Eur. Phys. J. A (2022) 58: 190
https://doi.org/10.1140/epja/s10050-022-00830-7

Regular Article - Experimental Physics

High-resolution measurement of hypernuclear events in a nuclear emulsion with hard X-ray microscopy

¹ Graduate School of Engineering, Gifu University, 1-1 Yanagido, 501-1193, Gifu, Japan
² High Energy Nuclear Physics Laboratory, Cluster for Pioneering Research, RIKEN, 2-1 Hirosawa, Wako, 351-0198, Saitama, Japan
³ Faculty of Education, Gifu University, 1-1 Yanagido, 501-1193, Gifu, Japan
⁴ GSI Helmholtz Centre for Heavy Ion Research, Planckstrasse 1, 64291, Darmstadt, Germany
⁵ School of Nuclear Science and Technology, Lanzhou University, 222 South Tianshui Road, 730000, Lanzhou, Gansu Province, China
⁶ Department of physics, Tohoku University, Aramaki, Aoba-ku, 980-8578, Sendai, Japan
⁷ International Center for Synchrotron Radiation Innovation Smart, Tohoku University, 980-8577, Sendai, Japan
⁸ RIKEN Nishina Center, RIKEN, 2-1 Hirosawa, Wako, 351-0198, Saitama, Japan

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Received: 1 March 2022
Accepted: 6 September 2022
Published online: 1 October 2022

Abstract

A high-resolution measurement method based on X-ray microscopy was developed to analyze double-strangeness hypernuclear events with a complex topology in a nuclear emulsion. In a feasibility study performed on $\alpha$-decay events in emulsions, the resolution of the X-ray microscopy in the focal plane was found to be 0.2 $\mathrm{\mu }\mathrm{m}$, which shows an improvement by $\sim 2.4$ times to that of the optical microscopy used for conventional analysis. The extent to which the emulsion underwent modification as a result of X-ray irradiation was also evaluated. The modification mainly occurred in the form of a change in its thickness; however, this affection was adequately small to perform X-ray imaging if the duration of the irradiation was sufficiently short. Stereo imaging with X-ray microscopy improved the resolution by $\sim 2.5$ times to 0.28 $\mathrm{\mu }\mathrm{m}$ along the optical axis compared with the depth of field of the optical microscope, 0.7 $\mathrm{\mu }\mathrm{m}$. We applied the developed method to the study of a double-strangeness hypernuclear event. The uncertainty on the position of the vertex point and the binding energy of the ${\mathrm{\Xi }}^{-}$ and ${}^{14}$N system was improved from 3 $\mathrm{\mu }\mathrm{m}$ to 0.04 $\mathrm{\mu }\mathrm{m}$ and $\pm 3$ MeV to $\pm 0.86$ MeV, respectively. The binding energy was deduced to be $-1.23\pm 0.86\mathrm{MeV}$, and this result indicates that a ${\mathrm{\Xi }}^{-}$ atomic state is produced in the observed event.