Low Mass Production Research Articles

A model analysis of the L.P.S. distributions for the process pp → p π−Δ++

The LPS distributions for the process pp → p π − Δ ++ are studied at 5, 8, 19 and 25 GeV/ c incident proton momentum in terms of simple models. It is found that the shape of these distributions together with their energy dependence provide severe constraints on the possible dynamical mechanisms. For instance although there is evidence for pion exchange it is observed that a large leading meson exchange contribution must also be present in this reaction. As a result of the model considerations it is suggested that the flat LPS distribution corresponding to baryon exchange and low-mass ( pΔ ++) production may be a feature of other reactions with a similar exotic subsystem. Moreover in view of certain ambiguities in the model fits, a new two dimensional plot is proposed which explicitly displays the angular dependence of a sub-system as well as the principle exchange mechanisms.

Yields of low-mass products in the fission of 232Th by 14·8 MeV neutrons

The products from the 14·8 MeV neutron induced fission of 232Th for the five mass chains. A = 66, 67, 72, 73, 77, were radiochemically determined. The absolute activities were determined from decay curves and cumulative fission yields were measured relative to 99Mo. These data were used to investigate two of the unusual pairs of independent-fractional yields in the mass region A = 72–78. These fission yields were also compared to corresponding mirror points, assuming 4·5 secondary neutrons emitted per fission of 232Th.

Kinetic energy effects on product yields from ion-molecule reactions

The effect of ion kinetic energy on the relative product yields from ion-molecule reactions in methane, methyl fluoride, propylene, and cyclopropane, as determined by repeller field variation in pressure studies, is discussed and compared with the effects observed in other laboratories or by other techniques. It is concluded that formation of low mass products by kinetic energy conversion is usually observed for reaction of the molecular ion. Peers' failure to observe the low mass products in the propylene system ( Int. J. Mass Spectrom. Ion Phys., 5 (1970) 483) must be due to instrumental artifacts.

Glass-Ceramic Surfaces, Straight Triangular Passages—Heat Transfer and Flow Friction Characteristics

Basic heat transfer and flow friction design data are presented for three straight, triangular passage, glass-ceramic heat exchanger surfaces. These surfaces have heat transfer area density ratios ranging from 1300–2400 ft2/ft3, corresponding to a passage count of 526–2215 passages per sq in. Glass-ceramic heat exchangers are of importance to vehicular gas turbine technology as they give promise of allowing low mass-production costs for the high effectiveness rotary regenerator required in most of the vehicular turbine engine concepts now under development. The present data are compared to previously available conflicting information and are recommended for design purposes, with stipulated specification relating to the uniformity of passages. Additionally, some limited information is provided relating to the low fouling characteristics of glass ceramic surfaces in the rotary regenerator application.

Distribution of Radionuclides from the Interaction of 3- and 29-GeV Protons with Silver

Formation cross sections have been measured of about 60 radionuclides isolated from Ag irradiated by 3- and 29-GeV protons. From these data, isobaric charge distributions and mass-yield curves were derived. At 3 GeV, the total isobaric cross sections are \ensuremath{\sim}40 mb near the target, and they decrease to a broad minimum of 4 mb at around $A=30\ensuremath{-}40$. For lighter products the cross sections increase again. At 29 GeV, light- and intermediate-mass products ($20<A<50$) have 20-100% higher cross sections than at 3 GeV; the heavier products ($A>65$) have 10-20% lower yields. Corresponding charge-distribution curves at the two energies are identical except for shifts in absolute magnitude. Comparison of the 3-GeV mass-yield curve with the results of a Monte Carlo calculation based on a cascade-evaporation model shows that such a mechanism can account for the observed cross sections down to about mass 50. The lower-mass products ($15<A<35$) must be formed mainly in a fragmentation or "fission-like" process. Comparisons are made with previous nuclear-emulsion and radiochemical results.

Ternary Fission of Uranium-236* and -234

A detailed study of the ternary fission of ${\mathrm{U}}^{236*}$ and ${\mathrm{U}}^{234*}$ has been completed using a triple-coincidence technique and a three-parameter energy measurement on the product fragments. Arguments based on experimental energy, angular, and frequency correlations are presented for elimination of phenomena other than ternary fission as explanations of the observed data. Among possible interfering effects considered were (1) accidental events, (2) instrumental malfunctions, and (3) scattering phenomena. In connection with the third factor, an experimental determination of the characteristics of binary-fission-fragment scattering confirmed the absence of this phenomenon from all but one of the angular arrangements investigated. It is concluded that the major portion of triple events observed arises from a ternary-fission process. A difference in the ternary-fission properties of ${\mathrm{U}}^{236*}$ and ${\mathrm{U}}^{234*}$ is interpreted as caused by the dominant effect of underlying shell structure in forming the product fragments, an effect which may result in the formation of unique (preselected) fragments masses. Mass distributions indicate the formation of low-mass fission products with mass peaks centered near 30 and 50 amu. A qualitative mechanism by which the ternary-fission process may occur is presented.

Lie Groups, Lie Algebras, and the Troubles of RelativisticSU(6)

Some of the difficulties of relativistic $\mathrm{SU}(6)$ are examined. Those arising from the use of continuous groups can be avoided by the use of algebras of finite sets of operators which are sufficient to give the desired properties of elementary particles. The nonconservation of probability associated with the relativistic separation of space and spin is pointed out. Quantum electrodynamics applied to atomic structure is shown to exhibit the type of peculiar symmetry which leaves the interaction invariant but is broken by free Dirac propagators. The implications of this analogy for $\mathrm{SU}(6)$ are discussed. The mixing of physical and non-physical states (positive- and negative-energy quark states) leads to noninvariance of the vacuum under the symmetry group, and to a degenerate vacuum in the exact symmetry limit. The existence of open inelastic channels for low-mass boson production is relevant to unitarity calculations and is implied in all energy regions where the symmetry is not badly broken.

Energy Dependence of Product Yields in Copper Spallation by Protons between 3 and 30 GeV

Careful comparisons of cross sections for formation of 19 products of copper spallation by 3- and 30-GeV protons indicate only a small energy dependence in this energy range. As the energy is increased from 3 to 30 GeV, products of $A>40$ decrease in yield by 15% or less, except for some highly neutron-deficient species, while low-mass products increase in yield by 10 to 50%. These findings are somewhat at variance with earlier reports from CERN.

Some Notes on Carburation and other Fuel System Problems

While both vertical down-draught and horizontal side-draught types of carburettor are produced in Great Britain, the majority of instruments manufactured are of the down-draught variety. There is a distinct trend in body style towards low bonnet-lines, and this has created a demand for shorter down-draught carburettors. A considerable portion of the paper deals with carburettor icing. This has become a most troublesome factor in fuel system performance throughout recent years, during conditions of critical atmospheric temperature and humidity. Various palliatives are possible. At the other end of the temperature scale come vaporizing troubles, causing hot starting difficulties in summer; conditions which assist the one are usually detrimental to the other. The need for every possible fuel economy has resulted in automatic economy systems being incorporated in most carburettors. By exploring the mixture range with loops the maximum economy of any particular engine can be determined. Too much attention is often given to some minor discrepancy in fuel flow between one carburettor and another, and not enough to the discrepancy between the fuel flow induced between one engine and another. Automatic chokes provide a controversial subject for discussion and their advantages and disadvantages are evaluated. The author has had a very wide experience with this form of starting. Petrol injection was once believed to be the panacea for all fuel system problems. Enough development has been carried out to indicate that while there are certain advantages to be obtained with some forms of petrol injection, it is likely to be too costly for employment on the medium and low priced mass production vehicle.