Giant monopole strength in 58

Previously, using inelastic scattering of 240-MeV alpha particles at small angles with a deformed potential analysis, we reported @1# 32% of the E0 EWSR in two Gaussian peaks in Ni and argued that no more than 50% of the E0 strength was located between Ex512 and 25 MeV. Satchler and Khoa @2# carried out a folding analysis of our data and on that basis concluded the two peaks contained ;50% of the E0 EWSR. The location of the remainder of the E0 strength in Ni was a puzzle. We have again measured the E0 strength in Ni, this time using a detector that extends the measurement up to Ex560 MeV, compared to Ex<30 MeV in the previous measurement, in order to locate strength at higher excitation and we report those results here. A 240-MeV a-particle beam from the Texas A & M K500 superconducting cyclotron was used to bombard a 4.02-mg/cm Ni metal foil located in the target chamber of the multipole-dipole-multipole spectrometer. Inelastically scattered a particles were detected in the focal plane detector that measured position and angle in the scattering plane. The out-of-plane scattering angle f was not measured. Position resolution of approximately 0.9 mm and scattering angle resolution of about 0.09° were obtained. The detector covers the range Ex57 – 62 MeV. The experimental technique and the detector have been described in detail in Refs. @3–5#. Data were taken with the spectrometer at 0.0° (0.0°,u ,2.0°) and at 3.5° (1.5°,u,5.5°). Each data set was divided into ten angle bins, each corresponding to du'0.4° using the angle obtained from ray tracing. f is not measured by the detector, so the average angle for each bin was obtained by integrating over the height of the solid angle defining slit and the width of the angle bin. Cross sections were obtained from the charge collected, target thickness, dead time, and known solid angle. Uncertainties in target thickness, solid angle, etc. result in about a 610% uncertainty in absolute cross sections. The target thickness was measured by weighing and checked with the energy-loss technique using the 240-MeV a-particle beam. A spectrum obtained in the present experiment is compared to the earlier data @1# in Fig. 1. Except for a somewhat larger background at lower excitation in the earlier data, they are in excellent agreement up to the Ex530 MeV limit of the earlier data. Multipole strength distributions were obtained using ‘‘slice analysis’’ @3,4# where a continuum is estimated and subtracted, leaving a giant resonance peak. This peak is then divided into several intervals and cross sections obtained for each interval. The resulting angular distributions are then fit