Emission Of Neutral Particles Research Articles

Reactions of StoppingK−in Helium

Branching ratios have been measured for reactions initiated by negative kaons coming to rest in a helium bubble chamber. The data were obtained from an analysis of \ensuremath{\sim}1000 events found in a careful scan using a very limited fiducial volume. Charged-$\ensuremath{\Sigma}$ emission accounts for (30.8\ifmmode\pm\else\textpm\fi{}3.2)% of the absorptions and $\frac{\ensuremath{\Lambda}}{{\ensuremath{\Sigma}}^{0}}$ emission for (69.2\ifmmode\pm\else\textpm\fi{}6.6)%. Evidence for $\ensuremath{\Sigma}$-to-$\ensuremath{\Lambda}$ conversion is clearly seen in the events with a visible $\ensuremath{\Lambda}+{\ensuremath{\pi}}^{\ensuremath{-}}$, and (66\ifmmode\pm\else\textpm\fi{}9)% of this final state results from such a process. Multinucleon (i.e., nonpionic) absorption is found to occur in (16.5\ifmmode\pm\else\textpm\fi{}2.6)% of the events, which is similar to the results reported from studies using heavy-liquid bubble chambers and nuclear emulsion. In general, the kinematic spectra for single-nucleon absorption events agree well with the predictions of a simple impulse approximation. The ratio of ${K}^{\ensuremath{-}}$ capture on neutrons to that on protons is examined using the $\ensuremath{\Lambda}{\ensuremath{\pi}}^{\ensuremath{-}}{\mathrm{He}}^{3}$ and the $\ensuremath{\Lambda}{\ensuremath{\pi}}^{0}{\mathrm{H}}^{3}$ final states. The data for charged- and neutral-particle emission are consistent with the predictions of isospin invariance for kaon absorption in ${\mathrm{He}}^{4}$.

Thermal Positive Ion Emission from Alkali-Metal Iodide Mixtures

Time variation of the emission of both positive ions and neutral particles was simultaneously examined with one-and two-component systems of alkali-metal iodides on a platinum wire heated to 1080°C. A “suppression effect” was observed: - by the presence of the heavier alkali-metal iodide, MHI, (1)the emission pattern of the lighter alkali-metal ion, ML+, was much changed, (2)the integrated emission current of ML+ was reduced to 40-60%, and(3)the reduction of ML+ emission current was accompanied by an increase in ML emission in the form of neutral particles by 20-30%, while the MH+ emission was not affected by the presence of WLI. Discussion on a mechanism of this effect is given from three view-points of the work function change, charge transfer, and recombination reaction. The conclusion is that the suppression effect is due to the recombination of ML+ and I- on the filament surface enhanced by the presence of MHI.

Production and interaction of mesons at very high energies

A shower containing ∼360 charged and neutral shower particles produced by a magnesium nucleus of 2×1014e.v. provides a source of mesons whose interactions have been studied over an aggregate track length of about 3 meters in emulsion. It is first shown that in very large showers not only the incident energy can be determined but also the energy of the shower particles. The angular distribution of the shower particles agrees closely and their multiplicity is consistent with Fermi’s theory. It is shown that the interaction cross-section of charged shower particles is geometric and that at an energy ∈ ∼ 1000µc 2 they produce on the average 5 to 6 mesons. The mesons are preferentially emitted in the backward direction in the reference system in which the momentum of the incident meson balances that of a nucleon in the target. The excitation produced in the target nucleus is much lower than in nucleon-produced showers of comparable multiplicity. The charged mesons arenot emitted in pairs by a heavier meson of short lifetime. Charged shower particles as well as electrons produce electron-positron pairs with a cross-section of the order of that predicted by theory. The number of neutral mesons decaying intoγ-rays in a time ≤10−14 sec. is nearly equal to the number of charged shower particles. There exists evidence for the emission of neutral particles, different from neutrons, capable of producing meson showers. The energy balance of the event suggests that a few shower particles carry an appreciable fraction of the total energy.