Testing the Mutually Enhanced Magicity Effect in Nuclear Incompressibility via the Giant Monopole Resonance in the 204,206,208^{204,206,208}Pb Isotopes

Using inelastic $\alpha$-scattering at extremely forward angles, including $0^\circ$, the strength distributions of the isoscalar giant monopole resonance (ISGMR) have been measured in the $^{204,206,208}$Pb isotopes in order to examine the proposed mutually enhanced magicity (MEM) effect on the nuclear incompressibility. The MEM effect had been suggested as a likely explanation of the "softness" of nuclear incompressibility observed in the ISGMR measurements in the Sn and Cd isotopes. Our experimental results rule out any manifestation of the MEM effect in nuclear incompressibility and leave the question of the softness of the open-shell nuclei unresolved still.Comment: Accepted for publication in Physics Letters B. Very minor changes in tex

Excitation of Giant Monopole Resonance in 208^{208}Pb and 116^{116}Sn Using Inelastic Deuteron Scattering

The excitation of the isoscalar giant monopole resonance (ISGMR) in $^{116}$Sn and $^{208}$Pb has been investigated using small-angle (including $0^\circ$) inelastic scattering of 100 MeV/u deuteron and multipole-decomposition analysis (MDA). The extracted strength distributions agree well with those from inelastic scattering of 100 MeV/u $\alpha$ particles. These measurements establish deuteron inelastic scattering at E$_d \sim$ 100 MeV/u as a suitable probe for extraction of the ISGMR strength with MDA, making feasible the investigation of this resonance in radioactive isotopes in inverse kinematics.Comment: 5 pages, 4 figures. To be published in Phys. Lett.

Proton decay from the isoscalar giant dipole resonance in 58^{58}Ni

Proton decay from the 3$\hbar\omega$ isoscalar giant dipole resonance (ISGDR) in $^{58}$Ni has been measured using the ($\alpha,\alpha'p$) reaction at a bombarding energy of 386 MeV to investigate its decay properties. We have extracted the ISGDR strength under the coincidence condition between inelastically scattered $\alpha$ particles at forward angles and decay protons emitted at backward angles. Branching ratios for proton decay to low-lying states of $^{57}$Co have been determined, and the results compared to predictions of recent continuum-RPA calculations. The final-state spectra of protons decaying to the low-lying states in $^{57}$Co were analyzed for a more detailed understanding of the structure of the ISGDR. It is found that there are differences in the structure of the ISGDR as a function of excitation energy.Comment: Minor changes after review. Accepted for publication in Phys. Rev. C. 19 pages; 7 figure

Development of portable NMR polarimeter system for polarized HD target

A portable NMR polarimeter system has been developed to measure the polarization of a polarized Hydrogen-Deuteride (HD) target for hadron photoproduction experiments at SPring-8. The polarized HD target is produced at the Research Center for Nuclear Physics (RCNP), Osaka university and is transported to SPring-8. The HD polarization should be monitored at both places. We have constructed the portable NMR polarimeter system by replacing the devices in the conventional system with the software system with PCI eXtensions for Instrumentation (PXI). The weight of the NMR system is downsized from 80 kg to 7 kg, and the cost is reduced to 25%. We check the performance of the portable NMR polarimeter system. The signal-to-noise (S/N) ratio of the NMR signal for the portable system is about 50% of that for the conventional NMR system. This performance of the portable NMR system is proved to be compatible with the conventional NMR system for the polarization measurement.Comment: 6 page, 8 figures, 2011/Mar/9 Replace Author

Uncomputably noisy ergodic limits

V'yugin has shown that there are a computable shift-invariant measure on Cantor space and a simple function f such that there is no computable bound on the rate of convergence of the ergodic averages A_n f. Here it is shown that in fact one can construct an example with the property that there is no computable bound on the complexity of the limit; that is, there is no computable bound on how complex a simple function needs to be to approximate the limit to within a given epsilon

Probing astrophysically important states in the ²⁶Mg nucleus to study neutron sources for the s process

Background: The ²²Ne(α,n) ²⁵Mg reaction is the dominant neutron source for the slow neutron capture process (s process) in massive stars, and contributes, together with C¹³(α,n)O¹⁶, to the production of neutrons for the s process in asymptotic giant branch (AGB) stars. However, the reaction is endothermic and competes directly with ²²Ne(α,γ)²⁶Mg radiative capture. The uncertainties for both reactions are large owing to the uncertainty in the level structure of ²⁶Mg near the α and neutron separation energies. These uncertainties affect the s-process nucleosynthesis calculations in theoretical stellar models. Purpose: Indirect studies in the past have been successful in determining the energies and the γ-ray and neutron widths of the Mg26 states in the energy region of interest. But, the high Coulomb barrier hinders a direct measurement of the resonance strengths, which are determined by the α widths for these states. The goal of the present experiments is to identify the critical resonance states and to precisely measure the α widths by α-transfer techniques. Methods: The α-inelastic scattering and α-transfer measurements were performed on a solid ²⁶Mg target and a ²²Ne gas target, respectively, using the Grand Raiden Spectrometer at the Research Center for Nuclear Physics in Osaka, Japan. The (α,α′) measurements were performed at 0.45°, 4.1°, 8.6°, and 11.1° and the (⁶Li,d) measurements at 0° and 10°. The scattered α particles and deuterons were detected by the focal plane detection system consisting of multiwire drift chambers and plastic scintillators. The focal plane energy calibration allowed the study of ²⁶Mg levels from Eₓ = 7.69–12.06 MeV in the (α,α′) measurement and Eₓ = 7.36–11.32 MeV in the (⁶Li,d) measurement. Results: Six levels (Eₓ = 10717, 10822, 10951, 11085, 11167, and 11317 keV) were observed above the α threshold in the region of interest (10.61–11.32 MeV). The α widths were calculated for these states from the experimental data. The results were used to determine the α-capture induced reaction rates. Conclusion: The energy range above the α threshold in ²⁶Mg was investigated using a high resolution spectrometer. A number of states were observed for the first time in α-scattering and α-transfer reactions. The excitation energies and spin-parities were determined. Good agreement is observed for previously known levels in ²⁶Mg. From the observed resonance levels the Eₓ = 10717 keV state has a negligible contribution to the α-induced reaction rates. The rates are dominated in both reaction channels by the resonance contributions of the states at Ex = 10951, 11167, and 11317 keV. The Eₓ = 11167 keV state has the most appreciable impact on the (α,γ) rate and therefore plays an important role in the prediction of the neutron production in s-process environments