Thermodynamic consistency for nuclear matter calculations

We investigate the relation between the binding energy and the Fermi energy and between different expressions for the pressure in cold nuclear matter. For a self-consistent calculation based on a Φ derivable T-matrix approximation with off-shell propagators, the thermodynamic relations are well satisfied unlike for a G-matrix or a T-matrix approach using quasi-particle propagators in the ladder diagrams. Received: 8 February 2001 / Accepted: 11 June 2001     

Cluster-variational calculations for extended nuclear systems

The energy as a function of density is calculated for neutron matter and for symmetrical nuclear matter, based on Jastrow trial wave functions. The energy expectation value is truncated in low cluster order. A detailed analysis of the two- and three-body cluster contributions and a special portion of the four-body contribution is given. Variation of a parameterized two-body correlation function is subjected to constraints designed to confine the trial wave function to the domain corresponding to rapid cluster convergence. Results are presented for a variety of model central potentials containing hard cores, for different sets of constraints, and for two- and three-parameter correlation functions. Calculations constrained by the “average Pauli condition” are found to yield results very close to those constrained by the “normalization” or “unitarity” condition, and the two-parameter correlation function appears to be quite adequate. The convergence of the cluster expansion, as reflected in the low orders, is good except at the highest densities considered. The three-body cluster contribution displays, in all cases, a remarkable internal cancellation between its “two-correlation-line” addends.     

Physical and numerical verification of discharge calculations

Calculations of radio frequency discharge parameters, and to a lesser extent DC discharge parameters, are apparently highly sensitive to the physical model used. The testing of numerical schemes for error, considering alternative formulations and simple physical models, is carefully considered. Within kinetic models a number of options exist, having different capabilities, the implications of which are examined. Particle simulations are discussed, and mesh-based kinetic calculations are considered in detail. An efficient and accurate mesh-based kinetic model which closely replicates the physical processes taking place is presented. Ways to improve its accuracy, which is limited by the resolution of the mesh, and their effects are presented. Cross-checking of various numerical formulations shows that the results for each are essentially the same. Physical reasoning and simple estimates of discharge parameters are used to further substantiate the predictions for a particular discharge, and the processes taking place in an RF discharge in helium are described in detail     

Some problems in nuclear reaction calculations

Convergence problems arise in nuclear reaction theories when approximate wave functions are used to describe the internal motion of composite particles involved in the reaction. Implications on the results of a reaction calculation are discussed and models with unique solutions are defined. Some tentative criteria are given as to which model might have solutions similar to the ones obtained with exact channel functions. A least-squares method for linear parameter variation which does not show spurious singularities is also discussed.     

Revision of calculations for kaon production in relativistic nuclear collisions

Due to an elementary mistake in plotting the data, our previous calculations of kaon production in relativistic nuclear collisions are approximately a factor of two too small. The revised results are in good agreement with the data on total kaon yields.     

Projection operators in nuclear structure calculations

Projection operators are an important tool in nuclear structure theory, because in many circumstances it is useful to construct wave-functions ψ which are not eigenfunctions of some operator Λ, although it is apparent that the physical states must be eigenstates of that operator. Thus one first constructs ψ and then projects from it onto eigenfunctions of Λ. We discuss the cases of angular momentum, isospin, centre of mass energy, particle number and antisymmetry. We describe the integral projection operator, an expansion in shift operators, the product operator of Löwdin and another product operator (the cosine product). Certain methods which appear in the literature are seen to be equivalent to one or the other of these. We consider factors that influence the choice of an appropriate method. Projection occurs frequently in the context of a variational method (such as Hartree-Fock or BCS). We consider the question of projection before or after variation.     

Methods and computer codes for nuclear systems calculations

Some numerical methods for reactor cell, sub-critical systems and 3D models of nuclear reactors are presented. The methods are developed for steady states and space-time calculations. Computer code TRIFON solves space-energy problem in (X, Y) systems of finite height and calculates heterogeneous few-group matrix parameters of reactor cells. These parameters are used as input data in the computer code SHERHAN solving the 3D heterogeneous reactor equation for steady states and 3D space-time neutron processes simulation. Modification of TRIFON was developed for the simulation of space-time processes in sub-critical systems with external sources. An option of SHERHAN code for the system with external sources is under development.      

Laser safety programs in general surgery

General surgery represents a speciality where, while any procedure can be performed with lasers, there are no procedures for which the laser is the sine quo non. The general surgeon may perform a variety of procedures with a multitude of laser wavelengths and technologies. Laser safety in general surgery requires a multidisciplinary approach. Effective laser safety requires the oversight of the hospital's "laser usage committee" and "laser safety officer" while providing a workable framework for daily laser use in a variety of clinical scenarios simultaneously. This framework must be user-friendly rather than oppressive. This presentation will describe laser safety at the Rochester General Hospital, a tertiary care, community-based teaching hospital. The safety program incorporates the following components: input to physician credentialing and training, education and in-servicing of nursing and technical personnel, equipment purchase and maintenance, quality assurance, and safety monitoring. The University of Rochester general surgery residency training program mandates laser training during the PGY-2 year. This program stresses the safe use of lasers and provides the basis for graded hands-on experience during the surgical residency. The greatest challenge for laser safety in general surgery centers on the burgeoning field of minimally invasive surgery. Safety assurance must be balanced so as to maintain a safe operating-room environment while ensuring patient safety and the ability to permit the surgery to proceed efficiently. Safety measures for laparoscopic procedures must be sensitive to the needs of the surgical team while not providing confusing signals for the "gallery" observers. This task is critical for the safe operation of lasers in general surgery. Effective laser safety in general surgery requires constant vigilance tempered with sensitivity to the needs of the surgeon and the patient as laser technology and its applications continue to evolve.     

About efficient quasi-Newtonian schemes for variational calculations in nuclear structure

The Broyden-Fletcher-Goldhaber-Shanno (BFGS) quasi-Newtonian scheme is known as the most efficient scheme for variational calculations of energies. This scheme is actually a member of a one-parameter family of variational methods, known as the Broyden b \beta -family. In some applications to light nuclei using microscopically derived effective Hamiltonians starting from accurate nucleon-nucleon potentials, we actually found other members of the same family which have better performance than the BFGS method. We also extend the Broyden b \beta -family of algorithms to a two-parameter family of rank-three updates which has even better performances.     

Dosimetric verification of treatment planning system superficial dose calculations for proton beam

To investigate the accuracy of Eclipse treatment planning system (TPS) dose calculations at the surface. It is desirable to know the accuracy of the proton treatment planning system in predicting dose at superficial region. All measurements were performed in a clinical proton beam at the National Cancer Center in Korea. Proton treatment plans were developed for a superficial planning target volume (PTV) contoured on a cylindrical polymethylmethacrylate phantom specially designed for this study. Dose was then measured at the surface and also in the PTV for these treatment plans and compared against the TPS calculations. For our study, a model GD-301 glass dosimeters were used. The proton treatment planning system overestimated the superficial dose without use of bolus as much as by 7–14% when compared to glass dosimeter. On the other hand, with use of bolus to cover the superficial region, surface dose between the calculation from Eclipse and measurement using the glass dosimeter are approximately within 3%.     

Monte Carlo calculations of electron scattering in solids for nuclear spectroscopy

Direct MC modelling of individual elastic and inelastic scattering events of electrons in solids is described. The examples cover transmission through thin solid layers as well as backscattering from flat surfaces of bulk solids. Divergent beams and isotropic emission of incident electrons with energies from 5 to 200 keV are treated.Presented at the Seminar on Secondary Electrons in Electron Spectroscopy, Microscopy, and Microanalysis, Chlum (The Czech Republic), 21–24 September, 1993.     

WLW 原子核质量模型在r过程研究中的应用

本工作利用最近提出的WLW宏观-微观原子核质量模型, 在经典 r过程框架下 很好地描述了太阳系r过程核素丰度分布. 与常用的FRDM质量模型相比, 新计算更好地再现了A≈ 135和A≈ 180质量区的太阳系r过程核素丰度, 尤其 避免了其他相似计算中A=135 附近出现的 与观测不符的丰度峰问题. 分析表明, 这种差异可能暗示WLW更为合理地处理了壳结构和对称能.     

Statistical description of nuclear break-up

We present an overview of concepts and results obtained with statistical models in the study of nuclear multifragmentation. Conceptual differences between statistical and dynamical approaches and the selection of experimental observables for identification of these processes are outlined. New and perspective developments, like inclusion of in-medium modifications of the properties of hot primary fragments, are discussed. We list important applications of statistical multifragmentation in other fields of research.     

Microscopic calculations of charge-exchange nuclear modes

Microscopic calculations of nuclear states excited by means of charge-exchange reactions and involving spin and isospin degrees of freedom, in particular, of the Gamow—Teller and the spin—dipole resonances, are discussed. The framework is a fully self-consistent nonrelativistic spherical quasiparticle random-phase approximation constructed on top of the Hartree—Fock—Bardeen—Cooper—Schrieffer approach. Our results are compared with available experimental data, and a critical discussion is attempted. The text was submitted by the authors in English.     

Variational calculations of asymmetric nuclear matter

We report on variational calculations of the energy E(ρ, β) of asymmetric nuclear matter having ? = ?_n + ?_p = 0.05 to 0.35 fm^?3, and β = (?_n ? ?_p/g9 = 0 to 1. The nuclear h used in this work consists of a realistic two-nucleon interaction, called v₁₄, that fits the available nucleon-nucleon scattering data up to 425 MeV, and a phenomenological three nucleon interaction adjusted to reproduce the empirical properties of symmetric nuclear matter. The variational many-body theory of symmetric nuclear matter is extended to treat matter with neutron excess. Numerical and analytic studies of the β-dependence of various contributions to the nuclear matter energy show that at ? < 0.35 fm^?3 the β⁴ terms are very small, and that the interaction energy EI(ρ, β) defined as E(ρ, β) ? T_F(ρ, β), where T_F is the Fermi-gas energy, is well approximated by EI₀(?) + β²EI₂(ρ). The calculated symmetry energy at equilibrium density is 30 MeV and it increases from 15 to 38 MeV as ? increases from 0.05 to 0.35 fm^?3.     

Statistical model of an atom in electron scattering calculations

The parameters describing scattering of electrons by atoms, which usually involve multiple integration of the atomic potentials, may be severely affected by the accuracy of these potentials. In the present work an iterative procedure is proposed providing a sequence of solutions of the Thomas-Fermi equation with increasing accuracy. Such a sequence makes it possible to establish the sensitivity of a given parameter to the accuracy of the atomic potential, and consequently to determine the accurate value of this parameter. Based on the present solutions, the differential scattering cross-sections for the Thomas-Fermi atom are calculated, and are found to deviate from the literature data.     

Comparison of coordinate-space techniques in nuclear mean-field calculations

We investigate three different numerical representations for nuclear mean-field calculations: finite differences, Fourier representation, and basis-splines. We compare these schemes with respect to precision and speed. It turns out that Fourier techniques and basis-splines are much superior in precision to finite differences. The Fourier representation in connection with the fast Fourier transformation is advantageous for large grids whereas matrix techniques, derived either from basis-splines or from Fourier representation, are preferable for smaller grids.     

Jastrow-type calculations for nuclear matter with the normalization condition

Results are given of constrained Jastrow calculations for the energy per particle and the density of nuclear matter using the test potentials IY and OMY-6, as well as several others, and various correlation functions involving parameters. The constraint chiefly employed is the normalization condition in first order, a condition naturally entering the Jastrow formalism. The energy in the minimization is approximated by the first two and in some cases by the first three terms of its FIY cluster expansion. In addition to the three-body terms in the FIY expansion, the corresponding terms of the AHT expansion are also calculated for comparison. From the computations which were performed it seems that, at least in some cases, the normalization condition constitutes a quite satisfactory constraint, leading to reliable results, when used in low order calculations. In addition, conclusions are drawn as to the sensitivity of the results to the constraint, correlation function and minimized energy expression.     

Radiation damage calculations for charged particle emission nuclear reactions

Taking the quantum tunneling and Coulomb barrier into account, the present work proposes the calculation of Primary Knock-on Atom (PKA) energy for charged particle emission reactions. The method proposed in this paper and that used in NJOY have a large difference of PKA energy for charged particle emissions. For a D+T fusion neutron-induced ⁶Li(n,t)⁴He PKA, the maximum PKA energy calculated with NJOY is 2.9 MeV, whereas 14.2 MeV is obtained with the formula proposed in the present work. The subsequent total neutron-induced Displacement per Atom (DPA) calculated with the two methods has a small difference for most isotopes of which the DPA is predominated by neutron scattering reactions, such as ⁵⁶Fe and ⁵⁸Ni. However, the difference can be important for nuclei with charged particle emission channels open at thermal energy, such as ⁶Li, ¹⁰B, and ⁵⁹Ni. Using the damage cross sections (calculated by NJOY with and without modifications) and SRIM/TRIM-2008 calculations, the relative differences on total DPA rates of the compound material 90%⁵⁶Fe-9%⁵⁸Ni-1%⁵⁹Ni are within 1% for two fast spectra, 1.5% for fusion first wall, about 5% for the heavy reflector, and 25% for a pressurized water reactor vessel.