Nuclear Physics Models Research Articles

Time-Dependent and/or Nonlocal Representations of Hilbert Spaces in Quantum Theory

A few recent innovations of the applicability of standard textbook Quantum Theory are reviewed. The three-Hilbert-space formulation of the theory (known from the interacting boson models in nuclear physics) is discussed in its slightly broadened four-Hilbert-space update. Among applications involving several new scattering and bound-state problems the central role is played by models using apparently non-Hermitian (often called “crypto-Hermitian”) Hamiltonians with real spectra. The formalism (originally inspired by the topical need for a mathematically consistent description of tobogganic quantum models) is shown to admit even certain unusual nonlocal and/or “moving-frame” representations H(S) of the standard physical Hilbert space of wave functions.

Measurement of Angular-Dependent Neutron Production with 140-MeV Protons

Neutron energy spectra at 90 deg produced from stopping-length graphite, aluminum, iron, and lead targets and at 180 deg produced from a thin lithium target bombarded with 140-MeV protons were measured in the irradiation room of the neutron time-of-flight (TOF) course at the Research Center of Nuclear Physics of Osaka University. The neutron energy spectra were obtained by using the TOF technique in the energy range from 10 MeV to the incident proton energy of 140 MeV. The experimental data for a thick target at 90 deg were compared with calculations performed with the Particle and Heavy Ion Transport code System (PHITS) using the evaluated nuclear data. It was shown that PHITS using the evaluated nuclear data is able to reproduce the secondary neutron spectra at 90 deg. The experimental data for a thin target at 180 deg were compared with calculations using the nuclear physics models in PHITS and the Monte Carlo N-Particle eXtended code (MCNPX). We found that the two codes work well at 180 deg in the neutron energy region above 10 MeV.

Probing particle and nuclear physics models of neutrinoless double beta decay with different nuclei

Half-life estimates for neutrinoless double beta decay depend on particle physics models for lepton-flavor violation, as well as on nuclear physics models for the structure and transitions of candidate nuclei. Different models considered in the literature can be contrasted---via prospective data---with a ``standard'' scenario characterized by light Majorana neutrino exchange and by the quasiparticle random phase approximation, for which the theoretical covariance matrix has been recently estimated. We show that, assuming future half-life data in four promising nuclei ($^{76}\mathrm{Ge}$, $^{82}\mathrm{Se}$, $^{130}\mathrm{Te}$, and $^{136}\mathrm{Xe}$), the standard scenario can be distinguished from a few nonstandard physics models, while being compatible with alternative state-of-the-art nuclear calculations (at 95% C.L.). Future signals in different nuclei may thus help to discriminate at least some decay mechanisms, without being spoiled by current nuclear uncertainties. Prospects for possible improvements are also discussed.

MO‐EE‐A2‐01: Nuclear Model Evaluation of Uncertainties in Therapeutic Absorbed Dose and Secondary Neutron Production in Proton Radiotherapy Using MCNPX

Purpose: To evaluate differences in nuclear physics models of MCNPX for uncertainties in 1) the dosimetric characteristics of the therapeutic dose for SOBP and cross‐field profiles and 2) stray neutron fields produced in a proton therapy unit using the default Bertini model option as the baseline. Methods and Materials: The general purpose Monte Carlo N‐Particle eXtended (MCNPX) code was used to calculate the therapeutic absorbed dose and spectral neutron fluence with three nuclear model options: the Bertini Model, the Cascade Exciton Model (CEM), and the Liège Intra‐Nuclear Cascade Model (INCL4). Each model is included as a physics option in MCNPX. For initial beam energy of 160 MeV, dose calculations were carried out in a water phantom positioned 24 cm downstream of the nozzle exit while in‐air calculations of the neutron spectral fluence were tallied in spheres positioned at isocenter, 100 cm downstream of isocenter and at lateral distances of ± 100 cm off‐axis. Calculations of secondary neutrons produced external to the nozzle housing were evaluated among the models for several parameters including the ambient neutron dose equivalent per therapeutic absorbed dose. Results: Our results indicate that calculations of the therapeutic absorbed dose were in close agreement (⩽1% difference) for all nuclear model options. On the other hand, the differences in the neutron spectral fluence calculations typically varied by a factor of 2 or more among the models. Conclusions: We found that all three inelastic nuclear interaction models provided excellent agreement in the therapeutic dose distributions. However, we observed substantial differences in the neutron spectral fluence calculations that suggest further investigation may be desirable for estimating the out of field radiation exposure uncertainties among the models.

Uncertainties for criticality-safety benchmarks and [formula omitted] distributions

In a previous paper, we have presented a new method to propagate uncertainties of fundamental nuclear physics model and parameters to large and complicated nuclear systems. In this study, we demonstrate that large-scale uncertainty calculations are feasible by applying this methodology to a series of criticality-safety benchmarks. Uncertainties and distributions for the k eff parameter are obtained, considering isotopes from 19F to 241Am. More than 200 criticality-safety benchmarks were studied and uncertainties on k eff due to nuclear data were extracted. For more than 40 cases, a complete k eff distribution is presented. In some cases where Zr, Pb and W nuclear data uncertainties were considered, an asymmetric k eff distribution is found, confirming our previous observations.

Mechanisms of nuclear reactions at interaction of cosmic rays with materials and nanostructures

The mechanism of failures of microelectronic elements, caused by ionization of atoms by recoil nuclei and secondary fragments formed at nuclear interactions of cosmic-ray protons and light ions with substance, has been analyzed. Models of nuclear physics are used to calculate the macroscopic failure cross section.

Measurement and parametrization of proton elastic scattering cross sections for nitrogen

The cross sections for the elastic scattering of protons from natural nitrogen at non-Rutherford scattering energies were measured at three laboratory scattering angles: 118°, 150°, and 165°. The experimental data were parametrized in the framework of nuclear physics models. A benchmark experiment was performed in order to prove that the excitation functions obtained in the present work can be used to adequately simulate the yield from a thick target containing nitrogen.

Towards sustainable nuclear energy: Putting nuclear physics to work

We have developed a new method to propagate the uncertainties of fundamental nuclear physics models and parameters to the design and performance parameters of future, clean nuclear energy systems. Using Monte Carlo simulation, it is for the first time possible to couple these two fields at the extremes of nuclear science without any loss of information in between. With the help of a large database of nuclear reaction measurements, we have determined the uncertainties of theoretical nuclear reaction models such as the optical, compound nucleus, pre-equilibrium and fission models. A similar assessment is done for the parameters that describe the resolved resonance range. Integrating this into one simulation program enables us to describe all open channels in a nuclear reaction, including a complete handling of uncertainties. Moreover, in one and the same process, values and uncertainties of nuclear reactor parameters are computed. This bypasses all the intermediate steps which have been used so far in nuclear data and reactor physics. Two important results emerge from this work: (a) we are able to quantify the required quality of theoretical nuclear reaction models directly from the reactor design requirements and (b) our method leads to a deviation from the commonly assumed normal distribution for uncertainties of safety related reactor parameters, and this should be taken into account for future nuclear energy development. In particular, calculated k eff distributions show a high-value tail for fast reactor spectra.

Dynamical symmetry in spinor Bose-Einstein condensates

We demonstrate that dynamical symmetry plays a crucial role in determining the structure of the eigenspectra of spinor Bose-Einstein condensates (BECs). In particular, the eigenspectra of spin-1 and spin-2 BECs in the single-mode approximation are shown to be completely determined by dynamical symmetries, where a spin-2 BEC corresponds to the U(5) limit of the interacting boson model in nuclear physics. The eigenspectrum of a spin-3 BEC is solved analytically for a specific class of coupling constants, while it is shown that dynamical symmetry alone is not sufficient to determine the spectrum for arbitrary coupling constants. We also study the low-lying eigenspectra of spin-1 and spin-2 BECs in the absence of external magnetic field, and find, in particular, that the quasidegenerate spectra emerge for antiferromagnetic and cyclic phases. This implies that these systems are highly susceptible to external perturbations and may undergo symmetry-breaking transitions to other states upon increasing the system's size.

SPHEROIDAL AND TORSIONAL MODES OF QUASISTATIC SHEAR OSCILLATIONS IN THE SOLID GLOBE MODELS OF NUCLEAR PHYSICS AND PULSAR ASTROPHYSICS

The past three decades of investigation on nuclear physics and pulsar astrophysics have seen gradual recognition that elastodynamic approach to the continuum mechanics of nuclear matter provides proper account of macroscopic motions of degenerate Fermi-matter constituting interior of the nuclear material objects, the densest of all known today. This paper focuses on one theoretical issue of this development which is concerned with oscillatory behavior of a viscoelastic solid globe in the regime of quasistatic, force-free, noncompressional oscillations less investigated in the literature compared to oscillations in the regime of standing shear waves. We show that in this case the problem of computing frequency and lifetime of spheroidal and torsional modes of nonradial shear vibrations damped by viscosity can be unambiguously resolved by working from the energy balance equation and taking advantage of the Rayleigh's variational method. The efficiency of this method is demonstrated by solid globe models of nuclear physics and pulsar astrophysics dealing with oscillations of a spherical mass of a viscoelastic Fermi-solid with homogeneous and nonhomogeneous profiles of the bulk density, the shear modulus, and the shear viscosity.

A treatment of medium-energy particle induced fission for spallation-systems’ calculations

A method for including medium-energy fission into neutronic calculations for spallation systems is described and discussed. The basis is a semi-empirical evaporation plus fission model able to treat a wide range of nuclear states in the mass region above about 100amu with nuclear excitation energies up to 1000MeV. In combination with suitable nuclear physics models describing the entrance channels and a suitable evaporation algorithm, this is able to give a full description of the de-excitation of the intermediate nuclear states formed in interactions with target nuclei from Ag to Cf by (i) medium energy (up to a few GeV) nucleons and pions, (ii) thermal and fast neutrons and (iii) light ions with energy up to several 100MeV/A.

Cosmochronometer andr-Process Nucleosynthesis

Nuclear cosmochronometry is a direct method to measure cosmic age. It has been believed that the abundance ratio of Th/Eu is a reliable chronometer and Th/Eu ratios of metal-poor stars have been studied intensively to obtain a lower limit of Galactic age. However, after the actinide-boosted metal-poor star CS 31082-001 had been found, applicability of Th/Eu chronometer to metal-poor stars became questionable. Furthermore, theoretical r -process calculations indicate that the Th/Eu production ratios strongly depend on the nucleosynthesis environment compared to other stable elements between the second and third peak, including Pb. It is impossible to determine the Th/Eu production ratio by theoretical study at this point, though it is essential for the chronometer. Besides, observed universality of r -process abundances does not guarantee a universal Th/Eu production ratio anymore. Th/Eu chronometer is now facing a serious crisis. On the other hand, the U/Th production ratio obtained by theoretical calculation does not depend on the nucleosynthesis environment significantly. Although there is only one U measurement of metal-poor stars at this point, the U/Th chronometer seems to be still robust. Many uncertainties related to data analyses and nuclear physics models still remain to be resolved.

Design and characterization of a compact multi-detector array for studies of induced gamma emission: Spontaneous decay of 178m2Hf as a test case

Reports that incident photons near 10 keV can induce the emission of gamma rays with concomitant energy release from the 31-year isomer of 178Hf challenge established models of nuclear and atomic physics. In order to provide a direct and independent assessment of these claims, a multi-detector system was designed as a specialized research tool. The YSU miniball is unique in its combination of performance characteristics, compact size and portability, enabling it to be easily transported to and placed within the confines of beamline hutches at synchrotron radiation sources. Monochromatic synchrotron radiation was used in the most recent studies from which evidence of prompt triggering was claimed, suggesting similar sites for independent tests of these results. The miniball array consists of six high-efficiency BGO scintillators coupled with a single 65% Ge detector and provides time-resolved gamma-ray calorimetry rather than purely spectroscopic data. The need to record high detected folds from the array (up to seven-fold gamma coincidences) makes this system different in practice from standard spectroscopic arrays for which data is typically restricted to triples or lower folds. Here the system requirements and design are discussed, as well as system performance as characterized using the well-known natural decay cascades of 178m2Hf. This serves as the foundation for subsequent high-sensitivity searches for low-energy triggering of gamma emission from this isomer.

Mathematical Analysis of a Generalized Chiral Quark Soliton Model

A generalized version of the so-called chiral quark soliton model (CQSM) in nuclear physics is introduced. The Hamiltonian of the generalized CQSM is given by a Dirac type operator with a mass term being an operator-valued function. Some mathematically rigorous results on the model are reported. The subjects included are: (i) supersymmetric structure; (ii) spectral properties; (iii) symmetry reduction; (iv) a unitarily equivalent model.

Spectral properties of a Dirac operator in the chiral quark soliton model

We consider a Dirac operator H acting in the Hilbert space L2(R3;C4)⊗C2, which describes a Hamiltonian of the chiral quark soliton model in nuclear physics. The mass term of H is a matrix-valued function formed out of a function F:R3→R, called a profile function, and a vector field n on R3, which fixes pointwise a direction in the isospin space of the pion. We first show that, under suitable conditions, H may be regarded as a generator of a supersymmetry. In this case, the spectra of H are symmetric with respect to the origin of R. We then identify the essential spectrum of H under some condition for F. For a class of profile functions F, we derive an upper bound for the number of discrete eigenvalues of H. Under suitable conditions, we show the existence of a positive energy ground state or a negative energy ground state for a family of scaled deformations of H. A symmetry reduction of H is also discussed. Finally a unitary transformation of H is given, which may have a physical interpretation.

Nuclear transparency with theγn→π−pprocess in4He

We have measured the nuclear transparency of the fundamental process γn→π−p in 4He. These measurements were performed at Jefferson Lab in the photon energy range of 1.6–4.5 GeV and at θcmπ=70° and 90°. These measurements are the first of their kind in the study of nuclear transparency in photoreactions. They also provide a benchmark test of Glauber calculations based on traditional models of nuclear physics. The transparency results suggest deviations from the traditional nuclear physics picture. The momentum transfer dependence of the measured nuclear transparency is consistent with Glauber calculations that include the quantum chromodynamics phenomenon of color transparency.Received 9 May 2003DOI:https://doi.org/10.1103/PhysRevC.68.021001©2003 American Physical Society

R-Process abundance universality and actinide cosmochronology

We review recent observational and theoretical results concerning the presence of actinide nuclei on the surfaces of old halo stars and their use as an age determinant. We present model calculations which show that the observed universality of abundances for 56< Z<75 elements in these stars does not necessarily imply a unique astrophysical site for the r-process. Neither does it imply a universality of abundances of nuclei outside of this range. In particular, we show that a variety of astrophysical r-process models can be constructed which reproduce the same observed universal r-process curve for 56< Z<75 nuclei, yet have vastly different abundances for Z≥75 and possibly Z<56 as well. This introduces an uncertainty into the use of the Th/Eu chronometer as a means to estimate the ages of the metal deficient stars. We do find, however, that the U/Th ratio is a robust chronometer. This is because the initial production ratio of U to Th is almost independent of the astrophysical nucleosynthesis environment. The largest remaining uncertainties in the U/Th initial production ratio are due to the input nuclear physics models.

Nuclear data for astrophysics

In order to address important astrophysics problems such as the origin of the chemical elements, the inner workings of our Sun, and the evolution of stars, crucial nuclear datasets are needed. Recent evaluation and dissemination efforts have produced a number of such datasets, many of which are online and readily available to the research community. Current international efforts in this field are, unfortunately, insufficient to keep pace with the latest nuclear physics measurements and model calculations. A dedicated effort is required to update and expand existing datasets. I discuss several strategies and new initiatives that would ensure a more effective utilization of nuclear data in astrophysics. These include launching a new web site www.nucastrodata.org to aid in locating available nuclear data sets, and an interactive online plotting program with an easy-to-use graphical user interface to over 8000 reaction rates. An enhanced effort in this field could be maintained by formalizing the position of a Nuclear Astrophysics Data Coordinator.

Improvements of Intra-Nuclear Cascade Model Stimulated by Recent Spallation Data

In high-energy transport codes used to design Accelerator Driven Systems or spallation neutron sources, elementary interactions are computed through nuclear physics models. Among these, Intra-Nuclear Cascade models play a major role since the excitation energy at the end of the INC stage determines the number of evaporated particles. Therefore, in simulation of spallation targets, INC influences the total number of emitted neutrons and the isotopic distribution of produced nuclei. Recent data regarding the production of neutrons and residual nuclei in proton induced reactions make it possible to test the reliability of INC models and to improve them. A new version (INCL4) of the Liège INC model including especially a realistic nuclear density and a consistent treatment of the Pauli principle is presented.

Quark models of nuclear physics

Quark models of nuclear physics