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.
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)
122912012
Canonical treatment of «noncanonical» gauges for constrained Hamiltonian systems
120793216
The coherent state variational algorithm: A numerical method for solving large-N gauge theories
This paper presents a new approach for studying large-N gauge theories which directly exploits the classical nature of the N → ∞ limit. This method supplies a practical algorithm for computing and minimizing the classical hamiltonian (or effective action) which governs N = ∞ dynamics, and allows one to calculate physical quantities such as the mass spectrum or scattering amplitudes of glueballs or mesons. Two different implementations of the basic ideas are discussed; one variant provides an algorithm for constructing N = ∞ master field matrices, while the other works directly with a list of expectation values of physical operators. Algorithms are developed for both the hamiltonian and euclidean formulations of lattice gauge theories. The inclusion of fermions in the hamiltonian version is also described. Detailed tests of the method in the context of the exactly solvable one-plaquette model are presented.
17943605
In)validity of large N orientifold equivalence
It has been argued that the bosonic sectors of supersymmetric SU(N) Yang-Mills theory, and of QCD with a single fermion in the antisymmetric (or symmetric) tensor representation, are equivalent in the N{yields}{infinity} limit. If true, this correspondence can provide useful insight into properties of real QCD (with fundamental representation fermions), such as predictions [with O(1/N) corrections] for the nonperturbative vacuum energy, the chiral condensate, and a variety of other observables. Several papers asserting to have proven this large N 'orientifold equivalence' have appeared. By considering theories compactified on R{sup 3}xS{sup 1}, we show explicitly that this large N equivalence fails for sufficiently small radius, where our analysis is reliable, due to spontaneous symmetry breaking of charge-conjugation symmetry in QCD with an antisymmetric (or symmetric) tensor representation fermion. This theory is also chirally symmetric for small radius, unlike super-Yang-Mills theory. The situation is completely analogous to large-N equivalences based on orbifold projections: simple symmetry realization conditions are both necessary and sufficient for the validity of the large N equivalence. Whether these symmetry realization conditions are satisfied depends on the specific nonperturbative dynamics of the theory under consideration. Unbroken charge-conjugation symmetry is necessary for validity of the large N orientifold equivalence. Whethermore » or not this condition is satisfied on R{sup 4} (or R{sup 3}xS{sup 1} for sufficiently large radius) is not currently known.« less