The (p,p’) experiment at 0o at RCNP 9th April Osaka Univ. Osaka Univ. RCNP Hiroaki MATSUBARA April 05 @ iThemba labs. Collaborators for E249 Osaka U. RCNP Osaka U. Dept. of Phys. Univ. of Witwatersrand CNS Univ. of Tokyo Kyoto U. Dept. of Phys. A. Tamii, K. Fujita, N. Hashimoto, K. Hatanaka, M. Itoh, K. Nakanishi, Y. Sakemi, Y. Shimbara, Y. Shimizu, Y. Tameshige T. Adachi, Y. Fujita J. Carter T. Kawabata H. Sakaguchi, M. Yosoi, J. Zenihiro iThemba LABs H.Fujita, F.D. Smit Gent Univ. L.A. Popescu April 05 @ iThemba labs. RCNP : overview 2. RING Cyclotron Accelerated up to Ep = 400 MeV 1. AVF Cyclotron WS : High-precision spectrograph N0 : Neutron TOF (100m) EN&ES : Unstable nuclei (Heavy ions) Accelerated up to Ep = 80 MeV April 05 @ iThemba labs. Introduction • The configuration mixing is an interesting subject in the study of nuclear structure. • Through the study of M1 excitations on 0+ T=0 nuclei, we can learn a lot. • Light nucleus is easier to be calculated, e. g. sd-shell one. 24Mg, 28Si, 32S April 05 @ iThemba labs. Quenching problems • Less strength is observed than predicted with sum rule. GT sum rule : 0 | [Y , Y ] | 0 3( N Z ) 60 → 90% of the strength is observed. T.Wakasa et al., PRC55(1997)2909 (p,n) reaction How about M1 strengths? , Common with GT Quenching is observed in T=0,1 M1 strengths in 28Si. N. Anantaraman et al.,PRL52(1984)1409 Almost no quenching is observed in 24,26Mg, 28Si, 32S. G.M. Crawley et al.,RPC39(1989)311 Improvement of the data quality is required. April 05 @ iThemba labs. Experimental Setup (@RCNP WS course) Under focus mode As a beam spot monitor in the vertical direction Q1 F.C. Intensity : 3 ~ 8 nA Target : natSi (1.9 mg/cm2) April 05 @ iThemba labs. Procedure of the beam tuning • Achromatic transport mode ~40keV (FWHM) : Au(p,p0) at 8° • Halo free beam tuning at 0° (achromatic mode) • Dispersion matching (faint beam method) ~3mm (FWHM) on the target : beam spot size It took about 2 days for beam tuning. April 05 @ iThemba labs. Sieve slit calibration ~ for the better vertical scattering angler resolution ~ 2 2 Around 0 deg, angel resolution is sensitive to both θ and φ. 48mm 2mmφ 18mm 58Ni(p,p 58Ni(p,p 16°GR ) at 16°GR 0) 0at April 05 @ iThemba labs. Before calibrations +4.0% F.C. Y : Vertical position [mm] +1.0% +2.5% Common scaling Θ : Horizontal scattering angle [deg] April 05 @ iThemba labs. Y : Vertical position [mm] Procedure for calibration Projected Gaussian fitting Θ : Horizontal scattering angle [deg] Each positions are obtained. April 05 @ iThemba labs. After calibrations Horizontal: Δθ= 0.15 deg F.C. φ: Vertical : Δφ= 0.5 deg at Ex = 6 MeV. 0.8 deg at Ex = 20 MeV. ΔΘ = 0.5 ~ 0.8 [deg] φ: φ: (at the target) April 05 @ iThemba labs. Horizontal plane (X-plane) correction Y : The vertical position [mm] Θ : Horizontal scattering angle [deg] ~for a better energy resolution~ X : The horizontal position [mm] X : The horizontal position [mm] Before calibrations Curving and broadened April 05 @ iThemba labs. X-THETA correction Small region is projected to X-axis. Gaussian fitting Projected to X-axis Another region is selected and projected. Gaussian fitting The curving shapes are represented numerically. April 05 @ iThemba labs. The progress of the energy resolution Ex = 11.45MeV ;1 + 20keV April 05 @ iThemba labs. Background subtraction (I) True events rotated projection φ: Backgraound Y : The vertical position [mm] This rotation corresponds to move the VDC to the Y focal plane. April 05 @ iThemba labs. Background subtraction (II) Uniform BKG April 05 @ iThemba labs. A high quality spectrum preliminary April 05 @ iThemba labs. G.M. Crawley et al, PRC39(1989)311, at Orsay 2000 1500 500 Present data preliminary April 05 @ iThemba labs. The Differential Cross Section OXBASH parameter from A. Willis et al., PRC 43(1991)5 preliminary April 05 @ iThemba labs. Strength distributions B(σ) (μn2) Ep = 200 MeV M1 states only B(σ) (μn2) All strengths are normalized by the data of Crawley at 11.45 MeV. preliminary Ep = 160 MeV preliminary Ep = 295 MeV Excitation Energy (MeV) M1 + unknown states M1 + unknown states April 05 @ iThemba labs. E249 : data These spectra were obtained in the E249 experiment. targets: 0°2.5°4.5° 28Si ◎ ◎ ◎ 48Ca ◎ ◎ ◎ 64Ni ◎ ◎ ◎ 12C ○ ○ ○ Mylar ○ ○ ○ 13CH2 ○ - - 24Mg ○ - - 26Mg ○ - - 40Ca ○ - - 90Zr △ - - 1.9 mg/cm2 (natural) 1.9 mg/cm2 4.7 mg/cm2 1.1 mg/cm2 1.0 mg/cm2 0.7 mg/cm2 1.8 mg/cm2 1.6 mg/cm2 13 mg/cm2 1.0 mg/cm2 ○... measured, ◎... good statistics, △... poor statistics, -... not measured April 05 @ iThemba labs. Summary • The (p,p’) experiments at forward angles were carried out at WS course, RCNP. • High quality data were obtained. • We realized under-focus mode (scattering angle : 0.5~0.8 deg) dispersion matching (excitation energy : ~20 keV) in the (p,p’) measurement at 0 degrees. • Background was subtracted reasonably. • The cross sections of both IS and IV type were compared with DWBA calculations. • The strength distributions were compared with other data. April 05 @ iThemba labs. Future • Jπ assignments of each peak • Extraction of M1 strengths and their distributions • Next beam time – At finite angles – Data for further calibrations April 05 @ iThemba labs.
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