The first elastic electron scattering has been successfully performed at the self-confining RI ion target (SCRIT) facility, the world's first electron scattering facility for exotic nuclei. The SCRIT technique achieved high luminosity (over 10 27 cm −2 s −1 , sufficient for determining the nuclear shape) with only 10 8 target ions. While 132 Xe used in this time as a target is stable isotope, the charge density distribution was firstly extracted from the momentum transfer distributions of the scattered electrons by comparing the results with those calculated by a phase shift calculation.The charge density distribution of the nucleus is one of the most important factors in the nuclear structure investigations, as it directly relates to the superimposition of the squared wave functions of all protons in the nucleus. Following the monumental measurements by R. Hofstadter and his colleagues [1] in the latter half of the 20th century, many stable nuclei have been studied by elastic electron scattering experiments. However, with few exceptions, electron scattering from short-lived unstable nuclei has been precluded by the difficulty in preparing the target material for these nuclei. Realizing electron scattering for unstable nuclei has been long waited, as it has been revealed that some of nuclei far from the stability valley exhibit exotic features such as neutron halo, neutron skin, etc.[2] which are totally unknown in stable nuclei.We have invented an internal target-forming technique called self-confining RI ion target (SCRIT) [3] in an electron storage ring, which three-dimensionally traps the target ions along the electron beam axis. The ions are confined by transverse focusing force given by the electron beam itself and an electrostatic potential well provided by electrodes put along the beam axis. After a successful feasibility study [4,5], we have recently completed the construction of the SCRIT electron scattering facility [6] at RIKEN's RI Beam Factory, which is dedicated to the study of exotic nuclei. The luminosity required for elastic electron scattering (10 27 cm −2 s −1 ) was achieved with only 10 8 target ions as available at an conventional isotope separation on line (ISOL) facility. In traditional electron scattering experiments, the number of target nuclei is typically of the order of 10 20 . This advancement enables electron scattering not only from unstable nuclei, but also from stable nuclei that have not been studied to date.In this Letter, we report the first elastic electron scattering results of 132 Xe nuclei obtained at the SCRIT facility. Although 132 Xe is a stable nucleus, it has never been investigated by electron scattering [7]. Interestingly, stable xenon isotopes have been recently utilized as targets for dark matter searches [8][9][10], and in neutrinoless double beta decay experiments [11]. To calculate the cross sections in these experiments, the form factors of the Xe isotopes are required. However, transition X-ray measurements of muonic atoms have yielded only the rootmean-squa...
The SCRIT electron scattering facility has been constructed at the RIKEN RI Beam Factory. The commissioning experiment was performed and the properties of the ion trapping were studied. The first electron elastic scattering experiment of 132 Xe was performed and the charge density distribution was obtained. The achieved luminosity in the experiment was 1.8 × 10 27 cm −2 s −1 with a 250 mA electron beam current and the injection of 10 8 ions. The production of unstable nuclei has been started with a new online isotope separator (ISOL) system at the SCRIT facility, and developments of the ISOL system for increasing rates of unstable nuclei are underway. Electron scattering with unstable nuclei will be performed in the near future.
The SCRIT electron scattering facility is under construction at the RIKEN RI Beam Factory. This is the world's first facility dedicated to the study of the structure of short-lived nuclei by electron scattering, which has been a long-standing dream for nuclear physics. A novel Self-Confining RI Target (SCRIT) technique makes this challenging research possible. A series of test experiments using stable nuclei performed at this partially completed facility show that the collision luminosity between electron beam and target nucleus reaches 10 27 cm −2 s −1 , which is required for an elastic electron scattering measurement to determine the charge density distribution of the target nucleus. The first electron scattering for unstable Sn isotopes will take place in the year 2014.
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