the majority of the quasiparticle random-phase approximation (QRPA) calculations are consistent with the experimental limit. However, part of the ξ_{31}^{2ν} range allowed by the QRPA is excluded by the present measurement at the 90% confidence level. Our analysis reveals that predicted ξ_{31}^{2ν} values are sensitive to the quenching of NMEs and the competing contributions from low- and high-energy states in the intermediate nucleus. Because these aspects are also at play in neutrinoless ββ decay, ξ_{31}^{2ν} provides new insights toward reliable neutrinoless ββ NMEs.

For several nuclei in the vicinity of shell closures an accumulation of electric dipole strength around the particle separation threshold has been reported. This strength accumulation is often referred to as pygmy dipole resonance (PDR). As part of the systematic survey of the PDR, the dipole responses of the even-even chromium isotopes \(^{50,52,54}\)Cr have been measured using the phenomenon of nuclear resonance fluorescence. Spin and parity quantum numbers as well as excitation energies and transition strengths were measured for numerous known and previously unknown states. The comparison to calculations within the quasi-particle phonon model and between the isotopes provide new insight about the onset of the PDR and its evolution to heavier and more neutron rich nuclei.

For the first time the excitation cross section of $^{115}\mathrm{In}$ to its first excited state at 336.24 keV has been measured with monoenergetic photon beams at 15 energies between 1.8 and 3.7 MeV. The measurements were performed at the High-Intensity Gamma-ray Source ($\mathrm{HI}\ensuremath{\gamma}\mathrm{S}$) facility with natural In targets and incident photon fluxes ranging from $0.7\ifmmode\times\else\texttimes\fi{}{10}^{7}\ensuremath{\gamma}/({\mathrm{cm}}^{2}\phantom{\rule{0.16em}{0ex}}\text{s})$ to $3.2\ifmmode\times\else\texttimes\fi{}{10}^{7}\ensuremath{\gamma}/({\mathrm{cm}}^{2}\phantom{\rule{0.16em}{0ex}}\text{s})$. The inelastic scattering cross section was obtained from the yield of the 336.24 keV deexcitation $\ensuremath{\gamma}$ rays. The cross-section values varied between $l0.05$ and 28.7 $\ensuremath{\mu}\mathrm{b}$ at 1.8 and 3.7 MeV, respectively. Compared to standard photon inelastic scattering cross-section data in this energy range of medium-mass nuclei, these extremely small values are not completely unexpected, given the nature of the low-lying nuclear levels of $^{115}\mathrm{In}$. Model calculations, however, overestimate the measured cross-section data by approximately one order of magnitude. Using different choices for the $E1 \ensuremath{\gamma}$-ray strength function, the data can be well described. The data are important for improving our knowledge of the level scheme of $^{115}\mathrm{In}$, especially spin and parity assignments of already known states.

Physics letters / B 756, 72 - 76(2016). doi:10.1016/j.physletb.2016.02.042, Published by North-Holland Publ., Amsterdam

Fission Product Yields (FPY) have historically been one of the most observable features of the fission process. They are known to have strong variations that are dependent on the fissioning species, the excitation energy, and the angular momentum of the compound system. However, consistent and systematic studies of the variation of these FPY with energy have proved challenging. This is caused primarily by the nature of the experiments that have traditionally relied on radiochemical procedures to isolate specific fission products. Although radiochemical procedures exist that can isolate all products, each element presents specific challenges and introduces varying degrees of systematic errors that can make inter-comparison of FPY uncertain. Although of high importance in fields such as nuclear forensics and Stockpile Stewardship, accurate information about the energy dependence of neutron induced FPY are sparse, due primarily to the lack of suitable monoenergetic neutron sources. There is a clear need for improved data, and to address this issue, a collaboration was formed between Los Alamos National Laboratory (LANL), Lawrence Livermore National Laboratory (LLNL) and the Triangle Universities Nuclear Laboratory (TUNL) to measure the energy dependence of FPY for 235 U, 238 U and 239 Pu. The measurements have been performed at TUNL, using a 10 MV Tandem Van de Graaff accelerator to produce monoenergetic neutrons at energies between 0.6 MeV to 14.8 MeV through a variety of reactions. The measurements have utilized a dual-fission chamber, with thin (10-100 μ g/cm2) reference foils of similar material to a thick (100-400 mg) activation target held in the center between the chambers. This method allows for the accurate determination of the number of fissions that occurred in the thick target without requiring knowledge of the fission cross section or neutron fluence on target. Following activation, the thick target was removed from the dual-fission chamber and gamma-ray counted using shielded HPGe detectors for a period of 1-2 months to determine the yield of various fission products. To the extent possible all irradiation and counting procedures were kept the same to minimize sources of systematic errors. FPY have been determined at incident neutron energies of 0.6, 1.4, 2.4, 3.5, 4.6, 5.5, 8.9 and 14.8 MeV.

96 Zr and 48 Ca are unique among double-β decay candidate nuclides in that they may also undergo single-β decay. In the case of 96 Zr, the single-β decay mode is dominated by the fourth-forbidden β decay with a 119 keV Q value. A search was conducted for the β decay of 96 Zr by observing the decay of the daughter 96 Nb nucleus. Two coaxial high-purity germanium detectors were used in coincidence to detect the γ-ray cascade produced by the daughter nucleus as it de-excited to the ground state. The experiment was carried out at the Kimballton Underground Research Facility and produced 685.7 days of data with a 17.91 g enriched sample. No counts were seen above background, producing a limit of T 1 / 2 > 2.4 × 10 19 year . This is the first experimental search that is able to discern between the β decay and the double-β decay to an excited state of 96 Zr.

Fission product yields (FPYs) are an important source of information that are used for basic and applied physics. They are essential observables to address questions relevant to nucleosynthesis in the cosmos that created the elements from iron to uranium, for example, in energy generating processes from fission recycling in binary neutron star mergers; resolving the reactor neutrino anomaly; decay heat release in nuclear reactors; and many national security applications. While new applications will require accurate energy-dependent FPY data over a broad set of incident neutron energies, the current evaluated FPY data files contain only three energy points: thermal, fast, and 14-MeV incident energies.Recent measurements using mono-energetic and pulsed neutron beams at the Triangle Universities Nuclear Laboratory (TUNL) tandem accelerator and employing a dual fission ionization chambers setup have produced self-consistent, high-precision data critical for testing fission models for the neutron-induced fission of the major actinide nuclei. This paper will present new campaign just beginning utilizing a RApid Belt-driven Irradiated Target Transfer System (RABITTS) to measure shorter-lived fission products and the time dependence of fission yields, expanding the measurements from cumulative towards independent fission yields.

A joint TUNL-LLNL-LANL collaboration was formed to measure the absolute fission product yields from the 235 U, 238 U, and 239 Pu isotopes. Our goal is to study the energy evolution of fission products using monoenergetic beams. In order to extend our successful fission product-yield studies to include products with shorter half-lives, a RApid Belt-driven Irradiated Target Transfer System, named RABITTS, was constructed. This system allows us to perform cyclic activation and quantify fission products with γ-ray spectroscopy using HPGe detectors. Both a 1 meter and 10 meter transfer system have been developed, with transit times of 0.4 and 1.1 seconds, respectively. Using these systems, we have measured sub-second half-lives. Our goal is to measure fission product yields from neutron-induced fission with En = 0.5 − 14.8 MeV and photofission with Eγ = 8 − 15 MeV. A detailed characterization of the system’s performance is presented, including preliminary fission product measurements, and the expected sensitivity.

This paper reports the results of the first measurements of the differential cross section of the $^{80}\mathrm{Se}(\ensuremath{\gamma},n)^{79}\mathrm{Se}$ reaction with a linearly polarized gamma-ray ($\ensuremath{\gamma}$-ray) beam. The cross section was measured at three incident $\ensuremath{\gamma}$-ray beam energies: 15.6, 15.8, and 16.0 MeV, with a beam energy spread of 3.0% full width at half-maximum (FWHM). The differential cross section for the excitation spectrum in $^{79}\mathrm{Se}$ was measured at two scattering angles in the plane of the beam polarization: $\ensuremath{\theta}={90}^{\ensuremath{\circ}}$ and ${135}^{\ensuremath{\circ}}$, and at one angle in the plane perpendicular to the plane of polarization: $\ensuremath{\theta}={90}^{\ensuremath{\circ}}$. The total photoneutron cross sections determined from these data are between 0.8 and 1.3 standard deviations smaller than previously published results. The excitation spectra measured in this work were fit with a Hauser-Feshbach model. Better fits to the data were obtained with a constant-temperature formulation of the nuclear level density (NLD) than with a Fermi-gas NLD model. The parameters for the constant-temperature NLD model obtained in this work are consistent with those obtained for medium-mass nuclei in previous studies.

Background: Observation of lepton number violation via detection of neutrinoless double $\ensuremath{\beta}$ decay requires that the neutrino be a Majorana particle. If the neutrino is a Dirac particle, a potential lepton-number violating process is neutrinoless quadruple $\ensuremath{\beta}$ decay. Only a few nuclei can undergo neutrinoless quadruple $\ensuremath{\beta}$ decay; one of these nuclei is $^{150}\mathrm{Nd}$.Purpose: This study yields the first half-life limit of the neutrinoless quadruple $\ensuremath{\beta}$ decay to the excited ${0}_{1}^{+}$ state of $^{150}\mathrm{Gd}$.Methods: We searched for neutrinoless quadruple $\ensuremath{\beta}$ decay events to excited final states of $^{150}\mathrm{Gd}$ by detecting the deexcitation $\ensuremath{\gamma}$ rays of the daughter nucleus in coincidence. These $\ensuremath{\gamma}$ rays have energies of 569.031 and 638.050 keV, and are emitted in coincidence through a ${0}_{1}^{+}\ensuremath{\rightarrow}{2}_{1}^{+}\ensuremath{\rightarrow}{0}_{gs}^{+}$ transition.Results: The enriched ${\mathrm{Nd}}_{2}{\mathrm{O}}_{3}$ sample consisted of $40.33\ifmmode\pm\else\textpm\fi{}0.02$ g $^{150}\mathrm{Nd}$ and was observed for 642.8 days at the Kimballton Underground Research Facility. A half-life limit for the decay to the ${0}_{1}^{+}$ state of $^{150}\mathrm{Gd}$ was found to be ${T}_{1/2}g1.76\ifmmode\times\else\texttimes\fi{}{10}^{20}$ years (90% CL).Conclusions: We report the first search for this decay to excited final states. Though the predicted half-life of this decay is many orders of magnitudes larger, constraining this value experimentally is vital to check for potential enhancements to the decay rate.

Background: In the $A\ensuremath{\approx}50$ mass region $M1$ spin-flip transitions are prominent around 9 MeV. An accumulation of ${1}^{\ensuremath{-}}$ states between 5 and 8 MeV generating additional $E1$ strength, also denoted as pygmy dipole resonance, has been established in many nuclei with neutron excess within the last decade.Purpose: The $\ensuremath{\gamma}$-decay behavior of $J=1$ states has been investigated in an NRF experiment. $M1$ excitations have been compared to shell model calculations.Methods: $J=1$ states were excited by quasi-monoenergetic, linearly polarized $\ensuremath{\gamma}$-ray beams generated by laser-Compton backscattering at the $\mathrm{HI}\ensuremath{\gamma}\mathrm{S}$ facility, Durham, NC, USA. Depopulating $\ensuremath{\gamma}$ rays were detected with the multidetector array ${\ensuremath{\gamma}}^{3}$.Results: For eleven beam-energy settings the $\ensuremath{\gamma}$-decay behavior of dipole states was analyzed by a state-to-state analysis and average $\ensuremath{\gamma}$-decay branching ratios have been investigated. 34 parity quantum numbers were assigned to $J=1$ states.Conclusions: Six ${1}^{\ensuremath{-}}$ states and two ${1}^{+}$ states have been investigated in NRF experiments for the first time. The $M1$ strength distribution is in good agreement with shell-model calculations.

Natural copper is commonly used as cooling and shielding medium in detector arrangements designed to search for neutrinoless double-$\ensuremath{\beta}$ decay. Neutron-induced background reactions on copper could potentially produce signals that are indistinguishable from the signals of interest. The present work focuses on radiative neutron capture experiments on $^{63,65}\mathrm{Cu}$ in the 0.4 to 7.5 MeV neutron energy range. The new data provide evaluations and model calculations with benchmark data needed to extend their applicability in predicting background rates in neutrinoless double-$\ensuremath{\beta}$ decay experiments.

The Majorana Collaboration is operating an array of high purity Ge detectors to search for neutrinoless double-β decay in ^{76}Ge. The Majorana Demonstrator comprises 44.1 kg of Ge detectors (29.7 kg enriched in ^{76}Ge) split between two modules contained in a low background shield at the Sanford Underground Research Facility in Lead, South Dakota. Here we present results from data taken during construction, commissioning, and the start of full operations. We achieve unprecedented energy resolution of 2.5 keV FWHM at Q_{ββ} and a very low background with no observed candidate events in 9.95 kg yr of enriched Ge exposure, resulting in a lower limit on the half-life of 1.9×10^{25} yr (90% C.L.). This result constrains the effective Majorana neutrino mass to below 240-520 meV, depending on the matrix elements used. In our experimental configuration with the lowest background, the background is 4.0_{-2.5}^{+3.1} counts/(FWHM t yr).

16TH INTERNATIONAL SYMPOSIUM ON CAPTURE GAMMA-RAY SPECTROSCOPY AND RELATED TOPICS (CGS16), Shanghai, China, 18 Sep 2017 - 22 Sep 2017; The European physical journal / Web of Conferences Web of Conferences : proceedings proceedings 178, 02022 (2018). doi:10.1051/epjconf/201817802022, This is an Open Access article distributed under the terms of the Creative Commons Attribution License 4.0, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. (http://creativecommons.org/licenses/by/4.0/)., Published by EDP Sciences, Les Ulis

Nuclear Resonance Fluorescence (NRF) experiments on the nuclei 82Kr and 82Se were performed, that are a candidates for a mother-daughter pair for the hypothetical neutrinoless double-beta (0νββ) decay. The experiment aimed at providing high-precision data to benchmark theoretical calculations of the nuclear matrix elements involved in this exotic decay mode. We have investigated the excitation energy range from 2.3MeV to 4.2MeV, where the nuclear scissors mode is expected to be located in nuclei of this mass region. Our experiment was able to constrain decay branches of the scissors mode down to a level of a few percents, comparable to previous experiments on heavy deformed 0νββ decay candidates. Reduced transition strengths of the magnetic dipole-excited states have been determined by a method that exploits the non-resonant background in the NRF spectra. They are compared to a calculation within the nuclear shell model for 82Se, which reveals their mixed orbital and spin character, hinting at a more complex microscopic structure of low-lying 1+ states.

Measurements of the $^{169}\mathrm{Tm}(n,2n)^{168}\mathrm{Tm}$ cross section have been performed via the activation technique at 13 energies between 8.5 and 15.0 MeV. The purpose of this comprehensive data set is to provide an alternative diagnostic tool for obtaining subtle information on the neutron energy distribution produced in inertial confinement deuterium-tritium fusion experiments at the National Ignition Facility (NIF) at Lawrence Livermore National Laboratory. The $^{169}\mathrm{Tm}(n,2n)^{168}\mathrm{Tm}$ reaction not only provides the primary 14-MeV neutron fluence, but also the important down-scattered neutron fluence, the latter providing information on the density achieved in the deuterium-tritium plasma during a laser shot.

Author(s): Gando, A; Gando, Y; Hachiya, T; Hayashi, A; Hayashida, S; Ikeda, H; Inoue, K; Ishidoshiro, K; Karino, Y; Koga, M; Matsuda, S; Mitsui, T; Nakamura, K; Obara, S; Oura, T; Ozaki, H; Shimizu, I; Shirahata, Y; Shirai, J; Suzuki, A; Takai, T; Tamae, K; Teraoka, Y; Ueshima, K; Watanabe, H; Kozlov, A; Takemoto, Y; Yoshida, S; Fushimi, K; Piepke, A; Banks, TI; Berger, BE; Fujikawa, BK; O'Donnell, T; Learned, JG; Maricic, J; Sakai, M; Winslow, LA; Krupczak, E; Ouellet, J; Efremenko, Y; Karwowski, HJ; Markoff, DM; Tornow, W; Detwiler, JA; Enomoto, S; Decowski, MP; Collaboration, KamLAND

The neutron radiative-capture cross section of 76Ge was measured between 0.4 and 14.8 MeV using the activation technique. Germanium samples with the isotopic abundance of ∼ 86 % Ge 76 and ∼ 14 % Ge 74 used in the 0 ν β β searches by the GERDA and Majorana Collaborations were irradiated with monoenergetic neutrons produced at eleven energies via the H 3 ( p , n ) He 3 , H 2 ( d , n ) He 3 and H 3 ( d , n ) He 4 reactions. Previously, data existed only at thermal energies and at 14 MeV. As a by-product, capture cross-section data were also obtained for 74Ge at neutron energies below 8 MeV. Indium and gold foils were irradiated simultaneously for neutron fluence determination. High-resolution γ-ray spectroscopy was used to determine the γ-ray activity of the daughter nuclei of interest. For the 76Ge total capture cross section the present data are in good agreement with the TENDL-2013 model calculations and the ENDF/B-VII.1 evaluations, while for the Ge 74 ( n , γ ) Ge 75 reaction, the present data are about a factor of two larger than predicted. It was found that the Ge 74 ( n , γ ) Ge 75 yield in the High-Purity Germanium (HPGe) detectors used by the GERDA and Majorana Collaborations is only about a factor of two smaller than the Ge 76 ( n , γ ) Ge 77 yield due to the larger cross section of the former reaction.

The ( J , T ) = ( 1 , 1 ) parity doublet in 20 Ne at 11.26 MeV is a good candidate to study parity violation in nuclei. However, its energy splitting is known with insufficient accuracy for quantitative estimates of parity violating effects. To improve on this unsatisfactory situation, nuclear resonance fluorescence experiments using linearly and circularly polarized γ -ray beams were used to determine the energy difference of the parity doublet Δ E = E ( 1 − ) − E ( 1 + ) = − 3.2 ( ± 0.7 ) stat ( − 1.2 + 0.6 ) sys keV and the ratio of their integrated cross sections I s , 0 ( + ) / I s , 0 ( − ) = 29 ( ± 3 ) stat ( − 7 + 14 ) sys . Shell-model calculations predict a parity-violating matrix element having a value in the range 0.46–0.83 eV for the parity doublet. The small energy difference of the parity doublet makes 20 Ne an excellent candidate to study parity violation in nuclear excitations.

The Majorana Collaboration is constructing a system containing 40kg of HPGe detectors to demonstrate the feasibility and potential of a future tonne-scale experiment capable of probing the neutrino mass scale in the inverted-hierarchy region. To realize this, a major goal of the Majorana Demonstrator is to demonstrate a path forward to achieving a background rate at or below 1 cnt/(ROI-t-y) in the 4 keV region of interest around the Q-value at 2039 keV. This goal is pursued through a combination of a significant reduction of radioactive impurities in construction materials with analytical methods for background rejection, for example using powerful pulse shape analysis techniques profiting from the p-type point contact HPGe detectors technology. The effectiveness of these methods is assessed using simulations of the different background components whose purity levels are constrained from radioassay measurements.

The MAJORANA DEMONSTRATOR will search for the neutrinoless double beta decay (ββ(0ν)) of the isotope 76Ge with a mixed array of enriched and natural germanium detectors. In view of the next generation of tonne-scale germanium-based ββ(0ν)-decay searches, a major goal of the MAJORANA DEMONSTRATOR is to demonstrate a path forward to achieving a background rate at or below 1 cnt/(ROI-t-y) in the 4 keV region of interest (ROI) around the 2039-keV Q-value of the 76Ge ββ(0ν)-decay. Such a requirement on the background level significantly constrains the design of the readout electronics, which is further driven by noise and energy resolution performances. We present here the low-noise low- background front-end electronics developed for the low-capacitance p-type point contact (P-PC) germanium detectors of the MAJORANA DEMONSTRATOR. This resistive-feedback front-end, specifically designed to have low mass, is fabricated on a radioassayed fused-silica substrate where the feedback resistor consists of a sputtered thin film of high purity amorphous germanium and the feedback capacitor is based on the capacitance between gold conductive traces.

High purity germanium (HPGe) crystals will be used for the MAJORANA DEMONSTRATOR, where they serve as both the source and the detector for neutrinoless double beta decay. It is crucial for the experiment to understand the performance of the HPGe crystals. A variety of crystal properties are being investigated, including basic properties such as energy resolution, efficiency, uniformity, capacitance, leakage current and crystal axis orientation, as well as more sophisticated properties, e.g. pulse shapes and dead layer and transition layer distributions. In this paper, we will present our measurements that characterize the HPGe crystals. We will also discuss our simulation package for the detector characterization setup, and show that additional information can be extracted from data-simulation comparisons., Comment: To appear in the Proceedings of the 13th International Conference on Topics in Astroparticle and Underground Physics, TAUP 2013 (F. Avignone & W. Haxton, editors, Physics Procedia, Elsevier)