D. O'Sullivan

The identification of a double hyperfragment

Abstract The detailed analysis is presented of an event which is interpreted as the mesonic cascade decay of a double hyperfragment produced by the capture of a Ξ− hyperon on a light emulsion nucleus. The most likely interpretations of the double hyperfragment are those in terms of either ΛΛBe10 or ΛΛBe11.

A determination of the binding-energy values of light hypernuclei

Abstract The results of an experimental study of the binding energies of light hypernuclei are presented, based on a sample of 2008 uniquely identified π − mesonic decays. The problems of the calibration procedure and the selection criteria are discussed. Various aspects of the Λ -N interaction are reviewed in the light of these new results.

The decay of heavy hypernuclei

In a sample of 38238 interactions found in photographic emulsions exposed to K− mesons of 1.3 and 1.5 GeV/c momenta, a total of 1385 heavy hypernuclei (40 < A < 100) were observed, of which 11 decayed mesonically. The following results were obtained: an upper limit of 27±3 MeV for the Λ0 nuclear potential well depth, a value of Q− in the range 100 to 200 and a fraction, n, in the range 0.6 to 0.9 of non-mesonic decays stimulated by the weak Λ0-neutron interaction.

Cosmic rays and dosimetry at aviation altitudes.

Recent concerns regarding the effects of the cosmic radiation field at aircraft altitudes on aircrew have resulted in a renewed interest in detailed measurements of the neutral and charged particle components in the atmosphere. CR-39 nuclear track detectors have been employed on a number of subsonic and supersonic aircraft to measure charge spectra and LET spectra at aircraft altitudes. These detectors are ideal for long term exposures required for these studies and their passive nature makes them suitable for an environment where interference with flight instrumentation could be a problem. We report here on measurements and analysis of short range tracks which were produced by high LET particles generated mainly by neutron interactions at aviation altitudes. In order to test the overall validity of the technique measurements were also carried out at the CERN-CEC field which simulates the radiation field at aviation altitudes and good agreement was found with dose values obtained using mainly heavy ion calibration.

Some comments on the investigation of nuclear and electromagnetic interactions of relativistic ultra heavy cosmic ray nuclei in the Dublin-ESTEC experiment

Abstract Recent results on the fragmentation of Z >70 nuclei with energies up to 10 GeV/nucleon have given new information on the energy dependence of nuclear and electromagnetic cross sections relevant to the study of high energy ultra heavy cosmic ray nuclei. The impact this new information could have on the Dublin-ESTEC Ultra Heavy Cosmic Ray Experiment, (UHCRE), is discussed and measurements being undertaken as part of the programme to provide a charge spectrum for nuclei with Z >70 are described. Preliminary results will be presented.

On the lifetime of the 3ΛH ypernucleus

The mean lifetime of the 3ΛH hypernucleus has been estimated in nuclear emulsion using the (π−+1H+2H) decays both at rest and in flight. The result, τ(3ΛH) = (1.28−0.26+0.35) · 10−10sec, is significantly lower than another recent experimental value [5] and the theoretical predictions. A possible explanation of the discrepancy with the theoretical predictions is briefly discussed.

Branching ratios for the π− mesonic decays of the hypernuclei Λ3H and Λ4H

Results are presented concerning the experimental determination, with large statistics, of the branching ratios for the π− mesonic decay of the hypernuclei Λ3H and Λ4H. The spin assignments J(Λ3H) = 12and J(Λ4H) = 0 are confirmed.

Production of hyperfragments from the interactions of 1.3 GeV/c and 1.5 GeV/c K− mesons with emulsion nuclei

Study of particle interactions in emulsion stacks exposed to 1.3 and 1.5 Bev/c K/sup -/ meson beams gives support to the idea that hyperfragments of range less than 10 mu m are residual spallation products containing trapped LAMBDA / sup o/ hyperons resulting from K/sup -/ interactions in emulsion nuclei. (D.C.W.)

The non-mesonic decay of helium hypernuclei

Abstract The analysis is reported of a sample of hypernuclei decaying non-mesonically with the emission of one or two charged particles which were obtained from K − meson captures at rest in nuclear emulsion. Making use of the decay parameters established for the 4 Λ He hypernucleus from observations in a helium bubble chamber, a value of Q − , the ratio of non-mesonic to π − mesonic decays, for λ 5 He together with the rates of certain decay modes have been determined.

European measurements of aircraft crew exposure to cosmic radiation.

Abstract—For more than 5 y, the European Commission has supported research into scientific and technical aspects of cosmic-ray dosimetry at flight altitudes in civil radiation. This has been in response to legislation to regard exposure of aircraft crew as occupational, following the recommendations of the International Commission on Radiological Protection in Publication 60. The response to increased public interest and concern, and in anticipation of European and national current work, within a total of three multi-national, multi-partner research contracts, is based on a comprehensive approach including measurements with dosimetric and spectrometric instruments during flights, at high-mountain altitudes, and in a high-energy radiation reference field at CERN, as well as cosmic-ray transport calculations. The work involves scientists in the fields of neutron physics, cosmic-ray physics, and general dosimetry. A detailed set of measurements has been obtained by employing a wide range of detectors on several routes, both on subsonic and supersonic aircraft. Many of the measurements were made simultaneously by several instruments allowing the intercomparison of results. This paper presents a brief overview of results obtained. It demonstrates that the knowledge about radiation fields and on exposure data has been substantially consolidated and that the available data provide an adequate basis for dose assessments of aircraft crew, which will be legally required in the European Union after 13 May 2000.