Nuclear Emulsion Research Articles

Nuclear emulsion techniques for muography

Nuclear emulsions are currently being used in the field of muography, more specifically muon radiography of volcanic edifices and fault regions. The peculiar features of such detector for cosmic muons demand appropriate data processing and analysis techniques. The paper shows the current development status of readout devices and analysis techniques developed by some research groups that established a collaborative network in Italy and Japan. An overview is given of nuclear emulsion-based detectors, from the detection principles to detector operation and set-up techniques, in connection with the expectations in terms of geophysics information. Two systems for readout are presented, one developed in the first decade of the 21st century and one that is entering duty now. The evolution in terms of data quality and speed is discussed. Finally, the most relevant data processing steps that allow working out muon absorption maps from nuclear emulsion data are described.

Muography of 1949 fault in La Palma, Canary Islands, Spain

Muography (muon radiography) is a new geophysical technique that allows investigation of inner structures of an edifice with a very detailed spatial resolution. It has been recently used for several volcanoes and different geoscientific targets. In 2011 Tanaka et al. succeeded to find hidden ancient seismic faults. In 1949 there was a volcanic activity of the Cumbre Vieja, La Palma, Canary Islands, Spain and a 1km long fault suddenly appeared during the active period. The fault might be the sign of a large scale land collapse. In order to get additional information, investigations by several geophysical exploration techniques are needed. We consider that muography can be applied to study the shallow part of the fault and it can clarify some important parameters: the bulk density, the width of the low density zone, and the depth. Previous investigations allowed detecting two ancient seismic faults that have 20m-wide mechanically fractured zone consisting of highly damaged rocks. The 1949 fault might be the result of large scale land slide and the slide length might be just a few meter. Therefore the expected width of the fault is only a few meter. In order to detect such narrow fault, the muon detector should have as high spatial resolution as possible. In addition, it is difficult to get continuous power supply near the fault. Nuclear emulsions are a kind of photographic films that have high sensitivity for high energy charged particles. They also have high spatial resolution for high energy muon paths and do not need any power supply to be operated. We placed an emulsion detector having 0.19 m 2 effective area near the 1949 fault. The exposure started on January 2014 and lasted 106 days. All the emulsion films were developed and they are under analysis. We also estimated the expected performance of this test exposure. Assuming a very simple model, we evaluated the detectable region as a function of the low density zone width and of the depth from the ground surface as well.

Intermittency Approach in the Nuclear Collisions of 28Si + AgBr at 14.6A GeV - Nuclear Emulsion Experiment a Particle Detector

A new method has been applied for the study of intermittency in the collisions of 28Si + AgBr at 14.6 A GeV for the produced relativistic charged particles by using the method of mixed factorial moment (MFM). In this paper an analysis has been made for the presence of fractal behavior with three different approaches of Scaled factorial Moments (SFMs) named as- horizontal, vertical and mixed (horizontal and vertical together). The non-statistical fluctuations of relativistic charged particles have been calculated on events with different degree of centrality. These results have been compared with the results of simulated data obtained from UrQMD model and we find a good agreement between experimental data and simulated data.

Intermittency Approach in the Nuclear Collisions of 28Si + AgBr at 14.6A GeV - Nuclear Emulsion Experiment a Particle Detector

A new method has been applied for the study of intermittency in the collisions of 28Si + AgBr at 14.6 A GeV for the produced relativistic charged particles by using the method of mixed factorial moment (MFM). In this paper an analysis has been made for the presence of fractal behavior with three different approaches of Scaled factorial Moments (SFMs) named as- horizontal, vertical and mixed (horizontal and vertical together). The non-statistical fluctuations of relativistic charged particles have been calculated on events with different degree of centrality. These results have been compared with the results of simulated data obtained from UrQMD model and we find a good agreement between experimental data and simulated data.

Latest nuclear emulsion technology

Nuclear emulsion is a extremely high-resolution 3D tracking detector. Since the discovery of the pion by C.F. Powell et al. in 1946, experiments with nuclear emulsions have contributed to the development of particle physics. (e.g. the OPERA collaboration reported the discovery of νμ * ντ oscillations in appearance mode in 2015) The technology of nuclear emulsion still keeps making progress. Since 2010, we have introduced a system of nuclear emulsion gel production to our laboratory in Nagoya University, and have started self-development of the new gel, instead of from the photographic film companies. Moreover, a faster automated emulsion scanning system is developed. Its scanning speed reaches 4000 cm2 /h, and the load for analyzing becomes more and more lighter. In this presentation, we report the status of nuclear emulsion technologies for cosmic ray experiments.

Cosmic ray nuclei detection in the balloon borne nuclear emulsion gamma ray telescope flight in Australia (GRAINE 2015)

Nuclear emulsion plates for studying elementary particle physics as well as cosmic ray physics are very powerful tracking tools with sub-micron spatial resolutions of charged particle trajectories. Even if gamma rays have to be detected, electron-positron pair tracks can provide precise information to reconstruct their direction and energy with high accuracy. Recent developments of emulsion analysis technology can digitally handle almost all tracks recorded in emulsion plates by using the Hyper Track Selector of the OPERA group at NAGOYA University. On the other hand, the potential of time resolutions have been equipped by emulsion multilayer shifter technology in the GRAINE (Gamma Ray Astro-Imager with Nuclear Emulsion) experiments, the aims of which are to detect cosmic gamma rays such as the Vela pulsar stellar object by precise emulsion tracking analysis and to study cosmic ray particle interactions and chemical compositions. In this paper, we focus on the subject of cosmic ray nuclei detection in the GRAINE balloon flight experiments launched at Alice Springs, Australia in May 2015.

Cosmic ray nuclei detection in the balloon borne nuclear emulsion gamma ray telescope flight in Australia (GRAINE 2015)

Nuclear emulsion plates for studying elementary particle physics as well as cosmic ray physics are very powerful tracking tools with sub-micron spatial resolutions of charged particle trajectories. Even if gamma rays have to be detected, electron-positron pair tracks can provide precise information to reconstruct their direction and energy with high accuracy. Recent developments of emulsion analysis technology can digitally handle almost all tracks recorded in emulsion plates by using the Hyper Track Selector of the OPERA group at NAGOYA University. On the other hand, the potential of time resolutions have been equipped by emulsion multilayer shifter technology in the GRAINE (Gamma Ray Astro-Imager with Nuclear Emulsion) experiments, the aims of which are to detect cosmic gamma rays such as the Vela pulsar stellar object by precise emulsion tracking analysis and to study cosmic ray particle interactions and chemical compositions. In this paper, we focus on the subject of cosmic ray nuclei detection in the GRAINE balloon flight experiments launched at Alice Springs, Australia in May 2015.

GRAINE balloon experiment in 2015

Observations of cosmic gamma rays are important for studying high energy phenomena in the universe. Since 2008, the Large Area Telescope on the Fermi satellite has surveyed the whole gamma-ray sky in the sub-GeV/GeV energy region, and accumurated a large amount of data. However, observations at the low galactic latitude remains difficult because of a lack of angular resolution, increase of background flux originating from galactic diffuse gamma rays, etc. The Gamma-Ray Astro-Imager with Nuclear Emulsion (GRAINE) is a gamma-ray observation project with a new balloon-borne emulsion gamma-ray telescope. Nuclear emulsion is a high-resolution 3D tracking device. It determines the incident angle with 0.1 ∘ resolution for 1 GeV gamma rays (1.0 ∘ for 100 MeV), and has linear polarization sensitivity. GRAINE aims at precise observation of gamma-ray sources, especially in the galactic plane, by repeating long-duration balloon flights with large-aperture-area (10 m 2 ) high-resolution emulsion telescopes. In May 2015, we performed a balloon-borne experiment in Alice Springs, Australia, in order to demonstrate the imaging performance of our telescope. The emulsion telescope that has an aperture area of 0.4 m 2 was employed in this experiment. It observed the Vela pulsar (the brightest gamma-ray source in the GeV sky) at an altitude of 37 km for 6 hours out of the flight duration of 14 hours. In this presentation, we will report the latest results and the status of the GRAINE project.

Unstable nuclei in dissociation of light stable and radioactive nuclei in nuclear track emulsion

A role of the unstable nuclei ${}^{6}$Be, ${}^{8}$Be and ${}^{9}$B in the dissociation of relativistic nuclei ${}^{7,9}$Be, ${}^{10}$B and ${}^{10,11}$C is under study on the basis of nuclear track emulsion exposed to secondary beams of the JINR Nuclotron. Contribution of the configuration ${}^{6}$Be + $\mit{n}$ to the ${}^{7}$Be nucleus structure is 8 $\pm$ 1% which is near the value for the configuration ${}^{6}$Li + $\mit{p}$. Distributions over the opening angle of $\alpha$-particle pairs indicate to a simultaneous presence of virtual ${}^{8}$Be$_{g.s.}$ and ${}^{8}$Be$_{2^+}$ states in the ground states of the ${}^{9}$Be and ${}^{10}$C nuclei. The core ${}^{9}$B is manifested in the {${}^{10}$C} nucleus with a probability of 30 $\pm$ 4%. Selection of the ${}^{10}$C "white" stars accompanied by ${}^{8}$Be$_{g.s.}$ (${}^{9}$B) leads to appearance in the excitation energy distribution of 2$\alpha$2$\mit{p}$ "quartets" of the distinct peak with a maximum at 4.1 $\pm$ 0.3 MeV. ${}^{8}$Be$_{g.s.}$ decays are presented in 24 $\pm$ 7% of 2He + 2H events of the ${}^{11}$C coherent dissociation and 27 $\pm$ 11% of the 3He ones. The channel ${}^{9}$B + H amounts 14 $\pm$ 3%. The ${}^{8}$Be$_{g.s.}$ nucleus is manifested in the coherent dissociation ${}^{10}$B $\to$ 2He + H with a probability of 25 $\pm$ 5% including 14 $\pm$ 3% of ${}^{9}$B decays. A probability ratio of the mirror channels ${}^{9}$B + $\mit{n}$ and ${}^{9}$Be + $\mit{p}$ is estimated to be 6 $\pm$ 1.

The search for primary particle tracks in nucleon-nucleus interactions with gamma ray energy ΣEγ ≥ 3 TeV registered in stratospheric X-ray emulsion chambers using data of the RUNJOB experiment

We present here the result of a retreatment of data from the RUNJOB (RUssia-Nippon JOint Balloon) experiment of nucleon-nucleus interactions registered in stratospheric X-ray emulsion chambers (REC) using a new method for searching and tracing of galactic particles in nuclear emulsions. In about halfcof these interactions (∼ 50) recorded in REC RUNJOB‘96-3B, RUNJOB‘97-6A and RUNJOB‘99-11A,B with energy released in the electromagnetic component ΣE γ ≥ 3 TeV and ΣE γ ≥ 5 TeV respectively, single charged particle tracks are not found within the search area defined individually by the particle track location accuracy. The absence of primary proton tracks is consistent with the original treatment of the RUNJOB experimental data. There is a difference in the zenith angular distribution for two groups of events in which a single charged particle track is observed or absent. The average penetration depth of the primary particles in REC to the interaction vertex in the zenith angle range from 60∘ to 79∘ differs by a factor two for these groups.

NEWSdm: Nuclear Emulsions for WIMP Search with directional measurement

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). The measurement of the direction of WIMP-induced nuclear recoils is a challenging strategy to extend dark matter searches beyond the neutrino floor and provide an unambiguous signature of the detection of Galactic dark matter. Current directional experiments are based on the use of gas TPC whose sensitivity is strongly limited by the small achievable detector mass. We present an innovative directional experiment based on the use of a solid target made by newly developed nuclear emulsions and read-out systems reaching a position resolution of the order of 10 nm.

Progress of analysis of dissociation of10C,10B and12C nuclei in nuclear track emulsion

Recent findings related with the unstable nuclei 8 Be and 9 B in the coherent dissociation of relativistic nuclei 10 C, 10 B and 12 C in nuclear track emulsion (“white”stars) are highlighted. Selection of the 10 C “white”stars accompanied by 8 Be (9 B) leads to appearance of the distinct peak with a maximum at 4.1 ± 0.3 MeV in the excitation energy distribution of 2α 2p ensembles. The 8 Beg.s. nucleus is manifested in the coherent dissociation 10 B → 2 He + H with a probability of 25 ± 5 % including 13 ± 3 % of 9 B decays. A probability ratio of the mirror channels 9 B + n and 9 Be + p is estimated to be 10 ± 1. Reanalysis of relativistic 12 C dissociation in lead enriched emulsion revealed 9 3α -events corresponding to the Hoyle state.

Dark matter directional detection: comparison of the track direction determination

Several directional techniques have been proposed for a directional detection of Dark matter, among others anisotropic crystal detectors, nuclear emulsion plates, and low-pressure gaseous TPCs. The key point is to get access to the initial direction of the nucleus recoiling due to the elastic scattering by a WIMP. In this article, we aim at estimating, for each method, how the information of the recoil track initial direction is preserved in different detector materials. We use the SRIM simulation code to emulate the motion of the first recoiling nucleus in each material. We propose the use of a new observable, D, to quantify the preservation of the initial direction of the recoiling nucleus in the detector. We show that in an emulsion mix and an anisotropic crystal, the initial direction is lost very early, while in a typical TPC gas mix, the direction is well preserved.

Analysis of Various Projectile Interactions with Nuclear Emulsion Detector Nuclei at ~1 GeV per Nucleon Using Coulomb Modified Glauber Model

The total nuclear reaction cross section is calculated considering the cases with and without medium effect by employing Coulomb modified Glauber model (CMGM) for interactions of projectiles 56Fe26, 84Kr36, 132Xe54, 197Au79, and 238U92 with nuclear emulsion detector (NED) nuclei at around 1 GeV per nucleon incident kinetic energy. These calculated nuclear reaction cross sections are correlated with the different target groups of the NED nuclei. The average value of various parameters is also calculated and compared with the corresponding experimental results. The number of shower particles emitted in an interaction is also calculated and showed good agreement with the experimental result. We observed that the total nuclear reaction cross section increases with increasing the target mass number in case of all the considered projectiles. In addition, it is shown that the average value of reaction cross section with nuclear medium effect is in good agreement with the experimental results for projectiles 56Fe, 84Kr, and 132Xe, although results of projectiles 197Au and 238U are not in agreement with the experimental observations. This study sheds some light on the energy dependence of the nuclear reaction cross section.

Results from the OPERA experiment

The OPERA neutrino experiment was designed to perform a unique v τ appearance measurement in the v μ CNGS beam to confirm the oscillation mechanism in the atmospheric sector v μ → v τ . The detection of v τ leptons produced in v τ CC interactions and of their decays is accomplished exploiting the high spatial resolution of nuclear emulsions. Five v τ candidate events have been detected in the full data sample from 2008-2012 CNGS runs, with an expected background of 0.25 events. The background only hypothesis is rejected with a significance larger than 5 σ. The analysis of the tau neutrino sample in the framework of the 3+1 neutrino model is also presented. Furthermore OPERA good capabilities in detecting electron neutrino interactions allow setting limits on the v μ → v e oscillation channel.

Super-resolution Tracking Technology using the Localized Surface Plasmon Resonance in the Fine-grained Nuclear Emulsion

Super-resolution Tracking Technology using the Localized Surface Plasmon Resonance in the Fine-grained Nuclear Emulsion

A Neutron Detector with Submicron Spatial Resolution using Fine-grained Nuclear Emulsion

We developed a neutron detector with submicron spatial resolution by incorporating 6Li into a fine-grained nuclear emulsion. Upon exposure to thermal neutrons, tracks from neutron capture events were observed. The detector spatial resolution was estimated from their grain density. Detection efficiency was measured using the detector response to cold neutrons.

Latest nuclear emulsion technology

Latest nuclear emulsion technology

Automatic track following system to study double strangeness nuclei in nuclear emulsion exposed to the observable limit

An automatic track following system has been successfully developed to follow tracks in nuclear emulsion sheets exposed with beam up to the limit to be observed for the first time. The track followed rate of the system is 99.5% with the assistance of the new techniques. The working speed for a track is less than 1min through one thick emulsion sheet, whereas it is 15 times faster than that of semiautomatic system with human. The system working for 24h is applied for the E07 experiment at J-PARC and makes it possible to detect ~102 nuclei with double strangeness (S=−2 nuclei) within one year. Regarding analyses to identify nuclear species of S=−2 nuclei, the system shows quite decent job for significant steps such as following tracks emitted to spherical directions from S=−2 nuclei, measurement of lengths of followed tracks, and so on.

Further Studies of BURSTS and Spallation in High-Energy Heavy Ion Reactions

Aspects of BURSTS and Spallation reactions induced by high-energy heavy ions in thick targets (>10 cm thick) will be investigated: BURSTS are reviewed from a historical and phenomenological point-of-view. Details of interactions in nuclear emulsions will be compared for irradiations of 72 GeV 22Ne-ions from Dubna with irradiations of 72 GeV 40Ar-ions from Berkeley. Measured correlations in individual interactions between multiplicities of “minimum ionizing particles”, ns, and “black prongs”, nb, will be shown as “ns-vs.-nb” per event for BURSTS and separately for Spallation in interactions of 72 GeV 22Ne-ions. Monte Carlo calculations, based on the MCNPX 2.7 code, have been carried out for 72 GeV 22Ne interacting in nuclear emulsions: The correlation between ns and nb in Spallation reactions could be understood. However, “ns-vs.-nb” correlations from BURST-interactions could not be reproduced with this model for events with small numbers of heavy prongs nh ≤ 10. For large numbers of heavy prongs with nh > 10 one could find some agreement between experiments and calculations, however, not in all details. Further experimental and theoretical studies are necessary before one has a complete understanding of BURST interactions in high-energy heavy ion reactions.