Nuclear Emulsion Research Articles

Irradiation of nuclear track emulsions with thermal neutrons, heavy ions, and muons

Exposures of test samples of nuclear track emulsion were analyzed. Angular and energy correlations of products originating from the thermal-neutron-induced reaction n$_{th} + ^{10}$B $\rightarrow ^{7}$Li $+ (\gamma) + \alpha$ were studied in nuclear tack emulsions enriched in boron. Nuclear track emulsions were also irradiated with $^{86}$Kr$^{+17}$ and $^{132}$Xe$^{+26}$ of energy about 1.2 MeV per nucleon. Measurements of ranges of heavy ions in nuclear track emulsions made it possible to determine their energies on the basis of the SRIM model. The formation of high-multiplicity nuclear stars was observed upon irradiating nuclear track emulsions with ultrarelativistic muons. Kinematical features studied in this exposure of nuclear track emulsions for events of the muon-induced splitting of carbon nuclei to three alpha particles are indicative of the nuclear-diffraction interaction mechanism.

Analysis system of submicron particle tracks in the fine-grained nuclear emulsion by a combination of hard x-ray and optical microscopy.

Analyses of nuclear emulsion detectors that can detect and identify charged particles or radiation as tracks have typically utilized optical microscope systems because the targets have lengths from several μm to more than 1000 μm. For recent new nuclear emulsion detectors that can detect tracks of submicron length or less, the current readout systems are insufficient due to their poor resolution. In this study, we developed a new system and method using an optical microscope system for rough candidate selection and the hard X-ray microscope system at SPring-8 for high-precision analysis with a resolution of better than 70 nm resolution. Furthermore, we demonstrated the analysis of submicron-length tracks with a matching efficiency of more than 99% and position accuracy of better than 5 μm. This system is now running semi-automatically.

Testing the Weak Equivalence Principle with an antimatter beam at CERN

The goal of the AEgIS experiment is to measure the gravitational acceleration of antihydrogen – the simplest atom consisting entirely of antimatter – with the ultimate precision of 1%. We plan to verify the Weak Equivalence Principle (WEP), one of the fundamental laws of nature, with an antimatter beam. The experiment consists of a positron accumulator, an antiproton trap and a Stark accelerator in a solenoidal magnetic field to form and accelerate a pulsed beam of antihydrogen atoms towards a free-fall detector. The antihydrogen beam passes through a moiré deflectometer to measure the vertical displacement due to the gravitational force. A position and time sensitive hybrid detector registers the annihilation points of the antihydrogen atoms and their time-of-flight. The detection principle has been successfully tested with antiprotons and a miniature moiré deflectometer coupled to a nuclear emulsion detector.

Large angle tracking and high discriminating tracking in nuclear emulsion

Nuclear emulsion is a high resolution and re-analyzable detector. Conventional “Track Selector” which have angle acceptance |tan θ|<0.6 are widely used to find tracks in emulsion. We made a new track selector “Fine Track Selector” (FTS) which has large angle acceptance and high discriminating ability. The FTS reduces fake tracks using new algorithms, navigation etc. FTS also keeps finding efficiency of tracks around 90% in an angle range of |tan θ| < 3.5. FTS was applied to the τ candidate in OPERA and no additional tracks found. FTS will be useful to our new J-PARC emulsion experiment.

Track reconstruction by GPU in 3D particle tracking detectors

3D detectors for high-energy physics have always needed large computing power. Its availability has sometimes determined the statistics and performance of experiments. The increasing specific computing power of GPUs in recent years offers new opportunities for this field of application that should not be missed. The paper shows a novel algorithm that supports, as a by-product of speed, wider angular acceptance with respect to established techniques based on CPUs. While the algorithm has been developed in the environment of nuclear emulsions, it has been conceived from the very beginning as a tool for general tracking in 3D detectors. The overall logic can apply to many operational contexts in which tracking occurs in high combinatorial background. The performances of the algorithm are evaluated from different points of view, describing the details of the computing technique that are common to tracking problems and discussing measurements and data from a test-beam exposure. Computing speed has been evaluated on a broad variety of hardware, investigating an approximated scaling formula.

Application of Emulsion Cloud Chamber to cosmic-ray muon radiography

Muon radiography (muography) is a powerful technique for probing the internal density profiles of volcanoes. A nuclear emulsion is a desirable detector for this purpose because of its light weight and because it does not require electricity for operation. One technical problem, however, is an existence of background noise signals caused by low energy charged particles. The present work proposes the use of Emulsion Cloud Chamber (ECC), which is a repeated structure of emulsion films and passive metal plates, to reject these noise particles. The performance of the background reduction is demonstrated by a test measurement at Showa-Shinzan Lava Dome, Hokkaido, Japan.

Automated method of tracing proton tracks in nuclear emulsions

The low performance of the manual recognition of proton-recoil tracks in nuclear emulsions has limited its application to energy spectrum measurement of a pulsed neutron source. We developed an automated microscope system to trace proton-recoil tracks in nuclear emulsions. Given a start point on the proton track of interest, the microscope system can automatically trace and record the entire track using an image processing algorithm. Tests indicate that no interaction of the operator is needed in tracing the entire track. This automated microscope greatly reduces the labor of the operator and increases the efficiency of track data collection in nuclear emulsion.

21pCF-9 大型原子核乾板の現像手法最適化

21pCF-9 大型原子核乾板の現像手法最適化

Proton Linear Energy Transfer measurement using Emulsion Cloud Chamber

This study proposes to determine the correlation between the Volume Pulse Height (VPH) measured by nuclear emulsion and Linear Energy Transfer (LET) calculated by Monte Carlo simulation based on Geant4. The nuclear emulsion was irradiated at the National Cancer Center (NCC) with a therapeutic proton beam and was installed at 5.2m distance from the beam nozzle structure with various thicknesses of water-equivalent material (PMMA) blocks to position with specific positions along the Bragg curve. After the beam exposure and development of the emulsion films, the films were scanned by S-UTS developed in Nagoya University. The proton tracks in the scanned films were reconstructed using the ‘NETSCAN’ method. Through this procedure, the VPH can be derived from each reconstructed proton track at each position along the Bragg curve. The VPH value indicates the magnitude of energy loss in proton track. By comparison with the simulation results obtained using Geant4, we found the correlation between the LET calculated by Monte Carlo simulation and the VPH measured by the nuclear emulsion.

The first evidence of a deeply bound state of Xi--14N system

We have observed a deeply bound state of the |$\Xi ^{-}$|–|${}^{14}{\rm N}$| system that decayed into twin single-hypernuclei in nuclear emulsion exposed in the E373 experiment at KEK-PS. The process is uniquely identified as |$\Xi ^{-} + {}^{14}{\rm N} \rightarrow {{}^{10}_{\Lambda }{\rm Be}} + {{}^{5}_{\Lambda }{\rm He}}$|⁠. We have measured the binding energy of the |$\Xi ^{-}$|–|${}^{14}{\rm N}$| system, |$B_{\Xi ^{-}}$|⁠, to be |$4.38 \pm 0.25$|MeV, which is significantly larger than that of the |$\Xi ^{-}$|–|${}^{14}{\rm N}$| 3|$D$| atomic state (0.17 MeV), if both single-hypernuclei are emitted in the ground state from at-rest capture of a |$\Xi ^{-}$| hyperon. If the |${{}^{10}_{\Lambda }{\rm Be}}$| nucleus is produced in an excited state, the |$B_{\Xi ^{-}}$| value mentioned above decreases by the excitation energy. Model calculations based on known values for |${{}^{9}{\rm Be}}$| excited states have predicted two excited states in the bound region. Even in the case of |${{}^{10}_{\Lambda }{\rm Be}}$| production in the highest excited state, the |$B_{\Xi ^{-}}$| value is far from the 3|$D$| atomic level of the |$\Xi ^{-}$|–|${}^{14}{\rm N}$| system by more than 3.7 standard deviations. The event provides the first clear evidence of a deeply bound state of the |$\Xi ^{-}$|–|${}^{14}{\rm N}$| system by an attractive |$\Xi$|N interaction.

Azimuthal correlation and collective behavior in nucleus-nucleus collisions

Various flow effects of nuclear and hadronic origin are investigated in nucleus-nucleus collisions. Nuclear emulsion data collected from 84Kr + Ag/Br interaction at an incident energy of 1.52 GeV per nucleon and from 28Si + Ag/Br interaction at an incident energy of 14.5 GeV per nucleon are used in the investigation. The transverse momentum distribution and the flow angle analysis show that collective behavior, like a bounce-off effect of the projectile spectators and a sidesplash effect of the target spectators, are present in our event samples. From an azimuthal angle analysis of the data we also see a direct flow of the projectile fragments and of the produced charged particles. On the other hand, for both data samples the target fragments exhibit a reverse flow, while the projectile fragments exhibit an elliptic flow. Relevant flow parameters are measured.

Latest Developments in Nuclear Emulsion Technology

Nuclear emulsion is high sensitive photographic film used for detection of three-dimensional trajectory of charged particles. These trajectories are recorded as tracks consist of a lot of silver grains. The size of silver grain is about 1μm, so that nuclear emulsion has submicron three-dimensional spatial resolution, which gives us a few mrad three-dimensional angular resolution. The important technical progress was speed-up of the read-out technique of nuclear emulsions built with optical microscope system. We succeeded in developing a high-speed three-dimensional read-out system named Super Ultra Track Selector (S-UTS) with the operating read-out speed of approximately 50 cm2/h. Nowadays we are developing the nuclear emulsion gel independently in Nagoya University by introducing emulsion gel production machine. Moreover, we are developing nuclear emulsion production technologies (gel production, poring and mass production). In this paper, development of nuclear emulsion technologies for the OPERA experiment, applications by the technologies and current development are described.

Development of Nuclear Emulsion Detector for Muon Radiography

Muon radiography is the non-destructive testing technique of large-scale constructions with cosmic ray muon. Cosmic ray muon has high penetrating power and it always comes from the whole sky. In the same way of taking a X-ray photograph, we can obtain integrated density of constructions which thickness are several tens to several hundreds. We had ever applied this technique to nuclear reactors, volcanos, and so on. Nuclear emulsion is three dimensional track detector with micrometric position accuracy. Thanks to high position resolution, Nuclear emulsion has mrad angular resolution. In addition, the features which require no power supply and can observe in a large area suitable for muon radiography. In Nagoya University, we launched emulsion manufacturing equipment at 2010. It has become possible to flexible development of our detector and succeeded to development of high sensitive nuclear emulsion film (Nagoya emulsion). An important factor is the temperature characteristic to withstand the outdoor observation as a detector to be used in the muon radiography. There is a phenomenon of a latent image fading, whichit is well known in the photographic industry, and this phenomenon is known that temperature and water are involved. So we examined temperature and humidity characteristic of latent image fading about Nagoya emulsion. As a result, we found latent image fading is strongly depends on both temperature and humidity. By dehydrating emulsion film in RH8%, over 95% (Grain Density>40) detection efficiency of muon track keeps over 3months in 25degree, for 2months in 35degree. Additionally it was showed in this test that increasing back ground noise “fog”, which may have occurred by sealing emulsion film in a narrow space, is reduced by buffer space in the bag.

Development of Nuclear Emulsion for Fast Neutron Measurement

Nuclear emulsion is high sensitive photographic film used for detection of three-dimensional trajectory of charged particles. Energy resolution of nuclear emulsion is 21% (12%) FWHM against neutron energy of 2.8 MeV (4.9 MeV). Nuclear emulsion has high gamma ray rejection power. For now, at least 2×104 gamma rays/cm2, no increase of as a background for neutron measurement when scan using automatic nuclear emulsion read out system HTS. This value suggests that it is applicable even under high gamma ray environment, such as nuclear fusion reactor.

Toward an Automated Analysis of Slow Ions in Nuclear Track Emulsion

Application of the nuclear track emulsion technique (NTE) in radioactivity and nuclear fission studies is discussed. It is suggested to use a HSP-1000 automated microscope for searching for a collinear cluster tri-partition of heavy nuclei implanted in NTE. Calibrations of α-particles and ion ranges in a novel NTE are carried out. Surface exposures of NTE samples to a 252Cf source started. Planar events containing fragments and long-range α-particles as well as fragment triples only are studied. NTE samples are calibrated by ions Kr and Xe of energy of 1.2 and 3 A MeV.

Application of Advanced Nuclear Emulsion Technique to Fusion Neutron Diagnostics

In order to measure the 2.5 MeV neutrons produced by DD nuclear fusion reactions, we have developed a compact neutron detector based on nuclear emulsion. After optimization of development conditions, we evaluated the response of the detector to an accelerator-based DD neutron source. The absolute efficiency at an energy of 2.5 MeV was estimated to be (4.1±0.2)×10-6 tracks/neutron.

Study of Double-strangeness Nuclear Systems with Nuclear Emulsion

Double strangeness nuclei such as double-Λ and Ξ hypernuclei have been studied with nuclear emulsion due to its fine position resolution. Recently, we have started an experiment to study Λ-Λ interaction more accurately than that information given by the NAGARA event with ∼102 double-Λ hypernuclei which may provide us understanding free from nuclear medium effect. It is necessary to develop treatment method for huge amount, 2.1 tons of the emulsion gel, even if very pure K− beams are available at J-PARC. We have developed the base film to support the emulsion, emulsion surface coating method with a special layer of 0.5μm thick, method for making large-size plate (35.0 x 34.5 cm2) and scanning method, called “overall scanning”. The first evidence of a deeply bound state of Ξ--14N system, named KISO, was successfully detected in the test operation of the overall scanning.

The Tau Neutrino Appearance Experiment with Nuclear Emulsion, OPERA

The Tau Neutrino Appearance Experiment with Nuclear Emulsion, OPERA

Neutrino Physics with Nuclear Emulsion

Neutrino Physics with Nuclear Emulsion

Emulsion Scanning Systems for Double-strangeness Nuclei

Nuclear emulsion is so far the best detector to investigate double-strangeness nucleus including double Lambda hypernucleus, which is a nucleus made up of two lambda hyperons in addition to nucleons. Two types of scanning system are being developed to search for more events of double Lambda hypernucleus rapidly. One is a system for automated Xi− hyperon tracking. The other is “Overall scanning”, high-speed scanning and image recognition for vertex-like-shapes from microscopic images of the tracks in nuclear emulsion plates.