Pulsed spallation neutron sources

This paper reviews the early history of pulsed spallation neutron source development ar Argonne and provides an overview of existing sources world wide. A number of proposals for machines more powerful than currently exist are under development, which are briefly described. The author reviews the status of the Intense Pulsed Neutron Source, its instrumentation, and its user program, and provide a few examples of applications in fundamental condensed matter physics, materials science and technology

Examination of disks from the IPNS depleted uranium target

This report describes the results of examining the Zircaloy-2 clad depleted uranium disks from the Intense Pulse Neutron Source (IPNS) Target. That target operated from August, 1981 to June, 1988 and from September, 1991 to September, 1992 at 450 MeV, pulsing at 30 Hz with a time average proton current of about 15 {micro}A. The target was removed from service when the presence of fission products ({sup 135}Xe) in the coolant cover gas indicated a failure in the Zircaloy-2 cladding. Altogether, the target had absorbed about 240 mA hours of proton current, and endured between 50,000 and 100,000 thermal cycles. The purpose of the examination was to assess the condition of the disks and determine the cause of the cladding failure. The results of visual, gamma ray scanning, and destructive metallurgical examination of two disks are described

Heat generation and neutron beam characteristics in a high power pulsed spallation neutron source

In the course of conceptual design of a high power pulsed spallation source, a Monte Carlo model was developed for heat generation and neutronics studies. In this paper, we present two sets of results. The first set of calculations was performed with a simple target model to investigate general characteristics of power distribution and neutron production with various proton energies ranging from 0.8 to 12 GeV. The second set was performed with a realistic target model including major components of the target system to provide basic parameters for engineering design of a high power pulsed spallation source. Calculated results generally confirm that higher proton energy provides and advantage in target cooling system requirements and yet somewhat lower neutron beam intensity as a counter effect. The heat generation in the systems surrounding the target was investigated in detail and found to have important variation with position and according to proton beam energy. Calculations of the neutron currents from the moderators showed that the neutron beam intensity from moderators in the front region of the target decreased fro higher proton energy while that from moderators in the back region of the target remained almost unchanged

Visual Search Without Selective Attention: A Cognitive Architecture Account

A key phenomenon in visual search experiments is the linear relation of reaction time (RT) to the number of objects to be searched (set size). The dominant theory of visual search claims that this is a result of covert selective attention operating sequentially to “bind” visual features into objects, and this mechanism operates differently depending on the nature of the search task and the visual features involved, causing the slope of the RT as a function of set size to range from zero to large values. However, a cognitive architectural model presented here shows these effects on RT in three different search task conditions can be easily obtained from basic visual mechanisms, eye movements, and simple task strategies. No selective attention mechanism is needed. In addition, there are little‐explored effects of visual crowding, which is typically confounded with set size in visual search experiments. Including a simple mechanism for crowding in the model also allows it to account for significant effects on error rate (ER). The resulting model shows the interaction between visual mechanisms and task strategy, and thus it represents a more comprehensive and fruitful approach to visual search than the dominant theory.Visual Search without Selective Attention calls into question the necessity of a covert selective attention mechanism by implementing a formal model that includes basic visual mechanisms, saccades, and simple task strategies. Across three search tasks, the model accounts for response times as well as the proportion of errors observed in human participants, including effects of item crowding in the visual stimulus.Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/147754/1/tops12406.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/147754/2/tops12406_am.pd

A stretched foil sample holder for liquids

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/33340/1/0000737.pd

Research opportunities with compact accelerator-driven neutron sources

Since the discovery of the neutron in 1934 neutron beams have been used in a very broad range of applications, As an aging fleet of nuclear reactor sources is retired the use of compact accelerator–driven neutron sources (CANS) are becoming more prevalent. CANS are playing a significant and expanding role in research and development in science and engineering, as well as in education and training. In the realm of multidisciplinary applications, CANS offer opportunities over a wide range of technical utilization, from interrogation of civil structures to medical therapy to cultural heritage study. This paper aims to provide the first comprehensive overview of the history, current status of operation, and ongoing development of CANS worldwide. The basic physics and engineering regarding neutron production by accelerators, target-moderator systems, and beam line instrumentation are introduced, followed by an extensive discussion of various evolving applications currently exploited at CANS

Limit on the fermion masses in technicolor models

Recently it has been pointed out that no limits can be put on the scale of fermion mass generation $(M)$ in technicolor models, because the relation between the fermion masses $(m_f)$ and $M$ depends on the dimensionality of the interaction responsible for generating the fermion mass. Depending on this dimensionality it may happens that $m_f$ does not depend on $M$ at all. We show that exactly in this case $m_f$ may reach its largest value, which is almost saturated by the top quark mass. We make few comments on the question of how large can be a dynamically generated fermion mass.Comment: 5 pages, 1 figure, RevTeX

Analysis of a Drum Chopper for Use on a New Small Angle Diffractometer at IPNS

Light-weight drum choppers rotating at 15 Hz have been in use on the IPNS powder diffractometers for several years, where they serve to eliminate the delayed-neutron background from much of the spectral region of interest. Monte Carlo simulations indicate that a similar chopper operated at 15 Hz should do an excellent job of delayed-neutron removal in the new small-angle diffractometer being designed at IPNS. The simulations also show that when the same chopper is operated at 7.5 Hz it performs quite successfully as a frame-elimination chopper, effectively eliminating neutrons from alternate pulses and allowing extension of the useful wavelength range of the instrument to {approximately}28 {Angstrom}. Thus the incorporation of such a chopper should add considerably to the range and flexibility of the new instrument. 7 refs., 9 figs

Neutron performance analysis for ESS target proposal

In the course of discussing different target types for their suitability in the European Spallation Source (ESS) one main focus was on neutronics' performance. Diverse concepts have been assessed baselining some preliminary engineering and geometrical details and including some optimization. With the restrictions and resulting uncertainty imposed by the lack of detailed designs optimizations at the time of compiling this paper, the conclusion drawn is basically that there is a little difference in the neutronic yield of the investigated targets. Other criteria like safety, environmental compatibility, reliability and cost will thus dominate the choice of an ESS target

ILLUMINATING THE DARKEST GAMMA-RAY BURSTS WITH RADIO OBSERVATIONS

We present X-ray, optical, near-infrared (IR), and radio observations of gamma-ray bursts (GRBs) 110709B and 111215A, as well as optical and near-IR observations of their host galaxies. The combination of X-ray detections and deep optical/near-IR limits establish both bursts as "dark." Sub-arcsecond positions enabled by radio detections lead to robust host galaxy associations, with optical detections that indicate z ≾ 4 (110709B) and z ≈ 1.8-2.9 (111215A). We therefore conclude that both bursts are dark due to substantial rest-frame extinction. Using the radio and X-ray data for each burst we find that GRB 110709B requires A_V^(host) ≳ 5.3 mag and GRB 111215A requires A_V^(host) ≳ 8.5 mag (assuming z = 2). These are among the largest extinction values inferred for dark bursts to date. The two bursts also exhibit large neutral hydrogen column densities of N H, int ≳ 10^(22) cm^(–2) (z = 2) as inferred from their X-ray spectra, in agreement with the trend for dark GRBs. Moreover, the inferred values are in agreement with the Galactic A_V -N_H relation, unlike the bulk of the GRB population. Finally, we find that for both bursts the afterglow emission is best explained by a collimated outflow with a total beaming-corrected energy of E_γ + E_K ≈ (7-9) × 10^(51) erg (z = 2) expanding into a wind medium with a high density, Ṁ ≈ (6-20) x 10^(-5) M_☉ yr^(–1) (n ≈ 100-350 cm^(–3) at ≈ 10^(17) cm). While the energy release is typical of long GRBs, the inferred density may be indicative of larger mass-loss rates for GRB progenitors in dusty (and hence metal rich) environments. This study establishes the critical role of radio observations in demonstrating the origin and properties of dark GRBs. Observations with the JVLA and ALMA will provide a sample with sub-arcsecond positions and robust host associations that will help to shed light on obscured star formation and the role of metallicity in GRB progenitors