stars in equation-of-state (EOS) calculations [38–41]; the asymmetry ratio, [( N − Z ) /A ], changes by more than 80% over the range of the investigated Sn isotopes. The experiment was performed at the ring cyclotron facility of the Research Center for Nuclear Physics (RCNP), Osaka University, using inelastic scattering of 386-MeV α particles at extremely forward angles, including 0 $^{◦}$. A $^{4}$He++ beam was accelerated by the Azimuthally Varying Field (AVF) cyclotron up to 86 MeV, injected into the K = 400 ring cyclotron for acceleration up to 386 MeV, and achromatically transported to the WS experimental hall without any defining slits. To reduce the background at and near 0 $^{◦}$, the beam halo has to be tuned carefully in the experiment. This was accomplished by tuning the beam profile of the injection beam for the ring cyclotron, and typically less than 1 out of 10000 events had contamination from the other bunches. The beam current was 1-20 nA, which was limited by the data acquisition rate and by the maximum available current of the accelerator. The energy resolution obtained was ∼ 150 keV full width at half maximum (FWHM). Self supporting target foils of enriched even-A 112 − $^{124}$Sn isotopes of thickness 5.0–9.25 mg/cm 2 were employed; we used special target frames with a large aperture in order to reduce the background caused by the beam-halo hitting the frames. Data were also taken with a $^{nat}$C target at the actual field settings used in the experiments and the energy calibration was obtained from the peak positions of the 7.652- and 9.641-MeV states in the $^{12}$C( α, α $^{′}$) spectra. Inelastically-scattered α particles were momentum-analyzed with the high-resolution magnetic spectrometer, “Grand Raiden” [36], and the vertical and horizontal positions of the α particles were measured with the focal-plane detector system comprised of two position- sensitive multi-wire drift chambers (MWDCs) and two scintillators [29]. The MWDCs and scintillators enabled us to make particle identification and to reconstruct the trajectories of the scattered particles. The scattering angle at the target and the momentum of the scat- tered particles were determined by the ray-tracing method. The vertical-position spectrum obtained in the double-focusing mode of the spectrometer was exploited to eliminate the instrumental background [28, 29]. 4 II. EXPERIMENTAL TECHNIQUES