G. Dellacasa

Measurement of the Annihilation Cross-Section for Antineutrons on Fe from 100 to 531 MeV/c

The cross-section for annihilation on Fe from 100 to 531 MeV/c was measured by means of a layered absorption detector. The cross-sections are related to the free N annihilation cross-sections by a simple A2/3 scaling law, indicating a surface process.

A Study of the bar n Production on Nuclei by bar p of 550 MeV/c

Inclusive spectra produced at 0° by the interaction of 550 MeV/c s on C, Al, Cu and Pb targets were measured. The results are discussed in the framework of simple models on incoherent particle production by complex nuclei.

A Low Energy Antineutron Detector

A detector for antineutrons in the momentum range 0.1 - 1 Gev/c, to be used at LEAR faci= lity at CERN, is described. The antineutrons are detected by means of the charged pions produced in an annihilation event and their energy is determined by a time of flight mea= surement. The detector consist of 10 equal modules; each one contains: an iron slab (the converter) of 20×20×1 cm , a scintillation of the same dimensions for T.O.F. measurements, an iron sheet of 100×100×0.2 cm that stops the low energy high ionizing particles and finally a plane of limited streamer tubes with 1 cm pitch and read-out on both horizontal and vertical cohordinates. Principal features of the detector are: T.O.F. resolution of 0.5 ns, spatial resolution of 1 cm in both vertical and horizontal directions, estimated efficien= cy of 0.65.

A Time-of-Flight Hodoscope Saving the Number of Photomultipliers

Results of measurements of the performances of a time-of-flight hodoscope consisting of 16 slabs of plastic scintillator, 90×4×1 cm3 each, viewed by only 8 (instead of 32) photomultipliers are described. The slabs are coupled to the photomultipliers in such a way that they are considered as the elements of a square matrix of rank 4. Thus only 2×4 photomultipliers are needed to identify unambiguously each of the 16 slabs, if only a particle at a time has to be detected. By means of a very simple electronics we obtained a local time-of-flight resolution of 570 ps fwhm and a spatial resolution along each slab of 5 cm fwhm. The cross-talk due to unrecognized events was less than 5%.

A Large Area, Fine Grained Neutron Hodoscope

Results of measurements of the performances of a time-of-flight neutron hodoscope consisting of 50 slabs of plastic scintillator, 100 × 2 × 5 cm3 each, are described. The efficiency and the spatial localization properties along a slab were studied with a variable energy (2.4 to 16.4 MeV) neutron beam. The hodoscope was finally used in the experiment PS 178 at the LEAR facility at CERN.

Methods of determining the electron drift velocity in drift chambers

Abstract A displacement method for measuring electron drift velocities in adjustable-field drift-chambers has been developed and its results have been compared to those of a track-reconstruction method, which uses a least-squares track-fitting procedure and computes drift velocities by iteration. The reconstruction method has been adapted for use with tracks of unknown momentum curved by a magnetic field. Drift-velocities in a set of chambers fitted with double sense-wires and operating in magnetic fields between zero and 0.8 T have been determined by the two methods. The results agree within the limits of error and show a non-linear time-distance relation.

Pivoting light guides

Abstract Pivoting joints allowing rotation of light guides were developed. Principal features are described.

Search for subthreshold K+ production by3He ions of 910 MeV on carbon

SummaryA search for the two-body reaction3He+12C →3He+12C→Λ15N+K+ with3He ions of 910 MeV furnished an upper limit of ∼ 14 μb/sr·MeV/c (one standard deviation).

A Method for Calculating the Efficiency of Large Aperture Gas Cherenkov Counters

A method for calculating the efficiency of large aperture gas Cherenkov counters is presented. It is based on a careful Monte Carlo simulation of the geometrical response of the apparatus and on the measurement of the number of photoelectrons detected by the photomultipliers for some selected directions of the particles traversing the radiating volume. An application to a counter whose efficiency was systematically measured with great care is presented. The results are very satisfactory.

Operation and performance of a system for πp and πd backward scattering

Abstract A simple, large-solid-angle apparatus, specially suited for the measurement of backward elastic scattering of medium-energy pions on protons and deuterons, is described. The method of analysis which reduces background and determines elastic events from a data sample of 185 MeV negative pions incident on a D 2 O target is discussed. Results for 141 MeV π + p and 185 MeV π − p backward cross-sections are also presented and compared with cross-sections calculated from known phase shifts.