Ⅰ. HIGHLIGHTS OF THE YEARRIKEN Accel. Prog. Rep. 50 (2017)

Electron scattering oﬀ 208 Pb and 132 Xe at SCRIT electron scattering
facility
K. Tsukada,∗1 ∗2 K. Adachi,∗3 A. Enokizono,∗1 ∗3 T. Fujita,∗3 M. Hori,∗2 S. Ichikawa,∗2 K. Kasama,∗1K. Kurita,∗3 K. Namba,∗1 T. Ohnishi,∗2 S. Sasamura,∗3 T. Suda,∗1 ∗2 T. Tamae,∗1 ∗2 M. Togasaki,∗3N. Uchida,∗3 M. Wakasugi,∗2 M. Watanabe,∗2 and K. Yamada∗3tribution of 132 Xe. This result will be published soon.

∗1∗2∗3L d σ [(cm -2s-1)(cm 2sr -1)]dΩThe SCRIT (Self-Conﬁning Radioactive IsotopeTarget) electron scattering facility has been constructed at RIKEN to realize electron scattering oﬀunstable nuclei1) . This year, commissioning studies ofthe spectrometers WiSES (Window-frame Spectrometer for Electron Scattering) and LMon (LuminosityMonitor) have been performed with several stable targets. The studies of LMon are reported elsewhere.3,4)
Here, some results with WiSES for 208 Pb and 132 Xetargets are reported.
Since 208 Pb is one of the most extensively investigated stable nuclei and the form factor is precisely
derived by electron scattering,2) it is the best target
to check the spectrometer performance. The 208 Pbion was extracted from the evaporation of natural leadheated up to 300◦ C and transported into SCRIT byERIS5) and FRAC.6) The number of ions introduced
was about 108 particles/pulse, and the achieved lumionsity was about 1027 cm−2 s−1 on average. The
acceptance of WiSES was evaluated by Geant4 simulation taking into account the inﬂuence of the radiation tail. Figure 1 shows the diﬀerential cross sections
multiplied by luminosity for elastic electron scattering oﬀ 208 Pb. By changing the electron beam energy,
a wide range of momentum transfer can be covered.
The line represents a phase shift calculation with thenuclear charge density distribution modeled as a sumof-Gaussian function.2) The luminosity is considered asa ﬁtting parameter in the present analysis because thestudy of the LMon to determine the absolute value ofluminosity is underway. The momentum-transfer dependence is well reproduced by the calculation.
Figure 2 shows the same plots for elastic electronscattering oﬀ 132 Xe. The number of introduced target
ions and the achieved luminosity were approximately
the same as those for 208 Pb. The parameters of a twoparameter Fermi distribution in the elastic scattering
calculation are determined to reproduce our data. The
contribution of inelastic scattering8) contaminated because of momentum resolution is negligibly small, as
shown in the ﬁgure. Although 132 Xe is a stable nucleus
and the root-mean-square radius is evaluated from themeasurement of X-rays from muonic atoms,7) electron
scattering has never been performed. This work is,therefore, the ﬁrst to determine the charge density dis-102

208

Exp. (Ee=151MeV)
Exp. (Ee=201MeV)
Exp. (Ee=301MeV)
Calculation with SOG

Pb target

101-1

10

10-2
10-30.4

Preliminary
0.6

0.8

1

1.2

q

1.4 -1[fm ]eff

L d σ [(cm -2s-1)(cm 2sr -1)]dΩFig. 1. Diﬀerential cross sections of 208 Pb(e,e) multipliedby the luminosity for the eﬀective momentum transfer
at Ee =151, 201, and 301 MeV. The line is a phase shift
calculation with the nuclear charge density distribution
modeled as a sum-of-Gaussian function.2)

102
101-1
1010-210-3
10-40.4

Exp. ( Ee =151MeV)
Exp. ( Ee =201MeV)
Exp. ( Ee =301MeV)
Calculation
inela. (2+)
ela.+inela.

132

Xe target

Preliminary
0.6

0.8

1

1.2

1.4

q eff [fm -1]

Fig. 2. Diﬀerential cross sections of 132 Xe(e,e) multipliedby the luminosity for the eﬀective momentum transfer
at Ee =151, 201, and 301 MeV. The lines are a phaseshift calculation with the nuclear charge density distribution modeled as a two-parameter Fermi distribution(solid), contributions of inelastic scattering calculated
by a beyond relativistic mean ﬁeld theory8) (dashed),and their sum (dot-dashed).

References
1) M. Wakasugi et al., Nucl. Instr. Meth. B317, 668(2013).
2) B. Frois et al., Phys. Rev. Lett. 38, 152 (1977).
3) T. Fujita: In this report.
4) A. Enokizono: In this report.
5) T. Ohnishi et al., Nucl. Instr. Meth. B317, 357 (2013).
6) M. Togasaki et al.: Proceedings of HIAT2015, WEPB25(2015).
7) G. Fricke et al., Atomic Data and Nuclear Data Tables
60, 177 (1995).
8) M. Hua, K. Hagino, private communication.

RIKEN Nishina Center
Research Center for Electron-Photon Science, Tohoku University
Department of Physics, Rikkyo University- 11 -