Nuclear Emulsion Research Articles

Different Detector Types Used in Plasma Physics Experiment

We analyzed the possibility of using different detector types (semiconductor, scintillator, thermoluminescent, nuclear emulsions) for plasma diagnostics. We investigated the main characteristics of such detectors, on the basis of which an X-ray spectrometer complex was created.

Discovery of a big void in Khufu's Pyramid by observation of cosmic-ray muons.

The Great Pyramid, or Khufu's Pyramid, was built on the Giza plateau in Egypt during the fourth dynasty by the pharaoh Khufu (Cheops), who reigned from 2509 bc to 2483 bc. Despite being one of the oldest and largest monuments on Earth, there is no consensus about how it was built. To understand its internal structure better, we imaged the pyramid using muons, which are by-products of cosmic rays that are only partially absorbed by stone. The resulting cosmic-ray muon radiography allows us to visualize the known and any unknown voids in the pyramid in a non-invasive way. Here we report the discovery of a large void (with a cross-section similar to that of the Grand Gallery and a minimum length of 30 metres) situated above the Grand Gallery. This constitutes the first major inner structure found in the Great Pyramid since the nineteenth century. The void, named ScanPyramids' Big Void, was first observed with nuclear emulsion films installed in the Queen's chamber, then confirmed with scintillator hodoscopes set up in the same chamber and finally re-confirmed with gas detectors outside the pyramid. This large void has therefore been detected with high confidence by three different muon detection technologies and three independent analyses. These results constitute a breakthrough for the understanding of the internal structure of Khufu's Pyramid. Although there is currently no information about the intended purpose of this void, these findings show how modern particle physics can shed new light on the world's archaeological heritage.

Experimental examination of ternary fission in nuclear track emulsion

Activities performed in preparation for the search for ternary fission of heavy nuclei and the analysis of fragment angular correlations with nuclear track emulsion and an automated microscope are detailed. Surface irradiation of nuclear emulsion by a Cf source was initiated. Planar events containing nothing but fragment triples were found and studied.

Dissociation of relativistic 10B nuclei in nuclear track emulsion

The structural features of 10B are studied by analyzing the dissociation of nuclei of this isotope at an energy of 1 A GeV in nuclear track emulsion. The fraction of the 10B → 2He + H channel in the charge state distribution of fragments is 78%. It was determined based on the measurements of fragment emission angles that unstable 8Beg.s. nuclei appear with a probability of (26 ± 4)%, and (14 ± 3)% of them are produced in decays of an unstable 9Bg.s. nucleus. The Be + H channel was suppressed to approximately 1%.

Study of the Involvement of 8Be and 9B Nuclei in the Dissociation of Relativistic 10C, 10B, and 12C Nuclei

The results obtained by estimating the contribution of 8Be and 9B nuclei to the coherent dissociation of 10C, 10B, and 12C relativistic nuclei in nuclear track emulsions (“white” stars) are presented. The selection of white stars accompanied by 9B leads to a distinct peak appearing in the distribution of the excitation energy of 2α2p ensembles and having a maximum at 4.1 ± 0.3 MeV. A 8Be nucleus manifests itself in the coherent-dissociation reaction 10B → 2He + H with a probability of (25 ± 5)%, (14 ± 3)% of it being due to 9B decays. The ratio of the branching fractions of the 9B + n and 9Be + p mirror channels is estimated at 6 ± 1. An analysis of the relativistic dissociation of 12C nuclei in a nuclear track emulsion revealed nine 3α events corresponding to the Hoyle state.

Time-integrated directional detection of dark matter

The analysis of signals in directional dark matter (DM) detectors typically assumes that the directions of nuclear recoils can be measured in the Galactic rest frame. However, this is not possible with all directional detection technologies. In nuclear emulsions, for example, the recoil events must be detected and measured after the exposure time of the experiment. Unless the entire detector is mounted and rotated with the sidereal day, the recoils cannot be reoriented in the Galactic rest frame. We examine the effect of this `time integration' on the primary goals of directional detection, namely: (1) confirming that the recoils are anisotropic; (2) measuring the median recoil direction to confirm their Galactic origin; and (3) probing below the neutrino floor. We show that after time integration the DM recoil distribution retains a preferred direction and is distinct from that of Solar neutrino-induced recoils. Many of the advantages of directional detection are therefore preserved and it is not crucial to mount and rotate the detector. Rejecting isotropic backgrounds requires a factor of 2 more signal events compared with an experiment with event time information, whereas a factor of 1.5-3 more events are needed to measure a median direction in agreement with the expectation for DM. We also find that there is still effectively no neutrino floor in a time-integrated directional experiment. However to reach a cross section an order of magnitude below the floor, a factor of 8 larger exposure is required than with a conventional directional experiment. We also examine how the sensitivity is affected for detectors with only 2D recoil track readout, and/or no head-tail measurement. As for non-time-integrated experiments, 2D readout is not a major disadvantage, though a lack of head-tail sensitivity is.

Hyper-track selector nuclear emulsion readout system aimed at scanning an area of one thousand square meters

Automatic nuclear emulsion readout systems have seen remarkable progress since the original idea was developed almost 40 years ago. After the success of its full application to a large-scale neutrino experiment, OPERA, a much faster readout system, the hyper-track selector (HTS), has been developed. HTS, which has an extremely wide-field objective lens, reached a scanning speed of 4700 cm$^2$/h, which is nearly 100 times faster than the previous system and therefore strongly promotes many new experimental projects. We will describe the concept, specifications, system structure, and achieved performance in this paper.

Searching for high energy cosmic-ray protons using a new way of finding and tracking particles in stratospheric X-ray emulsion chambers (According to data from the Russian–Japanese RUNJOB experiment)

An continuing search for primary particles is performed using a new means of finding and tracking particles in nuclear emulsions. Particle interactions registered in stratospheric X-ray emulsion chambers (XECs) are attributed to nucleon–nuclei interactions recorded in the Russian–Japanese RUNJOB experiment. According to the data from processing the interactions between galactic particles and matter in XECs RUNJOB-3B, 6A, and RUNJOB-11A, 11B with energy thresholds ΣE γ ≥ 3 and ΣE γ ≥ 5 TeV, respectively, around 50% of all proton tracks went unidentified, which coincides with the initial results from the RUNJOB experiment.

An investigation of Renyi entropy in high-energy nucleus–nucleus collisions

A study of Renyi entropy of shower particles has been carried out using 16O, 28Si, and 32S projectiles in interaction with AgBr and CNO target present in nuclear emulsion at an incident momentum of 4.5 AGeV/c. The analysis reveals interesting experimental observations for both groups of targets. A comparison of the experimental results with the results obtained from analyzing the event sample generated by the UrQMD code is also presented. Renyi entropy values increase with the increase of projectile mass. This increase is weaker in case of CNO target. The calculated values of second-order Renyi entropy H2 are shown to vary linearly with the logarithm of average particle multiplicity ln⟨n⟩ for both targets. The dependence of Renyi entropy on the logarithm of average particle multiplicity ln⟨n⟩ indicates the presence of long-range correlation in high-energy nucleus–nucleus interactions. The variation is found to be stronger in the case of experimental events in comparison to the UrQMD simulated events indicating stronger long-range correlation for the experimental data.

Measurements of 12C ions beam fragmentation at large angle with an Emulsion Cloud Chamber

Hadron radiotherapy is a powerful technique for the treatment of deep-seated tumours. The physical dose distribution of hadron beams is characterized by a small dose delivered in the entrance channel and a large dose in the Bragg peak area. Fragmentation of the incident particles and struck nuclei occurs along the hadron path. Knowledge of the fragment energies and angular distributions is crucial for the validation of the models used in treatment planning systems. We report on large angle fragmentation measurements of a 400 MeV/n 12C beam impinging on a composite target at the GSI laboratory in Germany. The detector was made of 300 micron thick nuclear emulsion films, with sub-micrometric spatial resolution and large angle track detection capability, interleaved with passive material. Thanks to newly developed techniques in the automated scanning of emulsions it was possible to extend the angular range of detected particles. This resulted in the first measurement of the angular and momentum spectrum for fragments emitted in the range from 34̂ to 81̂.

24aCD-13 原子核乾板を用いた荷電粒子識別法の開発

24aCD-13 原子核乾板を用いた荷電粒子識別法の開発

21pAA-10 J-PARC E07実験における大型原子核乾板現像手法の研究開発

21pAA-10 J-PARC E07実験における大型原子核乾板現像手法の研究開発

The development of a super-fine-grained nuclear emulsion

A nuclear emulsion with micronized crystals is required for the tracking detection of submicron ionizing particles, which are one of the targets of dark-matter detection and other techniques. We found that a new production method, called the PVA—gelatin mixing method (PGMM), could effectively control crystal size from 20 nm to 50 nm. We called the two types of emulsion produced with the new method the nano imaging tracker and the ultra-nano imaging tracker. Their composition and spatial resolution were measured, and the results indicate that these emulsions detect extremely short tracks.

First neutrino event detection with nuclear emulsion at J-PARC neutrino beamline

Precise neutrino--nucleus interaction measurements in the sub-multi GeV region are important to reduce the systematic uncertainty in future neutrino oscillation experiments. Furthermore, the excess of ${\nu_e}$ interactions, as a possible interpretation of the existence of a sterile neutrino has been observed in such an energy region. The nuclear emulsion technique can measure all the final state particles with low energy threshold for a variety of targets (Fe, C, H${_2}$O, and so on). Its sub-$\mu$m position resolution allows measurements of the ${\nu_e}$ cross-section with good electron/gamma separation capability. We started a new experiment at J-PARC to study sub-multi GeV neutrino interactions by introducing the nuclear emulsion technique. The J-PARC T60 experiment has been implemented as a first step of such a project. Systematic neutrino event analysis with full scanning data in the nuclear emulsion detector was performed for the first time. The first neutrino event detection and its analysis is described in this paper.

Discovery potential for directional dark matter detection with nuclear emulsions

Direct Dark Matter searches are nowadays one of the most exciting research topics. Several Experimental efforts are concentrated on the development, construction, and operation of detectors looking for the scattering of target nuclei with Weakly Interactive Massive Particles (WIMPs). In this field a new frontier can be opened by directional detectors able to reconstruct the direction of the WIMP-recoiled nucleus thus allowing to extend dark matter searches beyond the neutrino floor. Exploiting directionality would also give a proof of the galactic origin of dark matter making it possible to have a clear and unambiguous signal to background separation. The angular distribution of WIPM-scattered nuclei is indeed expected to be peaked in the direction of the motion of the Solar System in the Galaxy, i.e. toward the Cygnus constellation, while the background distribution is expected to be isotropic. Current directional experiments are based on the use of gas TPC whose sensitivity is limited by the small achievable detector mass. In this paper we show the potentiality in terms of exclusion limit of a directional experiment based on the use of a solid target made by newly developed nuclear emulsions and read-out systems reaching sub-micrometric resolution.

Study of the coordinate prediction accuracy for galactic particles with an energy of 10–1000 TeV/particle using a new method for searching and tracking particles in nuclear emulsion films. (Data of the Russia–Nippon Joint Balloon (RUNJOB) experiment)

Experimental and methodological errors in the coordinate prediction for primary cosmic ray nucleons and nuclei in nuclear emulsions using a new method for searching and tracing particle tracks in emulsion films of X-ray emulsion chambers (XRECs) exposed in the stratosphere in the Russia–Nippon Joint Balloon (RUNJOB) experiment are considered in detail. The dependence of errors on the relation between angular characteristics of the sought particle and auxiliary multiply charged nuclei is analyzed. Angular selection criteria for auxiliary nuclei, at which the methodological error of the particle track coordinate prediction decreases, are found.

Multiplicity distribution of shower particles in nucleus-nucleus collisions at 4.1-4.5 A GeV/c

A detailed study on multiplicity distribution has been carried out using 16O (at an incident momentum of 4.5A GeV/c, 22Ne (at an incident momentum of 4.1 A GeV/c, 28Si (at an incident momentum of 4.5 A GeV/c and 32S (at an incident momentum of 4.5 A GeV/c projectiles in interaction with AgBr target present in nuclear emulsion. A comparison of the experimental results with the results obtained from analyzing the event sample generated by the UrQMD model is also presented.

New readout system for submicron tracks with nuclear emulsion

In this paper, we summarize a newly developed automatic readout system, composed of a microscope with an optics stage, to analyze charged particle tracks of less than 1 μm recorded in a fine-grained nuclear emulsion. This system's optics have the high spatial resolution, epi-illumination, and xenon-mercury lamp necessary to achieve sufficient contrast and brightness for small silver grains up to about 40 nm in diameter. Methods of shape recognition and focus point acquisition were developed that enabled the system to identify submicron tracks corresponding to nuclei on the order of 10–100 keV.

Muography with nuclear emulsions - Stromboli and other projects

The muon radiography is a novel imaging technique to probe the volcanoes interior, using the capability of high energy cosmic ray muons to penetrate large thicknesses of rock. In this way it is possible to derive a 2D density map along the muon trajectory of volcanic edifices and deduce information on the variations in the rock density distribution, like those expected from dense lava conduits, or low density magma supply paths. This method is applicable also to study geological objects as glaciers, faults, oil underground reservoirs, engineering constructions, where a density contrast is present. Nuclear emulsions are well suited to be employed in this context for their excellent angular resolution; they are compact and robust detectors, able to work in harsh environments without need of power supply. On the other side, a long exposure time is required for a reasonable detector surface (~10 m2) in order to collect a sufficient statistics of muons, and a quasi-real time analysis of the emulsion data is rather difficult due to the scanning time needed by the optical microscopes. Such drawback is on the way to be overcome thanks to a recent R&D program on ultra-fast scanning systems. Muon radiography technique, even if limited to the summit part of the volcano edifice, represents an important tool of investigation, at higher spatial resolution, complementary to the conventional geophysics techniques. The first successful result in this field was obtained by a Japanese group that observed in 2007 the conduit structure of Mt. Asama. Since 2010, other interesting volcanoes have been probed with the same method: Stromboli in 2011, Mt. Teide in 2012 and La Palma in 2014. Here we discuss the muon imaging technique reporting the nuclear emulsion detector design exposed at Stromboli and results of the data analysis.

Development of nuclear emulsion for muography

Muography (cosmic-ray muon radiography) is the non-destructive inspection by using muons produced by interactions between primary cosmic-rays and the Earth’s atmosphere. The principle of this technology is the measurement of absorption of incoming cosmic-ray muons, just like x-ray imaging technology. A nuclear emulsion is the high sensitive photographic film used for detection of three-dimensional trajectory of charged particles such as muons with the position resolution of sub-micron. A nuclear emulsion has following properties: high spatial resolution with thin detector structure, lightweight, flexibility of detector size and no requirement of electric power supply. These properties of a nuclear emulsion are suitable for a detector of muography. We are developing the nuclear emulsion at Nagoya University. In this paper, the current performances of the nuclear emulsion and the fully self-production techniques developed at Nagoya University are described.