Emulsion Chamber Research Articles

Are protons still dominant at the knee of the cosmic-ray energy spectrum?

A hybrid experiment consisting of emulsion chambers, burst detectors and the Tibet-II air-shower array was carried out at Yangbajing (4300 m a.s.l., 606 g/cm2) in Tibet to obtain the energy spectra of primary protons and heliums. From three-year operation, these energy spectra are deduced between 1015 and 1016 eV by triggering the air showers associated with a high energy core and using a neural network method in the primary mass separation. The proton spectrum can be expressed by a single power-law function with a differential index of −3.01±0.11 and −3.05±0.12 based on the QGSJET+HD and SIBYLL+HD models, respectively, which are steeper than that extrapolated from the direct observations of −2.74±0.01 in the energy range below 1014 eV. The absolute fluxes of protons and heliums are derived within 30% systematic errors depending on the hadronic interaction models used in Monte Carlo simulation. The result of our experiment suggests that the main component responsible for the change of the power index of the all-particle spectrum around 3×1015 eV, so-called “knee”, is composed of nuclei heavier than helium. This is the first measurement of the differential energy spectra of primary protons and heliums by selecting them event by event at the knee energy region.

Cosmic-Ray Spectra and Composition in the Energy Range of 10-1000 TeV per Particle Obtained by the RUNJOB Experiment

This is a full report on the cosmic-ray spectra and composition obtained by the emulsion chambers on board 10 long-duration balloons, launched from Kamchatka between 1995 and 1999. The total exposure of these campaigns amounts to 575 m2 hr, with an average flight altitude of ~32 km. We present final results on the energy spectra of two light elements, protons and helium nuclei, and on those of three heavy-element groups, CNO, NeMgSi, and Fe, covering the very high energy region of 10-1000 TeV particle-1. We additionally present the secondary/primary ratio, the all-particle spectrum, and the average mass of the primary cosmic rays. We find that our proton spectrum is in good agreement with other results, but the intensity of the helium component is nearly half that obtained by JACEE and SOKOL. The slopes of the spectra of these two elements obtained from RUNJOB data are almost parallel, with values of 2.7-2.8 in the energy range of 10-500 TeV nucleon-1. RUNJOB heavy-component spectra are in agreement with the extrapolation from those at lower energies obtained by CRN (Chicago group), monotonically decreasing with energy. We have also observed secondary components, such as the LiBeB group and the sub-Fe group, and present the secondary/primary ratio in the TeV nucleon-1 region. We determine the all-particle spectrum and the average mass of the primary cosmic rays in the energy region of 20-1000 TeV particle-1. The intensity of the RUNJOB all-particle spectrum is 40%-50% less than those obtained by JACEE and SOKOL, and the RUNJOB average mass remains almost constant up to ~1 PeV.

On coplanarity of most energetic cores in gamma-ray–hadron families and hadron interactions at (s)1/2gtrsim 4 TeV

The phenomenon of coplanarity of the most energetic subcores of atmospheric nuclear-electromagnetic cascades found in X-ray?emulsion chamber experiments with gamma-ray?hadron families is considered. It is shown that the phenomenon cannot be explained with cascade development fluctuations and external fields within the framework of present-day versions of quark-gluon string models as well as without assuming the manifestation of a process in hadron interactions characterized with large transverse momenta in the Lab frame of reference at energies (s)1/2??4 TeV.

Coplanar emission in very high energy cosmic ray interactions

The alignment of very high energy secondary cosmic rays, implying coplanar emissions, was observed at both stratospheric and mountain altitudes by several x-ray emulsion chamber experiments. This paper investigates the physical relevance of the experimental observations through detailed Monte Carlo calculations carried out with the CORSIKA program combining different models of high energy hadronic interaction. The physical factors likely to induce or to influence this phenomenon are discussed.

Peculiar high energy cosmic ray stratospheric event reveals a heavy primary origin particle above the knee region of the cosmic ray spectrum

We wish to put forward an explanation for a peculiar cosmic ray event with energy {sigma}E{sub {gamma}}{>=}2x10{sup 15} eV detected in 1975 by the balloon borne emulsion chamber experiment performed in the stratosphere, at the altitude {>=}30 km above sea level. For almost 30 years the event has been described as unusual, invoking new exotic mechanisms or models. In our opinion there is no need for an extraordinary explanation. Contrary to the widespread belief, the event gives us an example of 'unrecognized standard physics'. At the same time this event revealed a variety of features which are of considerable interest for cosmic rays, nuclear physics, and astrophysics. Here we show that the observed family is most likely to be a result of a heavy nucleus interaction with an air nucleus. In this case a primary particle would originally have been in the energy region above 'the knee' of the cosmic ray spectrum.

ESTIMATIVE OF INELASTICITY COEFFICIENT FROM EMULSION CHAMBER DATA

Atmospheric diffusion of high energy cosmic rays is studied analytically and the obtained integral electromagnetic fluxes are compared with the data measured by emulsion chamber detectors at mountain altitudes. We find a good consistency between them when the average nucleon inelasticity coefficient is varying between 0.50 and 0.65.

On inconsistency of experimental data on primary nuclei spectra with sea level muon intensity measurements

For the first time a complete set of the most recent direct data on primary cosmic ray spectra is used as input into calculations of muon flux at sea level in a wide energy range Eμ = 1 − (3 × 105) GeV. Computations have been performed with the CORSIKA/QGSJET and CORSIKA/VENUS codes. Comparison of the obtained muon intensity with the data of muon experiments shows that measurements of primary nuclei spectra conform to sea level muon data only up to several tens of GeV and result in essential deficit of muons at higher energies. As it follows from our examination, uncertainties in muon flux measurements and in the description of nuclear cascades development are not suitable to explain this contradiction, and the only remaining factor, leading to this situation, is underestimation of primary light nuclei fluxes. We have considered systematic effects, that may distort the results of the primary cosmic-ray measurements with the application of the emulsion chambers. We suggest, that re-examination of these measurements is required with the employment of different hadronic interaction models. Also, in our point of view, it is necessary to perform estimates of the possible influence of the fact that a sizable fraction of events, identified as protons, actually are antiprotons. Study of this cosmic-ray component begins to draw much attention, but today nothing definite is known for the energies >40 GeV. In any case, to realize whether the mentioned, or some other reasons are the sources of disagreement of the data on primaries with the data on muons, the indicated effects should be thoroughly analysed.

Automatic analysis of the emulsion chamber using the image scanner applied to the Tibet hybrid experiment

A new method of emulsion chamber analysis by using an image scanner is developed in order to process a large number of X-ray films used in the Tibet hybrid experiment which is carried out to observe primary proton spectrum in the PeV region. The experimental procedure in this method consists of multiple steps of processing the image of the X-ray films, i.e. the detection of cascade showers induced by high-energy γ-rays, the noise reduction, the spatial reconstruction of γ-families and their energy determination. The quality of the results obtained by the new method is compared with that obtained by the current manual method or Monte Carlo simulations. It is shown that sufficiently high quality of the emulsion chamber analysis is realized by the automatic method both in energy and geometrical resolution.

A halo event observed with an emulsion chamber and air shower array at Mt Chacaltaya

A hybrid experiment to operate simultaneously an air shower array, a hadron calorimeter and an emulsion chamber is under way at Mt Chacaltaya (5200 m, Bolivia). An event with a halo, a blackened area of ∼1 cm on x-ray film of the emulsion chamber, was observed with the experiment. Information about the halo (Ehalo = 850 TeV) and on high energy particles of electromagnetic and hadronic components outside the halo (∑Eγ = 632.5 TeV and ∑E(γ)h = 278.8 TeV with a detection threshold of 2 TeV) was obtained from emulsion chamber data. Details about low energy hadrons were determined from the hadron calorimeter data, and characteristics of the accompanying air shower (Ne = 7.0 × 107, s = 0.59) were determined by the air shower array. We reconstruct the event, based on the observed data. The event is compared with simulated events, which supports the conclusion that nuclear interactions change their characteristics in the high energy region so as to result in stronger energy subdivision.

Solution to the Centauro puzzle

An unusual Centauro phenomenon in which cosmic rays enter the atmosphere producing tens of charged hadrons, but virtually no neutral pions, has been a mystery for more than 30 years. Since the discovery of Centauro I in 1972 by the Brazil-Japan Collaboration operating x-ray emulsion chambers at 5200 m on Mt. Chacaltaya in the Bolivian Andes, a variety of models have been proposed (including new types of interaction or the creation of new types of matter). Here we show that the solution to a long-standing scientific puzzle lies with the details of the Chacaltaya detector. The new analysis of the original Centauro I event reveals that there is a difference in the angle between the upper block and lower block events, so the two are not products of the same interaction. That leaves only the lower chamber data connected to the Centauro I event. It is shown that, with the revised understanding of the event, new physics is no longer required for the explanation.

A halo event observed by hybrid detectors at Mt. Chacaltaya

An experiment of an air shower array, a hadron calorimeter and an emulsion chamber is under way at Mt. Chacaltaya (5,200 m). Analysis of a halo event, detected by hybrid detectors, is presented. The data available for the event are on the halo ( E halo = 750 TeV), on the height of the interaction, the energy of the electron/photon and hadronic components from the emulsion chamber, on low energy hadrons from the hadron calorimeter, and on the characteristics of the accompanied air shower ( Ne = 7.0 × 10 7, s = 0.59) using the air shower array. The structure and origin of the event is discussed based on the observed data of various components obtained by the hybrid detectors. The event is compared to simulated events, which support the conclusion that nuclear interactions change their characteristics in the high energy region resulting in a stronger energy subdivision.

Identification of hadrons in Centauro events

Since the observation of a remarkable cosmic ray induced event, in experiments with emulsion chambers, a search for similar events was started. In spite of no observation of events showing the unusual aspect of Centauro I, another remarkable event with a high content of hadrons was observed. Moreover, this Centauro V has a hadron that interacts twice at deeper layers of the detector and has energy between (16–20)% of the total energy of the main interaction, the former figure for all showers and the last only for hadron-induced showers. Therefore, to classify it as a Centauro type event it is crucial to look for reasonable criterion to identify hadronic particles. Previous analysis adopted only one criterion for each shower observed in the films. Nowadays, an improved re-analysis uses at least two criteria for each shower. The main purpose of this paper is to show that the showers observed are properly identified as of hadronic origin and so we conclude that is an authentic Centauro event produced by the interaction of a hadron 500 m above the detector and interacting twice in the lower part of the chamber.

PCR nuclear composition at 1–30 PeV according to lateral distributions of electrons in EAS accompanied by high energy particles in emulsion chambers

New data on the primary cosmic ray nuclear composition were derived from the electron lateral distributions of EAS at Tien-Shan. The dependence on EAS electron size is presented from N e = 5·10 5 to 3·10 7. Data were obtained for all EAS as well as for EAS accompanied by high energy gamma-rays and hadrons in X-ray emulsion chambers. According to model simulations the latter events are generated predominantly by primary protons. Results showed that the fraction of protons and light nuclei does not decrease above the “knee” from N e = 10 6 up to 10 7 (∼10 – 20 PeV primary energy).

Intense bundles of particles in cores of nuclear-electromagnetic cascades in the atmosphere with energies around 100 PeV (gamma-families with halo)

An appreciable fraction of gamma-families are accompanied by a halo, a narrow bundle of high-energy particles (energy density > 20 TeV/mm 2) recorded in X-ray emulsion chambers as a diffuse dark spot in the central region of a gamma-family. Gamma-families in the experiment “Pamir” are compared with simulations by three different codes of quark-gluon string model (MQ, MCO and QGSJet) based on extrapolating accelerator data up to energy E o = 3 ∗ 10 18 eV and under various assumptions on mass composition of primary cosmic rays (PCR). The spectrum of halo area, S, is analyzed, especially at S > 100 mm 2. Simulations by different codes predict that at a PCR energy E o ∼ 10 18 eV the probability of initiating a halo with S ∼ 1000 mm 2 is 60% for primary protons and 40% for Fe nuclei. The fraction of protons in PCR composition at E 0 = 10 16 ÷ 10 17 eV is estimated.

Penetrating cascade showers and mini-clusters

The penetrating nature of the cascade showers in the high-energy atmospheric families observed by Chacaltaya two-storey emulsion chambers are studied by comparing with those in the simulated events obtained by the full Monte Carlo calculation through the atmosphere and the detector. We find an excess of the number of penetrating showers over the expectations and these penetrating showers are mostly found as members of shower-clusters with small lateral spread.

Results of emulsion chamber experiments with very high-energy cosmic rays which are difficult to explain in the framework of the standard model

Recent results of emulsion chamber experiments on the observation of unusual events and new phenomena in cosmic ray particle interactions in the energy range beyond 10 PeV are presented in this review. Particular attention is given to the following items: 1. 1. Centauro-type events with violation of charge (isotopic) symmetry in hadron production; 2. 2. fan-shaped events which argue in favour of a new mechanism of coplanar emission of secondaries; 3. 3. events with halos produced by collimated bundles of high energy gammas and hadrons; 4. 4. penetrating hadrons with abnormal absorption in lead. The present paper contains main characteristics of the events and phenomena under review as well as discussion of their possible interpretation. It is conceivable that the observed events are the manifestation of New Physics beyond the Standard Model. Further progress in studying the new phenomena in cosmic ray experiments for the next few years, in view of LHC startup, is considered.

Energy determination of the cascade shower by means of a new type of emulsion chamber with diffuser module

An account is given of a new type of emulsion chambers which have been in our use since 1997 in our RUNJOB program (RUssia–Nippon JOint Balloon-program). Each chamber is equipped with an additional “diffuser module” placed under the usual set of modules. We have made the experiments using 4 cm thick diffuser modules composed of several photo-sensitive layers (X-ray films and/or nuclear emulsion plates) sandwiched with spacers. The result is as follows. Even in the case where the path length of only 6 radiation lengths is available within the calorimeter module placed above, the visible energy sum is determined with an accuracy better than σ∼0.2 for a group of electromagnetic cascade showers induced by a proton of energy up to several tens of TeV, or by an iron nucleus of energy up to one hundred TeV. If the available path length in the calorimeter module is 9 radiation lengths, we can estimate the energy sum up to ∼100 TeV within an accuracy of σ∼0.2 for a proton-induced cascade shower group. It means that the use of our new-type emulsion chamber can reduce the detector payload dramatically, which is essentially important for the high-energy cosmic-ray observations made on board the vehicles such as balloons, satellites and so on.

Nuclear composition of 1-to 20-PeV primary cosmic rays according to lateral features of the electron-photon component of all extensive air showers and of extensive air showers accompanying high-energy gamma rays and hadrons in x-ray emulsion chambers at the Tien Shan level

Data from the Tien Shan array Adron on the dependence of the lateral distributions of the electron-photon component (age parameter S) in extensive air showers of cosmic rays on the number of electrons, Ne, which is a quantity that characterizes the primary-nucleus energy E0, are subjected to a comparative analysis. The distributions in question are given both for all showers and for showers accompanying high-energy gamma rays and hadrons in x-ray emulsion chambers. According to calculations, events associated with the latter are generated predominantly by primary protons, and this makes it possible to assess their role at various values of E0. The distributions with respect to S suggest a significant fraction of light nuclei, predominantly protons, in the region after the knee in the spectrum for Ne>106, at least up to Ne=5.6×106 (E0 ∼ 10 PeV).

Fast high-resolution 3D segmented echo planar imaging for dose mapping using a superheated emulsion chamber.

The superheated emulsion chamber (SEC) consists of superheated droplets of halocarbons in an aqueous gel. The gel resides in a pressure chamber. Brachytherapy sources can be implanted in the SEC for radiation dosimetry studies. Upon irradiation by ionizing radiation, the metastable droplets vaporize to form microbubbles. MRI can be used to determine the distribution of bubbles following irradiation of the SEC. In order to generate sufficient statistical accuracy in the determination of dose distributions around brachytherapy sources, it is necessary to use hundreds of irradiation cycles. Susceptibility-weighted images provide contrast between the gel and the vapor microbubbles. This article describes a 3D, blipped, double-sampled, segmented echo-planar imaging technique for rapidly imaging the SEC at 650 microm isotropic 3D resolution in about 2 min. This method was used with a pressure cycling SEC to acquire hundreds of images in several hours. Results are presented showing the 2D dose distribution generated by an (125)I source as measured in the SEC using this new imaging method.

System for automated magnetic resonance imaging of a superheated emulsion chamber for brachytherapy dosimetry

This manuscript describes a pressure cycling and brachytherapy source insertion/removal system developed to automate magnetic resonance imaging (MRI) of a superheated emulsion chamber (SEC), a position-sensitive radiation dosimeter. Previous MRI studies of a SEC demonstrated its efficacy for obtaining two-dimensional relative radiation dose profiles from brachytherapy sources. The SEC detector is a 0.5 l chamber containing an emulsion of highly superheated halocarbon droplets suspended in a tissue-equivalent glycerin-based gel. When irradiated by a source, the halocarbon droplets vaporize into microbubbles. Relative dose profiles are determined by mapping, via MRI, the resulting microbubble distributions. During use the SEC is repeatedly cycled through a series of steps including source insertion, exposure, and source removal, MRI data collection, and chamber pressurization and depressurization. To acquire microbubble counts sufficient to derive dose profiles having good statistics, it is necessary to collect hundreds of MRI data sets as the SEC is cycled. Clearly, automation of SEC cycling is essential for its practical use as a radiation dosimeter. The operations required to use the SEC as a radiation dosimeter have been fully automated on a commercial 3.0 T MRI scanner. The hardware and software developed to achieve automated cycling of a SEC are described. Microbubble distributions and calculated microbubble density maps generated from MRI data collected while cycling a SEC are presented to demonstrate the utility of the automated system.