Nuclear Experiment

Several experiments have been conducted in the YangYang Underground Laboratory in the Republic of Korea such as the search for dark matter and the search for neutrinoless double-beta decay, which require an extremely low background event rate due to the detector system and the environment. In underground experiments, neutrons have been identified as one of the background sources. The neutron flux in the experimental site needs to be determined to design a proper shielding system and for precise background estimation. We measured the neutron spectrum with a Bonner sphere spectrometer, with Helium-3 ( 3 He) proportional counters. The neutron flux at the underground laboratory was so low that the radioactive decays from the radioisotopes contained in the detector created a significant background interference to the neutron measurement. Using Monte Carlo simulations, the intrinsic α background distribution due to the radioactive isotopes in the detector materials, was estimated. The neutron count rate of each Bonner sphere was measured from the pulse height spectrum of the 3 He proportional counter, after subtracting the α particle background. The neutron flux and the energy spectrum were determined using the unfolding technique. The total neutron flux measured was (4.46 ± 0.66) ? 10 ?? c m ?? s ?? , and the thermal and fast neutron flux (in the range 1 to 10 MeV) were (1.44 ± 0.15) ? 10 ?? c m ?? s ?? and (0.71 ± 0.10) ? 10 ?? c m ?? s ?? , respectively.

A systematic study of neutron-hole strength in the N = 81 nuclei 137Ba, 139Ce, 141Nd and 143Sm is reported. The single-neutron removal reactions (p,d) and (3He,4He) were measured at energies of 23 and 34 MeV, respectively. Spectroscopic factors were extracted from measured cross sections through a distorted-wave Born approximation analysis and centroids of single-particle strength have been established. The change in these centroid energies as a function of proton number have been compared to calculations of the monopole shift for the s1/2 and h11/2 orbitals, where the majority of the strength has been observed. Significant fragmentation of strength was observed for the d and g7/2 orbitals, particularly for the latter orbital which is deeply bound, with summed strengths that indicate a significant amount lies outside of the measured excitation energy range.

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 ±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±0.5(stat)±1.1(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.

A new α -emitting isotope 214 U, produced by fusion-evaporation reaction 182 W( 36 Ar, 4n) 214 U, was identified by employing the gas-filled recoil separator SHANS and recoil- α correlation technique. More precise α -decay properties of even-even nuclei 216,218 U were also measured in reactions of 40 Ar, 40 Ca with 180,182,184 W targets. By combining the experimental data, improved α -decay reduced widths δ 2 for the even-even Po--Pu nuclei in the vicinity of magic neutron number N=126 were deduced. Their systematic trends are discussed in terms of N p N n scheme in order to study the influence of proton-neutron interaction on α decay in this region of nuclei. It is strikingly found that the reduced widths of 214,216 U are significantly enhanced by a factor of two as compared with the N p N n systematics for the 84?�Z??0 and N<126 even-even nuclei. The abnormal enhancement is interpreted by the strong monopole interaction between the valence protons and neutrons occupying the ?1 f 7/2 and ν1 f 5/2 spin-orbit partner orbits, which is supported by a large-scale shell model calculation.

Correlations of symmetry planes are important observables used to quantify anisotropic flow phenomenon and constrain independently the properties of strongly interacting nuclear matter produced in the collisions of heavy ions at the highest energies. In this paper, we point out current problems of measuring correlations between symmetry planes and elaborate on why the available analysis techniques have a large systematic bias. To overcome this problem, we introduce a new approach to approximate multi-harmonic flow fluctuations via a two-dimensional Gaussian distribution. Employing this approximation, we introduce a new estimator, dubbed Gaussian Estimator (GE), to extract pure correlation between symmetry planes. We validate GE by using the realistic event-generator iEBE-VISHNU and demonstrate that it outperforms all existing estimators. Based on event-shape engineering, we propose an experimental procedure to improve GE accuracy even further.

Carbon and oxygen burning reactions, in particular, 12 C+ 12 C fusion, are important for the understanding and interpretation of the late phases of stellar evolution as well as the ignition and nucleosynthesis in cataclysmic binary systems such as type Ia supernovae and x-ray superbursts. A new measurement of this reaction has been performed at the University of Notre Dame using particle- γ coincidence techniques with SAND (a silicon detector array) at the high-intensity 5U Pelletron accelerator. New results for 12 C+ 12 C fusion at low energies relevant to nuclear astrophysics are reported. They show strong disagreement with a recent measurement using the indirect Trojan Horse method. The impact on the carbon burning process under astrophysical scenarios will be discussed.

Reactor neutrino experiments have seen major improvements in precision in recent years. With the experimental uncertainties becoming lower than those from theory, carefully considering all sources of ν ¯ ¯ ¯ e is important when making theoretical predictions. One source of ν ¯ ¯ ¯ e that is often neglected arises from the irradiation of the nonfuel materials in reactors. The ν ¯ ¯ ¯ e rates and energies from these sources vary widely based on the reactor type, configuration, and sampling stage during the reactor cycle and have to be carefully considered for each experiment independently. In this article, we present a formalism for selecting the possible ν ¯ ¯ ¯ e sources arising from the neutron captures on reactor and target materials. We apply this formalism to the High Flux Isotope Reactor (HFIR) at Oak Ridge National Laboratory, the ν ¯ ¯ ¯ e source for the the Precision Reactor Oscillation and Spectrum Measurement (PROSPECT) experiment. Overall, we observe that the nonfuel ν ¯ ¯ ¯ e contributions from HFIR to PROSPECT amount to 1\% above the inverse beta decay threshold with a maximum contribution of 9\% in the 1.8--2.0~MeV range. Nonfuel contributions can be particularly high for research reactors like HFIR because of the choice of structural and reflector material in addition to the intentional irradiation of target material for isotope production. We show that typical commercial pressurized water reactors fueled with low-enriched uranium will have significantly smaller nonfuel ν ¯ ¯ ¯ e contribution.

Isomeric states in 128 In and 130 In have been studied with the JYFLTRAP Penning trap at the IGISOL facility. By employing novel ion manipulation techniques, different states were separated and masses of six beta-decaying states were measured. JYFLTRAP was also used to select the ions of interest for identification at a post-trap decay spectroscopy station. A new beta-decaying high-spin isomer feeding the 15 − isomer in 128 Sn has been discovered in 128 In at 1797.6(20) keV. Shell-model calculations employing a CD-Bonn potential re-normalized with the perturbative G-matrix approach suggest this new isomer to be a 16 + spin-trap isomer. In 130 In, the lowest-lying ( 10 − ) isomeric state at 58.6(82) keV was resolved for the first time using the phase-imaging ion cyclotron resonance technique. The energy difference between the 10 − and 1 − states in 130 In, stemming from parallel/antiparallel coupling of (π0 g −1 9/2 )⊗(ν0 h −1 11/2 ) , has been found to be around 200 keV lower than predicted by the shell model. Precise information on the energies of the excited states determined in this work is crucial for producing new improved effective interactions for the nuclear shell model description of nuclei near 132 Sn.

Short Range Correlations (SRCs) have been identified as being responsible for the high momentum tail of the nucleon momentum distribution, n(k). Hard, short-range interactions of nucleon pairs generate the high momentum tail and imprint a universal character on n(k) for all nuclei at large momentum. Triple coincidence experiments have shown a strong dominance of np pairs, but these measurements involve large final state interactions. This paper presents the results from Jefferson Lab experiment E08014 which measured inclusive electron scattering cross-section from Ca isotopes. By comparing the inclusive cross section from 48Ca to 40Ca in a kinematic region dominated by SRCs we provide a new way to study the isospin structure of SRCs.

We present mass excesses (ME) of neutron-rich isotopes of Ar through Fe, obtained via TOF- Bρ mass spectrometry at the National Superconducting Cyclotron Laboratory. Our new results have significantly reduced systematic uncertainties relative to a prior analysis, enabling the first determination of ME for 58,59 Ti , 62 V , 65 Cr , 67,68 Mn , and 69,70 Fe . Our results show the N=34 subshell weaken at Sc and vanish at Ti, along with the absence of an N=40 subshell at Mn. This leads to a cooler accreted neutron star crust, highlighting the connection between the structure of nuclei and neutron stars.