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At least 433 records · Page 24Linked to original sources
arXiv2014

Comparison of Expanded Preequilibrium CEM Model with CEM03.03 and Experimental Data, FY2013

Emission of light fragments (LF) from nuclear reactions is an open question. Different reaction mechanisms contribute to their production; the relative roles of each, and how they change with incident energy, mass number of the target, and the type and emission energy of the fragments is not completely understood. None of the available models are able to accurately predict emission of LF from arbitrary reactions. However, the ability to describe production of LF (especially at energies $\gtrsim 30$ MeV) from many reactions is important for different applications, such as cosmic-ray-induced Single Event Upsets (SEUs), radiation protection, and cancer therapy with proton and heavy-ion beams, to name just a few. The Cascade-Exciton Model (CEM) version 03.03 and the Los Alamos version of the Quark-Gluon String Model (LAQGSM) version 03.03 event generators in Monte Carlo N-Particle Transport Code version 6 (MCNP6) describe quite well the spectra of fragments with sizes up to $^{4}$He across a broad range of target masses and incident energies (up to $\sim 5$ GeV for CEM and up to $\sim 1$ TeV/A for LAQGSM). However, they do not predict the high-energy tails of LF spectra heavier than $^4$He well. Most LF with energies above several tens of MeV are emitted during the precompound stage of a reaction. The current versions of the CEM and LAQGSM event generators do not account for precompound emission of LF larger than $^{4}$He. The aim of our work is to extend the precompound model in them to include such processes, leading to an increase of predictive power of LF-production in MCNP6. Extending our models to include emission of fragments heavier than $^4$He at the precompound stage has already provided preliminary results that have much better agreement with experimental data.

nucl-th↗
arXiv2014

Decay data of radionuclides along the valley of nuclear stability for astrophysical applications

Several directions of the demand of decay data in nuclear astrophysics are discussed for radionuclides near the valley of nuclear stability. The current decay data evaluation results have been presented for a number of radionuclides of astrophysical interest. An extended list of such nuclides is offered for their nuclear characteristics to be further evaluated by the Decay Data Evaluation Project cooperation participants.

nucl-ex↗
arXiv2014

High electric field development for the SNS nEDM Experiment

A new experiment to search for the permanent electric dipole moment of the neutron is being developed for installation at the Spallation Neutron Source at Oak Ridge National Laboratory. This experiment will be performed in liquid helium at ? 0:4 K and requires a large electric field (E ~ 75 kV/cm) to be applied in liquid helium. We have constructed a new HV test apparatus to study electric breakdown in liquid helium. Initial results demonstrated that it is possible to apply fields exceeding 100 kV/cm in a 1 cm gap between two electropolished stainless steel electrodes12 cm in diameter for a wide range of pressures.

physics.ins-det↗
arXiv2014

Light WIMPs, Equivalent Neutrinos, BBN, and the CMB

Recent updates to the observational determinations of the primordial abundances of helium and deuterium are compared to the predictions of BBN to infer the universal ratio of baryons to photons (or, the present Universe baryon mass density parameter Omega_B h^2), as well as to constrain the effective number of neutrinos (N_eff) and the number of equivalent neutrinos (Delta N_nu). These BBN results are compared to those derived independently from the Planck CMB data. In the absence of a light WIMP (chi), N_eff = 3.05(1 + Delta N_nu/3). In this case, there is excellent agreement between BBN and the CMB, but the joint fit finds that Delta N_nu = 0.40 +/- 0.17, disfavoring standard big bang nucleosynthesis (SBBN: Delta N_nu = 0) at 2.4 sigma, as well as a sterile neutrino (Delta N_nu = 1) at 3.5 sigma. In the presence of a light WIMP, the relation between N_eff and Delta N_nu depends on the WIMP mass, leading to degeneracies among N_eff, Delta N_nu, and m_chi. The complementary and independent BBN and CMB data can break some of these degeneracies. Depending on the nature of the light WIMP (Majorana or Dirac fermion, real or complex scalar) the joint BBN + CMB analyses set a lower bound to m_chi in the range from 0.5 to 5 MeV, and they identify best fit values for m_chi in the range from 5 to 10 MeV. The joint BBN + CMB analyses find a best fit value for the number of equivalent neutrinos, Delta N_nu = 0.65, nearly independent of the nature of the WIMP. The best fit still disfavors the absence of dark radiation (Delta N_nu = 0 at 95% confidence), while allowing for the presence of a sterile neutrino (Delta N_nu = 1 at less than 1 sigma). For all cases considered here, the lithium problem persists. These results, presented at the 2013 Rencontres de l'Observatoire de Paris - ESO Workshop, are based on Nollett & Steigman 2013 (arXiv:1312.5725 [astro-ph.CO]).

astro-ph.CO↗
arXiv2014

Voluminous D2 source for intense cold neutron beam production at the ESS

The development of the flat moderator concept at ESS recently opened up the possibility that a single flat moderator above the target could serve all the scattering instruments, that rely on high brightness. This would allow for the introduction of a fundamentally different moderator below the target for the complementary needs of certain fundamental physics experiments. To facilitate experiments depending on the total number of neutrons in a sizable beam, the option of a voluminous D2 moderator, in a large cross-section extraction guide is discussed and its neutronic performance is assessed.

physics.ins-det↗
arXiv2014

Further investigations on the Neutron Flux Generation in a Plasma Discharge Electrolytic Cell

Our recent paper on the "Search for Neutron Flux Generation in a Plasma Discharge Electrolytic Cell" [1] has as main goal the validation of the experiment in Ref.[2]. As a follow-up, Ref.[3] moves a set of objections on our procedure and presents argumentations on why the experiments should not yield the same results. We collect here additional material and calculations that contribute to understanding the observed discrepancies. Furthermore we prove that the absence of signals from Indium activation detectors reported also for the experiment of Ref.[2] is a clear indication that neutron production does not occur. [1] R.Faccini et al arXiv:1310.4749 [2] D.Cirillo et al, Key Engineering Materials 495, 104 (2012). [3] A.Widom et al. arXiv:1311.2447

nucl-ex↗
arXiv2014

On the existence of the $\it NN$-decoupled dibaryon $d^\ast_1$(1956)

We present strong experimental evidence for the existence of a nonstrange $\it NN$-decoupled dibaryon with a mass of about 1956 MeV stable against strong decay, which is a very likely candidate for long-sought multiquark hadrons with the baryon number B=2. We start by presenting the first evidence for the existence of this dibaryon called $d^{\ast }_{1}$(1956), that was found in the energy spectrum of coincident photons emitted at $\pm 90^0$ from the reaction $pp \to pp γγ$ at an energy of 216 MeV measured at JINR. We then show its signatures found in several experimental energy spectra of single photons and invariant mass spectra of photon pairs from photon production processes induced by nucleon-nucleon and nucleon-nucleus collisions at intermediate energies.

hep-ph↗
arXiv2014

A new approach in the detection of weak γ-ray peak of the radioactive waste in tomography γ scanning

We demonstrate a new approach to efficiently detect weak γ-ray peak of the radioactive waste in tomographic γ scanning (TGS). In the TGS measurement, γ-ray peak identification is usually difficult due to the short measurement time that results in a lower γ-ray energy produced by the decay. Consequently, the resulting significant scattering in the low-energy side leads to strong statistical fluctuations and low detection efficiency that overwhelm the γ-ray peak. Here, we propose the use of shift invariance wavelet algorithm for low-energy part of the spectrum for weak γ-ray peak smoothing. The proposed algorithm not only overcomes the pseudo-Gibbs in the high-resolution γ-ray spectrum de-noising by the traditional wavelet transform, but also keeps quality of the weak γ-ray characteristic peak as well. Our new approach shows a significantly improved performance of the figure of merit (FOM) together with lower limit of quantitation (LLOQ) compared with the traditional wavelet transform. These results indicate the significant potential of our approach that could effectively increase the accuracy of weak γ-ray detecting activation analysis in TGS.

nucl-ex↗
arXiv2014

A new concept for safeguarding and labeling of long-term stored waste and its place in the scope of existing tagging techniques

The idea of a novel labeling method is suggested for a new way of long-term security identification, inventory tracking, prevention of falsification and theft of waste casks, copper canisters, spent fuel containers, mercury containers, waste packages and other items. The suggested concept is based on the use of a unique combination of radioisotopes with different predictable half life. As an option for applying the radioisotope tag to spent fuel safeguarding it is suggested to use a mixture of α-emitting isotopes, such as 241Am etc., with materials that easily undergo α-induced reactions with emission of specific γ-lines. Thus, the existing problem of the disposing of smoke detectors or other devices [1] which contain radioisotopes can be addressed, indirectly solving an existing waste problem. The results of the first pilot experiments with two general designs of storage canisters, namely a steel container which corresponds to the one which is commonly used for long-term storing of mercury in Europe and USA and a copper canister, the one which is in applications for nuclear repositories, are presented. As one of the options for a new labeling method it is proposed to use a multidimensional bar code symbology and tungsten plate with ultrasound techniques. It is shown that the new radioisotope label offers several advantages in the scope of existing tagging techniques (overview is given) and can be implemented even with low activity sources.

physics.ins-det↗
arXiv2014

Nucleon-Nucleon scattering from dispersion relations: next-to-next-to-leading order study

We study nucleon-nucleon ($NN$) scattering by applying the $N/D$ method in chiral perturbation theory up to next-to-next-to-leading (NNLO) order in the calculation of the imaginary part of the $NN$ partial-wave amplitudes along the left-hand-cut, which is the dynamical input for this approach. A quite good reproduction of the Nijmegen partial-wave analysis phase shifts and mixing angles is obtained, which implies a steady improvement in the accurateness achieved by increasing the chiral order in the calculation of the dynamical input. A power counting for the subtraction constants is established, which is appropriate for those subtractions attached to both the left- and right-hand cuts. We discuss that it is not necessary to modify the $NN$ chiral potential at NNLO to agree with data, but instead one should perform the iteration of two-nucleon intermediate states to finally achieve analytic and unitarity $NN$ partial-wave amplitudes in a well-defined way. We also confirm at NNLO the long-range correlations between the $NN$ $S$-wave effective ranges and scattering lengths, when employing only once-subtracted dispersion relations, that holds up to around 10% when compared with experimental values.

nucl-th↗
arXiv2014

Azimuthal Jet Tomography at RHIC and LHC

A generic jet-energy loss model that is coupled to state-of-the-art hydrodynamic fields and interpolates between a wide class of running coupling pQCD-based and AdS/CFT-inspired models is compared to recent data on the azimuthal and transverse momentum dependence of high-pT pion nuclear modification factors and high-pT elliptic flow measured at RHIC and LHC. We find that RHIC data are surprisingly consistent with various scenarios considered. However, extrapolations to LHC energies favor running coupling pQCD-based models of jet-energy loss. While conformal holographic models are shown to be inconsistent with data, recent non-conformal generalizations of AdS holography may provide an alternative description.

hep-ph↗
arXiv2014

Observation of anti-magnetic rotations in 104Pd

The electric quadrupole transition rates for the high spin yrast states of 104 Pd have been measured by using the DSAM technique. These values decrease with the increase of angular momentum which is a signature of anti-magnetic rotation. A numerical calcula- tion based on semi-classical particle plus rotor model for anti-magnetic rotation gives a good description of the experimental routhian and the transition rates. This is the first observation of AMR in a nucleus other than Cadmium.

nucl-ex↗
arXiv2014

Net-proton measurements at RHIC and the QCD phase diagram

Two measurements related to the proton and anti-proton production near midrapidity in center of mass energies of 7.7, 11.5, 19.6, 27, 39, 62.4 and 200 GeV Au+Au collisions using the STAR detector at the Relativistic Heavy Ion Collider (RHIC) are discussed. At intermediate impact parameters the slope parameter of the directed flow versus rapidity (dv1/dy) for the net-protons shows a non-monotonic variation as a function of the beam energy. This non-monotonic variation is characterized by the presence of a minimum in dv1/dy between 11.5 and 19.6 GeV and a change in the sign of dv1/dy twice between 7.7 and 39 GeV. At small impact parameters the product of the moments of net-proton distribution, kurtosis x variance and skewness x standard deviation are observed to be significantly below the corresponding measurements at large impact parameter collisions for 19.6 and 27 GeV. The kurtosis x variance and skewness x standard deviation at these beam energies deviate from the expectations from Poisson statistics and that from a Hadron Resonance Gas model. Both these measurements have implications towards the understanding of the QCD phase structures, the first order phase transition and the critical point in the high baryonic chemical potential region of the phase diagram.

nucl-ex↗
arXiv2014

Simulations of beta-decay of 6He in an Electrostatic Ion Trap

Trapped radioactive atoms present exciting opportunities for the study of fundamental interactions and symmetries. For example, detecting beta decay in a trap can probe the minute experimental signal that originates from possible tensor or scalar terms in the weak interaction. Such scalar or tensor terms affect, e.g., the angular correlation between a neutrino and an electron in the beta-decay process, thus probing new physics of beyond-the-standard-model nature. The present system focuses on a novel use of an innovative ion trapping device, the Electrostatic Ion Beam Trap. Such a trap has not been previously considered for Fundamental Interaction studies and exhibits potentially very significant advantages over other schemes. These advantages include improved injection efficiency of the radionuclide under study, an extended field-free region, ion-beam kinematics for better efficiency and ease-of operation and the potential for a much larger solid angle for the electron and recoiling atom counters. The beta-decay of trapped 6He is discussed and preliminary Monte-Carlo (MC) simulation and error-analysis considerations are presented.

nucl-ex↗
arXiv2014

Present Status of the EMC effect

The present status of the EMC effect, the modification of the per nucleon cross section in deep-inelastic lepton nucleus scattering by the nuclear environment, is reviewed.

hep-ex↗