120631837
A bifilar helical multiware proportional chamber for position sensitive detection of minimum ionizing particles
Abstract A new type of multiware proportional chamber with a helical cathode for delay line readout has been developed and studied in detail. It gives cathode delay line pulses nearly as large as the anode pulses, and hence is well-suited for minimum ionizing particles. Measurements on such a chamber yielded spatial resolution better than 0.33 mm fwhm for 90 Sr β particles, a resolving time less than 30 ns, and maximum counting rate greater than 2 MHz. The most probable pulse height induced on the delay line by minimum ionizing particles in this chamber is approximately 8 mV.
110905526
The GEM Silicon Tracking System
The GEM Collaboration has produced a baseline design for the GEM detector. The baseline design of the GEM Silicon Tracking System (STS) is discussed in this article. Mechanical and electrical engineering progress on the GEM STS is described. Results from simulations of detector performance and the implications on engineering issues are described.
89609083
Evidence for a New Phase of Solid He-3
)Permanent address: Faculte des Sciences, Orsay, France. See, for exaxnple, I. Prigogine, Non Equi/ibrinm Statistica/ Mechanics (Wiley, New York, 1962); P. Resibois, in-Many Pmticle Physics, edited by K. Meeron (Gordon and Breach, New York, 1966). J. Van der Waals, Dissertation, University of Leiden, 1873 (unpublished) . See M. Kac, G. Uhlenbeck, and P. Hemmer, J. Math. Phys. 4, 216, 229 (1963), and 5, 60 (1964); J. Lebowitz, G. Steli, and S. Baer, J. Math. Phys. (N.Y.) 4, 1282 (1965). See K. Kawasaki, Progr. Theor. Phys. 41, 1190 (1969), snd references quoted therein. ~H. Mori, Progr. Theor. Phys. 28, 763 (1962}. P. Resibois, J. Chem. Phys. 41, 2979 (1964). P. Resibois, J. Stat. Phys. 2, 21 (1970). J. Dorfman and E. Cohen, Phys. Rev. Lett. 25, 1257 (1970). L. Kadanoff and J. Swift, Phys. Rev. 166, 89 (1968). M. Ernst, E. Hauge, and J. Van Leeuwen, Phys. Rev. Lett. 25, 1254 (1970), and Phys. Rev. A 4, 2055 (1971). "B.Alder and T. Wainwright, Phys. Rev. A 1, 18 (1970); see also Refs. 8 and 10; and Y. Pomeau, to be published.
110867317
Fail-safe ion chamber errant beam detector tailored for personnel protection
A description is given of a fail-safe ion chamber system designed to be part of the personnel safety system (PSS) for the Los Alamos Neutron Scattering Center (LANSCE) at the Los Alamos National Laboratory. It protects the occupants of experiment areas from large radiation doses caused by errant beam conditions during beam transport from the proton storage ring to the LANSCE neutron spallation target. The layered system consists of three types of highly reliable detector systems: a current limiter system located in the beam line, a neutron detector system located in experimental areas, and an ion chamber system located on the walls of the beam line tunnels. The ion chamber system is capable of shutting off the beam in less that 0.5 s, resulting in a worst-case personnel exposure of 0.005 Gys (0.5 rd).<<ETX>>
121875662
Correlated neutron-deuteron and neutron-triton emission after pion capture on 12C
Abstract Energy and angle measurements of neutron-deuteron and neutron-triton pairs emitted following negative-pion capture on 12 C have been made. Strong 180° correlation is observed in the angular distributions of both types of pairs, indicating substantial absorption by clusters in the 12 C nucleus.
123479705
Design and construction of double-sided silicon ladders for the L3 microvertex detector
Abstract The techniques used in the construction of the double-sided ladders for the L3 Silicon Microvertex Detector (SMD) are presented. The detector consists of two cylindrical layers, each of 12 ladders, with double-sided silicon detectors which provide r -phi and z coordinates measurements. This description includes ladder mechanical design and the assembly. A novel solution to readout the z -coordinates is presented. It optimizes very effectively the removal of heat generated by the readout electronics and minimizes the radiation length in the central region. Some results from the survey of the individual ladders are also discussed.
119188278
Causality bounds for neutron-proton scattering
We consider the constraints of causality and unitarity for the low-energy interactions of protons and neutrons. We derive a general theorem that non-vanishing partial-wave mixing cannot be reproduced with zero-range interactions without violating causality or unitarity. We define and calculate interaction length scales which we call the causal range and the Cauchy-Schwarz range for all spin channels up to J = 3 . For some channels we find that these length scales are as large as 5fm. We investigate the origin of these large lengths and discuss their significance for the choice of momentum cutoff scales in effective field theory and universality in many-body Fermi systems.
16441248
Nuclear lattice simulations with chiral effective field theory
We study nuclear and neutron matter by combining chiral effective field theory with nonperturbative lattice methods. In our approach, nucleons and pions are treated as point particles on a lattice. This allows us to probe larger volumes, lower temperatures, and greater nuclear densities than in lattice QCD. The low-energy interactions of these particles are governed by chiral effective theory, and operator coefficients are determined by fitting to zero temperature few-body scattering data. The leading dependence on the lattice spacing can be understood from the renormalization group and absorbed by renormalizing operator coefficients. In this way, we have a realistic simulation of many-body nuclear phenomena with no free parameters, a systematic expansion, and a clear theoretical connection to QCD. We present results for hot neutron matter at temperatures 20-40 MeV and densities below twice the nuclear matter density.
118528327
Uncertainties of Euclidean time extrapolation in lattice effective field theory
Extrapolations in Euclidean time form a central part of nuclear lattice effective field theory (NLEFT) calculations using the projection Monte Carlo method, as the sign problem in many cases prevents simulations at large Euclidean time. We review the next-to-next-to-leading order NLEFT results for the alpha nuclei up to 28Si, with emphasis on the Euclidean time extrapolations, their expected accuracy and potential pitfalls. We also discuss possible avenues for improving the reliability of Euclidean time extrapolations in NLEFT.
43493679
Precision benchmark calculations for four particles at unitarity
The unitarity limit describes interacting particles where the range of the interaction is zero and the scattering length is infinite. We present precision benchmark calculations for two-component fermions at unitarity using three different ab initio methods: Hamiltonian lattice formalism using iterated eigenvector methods, Euclidean lattice formalism with auxiliary-field projection Monte Carlo methods, and continuum diffusion Monte Carlo methods with fixed and released nodes. We have calculated the ground-state energy of the unpolarized four-particle system in a periodic cube as a dimensionless fraction of the ground-state energy for the noninteracting system. We obtain values of 0.211(2) and 0.210(2) using two different Hamiltonian lattice representations, 0.206(9) using Euclidean lattice formalism, and an upper bound of 0.212(2) from fixed-node diffusion Monte Carlo methods. Released-node calculations starting from the fixed-node result yield a decrease of less than 0.002 over a propagation of 0.4E{sub F}{sup -1} in Euclidean time, where E{sub F} is the Fermi energy. We find good agreement among all three ab initio methods.
118932195
Study of relativistic bound states in a scalar model using diagonalization/Monte Carlo methods
Abstract We use a recently proposed diagonalization/Monte Carlo computational scheme to study relativistic two-body and three-body bound states in ( φ 6 − φ 4 ) 1+1 theory. We find that the approach is well-suited for calculating bound-state energies and wave-functions.