PLASTEX: the palermo-leeds air shower tracking experiment

Summary An experiment is described in which air shower measurement are carried out by means of a ?track detector? placed in a test location near the center of a conventional array telescope currently in use for gamma-ray astronomy. This array, consisting of scintillators (GREX, operated at Haverah Park (U.K.) by the Department of Physics of the University of Leeds), provides, in the usual way, for each shower it selects, its own estimates of shower direction and shower particle density at the test location. Estimates of the muon density at the test location are provided by a large muon detector in operation nearby. The scintillator array triggers this muon detector and it is able to provide flexibly tailored trigger signals for the track detector. This detector named PLASTEX (acronym for Palermo Leeds Air Shower Tracking Experiment), consisting of tracking chambers above and below a thin sheet of lead, designed to provide data on charged particles incident from the air, on the stopping, scattering and multiplication of these particles in the lead sheet and on charged particles created in the lead sheet by shower photons. From these data estimates are derived of the densities and directional properties of the electrons, photons and muons striking the track detector. These results are to be compared with those given by the conventional detectors and with theoretical predictions given by simulations that are being carried out. The objective is to develop and assess optimal procedures for employing clusters of PLASTEX-type detectors as telescopes for the observation of UHE cosmic rays, including cosmic gammarays, over a very wide energy range. To speed up publication, the proofs were not sent to the authors and were supervised by the Scientific Committee.     

Secondary protons in the atmosphere at different latitudes

Summary We present a semiempirical method to study the production and propagation of atmospheric secondary protons with energy>100 Mev, moving in the vertical direction. The derived production functions are fitted by the least-square method for the only previously published splash (SP) and return (RE) albedos observed data using the same instrument and measurement sites. The closed agreements between the measurement data and the calculations over a wide range of atmospheric depths lead to a possible extension of the method for other latitudes. The spectra of SP and RE intensitiesversus the geomagnetic cut-off reveal similar behaviour as assumed earlier by the theory for those components in the Earth's magnetic field.     

Imaging of atmospheric EAS Cherenkov light at EAS-TOP

Summary Images of atmospheric EAS Cherenkov light have been recorded in connection with the EAS-TOP experiment. We describe the technique (based on a multianode photomultiplier Philips XP4702) and present some preliminary data analysis.     

On the problematic rising ratio of cosmic-ray positrons at ultra-high energies

Summary The rising ratio of cosmic-ray positrons at ultra-high energies of interactions seems to have puzzled the theorists to a great extent. We have made here a somewhat successful attempt to interpret the behaviour of this ratio,R=e⁺/(e⁺+e⁻), by putting into use the main physical ideas from our two previous works. The importance and the implications of this observation have also been highlighted and emphasized in the proper background.

---

Riassunto Il crescente rapporto dei positroni dei raggi cosmici ad energie ultra-alte di interazioni sembra aver non poco confuso i teorici. Qui si tenta con un certo successo di interpretare il comportamento di questo rapportoR=e⁺/(e⁺+e⁻) usando i principali concetti fisici dei nostri due precedenti lavori. L'importanza e le implicazioni di questa osservazione sono state sottolineate ed enfatizzate nell'appropriato contesto.

---

Резюме Увеличивающиеся отношение позитронов космических лучей при ультравыс оких энергиях, по-видимому, представляет загадку для теоретиков. В этой статье мы предпринимает отчасти успешную попытку интерпретировать поведение этого отношенияR=e⁺/(e⁺+e⁻), используя основные физические идеи из наших двух предыдущих публикаций. Отмчаются важностя и приложения полученных результатов.

     

The EAS-TOP calorimeter

Summary The muon-hadron detector of EAS-TOP is a 270 m² calorimeter constructed inside the air shower array on the top of the underground Gran Sasso Laboratory (Italy). The general layout of the detector and the performances of the active part (streamer and proportional chambers) are presented. Paper presented at the V Cosmic Physics National Conference, S. Miniato, November 27–30, 1990.     

EAS-TOP: Results of the gamma-ray astronomy at 1014 eV

Summary The EAS-TOP Extensive Air Shower array, on top of the under-ground Gran Sasso Laboratory, is fully operating as a γ-ray astronomy observatory since the beginning of 1989. After showing the measured angular resolution of the detector, we present the results obtained from the analysis of 280 days of measurements in 1989–1990, with the purpose of investigating possible emission (d.c. and sporadic) from the candidate sources in the Northern hemisphere at an energy, >200 TeV. Paper presented at the V Cosmic Physics National Conference, S. Miniato, November 27–30, 1990.     

Sea level muon spectra at large zenith angles derived from the latest JACEE primary nucleon spectrum

Summary Sea level muon energy spectra at large zenith angles have been derived from the latest JACEE primary spectrum using the Fermilab Single-Arm Spectrometer data on charged-meson production. The role of increasing total cross-section on the final result for the energy spectra has been investigated here with special emphasis. The inclusion of the rising total cross-section at cosmic range of energies, it is seen, has come into much use in explaining the observed data at very high energies. The autors of this paper have agreed not to receive the proofs for correction.     

Study of fragmentation in56Fe+27Al interactions at 1.88 A GeV using CR-39 (DOP) solid-state nuclear-track detector

Summary 1.88A GeV⁵⁶Fe beam of Lawrence Berkeley Laboratory BEVALAC irradiated at an angle 30° to the stack, composed of Al target and CR-39 (DOP) solid-state nuclear-track detector. These polymer sheets were etched in 6.25N NaOH solution at 70°C for 48 hours. The minor axes of the elliptic etch pits were measured by a Leitz Ortholux microscope. The measured projectile fragmentation cross-section for nuclei of chargeZ ranging from 21 to 25 is in approximate agreement with the calculated result from the semi-empirical nuclear fragmentation model after Wilson, Townsend and Badavi. The existence of trans Fe nuclei was noticed. The measured double-cone charge resolution was found to be 0.20e.     

The use of high-frequency filters in the investigation of the coloured-random-noise properties of cosmic-ray data

Summary This paper investigates the influence of high-frequency filtering the background white noise on the determination of the coloured-random-noise properties of cosmic-ray experimental signals. We consider fractal methods (Grassberger-Procaccia method, scaling exponent method and fractal length method) and statistical methods (comparison with the Gaussian curve, and the multivariate scaling-analysis technique). The investigation is carried out using two experimental time series with differentcolour (spectral indices α=1.6 and α=1.2) and their computer simulations of pure noise-freecoloured-random-noise signals. The results of the investigation is that the use of high-frequency filtering allows the algorithms employed in the various analyses to see the physical characteristics of the particular data set; the procedure should be reserved, however, to researchers with a good experience in the methods of fractal analysis so that they can identify and discard the artifacts introduced by the truncation applied to the power spectrum.     

The EAS-TOP atmospheric-?erenkov-light telescope and its combined operation with the e.m. Detector

Summary The study of extensive air showers is performed at EAS-TOP by means of the combined operation of the first imaging Čerenkov telescope and the particle e.m. array. We discuss the technical characteristics of the Čerenkov detector and its resolutions. First data on the shape of the Čerenkov-light spots as a function of the EAS detection geometry, and on a first approach to the study of the longitudinal development of the cascades are also presented. Paper presented at the 6th Cosmic Physics National Conference, Palermo, 3–7 November 1992.     

Energetic-position population in the inner zone

Summary The possibility of the existence of a natural positron belt in the Earth's magnetosphere is considered. It is suggested that the positrons can be produced in the nuclear reactions of trapped relativistic protons of the inner zone with the residual atmosphere. The positron spectrum in the range of 10–100 MeV at the top ofL=1.2 is calculated and compared with the experimental results.     

On cosmic-ray cut-off terminology

Summary The study of cosmic-ray access to locations within the geomagnetic field has evolved over the past fifty years. Cosmic-ray cut-off terminology, originally developed to describe particle access and cut-off rigidities, has not evolved with the scientific advances in the field, and misunderstandings and misapplications of historical work have occurred. This paper is an attempt to remedy this situation by clarifying the areas in which changes have occurred and by providing a cross reference between the historical terms and those terms now in use for innovative cosmic-ray studies which are underway in several laboratories.     

High-energy electron and gamma-ray fluxes in the Brazilian Magnetic-Anomaly Region

Summary Fluxes of electrons and gamma-rays with energies around a few tens of MeV were measured with a balloon-borne detector in November, 1991, in Bauru, (Brazil). The altitude dependences of fluxes and the indices of the differential energy spectra obtained at rigidity 12 GV (Bauru) are compared with results obtained with the same detector at rigidity 3.5 GV in the Volga region (Volsk), Russia.     

Chemical composition of the primary cosmic rays near the top of the atmosphere

Summary A stack of CR-39 (HCB 0.5%) passive solid-state nuclear track detectors were irradiated by primary cosmic rays near the top of the atmosphere. The stack of detectors were flown by balloons launched from Alice Springs, Australia in 1983. After 16 h 41 min flight exposure at an atmospheric pressure of 9.5 mb the plates were collected and chemically etched in 6.7 N NaOH aqueous solution at 70°C for 27 hours. The diameter distribution of the 1208 etch pits caused by the presence of heavy ions in primary cosmic rays was measured by a transmitted light Leitz Ortholux microscope having an objective×10 and a×15 filar micrometer eyepiece attachment. The diameter distribution was standardised and calibrated against the conventional cosmic-ray results found by Tasakaet al. The estimated charge spectrum is in accord with the nuclear emulsion data of Daniel and Durgaprasad, Kristianssonet al., Saito and Chohanet al.     

Short-period variation of cosmic-ray intensity and ozone density observed in the stratosphere

Summary The energy deposition by slowing-down of energetic ionizing particles in the atmosphere enhances the production of constituent concentration which perturbs and eventually destroys the ozone (OZ) layer. Near the Brazilian anomaly region the cosmic-ray (CR) intensity varies greatly due to the magnetic activity in that region. In order to study these variations, stratospheric balloons were launched to measure, simultaneously, the CR and OZ fluxes in the atmosphere. The Fourier-analysed data collected during the flight on April 22, 1989 show evidences of a short-period variation for both fluxes measured. Attempts to verify the physical mechanisms which associate the CR change with the OZ one are not conclusive due to limited data observed on that event.     

Search for cosmic γ-ray bursts in the (1÷50) GeV energy range

Summary A search for cosmic gamma-ray bursts in the GeV energy range has been performed by means of the EAS-TOP Extensive Air Shower array at Campo Imperatore (Gran Sasso Laboratories) during the period March–December 1990. In 2566.5 hours of measurement the obtained upper limit to the rate of bursts of amplitude >2% of the cosmic-ray intensity and time duration τ=1 s, isR≤7.9y⁻¹ (90% c.l.). Assuming for γ-rays a differential energy spectrumS(E ₀ )≈E ₀ ^−2.5 , the corresponding upper limit to the energy flux of γ-rays with energy >5 GeV in bursts of duration τ≤1 s is Φ<8.3·10⁻⁵erg cm⁻².     

Search for νμ and ντ supernova neutrinos with massive liquid-scintillation detectors

Summary In this paper we have estimated the sensitivity of a large-mass liquid-scintillation detector to search for supernova neutrinos of different flavours. Events produced by ν_μ and ν_τ interactions can be identified by looking at the distorsion in the neutrino energy spectrum. We have shown here that, overlapped to the main energy distribution produced by interactions with protons a peak at 15.11 MeV (due to the de-excitation of¹²C^* nuclei excited by neutral-current neutrino interactions) gives a possible signature of these neutrino flavours. Due to the relevance of its scientific content, this paper has been given priority by the Journal Direction.     

On the possibility of investigation of the mass composition and energy spectra of primary cosmic ray (PCR) in the energy range from 1015 to 1017 eV using EAS data

Summary A method allowing one to determine the mass composition of primary cosmic radiation by means of simultaneous analysis of model and experimental data is presented in this paper. The most important part of this work is the quantitative comparison of multivariate distributions and the use of methods of nonparametric statistics for probability density estimation in a multivariate space of features. To check the method offered, events withE ₀>500TeV were generated by the Monte Carlo method. The showers generated were preliminarily processed by algorithms used in experimental data handling. The apparatus-induced distortions of the measured EAS characteristics have been taken into account. The method allows one to select an experimental event initiated by primary protons and iron nuclei with an efficiency of (70÷80)%. Also a new multivariate method of incident particle energy estimation based on the nonparametric regression is described. The method proposed, together with the above-mentioned multivariate EAS classification, allows one to determine the energy spectrum of incident protons and nuclei. Detection and investigation of the products of interaction of these particles with the atmosphere will allow us to study proton-nuclei and nuclei-nuclei interactions at energies from 10¹⁵ to 10¹⁷ eV.     

Thermoluminescence in sea sediments during the cosmogenic isotopes enhancement 35000 y BP

Summary We have measured the thermoluminescence (TL) profile of the Mediterranean Sea core CT85.5 at the same depths where the cosmogenic-isotope¹⁰Be production peak at 35 ky BP was found. Strong TL peaks are evident at 37.5 ky and 35.6 ky BP. The Fourier analysis of the TL time series running from 32.5 ky to 42.6 ky at 100 y sampling interval shows 2500 y and 500 y periodicities. We suggest that the Sun was ?active? at the time of the¹⁰Be enhancement. Paper presented at the 6th Cosmic Physics National Conference, Palermo, 3–7 November 1992.     

Is there an excess of electron neutrinos in the atmospheric flux?

Summary The background produced by isolated neutrons in Cherenkov detectors studying the atmospheric neutrinos is discussed. The neutrons are generated in nuclear showers initiated by muons in the rock surrounding the detectors. It is shown that, taking into account the detection of π⁰ events from reactions of nA→π⁰X, which look likev _e detection, results in an observedI(v _μ)/I(v _e) ratio close to the expected one for the energy range 0.2–5 GeV.