Study on the reusability of fluorescent nuclear track detectors using optical bleaching

Fluorescent nuclear track detectors (FNTDs) based on Al${_2}$O${_3}$:C,Mg crystals are luminescent detectors that can be used for dosimetry and detection of charged particles and neutrons. These detectors can be utilised for imaging applications where a reasonably high track density, approximately of the order of 1 $\times$ $10^4$ tracks in an area of 100 $\times$ 100 $\mu$m$^2$, is required. To investigate the reusability of FNTDs for imaging applications, we present an approach to perform optical bleaching under the required track density conditions. The reusability was assessed through seven irradiation-bleaching cycles. For the irradiation, the studied FNTD was exposed to alpha-particles from an $^{241}$Am radioactive source. The optical bleaching was performed by means of ultraviolet laser light with a wavelength of 355 nm. Three dedicated regions on a single FNTD with different accumulated track densities and bleaching conditions were investigated. After every irradiation-bleaching cycle, signal-to-noise ratio was calculated to evaluate FNTD performance. It is concluded that FNTDs can be reused at least seven times for applications where accumulation of a high track density is required

J-PARCにおけるハイブリッドエマルション法を用いたΛΛBeダブルラムダハイパー核の観測

京都大学0048新制・課程博士博士(理学)甲第22142号理博第4542号新制||理||1653(附属図書館)京都大学大学院理学研究科物理学・宇宙物理学専攻(主査)教授 永江 知文, 教授 鶴 剛, 准教授 成木 恵学位規則第4条第1項該当Doctor of ScienceKyoto UniversityDGA

WASA-FRS HypHI experiment at GSI for studying light hypernuclei

From January till March 2022, the WASA-FRS HypHI experiment performed a precise measurement of the hypertriton and the 4ΛH hypernucleus lifetime at GSI. The data collected should also confirm whether or not the nnΛ bound state can exist. The experiment were carried out with the WASA central detector with a complex of additional dedicated detectors mounted together at the mid-focal plane of the high-momentum-resolution forward spectrometer, the so-called fragment separator FRS. Hypernuclei of interest were produced by induced reactions of 6Li projectiles at 1.96 A GeV on a diamond target with a thickness of 9.87 g/cm2. Negatively charged π mesons from two-body decays of the hypernuclei of interest were measured by theWASA and the other detectors, and the residual nuclei after the π− decay were measured by the FRS with a momentum resolving power of 104

Novel method for producing very-neutron-rich hypernuclei via charge-exchange reactions with heavy ion projectiles

We propose a novel method for producing very-neutron-rich hypernuclei and corresponding resonance states by employing charge-exchange reactions via pp($$^{12}$$C, $$^{12}$$N $$K^+$$)n$$\varLambda$$ with single-charge-exchange and ppp($$^{9}$$Be, $$^{9}$$C $$K^+$$)nn$$\varLambda$$ with double-charge-exchange, both of which produce $$\varLambda K^+$$ in a target nucleus. The feasibility of producing very-neutron-rich hypernuclei using the proposed method was analysed by applying an ultra-relativistic quantum molecular dynamics model to a $$^6$$Li + $$^{12}$$C reaction at 2 A GeV. The yields of very-neutron-rich hypernuclei, signal-to-background ratios, and background contributions were investigated. The proposed method is a powerful tool for studying very-neutron-rich hypernuclei and resonance states with a hyperon for experiments employing the Super-FRS facility at FAIR and HFRS facility at HIAF

Trapping probability of strangeness via Xi− hyperon capture at rest in nuclear emulsion

In the E373 experiment at KEK-PS, we have located nearly 2 × 104 stopping events of Ξ− hyperon candidates in nuclear emulsion. Among these, the identification of the Ξ− hyperon was performed with the constant sagitta (CS) method, by measuring multiple Coulomb scattering for 695 clear stopping events, σ-stop, with emission of nuclear fragments due to negatively charged hadrons. With use of a Geant4 simulation, the parameters for the CS method were optimized and we obtained the number of real Ξ− stopping events to be 432.3±7.6+ 0.0−14.0 with 3.2% systematic error by contamination by the Σ− hyperon. We have classified the events for Ξ− hyperon capture by light (C, N, O) and heavy (Ag, Br) elements in the emulsion. The trapping probabilities of two Λ hyperons for light and heavy nuclei were found to be 5.0±1.7% and 4.2±1.4%⁠, respectively, for σ-stop via Ξ− hyperon capture at rest in the emulsion. For at least one Λ trapping, the probabilities were 69.4±8.1% for light nuclei and 51.1±5.7% for heavy nuclei. These results allow us to present the trapping probabilities of Λ hyperons via Ξ− hyperon capture at rest in emulsion for the first time, because the previous E176 experiment showed the lower limits due to fewer statistics

Unique approach for precise determination of binding energies of hypernuclei with nuclear emulsion and machine learning

Hypertriton is the lightest hypernucleus and a benchmark in hypernuclear physics. However, it has recently been suggested that its lifetime and binding energy values may differ from the established values. To solve this puzzle, it is necessary to measure both values with a higher precision. For the precise measurement of the binding energy, we are aiming at developing a novel technique to measure the hypertriton binding energy with unprecedented accuracy by combining nuclear emulsion data and machine learning techniques. The analysis will be based on the J-PARC E07 nuclear emulsion data. Furthermore, a machine-learning model is being developed to identify other single and double-strangeness hypernuclei