Fri·Nov 15, 2019Friday·November 15, 2019

1. 01*

   Discriminating Uranium Isotopes Based on Fission Signatures Induced by Delayed Neutrons

   Kristofer Ogren · Jason Nattress🇺🇸 · Igor Jovanovic🇺🇸

   The use of active interrogation (AI) to induce delayed neutron emission is a well-established technique for the characterization of special nuclear materials (SNM). Delayed neutrons have isotope-characteristic spectral and temporal signatures, which provide the basis for isotope identification. However, in bulk materials that contain an appreciable fissile (e.g., ${}^{235}$U or ${}^{233}$U) fraction, such as highly-enriched uranium (HEU), delayed neutrons have a high probability of inducing additional fissions. As a result, the overall delayed neutron signature consists of two distinct components: the "primary" delayed neutrons (emitted directly by fission fragments), and the "secondary prompt" fission neutrons produced in fission induced by primary delayed neutrons. These prompt products differ from "primary" delayed neutrons both in their energy spectra and in the presence of coincident radiation released by the parent fission event. The presence and relative quantity of prompt products from delayed fission depend on the cross-section of the material in the energy range of delayed neutrons, which may differ significantly between isotopes, thus providing an exploitable means for isotope differentiation. In this work, we demonstrate two experimental approaches for discriminating between ${}^{235}$U and ${}^{238}$U isotopes based on the measurement of delayed neutron-induced fission products. First, HEU and depleted uranium objects are differentiated through the detection of high-energy prompt neutrons from delayed fission using both recoil-based organic liquid scintillators and thermalization spectra from a custom-built capture-gated composite detector. Secondly, coincident radiation measurements are used as the basis for discrimination by comparing the overall rates and time evolution of fission events when delayed neutrons are present.

   nucl-exphysics.ins-detPhys.Rev.Applied(2020)·0 citations
2. 02*

   Improved limits on Fierz Interference using asymmetry measurements from the UCNA experiment

   Xuan Sun🇺🇸 · E. Adamek🇺🇸 · B. Allgeier🇺🇸 · Y. Bagdasarova🇺🇸 · D. B. Berguno🇺🇸 · M. Blatnik🇺🇸 · T. J. Bowles🇺🇸 · L. J. Broussard🇺🇸 · M. A.-P. Brown🇺🇸 · R. Carr🇺🇸 · S. Clayton🇺🇸 · C. Cude-Woods🇺🇸 and 47 other authors

   The Ultracold Neutron Asymmetry (UCNA) experiment was designed to measure the $\beta$-decay asymmetry parameter, $A_0$, for free neutron decay. In the experiment, polarized ultracold neutrons are transported into a decay trap, and their $\beta$-decay electrons are detected with $\approx 4\pi$ acceptance into two detector packages which provide position and energy reconstruction. The experiment also has sensitivity to $b_n$, the Fierz interference term in the neutron $\beta$-decay rate. In this work, we determine $b_n$ from the energy dependence of $A_0$ using the data taken during the UCNA 2011-2013 run. In addition, we present the same type of analysis using the earlier 2010 $A$ dataset. Motivated by improved statistics and comparable systematic errors compared to the 2010 data-taking run, we present a new $b_n$ measurement using the weighted average of our asymmetry dataset fits, to obtain $b_n=0.066\pm 0.041_{\text{stat}}\pm 0.024_{\text{syst}}$ which corresponds to a limit of $-0.012<b_n<0.144$ at the 90% confidence level.

   nucl-exPRC(2020)·39 citations
3. 03*

   Fusion of Borromean nucleus ${}^9$Be with ${}^{197}$Au target at near barrier energies

   Malika Kaushik🇮🇳 · G. Gupta🇮🇳 · Swati Thakur🇮🇳 · H. Krishnamoorthy🇮🇳 · Pushpendra P. Singh🇫🇷 · V.V. Parkar🇮🇳 · V. Nanal🇮🇳 · A. Shrivastava🇮🇳 · R.G. Pillay🇮🇳 · K. Mahata🇮🇳 · K. Ramachandran🇮🇳 · S. Pal🇨🇦 · C.S. Palshetkar🇮🇳 · S.K. Pandit🇮🇳

   To probe the role of the intrinsic structure of the projectile on sub-barrier fusion, measurement of fusion cross sections has been carried out in ${}^9$Be + ${}^{197}$Au system in the energy range E${}_{c.m.}$/V${}_B$ $\approx$ 0.82 to 1.16 using off-beam gamma counting method. Measured fusion excitation function has been analyzed in the framework of the coupled-channel approach using CCFULL code. It is observed that the coupled-channel calculations, including couplings to the inelastic state of the target and the first two states of the rotational band built on the ground state of the projectile, provide a very good description of the sub-barrier fusion data. At above barrier energies, the fusion cross section is found to be suppressed by $\approx$ 39(2)\% as compared to the coupled-channel prediction. A comparison of reduced excitation function of ${}^9$Be + ${}^{197}$Au with other $x$ + ${}^{197}$Au shows a larger enhancement for ${}^9$Be in the sub-barrier region amongst Z=2-5 weakly and tightly bound projectiles, which indicates the prominent role of the projectile deformation in addition to the weak binding.

   nucl-exnucl-thPRC(2020)·23 citations
4. 04*

   Indirect Methods in Nuclear Astrophysics

   Livius Trache🇺🇸 · Florin Carstoiu

   This paper follows the inaugural talk one of the authors (LT) gave at the opening of the ECT* workshop with the same title, which he co-organized in Trento, Italy, November 5-9, 2018. As such it follows the ideas expressed there, which were to out-line the discussions that the organizers intended for that meeting. Therefore, the paper will review the indirect methods in nuclear astrophysics, their use and their specific problems, old and new, the need to further developments rather than giving complete treatments of each method or reviewing exhaustively the existing literature. The workshop was from its inception aiming also at reviewing the status of the field of nuclear astrophysics and its connections with adjacent branches of physics. Some lines on these are included here.

   nucl-exnucl-th2 citations
5. 05*

   High-resolution study of excited states in 158Gd with (p,t) reactions

   A. I. Levon🇺🇦 · D. Bucurescu🇷🇴 · C. Costache🇷🇴 · T. Faestermann🇩🇪 · R. Hertenberger🇩🇪 · A. Ionescu🇷🇴 · R. Lica🇷🇴 · A. G. Magner🇺🇦 · C. Mihai🇷🇴 · R. Mihai · C. R. Nita · S. Pascu🇷🇴 and 4 other authors

   The excitation spectra in the deformed nucleus 158Gd have been studied with high energy resolution by means of the (p,t) reaction using the Q3D spectrograph facility at the Munich Tandem accelerator. The angular distributions of tritons were measured for more than 200 excited states seen in the triton spectra up to 4.3 MeV. A number of 36 excited 0+ states (five tentative), have been assigned by comparison of experimental angular distributions with the calculated ones using the CHUCK code. Assignments for levels with higher spins are the following: 95 for 2+ states, 64 for 4+ states, 14 for 6+ states and about 20 for negative parity states. Sequences of states which can be treated as rotational bands are selected. The analysis of the moments of inertia defined for these bands is carried out. This high number of excited states in a deformed nucleus, close to a complete level scheme, constitutes a very good ground to check models of nuclear structure. The large ensembles of states with the same spin-parity offer unique opportunities for statistical analysis. Such an analysis for the 0+, 2+ and 4+ states sequences, for all K-values and for well-determined projections K of the angular momentum is performed. The obtained data may indicate on a K symmetry breaking. Experimental data are compared with interacting boson model (IBM) calculations using the spdf version of the model. The energies of the low-lying levels, the transition probabilities in the first bands and the distribution in transfer intensity of the 0+ states are calculated and compared with experiment.

   nucl-exPRC(2020)·10 citations
6. 06*

   Study of Three-Nucleon Dynamics in the dp breakup collisions using the WASA detector

   P. Adlarson🇸🇪 · W. Augustyniak🇵🇱 · W. Bardan🇵🇱 · M. Bashkanov🇬🇧 · F. S. Bergmann🇩🇪 · M. Berlowski🇵🇱 · A. Bondar🇷🇺 · M. Buscher🇩🇪 · H. Calen🇸🇪 · I. Ciepal🇵🇱 · H. Clement🇩🇪 · E. Czerwinski🇵🇱 and 77 other authors

   Differential cross section for the 1H(d,pp)n breakup reaction at deuteron beam energy of 340 MeV has been measured with the use of WASA detector at COSY-Juelich. The set of proton-proton coincidences registered at Forward Detector has been analysed on dense grid of kinematic variables, giving in total around 5600 data points. The cross section data are compared to theoretical predictions based on the state-of-the-art nucleon-nucleon potentials, combined with three-nucleon force, Coulomb interaction or carried out in a relativistic regime.

   nucl-exPRC(2020)·10 citations
7. 07*

   Signal Readout Electronics for LEGEND-200

   Michael Willers🇩🇪

   LEGEND (Large Enriched Germanium Experiment for Neutrinoless Double-Beta Decay) is a ton-scale experimental program to search for neutrinoless double beta ($0\nu \beta \beta$) decay using high-purity germanium detectors enriched in the isotope ${}^{76}$Ge. An observation of $0\nu \beta \beta$ decay would unequivocally prove the existence of lepton number violation and provide insight into the nature of neutrino masses. On-site construction for the first 200-kg phase (LEGEND-200) of the experiment will start at the Gran Sasso underground laboratory (Laboratory Nazionali del Gran Sasso, Italy) in mid-2020. In order to achieve a sensitivity of $10^{27}$ years on the $0\nu \beta \beta$ half-life, ultra-clean low-noise signal readout electronics are essential as they impact both the background budget of the experiment and the efficiency of background rejection. In this contribution, the current status of the signal readout electronics for LEGEND-200 is presented.

   ↳ physics.ins-detnucl-exJ.Phys.Conf.Ser.(2020)·8 citations
8. 08*

   Subbarrier fusion reactions of an aligned deformed nucleus

   K. Hagino🇯🇵 · S. Sakaguchi🇯🇵

   We discuss heavy-ion fusion reactions of a well-deformed odd-mass nucleus at energies around the Coulomb barrier. To this end, we consider the ${}^{16}$O+${}^{165}$Ho reaction and take into account the effect of deformation of ${}^{165}$Ho using the orientation average formula. We show that fusion cross sections are sensitive to magnetic substates of the target nucleus, and cross sections for the side collision, which are relevant to a synthesis of superheavy elements, may be enhanced by a factor of around two by aligning the deformed target nuclei. We also discuss the effect of alignment on the fusion barrier distribution. We find that, for a particular choice of alignment, the shape of barrier distribution becomes similar to a typical shape of barrier distribution for a deformed nucleus with a negative hexadecapole deformation parameter, ${\beta }_4$, even if the intrinsic ${\beta }_4$ is positive in the target nucleus.

   ↳ nucl-thnucl-exPRC(2019)·8 citations
9. 09*

   System and event activity dependent inclusive jet production with ALICE

   Yongzhen Hou🇨🇳

   Jets are produced by processes involving high momentum transfer of initial partons at high energies. Comparing jet production in pp and nucleus-nucleus collisions will allow us to study the jet-quenching effect caused by the hot and dense QCD medium produced in nucleus-nucleus collisions when energetic partons traverse the medium. In particular, systematic studies of jet production in different multiplicity environments will provide in-depth understanding of the medium properties and their evolution from small to large systems. In small systems and high multiplicity events, the bulk properties extracted by the low transverse momentum particle production behaves as if a hot QCD medium was created, but such behaviour is not observed with hard probes. Study of jet production in different multiplicity proton-proton collisions then helps to explore the QGP existence in small systems. In this proceeding, the jet cross section measurements in different collision systems using the data taken by ALICE during the LHC Run 2 are presented. The nuclear modification factor of jets are presented to characterize the jet-quenching effect. We observe that more jets are produced in high multiplicity bins compared to the inclusive one, while the jet production enhancement in high multiplicity environments has weaker jet $p_{\mathrm{T}}$ or resolution parameter dependences. In order to study the jet collimation properties, the jet cross section ratios for different jet resolution parameters are also measured and compared to theoretical models. As expected, the jets get more collimated at high $p_{\mathrm{T}}$ in numerous multiplicity bins, with no collision energy or multiplicity dependence when compared to earlier results.

   ↳ hep-exnucl-exPoS(2020)·1 citation
10. 10*

    Statistical double $\Lambda$ hypernuclear formation from ${\Xi }^{-}$ absorption at rest in light nuclei

    Akira Ohnishi🇯🇵 · Chikako Ishizuka🇯🇵 · Kohsuke Tsubakihara🇯🇵 · Yuichi Hirata🇯🇵

    We investigate double $\Lambda$ hyperfragment formation from the statistical decay of double $\Lambda$ compound nuclei produced in the ${\Xi }^{-}$ absorption at rest in light nuclei, ${}^{12}\mathrm{C}$, ${}^{14}\mathrm{N}$ and ${}^{16}\mathrm{O}$. We examine the target and the $\Lambda \Lambda$ bond energy dependence of the double $\Lambda$ hyperfragment formation probabilities, especially of those double hypernuclei observed in experiments. For the ${}^{12}\mathrm{C}$ (${}^{14}\mathrm{N}$) target, the formation probabilities of ${}_{\Lambda \Lambda }^6\mathrm{He}$ and ${}_{\Lambda \Lambda }^{10}\mathrm{Be}$ (${}_{\Lambda \Lambda }^{13}\mathrm{B}$) are found to be reasonably large as they are observed in the KEK-E373 (KEK-E176) experiment. By comparison, for ${}^{16}\mathrm{O}$ target, the formation probability of ${}_{\Lambda \Lambda }^{11}\mathrm{Be}$ is calculated to be small with $\Delta B_{\Lambda \Lambda }$ consistent with the Nagara event. We also evaluate the formation probability of ${}_{\Lambda \Lambda }^5\mathrm{H}$ from a ${\Xi }^{-}$-${}^6\mathrm{He}$ bound state, ${}_{\Xi }^7\mathrm{H}$.

    ↳ nucl-thnucl-exPTEP(2020)·2 citations
11. 11*

    The d*(2380) and its family of pion assisted dibaryons

    Avraham Gal🇮🇱

    The status of $N\Delta$ and $\Delta \Delta$ dibaryons introduced by Dyson and Xuong in 1964 is briefly reviewed with focus on the d*(2380), tentatively assigned as a $\Delta \Delta$ dibaryon resonance. It is argued that the apparently small value of width, ${\Gamma }_{d^{\ast }}$$\approx$70 MeV, favors hadronic structure for the d*(2380) dibaryon rather than a six-quark structure.

    ↳ nucl-thhep-phnucl-ex0 citations

* Reconstructed cohort: no mailing for this day survives in the archive. Papers are grouped by their submission times and arXiv's announcement cut-off, assuming announcement without delay; positions follow identifier order. Validated at ~91% exact-day agreement against the archived era.