Field Of Nuclear Physics Research Articles

Hugh Campbell Paxton

Hugh Campbell Paxton, who made pioneering contributions in experimental criticality and the specialty of criticality safety, died on 25 December 2003 in Albuquerque, New Mexico.Born in Los Angeles on 29 April 1909, Hugh attended UCLA, where he studied physics and earned an AB degree in 1930. During the early 1930s, he worked in the development division of the Bell Telephone Laboratories in California. He began graduate studies at the University of California, Berkeley, in 1932 and received his PhD in physics in 1937 under the direction of Ernest Lawrence.That same year, he joined Frédéric Joliot at the Laboratory of Nuclear Chemistry of the Collège de France in Paris and began work to design and build a cyclotron. However, his planned two-year stay was cut short in 1938, when he and his wife were advised to return to the US because of the perceived threat of war. For the next four years, Hugh was an instructor in physics at Columbia University in New York City and continued his work in nuclear physics. He shifted to wartime activity in gaseous diffusion technology at Columbia’s Substitute Alloy Materials Laboratory and at the Oak Ridge Gaseous Diffusion Plant in Oak Ridge, Tennessee. Peacetime found him engaged in precision casting development at the Sharples Research Laboratories in Philadelphia.In 1948, Hugh became leader of the criticality group at the Los Alamos Scientific Laboratory when the science of criticality was just beginning and the safety of operations with fissionable materials was not yet formalized. He and Dixon Callihan of Oak Ridge Laboratory organized and systematized the existing data in a series of Atomic Energy Commission, Los Alamos, and Oak Ridge documents. Those data provided a foundation for conducting experiments and calculational studies, whose results were the basis for safety in operations of fissionable materials. Some especially important experiments carried out under Hugh’s direction established the bare and reflected metallic critical masses of plutonium-239 and highly enriched uranium-235. Further experiments at Los Alamos with various assemblies used to establish the bare critical mass of metallic 235U led to the design of the Godiva Reactor. After the reactor’s reactivity was quickly forced to prompt criticality, it safely provided, within a few microseconds, large bursts of neutrons. In the late 1950s, the program to find how to apply nuclear energy to rockets was begun. Facilities at Los Alamos provided the critical experiments necessary to design the graphite-moderated, hydrogencooled propulsion units. That program was terminated before operational rockets were achieved.Under Hugh’s leadership of the criticality group, the experimental facility, designated Technical Area 18, in Pajarito Canyon, New Mexico, became world famous. During Hugh’s tenure, no criticality experiment harmed any person—a remarkable record considering the number of experimental assemblies that have achieved criticality.Hugh provided criticality and safety advice to the government on a number of occasions. He was active in the American Nuclear Society and associated organizations. A member of numerous and various committees, he also served on the board of directors of the American Nuclear Society (1966–69). Hugh retired from Los Alamos in 1976 and moved with his wife to Albuquerque in 2001.Hugh’s interests ranged from his work with colleagues in the field of nuclear physics to bird watching, excursions with friends, observations of wildlife, writing, photography, and treasured reunions with his brothers and sister and their extended families.Hugh Campbell PaxtonPPT|High resolution© 2004 American Institute of Physics.

Hardware for multiconnected networks: a case study

This paper presents the experimental results of a research project financed by INFN (National Institute for Nuclear Physics). The goal of this project is to realize a cluster of personal computers (PCs) suitable for distributed software in the field of nuclear physics. The developed hardware must have a low cost and must be able to interconnect 32 PCs with an expansion capacity of up to 100. Due to the requirements of this research project, it seems natural to look at it as an application of our general hardware architecture presented in [Campobello et al., Hardware for Multiconnected Networks: The Design Flow]. Here, we present the results obtained and compare them with other works in literature. The results show that our architecture is preferable when low cost hardware and high performance are the goals.

The GSI plans for an international accelerator facility for beams of ions and antiprotons

GSI proposes to build a next-generation facility for research with relativistic beams of ions and antiprotons. This facility allows a broad range of topics in nuclear and astrophysics, plasma and atomic physics to be addressed. The topic most interesting in the context of this conference is physics with high-intensity beams of exotic nuclei. In addition, a short overview of the opportunities in the other fields of nuclear physics is given.

Ion traps --Precision measurements and more

Today ion traps are an important experimental tool. Applications range from high-precision measurements of masses and moments, realization of atomic clocks, to the study of ion chemical reactions. Ion traps have gained particular importance in the field of nuclear physics where they are used for the precise determination of nuclear binding energies, decay studies, and radioactive ion beam manipulation.

Effects of ps and ns laser pulses for giant ion source

Laser driven ion sources produce giant ion emission current densities at the emission area which exceed the few mA/cm 2 of classical ion sources (MEVVA or ECR) by many orders of magnitude. Very energetic highly charged fast ions, separated by their charge number Z, from ns laser pulses were explained by relativistic self-focusing and nonlinear force effects. Recently a strong difference with ps pulses was found in contrast to the ns pulses depending on the prepulses. We present an explanation based on a skin layer process. This has consequences to sub-picosecond laser-plasma interaction for the studies of the fast ignitor physics for laser fusion and to the new field of nuclear physics opened by these laser pulses which produce up to 100 MeV particles and gammas of high density as well as for ion source applications.

RNB production with thermal neutrons

Thermal neutron induced nuclear fission is the most suitable method to produce neutron-rich isotopes (70⩽ A⩽160) due to the large fission cross section and the high thermal neutron fluxes in modern reactors. Intensities of mass separated neutron rich nuclei of some 10 11 ions/s are expected, e.g. for 91Kr, 132Sn or 144Cs from 235U diluted in a porous graphite target. Several front runners with low-energy fission-fragment beams exist like OSIRIS in Studsvik. In order to get beams of neutron-rich nuclei at the Coulomb barrier, the PIAFE project worked out a first concept of production and mass separation of high-intensity beams of fission fragments. At the new Munich high-flux reactor FRMII, the Munich Accelerator for Fission Fragments (MAFF) is under development to make use of post accelerated beams of neutron rich isotopes for experiments in many different fields of nuclear physics, solid state physics and medicine. One key experiment will be the production and the study of very heavy elements. An overview of the production method of neutron-rich isotopes by thermal neutron induced fission, and of the expected yields will be given and the development of target–ion-sources and of the fission targets for MAFF will be characterized.

Herman Feshbach

Herman Feshbach

Heinz Maier-Leibnitz

Heinz Maier-Leibnitz

Investigations with radioactive ion beams

The present status of experimental research in a new field of nuclear physics connected with the production and use of radioactive nuclear beams is described.

I. V. Kurchatov and the development of nuclear weapons in the USSR

An anniversary meeting, of the Scientific Council of the Kurchatov Institute, devoted to the 96th anniversary of the birthday, of the founder of the Institute, the prominent scientist and orgnaizer of science Academician Igor' Vasil'evich Kurchatov, was held on January 12, 1999 at the Institute. The report “Igor'Vasil'evich, Kurchatov and the Development of Nuclear Weapons in the USSR” was heard at the meeting. Many discoveries and important scientific results in the field of nuclear physics, the creation of nuclear centers and scientific schools in our country, the birth of the nuclear industry and nuclear power, the initiation of work on the problem of thermonuclear fusion, and the development of international collaboration for peaceful uses of atomic energy are all linked with I. V. Kurchatov’s name. The path that I. V. Kurchatov and his closest collaborators had to follow, from the inception of work on the atomic project up to the successful test of the first atomic bomb in USSR at the Semipalatinsk test site on August 29, 1949 is carefully analyzed on the basis of unique archival materials.

Reminiscences and discoveries: James Chadwick at Liverpool

There have been recent articles in Notes and Records concerning James Chadwick’s contributions to the development of the atomic bomb, and it seemed worthwhile to supplement these with some remarks on Chadwick’s establishment of an important centre of nuclear physics research in Liverpool, especially since I believe this was the achievement which gave him more satisfaction than any other. The following is the abridged text of a lecture given at the Centenary Celebrations at the University of Liverpool in October 1991. Chadwick came to Liverpool in 1935, the year in which he was awarded the Nobel Prize, and held the Lyon Jones Chair of Physics for 13 years. During that time he transformed the department from one which was quite ill-equipped for research, into one which would be able to stand comparison with any in the world in the fields of nuclear physics and high-energy particle physics. The University had been able to attract him by promising to support him with the provision of new staff posts and with help in building up new facilities for research. In addition he already had friends within the university and the business community through his wife, who came from a well-known Liverpool family. He had also, I think, begun to feel that the time had come to leave Cambridge, perhaps because Rutherford was reluctant to contemplate the sort of expenditure which Chadwick realized was necessary to carry forward research in nuclear physics. Chadwick’s plans for Liverpool were centred around the construction of a cyclotron which would cost about £5000, roughly equal to Rutherford’s laboratory budget for one year

A 400KV multi-functional electron and ion radiation accelerator

In this paper we describe a 400kV multi-functional electron and positive ion irradiation accelerator based upon a 400kV Cockcroft-Walton, which was successfully used to accelerate electrons and positive ions with electron beam current of more than 5 mA. It has a scanning window of 1200mm in width, a scanning frame of 4500×1400mm. The transmitting speed of the scanning frame is between 0.1–5m backward and forward, continuously adjustable. The conversion time from accelerating positive ions to electrons is less than twenty minutes, and vice versa. It is proved that this accelerator can meet more requirements in the fields of nuclear physics and electron irradiation applications.

On the use of Lanczos sigma factors for separable approximation of non-local exchange forces

It is well known that separable approximations of non-local exchange forces represent a very efficient technique for solving electron-atom and electron-molecule scattering problems. The authors combine this technique with the application of Lanczos sigma factors. This combination was proposed recently in the field of nuclear physics and proved to be fairly efficient for simple local potentials. It is shown, using the example of low-energy electron-hydrogen-atom elastic scattering that the introduction of Lanczos sigma factors may improve the convergence but the effect is not as strong as in the nuclear physics case.

Ultra-high-pressure proportional counter: Part I: Argon

Low-pressure argon/xenon-filled proportional counters have been used extensively for the detection of photons and charged particles in the fields of nuclear physics and X-ray astronomy. In general, gas counters have better energy resolution, lower background, simplicity of structure and lower cost compared to semiconductor and scintillation detectors but suffer from low detection efficiency at higher photon energies. To extend the use of gas detectors into the low-energy gamma-ray region, and examine their physical limitations, we have been pursuing a programme to develop and fabricate ultra-high-pressure argon/xenon-filled counting modules with pressures up to 2750 kPa (∼ 400 psi) for the detection of X-ray photons up to 1 MeV. This development is aimed at a new large-area balloon-borne detector system for low-energy gamma-ray astronomy. This paper concerns the detailed description of the gas multiplication behaviour and pulse properties for a detector filled with argon mixtures at high pressures.

Polarizer for Epithermal Neutrons : Development in New Fields of Nuclear Physics, Particle Physics, Condensed Matter Physics and Bio-Physics

Polarizer for Epithermal Neutrons : Development in New Fields of Nuclear Physics, Particle Physics, Condensed Matter Physics and Bio-Physics

Early years of Soviet nuclear physics

Despite hardships, Soviet physicists made remarkable advances in the 1930s in the nascent field of nuclear physics, and by the eve of the Nazi invasion they had laid the foundations for work on the atomic bomb.

β − Strength function phenomena of exotic nuclei: A critical examination of the significance of nuclear model predictions

Reliable predictions of β-decay properties of nuclei far from stability require knowledge of the β-strength distribution, S β ( E). By comparison of experimental strength functions of neutron-rich Rb isotopes in the transitional region around A = 100 with S β ( E) from different nuclear models, the sensitivity and physical significance of S β ( E) on various integral and spectral β-decay properties are examined. The reliability of extrapolations and the applicability to different fields in nuclear physics, astrophysics and reactor technology are discussed. It is shown that, although there has been considerable progress in the physical understanding of the decay properties of nuclei far from β-stability over the past few years, there are still open questions which make recent statements on the solution of long-standing problems related to the standard processes of β-decay premature.

Self-Consistent Description of Nuclear Excitations

The nuclear response function is calculated in the framework of the self­ consistent continuum RPA. The method is illustrated by applications to low­ lying collective states, and to various isoscalar giant resonances. § l. Introduction The study of nuclear excitations in the energy region of a few ha>-the so-called giant resonance region-has been, and still is one of the most active fields of nuclear physics. In the last ten years, the large amount of experi­ mental effort has led to a fairly good systematics of electric (non-spin-flip) giant resonances.D This effort is still going on, and it will eventually bring a more complete knowledge of electric giant resonances along with our deve­ loping understanding of magnetic (spin-flip) resonances. At the same time, various theoretical approaches ranging from fluid dynamics to microscopic models have aimed at describing the observed resonances. In this paper we shall focus on one particular approach, namely, the self-consistent RPA modeL An interesting feature of the RPA is its well-known ability to let the collective character of the excitations emerge from the properties of the residu­ al interactions, in contrast to non-microscopic models where the collectiveness is built-in from the start. On the other hand, the RPA model has its own limitations. For instance, we know that the actual states contain admixtures of complex configurations outside the RPA space and they are consequently more fragmented than the RPA would predict. This question is discussed in Yoshida's lectures!> Nevertheless, the RPA has proved to be quite suc­ cessful in describing the bulk properties of giant resonances such as their energies and strengths.

Book reviewsThe Physics and Instrumentation of Nuclear Medicine. By SprawlsP., pp. ix + 190, 1981 (University Park Press, Baltimore), £13.50. ISBN 0–8391–0544–4

In the preface, the author states that the book is “intended for persons entering the field of nuclear physics”. The first five chapters, about one-half of the text, are devoted to basic nuclear and radiation physics, including radiation dosimetry. Technical details of instruments are dealt with in the following three chapters, totalling 40 pages, covering “radiation detectors”, “spectrometry” and “the gamma camera”. The last three chapters deal with image quality, counting statistics and image and data processing. There is a 13-page appendix on digital computers.

Some aspects of nuclear electro- and photoproduction at medium energies

The perspectives of Nuclear Research with electromagnetic probes are widely determined by the characteristics of the new generation of electron accelerators; the machines to be built in the future will be characterized by two parameters which for the following discussion will be quite relevant: - high duty cycle (up to 100 per cent); this will allow to perform systematically coincidence experiments, which have been quite difficult and timeconsuming at the presently available machines; - high end point energies (up to one or several GeV); this will lead us into a new field of Nuclear Physics, which is related to the excitation of the internal or subnucleonic degrees of freedom of a bound nucleon. Quite naturally, this report will, therefore, be concentrated on two topics: (i) the discussion of coincidence experiments, especially of the (e,e'x) reaction as a tool to investigate nuclear properties; here, two types of mechanisms will be dealt with: the direct and the resonance reaction, respectively; (ii) the discussion of the physical phenomena that can be exploited at medium energies; as a convenient ordering parameter we will use the excitation energy which is deposited onto the nucleus in such an (e,e') reaction. We emphasize one particular aspect which we find most attractive, both from a conceptual and from a phenomenological point of view: the (electro)excitation of the subnucleonic (or quark) degrees of freedom of a nucleon bound in a complex nucleus; in this energy domain a new frontier of Nuclear Research is presumably going to open up: the investigation of the nuclear analogues of the elementary N ∗-resonances; their properties are related both to the internal (or quark-) structure of the baryon and to the interaction between two and more baryons with each other. The corresponding many body modes of motion are obviously rather complicated; their investigation necessitates a careful analysis of highly exclusive experiments. The explanation of the corresponding excitation spectrum, however, is quite essential for a deeper understanding of the dynamics of a system of strongly interacting particles.