120217954
( p , xn ) and ( p , pxn ) Reactions of Yttrium-89 with 5-85-MeV Protons
121807340
EXCITATION FUNCTIONS AND NUCLEAR CHARGE DISPERSION IN THE FISSION OF URANIUM BY 0.1- TO 6.2-Gev PROTONS
Cross sections for formation of cesium and rubidium isotopes produced by bombardment of uranium with protons ranging in energy from 0.1 to 6.2 Bev were measured both radiochemically and mass spectrometrically. Independent yields were determined for Rb/sup 84/, Rb/sup 86/, Cs/sup 127/, Sc, su p 129/. Cs/sup 130/, Cs/sup 131/, Cs/sup 132/, Cs/sup 134/, Cs/sup 136/, and, at some e nergies, Rb/sup 83 and Cs/sup 135/. In addition, the independent yield of Ba/sup 131/ and the chain yields of Cs/sup 125/, Cs/sup 127/, Cs/sup 129/, La/sup 131/, Cs/sup 135/, Cs/sup 137/, ion cross sections of the Cs and Ba products on the neutron- excess side of stability decrease monotonically with increasing energy above 0.1 Bev, whereas the excitation functions for independent formation of the more neutron-deficient products in the Cs-Ba region and of Rb/sup 84/ and Rb/sup 86/ all go through maxima. The proton energies at which these maxima occur fall on a smooth curve when plotted against the neutronproton ratio of the product, with the peaks moving to higher energies with decreasing neutron-proton ratio. Under the assumption that the mass-yield curve in the region 125 < A < 140 is rather flat at each proton energy, the crosssection datamore » in the Cs region can be used to deduce the charge dispersion in this mass range. Plots of log sigma vs N/Z (or Z--Z/sub A/) show symmetrical bell-shaped peaks up to a bombarding energy of 0.38 Bev, with full width at halfmaximum increasing from 3.3 Z units at 0.10 Bev to about 5 Z units at 0.38 Bev, and with the peak position (Z/sub p/) moving from Z/ sub A/ -- 1.44 to Z/sub A/ -- 0.85 over the same energy range. At all higher energies, a double-peaked charge distribution was found, with a neutron-excess peak centered at N/Z approximates 1,515(Z/sub p/ approximates Z/sub A/ -- 1.9), and having approximately constant width and height at bombarding energies greater than 1 Bev. The peak on the neutron-deficient side which first becomes noticeable at 0.68 Bev appears to become broader and shift slightiy to smaller N/ Z values with increasing energy, The two peaks are of comparable height in the Bev region, and the peak-to-valley ratio is only approximates 2. The total formation cross section per mass number in the Cs region decreases from approximates 52 mb at 0.1 Bev to about 29 mb at 1 Bev and then stays approximately constant; the contribution of the neutron-excess peak above 1 Bev is about 12 mb. The neutron-excess peak corresponds in width and position to that obtained in fission by approximates 50-Mev protons. The recoil behavior of Ba/sup 140/ lends support to the idea that the neutron-excess products are formed in a lowdeposition-energy process. The recoil behavior of Ba/sup 131/ indicates that it is formed in a high-deposition-energy process. Post-fission neutron evaporation is required for the observed characteristics of the excitation functions of the rubidium isotopes and the neutron-deficient species in the Cs region. The correlation between neutron-proton ratios and positions of excitation function maxima is semiquantitatively accounted for if fission with unchanged charge distribution, followed by nucleon evaporation, is assumed. (auth)« less
120315024
CROSS SECTIONS FOR THE PRODUCTION OF Cl, K, Ca, AND Sc ISOTOPES IN THE BOMBARDMENT OF Pb AND U WITH 3.0-Bev PROTONS
Cross sections for the formation of some nuclides in the mass number range 38 to 48 in the bombardment of Pb and U with 3.0-Bev protons were measured. The maximum of the isobaric yield distributions for the nuclides from the Pb bombardnnent occurs at the stability line, while that from U is somewhat on the neutron-excess side. Total cross sections of 4 to 5 mb per mass number are deduced from the Pb data leading to a revision of the mass-yield curve in this region as proposed by Wolfgang et al.The cross sections from uranium are approximately twice as large as those from Pb. The data are shown to be consistent with a cascade-fission-evaporation mechanism. (auth)
122070464
Preparation of thin Films, Sources, and Targets
and targets are an obvious need in many applic a­ tions in nuclear physics and nuclear chemistry experiments. Publis hed in­ formation regarding the production and measurement of these materials is exceedingly sparse. The information. if given at all in the li terature, is usuaIJy ancillary to the "re sult s," and thus is given in such meager form that duplic a­ tion by other laboratories is difficult, if not well-nigh impossible. The most recent comprehensive article on the subject is that pub lished by Dodson et at. in the National Nuclear Energy Series, 1952, entitled Miscellaneous Physical and Chemical Techniques of the Los Alamos Series [referred to later as (58 )]. 2 Often the information exists as the "propert y" of a few exceedingly valuable individuals in various labor atories who prepare the materials but never publis h. The situat ion has impr oved somewhat since the appe arance of two journals devoted exclus ively to techniques, viz. Nuclear Instruments and Methods (North-Holland Publi shing Co.) and the Rus sian journal Pribory i Technika Eksperimenta (Instru ments and Experimental Tech­ niques) . The aim of this review article is to collate as much of this information as is possible. In this task the reviewer has been aided by peo ple too numerous to mention, and it is hoped that this assistance is reflected in the references. In addition, a literature search has been made, which, no matter how exhaus­ tively undertaken, must by its very nature be incomplete. It is hoped that this article will stimulate others int o rectifying these om issions by sending references and unpu blished information to the author for later publication.
123234798
Large N limits as classical mechanics
This paper discusses the sense in which the large $N$ limits of various quantum theories are equivalent to classical limits. A general method for finding classical limits in arbitrary quantum theories is developed. The method is based on certain assumptions which isolate the minimal structure any quantum theory should possess if it is to have a classical limit. In any theory satisfying these assumptions, one can generate a natural set of generalized coherent states. These coherent states may then be used to construct a classical phase space, derive a classical Hamiltonian, and show that the resulting classical dynamics is equivalent to the limiting form of the original quantum dynamics. This formalism is shown to be applicable to the large $N$ limits of vector models, matrix models, and gauge theories. In every case, one can explicitly derive a classical action which contains the complete physics of the $N=\ensuremath{\infty}$ theory. "Solving" the $N=\ensuremath{\infty}$ theory requires minimizing the classical Hamiltonian, and this has been possible only in simple theories. The relation between this approach and other methods which have been proposed for deriving large $N$ limits is discussed in detail.
15964944
Large-N volume independence in conformal and confining gauge theories
Consequences of large N volume independence are examined in conformal and confining gauge theories. In the large N limit, gauge theories compactified on $ {\mathbb{R}^{d - k}} \times {\left( {{S^1}} \right)^k} $ are independent of the S1 radii, provided the theory has unbroken center symmetry. In particular, this implies that a large N gauge theory which, on $ {\mathbb{R}^d} $, flowstoan IR fixed point, retains the infinite correlation length and other scale invariant properties of the decompactified theory even when compactified on $ {\mathbb{R}^{d - k}} \times {\left( {{S^1}} \right)^k} $. In other words, finite volume effects are 1/N suppressed. In lattice formulations of vector-like theories, this implies that numerical studies to determine the boundary between confined and conformal phases may be performed on one-site lattice models. In $ \mathcal{N} = 4 $ supersymmetric Yang-Mills theory, the center symmetry realization is a matter of choice: the theory on $ {\mathbb{R}^{4 - k}} \times {\left( {{S^1}} \right)^k} $ has a moduli space which contains points with all possible realizations of center symmetry. Large N QCD with massive adjoint fermions and one or two compactified dimensions has a rich phase structure with an infinite number of phase transitions coalescing in the zero radius limit.
16866234
Non-perturbative equivalences among large Nc gauge theories with adjoint and bifundamental matter fields
We prove an equivalence, in the large N c limit, between certain U(Nc) gauge theories containing adjoint representation matter fields and their orbifold projections. Lattice regularization is used to provide a non-perturbative definition of these theories; our proof applies in the strong coupling, large mass phase of the theories. Equivalence is demonstrated by constructing and comparing the loop equations for a parent theory and its orbifold projections. Loop equations for both expectation values of single-trace observables, and for connected correlators of such observables, are considered; hence the demonstrated non-perturbative equivalence applies to the large Nc limits of both string tensions and particle spectra.
15981785
Periodic Euclidean solutions of SU(2)-Higgs theory
We examine periodic, spherically symmetric, classical solutions of SU(2)-Higgs theory in four-dimensional Euclidean space. Classical perturbation theory is used to construct periodic time-dependent solutions in the neighborhood of the static sphaleron. The behavior of the action, as a function of period, changes character depending on the value of the Higgs boson mass. The required pattern of bifurcations of solutions as a function of the Higgs boson mass is examined, and implications for the temperature dependence of the baryon number violation rate in the standard model are discussed. {copyright} {ital 1999} {ital The American Physical Society}