Ⅱ-1. Nuclear Physics

RIKEN Accel. Prog. Rep. 53

Performance study of electron spectrometer for SCRIT experiments

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Fig. 1. Reconstructed momentum spectra of scattered electrons for diﬀerent scattering-angle regions.
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neously. In addition, a magnetic-ﬁeld measurement
was performed to study the momentum resolution ofWiSES.
In 2019, we performed a series of electron-scatteringexperiments with carbon targets to evaluate the acceptance and momentum resolution of the spectrometer
after the measurement of the magnetic-ﬁeld distribution of the spectrometer magnet. The status of theﬁeld measurement is reported elsewhere.3)
Figure 1 shows reconstructed momentum spectrafrom the center of targets for an electron beam energyof 300 MeV and three scattering angle regions: 40◦ –45◦ , 45◦ –50◦ , and 50◦ –55◦ . One elastic peak and two
inelastic peaks are clearly observed. Figure 2 shows
yield distributions with varying eﬀective momentum
transfer after acceptance corrections. In the present
analysis, only the radiation tail from the elastic peakis taken into account for counting the yields. Moreover,
the acceptances for the elastic and inelastic events are
assumed to be the same. Although the distributions of
the elastic events are consistent between this work anda previous experiment,4) those of the inelastic eventsshow ﬁnite discrepancies.
Further analysis is ongoing to evaluate the performance of the spectrometer.

ak02606404.4 MeV, this workFig. 2. Yield distributions with varying eﬀective momentum transfer after acceptance corrections. Filled circles
indicate preliminary results from this work. Openedcircles are from Ref. 4).

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We constructed the Self-Conﬁning Radioactive Ion
Target (SCRIT) electron scattering facility1) to perform electron scattering experiments for short-lived
unstable nuclei. Such experiments have been long desired but unrealized thus far because of the diﬃculties in preparing a thick target from such short-lived
nuclei. SCRIT is a novel technique to achieve a sufﬁciently high luminosity to perform electron scattering experiments by trapping the target ions along theelectron beam. After successful commissioning experiments with stable targets,2) we started to prepare foran experiment with an unstable nuclear target.
The SCRIT electrode was replaced with a new one
that has a larger cross section and less material aroundthe trapping region, in addition to providing a much
more uniform electric potential. Simultaneously, threeidentical carbon foils with a thickness of 35 µm wereinstalled as ﬁxed targets at the center and both edgesof the SCRIT electrodes, respectively, to evaluate theperformance of the electron spectrometer, windowframe spectrometer for electron scattering (WiSES).
The carbon targets can be moved out of the electronbeam axis when they are not in use. For WiSES, thedrift chamber in front of the spectrometer magnet wasreplaced with a new one with both vertical and horizontal wires to reconstruct the horizontal and verticaltrajectory information of scattered electrons simulta-Yield (arb. units)

K. Tsukada,∗1,∗2 A. Enokizono,∗2 Y. Honda,∗1,∗2 K. Kurita,∗3 H. Ohnishi,∗2 S. Sato,∗3 T. Suda,∗1,∗2 S. Takagi,∗4
D. Taki,∗1,∗2 T. Tamae,∗1,∗2 M. Watanabe,∗2 M. Wakasugi,∗2,∗4 and H. Wauke∗1,∗2References

1) M. Wakasugi et al., Phys. Rev. Lett. 100, 164801(2008).
2) K. Tsukada et al., Phys. Rev. Lett. 118, 262501 (2017).
3) H. Wauke et al., in this report.
4) J. H. Fregeau et al., Phys. Rev. 104, 225 (1956).

ELPH, Tohoku University
RIKEN Nishina Center
Department of Physics, Rikkyo University
Institute for Chemical Research, Kyoto University- 49 -