M.G.K. Menon

LIV. Nuclear reactions produced by slow negative π-mesons

Abstract Reactions produced by the nuclear capture of slow negative π-mesons have been studied by the photographic method. The disintegrations of the light and heavy elements of the emulsion have been distinguished by methods which are described in detail. Because of the large number of “stars” observed—more than 2500—it has been possible to make a statistical approach to the study of the disintegrations. The general features of the “stars” produced by the disintegration of heavy nuclei are in satisfactory agreement with the predictions of the evaporation theory. In addition, the emission of fast, singly-charged particles has been observed, most of which must be attributed to an alternative process to that of evaporation. Preliminary results have been obtained for the frequency of emission and the energy “spectrum” of these particles. The conclusion is reached that in the initial process of capture—the so-called “primary” process—the energy corresponding to the rest-mass of the φ− meson is shared among a ...

Observations on the multiple scattering of ionizing particles in photographic emulsions - Part I. The value of the scattering constant

Summary The theories of multiple scattering of Williams, Moliere, Snyder and Scott are briefly surveyed. The results of five independent determinations of the scattering constant for G.5 nuclear research emulsions, details of which are to be presented in the following papers, are compared and discussed. The constant has been found to vary with cell-size and β in a manner which is in agreement with theory. The effect of rejecting large angles due to plural scattering is considered, and also those errors which arise from the presence of spurious scattering.

XCIV. Observations on the multiple scattering of ionizing particles in photographic emulsions.—Part II. The scattering of positrons at 105 and 185 MeV

Summary The coordinate method has been used to measure the multiple scattering in Ilford G5 emulsions of positrons of nominal energy 113 and 196 MeV. The energies of the positrons corrected for loss by ionization and radiation are calculated to be 105 and 185 MeV. respectively. The experimental distributions of second differences have been compared with those predicted by the theory of Moliere (1947, 1948) and the agreement found to be very satisfactory. Methods of minimizing the effects of spurious scattering and of taking into account the influence of distortion are discussed. Values are found for the scattering constant which are in good agreement with those calculated from the theory of Moliere. A discussion of these results has been given in a previous paper of this series (Gottstein et al. 1951). A mathematical treatment is given in the Appendices: (I.) the correlation existing between successive second differences, (II.) the distribution of second differences when measured in the presence of spurio...

Hyperon events in photographic emulsions

SummaryDetails are given of six hyperon events observed in photographic emulsions. Two of these decay at rest into protons and giveQ-values of 115.8±1.0 MeV and 113.5±1.7 MeV for the assumed decay scheme: Y+ → p+π0+Q. Three others decay in flight; two giveQ-values 115±7 MeV and 103±10.5 MeV for the decay mode: Y± → n+π±+Q; the third is in agreement with the cascade type of decay: Y− → A0+π−+Q and has aQ=59±11 MeV. The sixth event has been interpreted as the interaction at rest of a negative hyperon; from the parent star of this hyperon there also emerges a K-meson.RiassuntoSi descrivono in dettaglio sei iperoni osservati in emulsioni fotografiche. Due di di essi decadono a riposo in protoni e danno perQ valori di 115,8 ± 1,0 MeV e 113,5±1,7 MeV per il presunto schema di decadimento Y+ → p+π0+Q. Tre altri decadono in volo: due danno perQ valori di 115±7 MeV e 103±10,5 MeV per lo schema di decadimento Y± → n+π±+Q: il terzo si accorda col tipo di decadimento in cascata: Y− → A0+π−+Q e ha unQ=59±11 MeV. Il sesto evento è stato interpretato come l’interazione a riposo di un iperone negativo; dalla stella da cui origina questo iperone emerge anche un mesone K.

CXV. Evidence for the β-decay of a K-meson

Summary The decay at rest of a K-meson in which the secondary particle appears to be an electron of ∼90mev has recently been observed. The secondary particle, after traversing a distance of 2·3 cm in the emulsion, appears to have been sharply deviated; thereafter, the track is closely similar to that of a slow electron. The grain density in the track, before and after the deviation, is indistinguishable from the ‘plateau value’. The most plausible explanation of this behaviour is that it is due to the sudden loss of energy of an electron through the production of bremsstrahlung. Alternatively, the secondary particle could be assumed to be (a) a π-meson which interacts with a nucleus and undergoes change exchange, the product nucleus subsequently suffering β-decay, or (b) a μ-meson which decays in flight. The last two possibilities have been considered and appear very improbable.

Some aspects of the nuclear capture of hyperons and K-mesons

SummarySome predictions are made concerning the characteristics of the interactions produced by the nuclear capture of K−- and Y−-particles. It is assumed that the capture reaction is the inverse of the «associated production mechanism». A comparison is made between these predictions and the experimental data. The significant conclusions are: (i) the capture process sometimes involves two or more nucleons rather than a single nucleon; (ii) in view of the possible existence of Σ0-particles and their rapid transformation to Λ0-particles, the observation of Λ0-particles as end products of a capture process does not necessarily indicate that they were produced in the initial reaction; (iii) there appears to be an absence of μ-mesons of ∼ 120 MeV; this might indicate the production of a Σ0-particle instead of a Λ0-particle in the initial reaction or that the capture involves two or more nucleons; (iv) the available observations on capture stars are consistent with the general features of the theory of Gell-Mann and Pais.RiassuntoSi fanno alcune previsioni riguardanti le caratteristiche delle interazioni prodotte dalla cattura nucleare di particelle K− e Y−. Si assume che la reazione di cattura sia l’inversa del «meccanismo delle produzioni associate». Si istituisce un confronto tra queste previsioni e i dati sperimentali. Le conclusioni di rilievo sono: (i) il processo di cattura coinvolge a volte due o più nucleoni anzichè uno solo; (ii) in vista della possible esistenza di particelle Σ0 e della loro rapida trasformazione in particelle Λ0, l’osservazione di particelle Λ0 quali prodotti finali di un processo di cattura non è necessariamente un indice che esse sono state prodotte nella reazione iniziale; (iii) si constata l’assenza di mesoni μ di ∼ 120 MeV; questo potrebbe essere un indice della produzione nella reazione iniziale di una particella Σ0 invece di una Λ0, o che la cattura coinvolge due o più nucleoni; (iv) le osservazioni di stelle di cattura note sono in accordo con le linee generali della teoria di Gell-Mann e Pais.

CV. Masses and modes of decay of heavy mesons.—Part II. τ-particles

Summary Further evidence which establishes the existence of heavy charged mesons which decay into three charged particles is presented. It is shown that the three secondary particles are probably π-particles, and that the mass of the parent mesons, called τ-particles, is 966±8me . The frequency of occurrence of κ- and τ-particles at the Jungfraujoch, in comparison with the number of π-particles, is discussed, and it is shown that in the nuclear collisions involving protons of energy greater than 10 BeV., a large fraction of the energy lost in the creation of mesons, must appear as κ- and τ-particles. The evidence suggests that the life-time of the heavy mesons is about 10-9 sec. The most favourable conditions for the detection of the particles by the photographic method are discussed.

CXXIII. Observations on the multiple scattering of ionizing particles in photographic emulsions.-Part V. Scattering measurements on tracks of slow protons

The scattering constant has been determined by measurements of the multiple scattering along proton tracks ending in the emulsion. A value of 27.8±0.5 has been obtained (for β 2 ~0.03 and an average cell-size of 72 μ). A simple method involving the combined measurements of multiple scattering and residual range has been used to identify the particles. A parameter P = 2.37 log α^ 100μ + 1.37 log R was determined for each track (R being the range in microns and α 100μ the mean angle of multiple scattering-per 100 μ-measured along the faster half of the trajectory); P is a linear function of the logarithm of the mass of the particle. A scale of values of P has been calibrated experimentally using tracks of protons from artificial sources and those of σ-mesons. Using this method tracks of 83 protons have been identified amongst a group of 136 particles of charge |e| ejected from cosmic ray stars. The mean value of P for the 83 protons was found to be 4.275±0.013. The resolution between τ-mesons, protons, deuterons and tritons was found to be satisfactory. An appendix gives the coupling matrix calculated for the sagitta method, taking into account the loss of energy.

The production of a pair of heavy mesons in a high-energy nuclear interaction

Recent ly there have been reported several examples of nuclear interact ions in which occur the associated production of a hyperon and a heavy meson; in those examples where an identificat.ion of the charge of the heavy meson has been possible it has always been shown to be posi t ive or neutral . In this communica t ion we describe an even t in which a negative K-mesm,, K (Brd), is produced in association with a~+other heavy meson. The nega | ive K-meson capture s tar was found in the course of scanning in photographic emulsion. The t rack of tim incoming part ic le was /:raced back to its origin which was foui~d to be a s tar of type 6 + 5p. The or ientat ions of the remaining t racks f rom the s tar were such that , wi th one except ion, reliable measurements could be made on all, and the i r na ture defined. The details and results of the measurements on the tracks are shown i~ Ta.ble l . The to ta l

THE RANGE IN G5 NUCLEAR EMULSION OF PROTONS WITH ENERGIES 87, 118, AND 146 MEV

SummaryA comparison was made between the ranges of artificially accelerated protons in Aluminium and in Ilford G5 photographic emulsion. The ranges in emulsion were obtained by direct measurements along the particle tracks, and those in Aluminium by an attenuation method. The ranges of protons of three different energies were 19.31, 13.23 and 7.82 g/cm2 in Aluminium, and 22.85, 15.58 and 9.50 g/cm2 in emulsion of density 3.791 g/cm3 conditioned to 58% relative humidity. The corresponding energies were 146.5 MeV, 117.9 MeV and 87.4 MeV. Assuming the range-energy relation for protons to be at present better determined for Aluminium than for photographic emulsion, this experiment provides new information concerning the relation between particle range and energy in nuclear emulsion.RiassuntoSi è fatto un confronto fra i range di protoni artificialmente accelerati in alluminio e in emulsioni fotografiche Ilford G5. I range in emulsione furono ottenuti per misura diretta delle tracce delle particelle, quelli in alluminio con un metodo di attenuazione. I range dei protoni di tre differenti energie furono di 19.31, 13.23 e 7.82 g/cm2 in alluminio e di 22.85, 15.58 e 9.50 g/cm2 in emulsione di densità 3.791 g/cm3 condizionata a 58% di umidità relativa. Le corrispondenti energie erano 146.5 MeV, 117.9 MeV e 87.4 MeV. Assumendo che la relazione range-energia pei protoni sia attualmente meglio determinata per l’alluminio che per l’emulsione fotografica, il presente esperimento fornisce nuovi dati sulla relazione, nelle emulsioni nucleari, tra il range delle particelle e l’energia.