G.P.A. Berg

The Deeply Bound Pionic States in 121Sn Produced by (d,3He) Reaction

T. Nishi , G.P.A. Berg, M. Dozono, H. Fujioka, N. Fukuda, T. Furuno, H. Geissel, R.S. Hayano, N. Inabe, K. Itahashi, S. Itoh, D. Kameda, T. Kubo, H. Matsubara, S. Michimasa , K. Miki, H. Miya , Y. Murakami, M. Nakamura, N. Nakatsuka, S. Noji, K. Okochi, S. Ota , H. Suzuki, K. Suzuki, M. Takaki , H. Takeda, Y.K. Tanaka, K. Todoroki, K. Tsukada, T. Uesaka, Y.N. Watanabe, H. Weick, H. Yamada, and K. Yoshida

High-precision {sup 28}Si(p,t){sup 26}Si reaction to determine {sup 22}Mg({alpha},p){sup 25}Al reaction rates

The rise time of stellar x-ray bursts is a signature of thermonuclear runaway processes in the atmosphere of neutron stars and is highly sensitive to a series of (alpha, p) reactions via high-lying resonances in sd-shell nuclei. Lacking data for the relevant resonance levels, the stellar reaction rates have been calculated using statistical, Hauser-Feshbach models, assuming a high-level density. This assumption may not be correct in view of the selectivity of the (alpha, p) reaction to natural parity states. We measured the Si-28(p,t)Si-26 reaction with a high-resolution spectrometer to identify resonance levels in Si-26 above the alpha-emission threshold at 9.164 MeV excitation energy. These resonance levels are used to calculate the stellar reaction rate of the Mg-22(alpha,p)Al-25 reaction and to test the validity of the statistical assumption.

High-precision (p,t) reaction to determine {sup 25}Al(p,{gamma}){sup 26}Si reaction rates

Since the identification of ongoing Al-26 production in the universe, the reaction sequence Mg-24(p,gamma)Al-25(beta(+)nu)Mg-25(p,gamma)Al-26 has been studied intensively. At temperatures where the radiative capture on Al-25 (t(1/2) = 7.2 s) becomes faster than the beta(+) decay, the production of Al-26 can be reduced due to the depletion of Al-25. To determine the resonances relevant for the Al-25(p,gamma) Si-26 bypass reaction, we measured the Si-28(p,t)Si-26 reaction with high-energy precision using the Grand Raiden spectrometer at the Research Center for Nuclear Physics, Osaka. Several new energy levels were found above the p threshold and for known states excitation energies were determined with smaller uncertainties. The calculated stellar rates of the bypass reaction agree well with previous results, suggesting that these rates are well established.

High-precision (p,t) reaction measurement to determine {sup 18}Ne({alpha},p){sup 21}Na reaction rates

x-ray bursts are identified as thermonuclear explosions in the outer atmosphere of accreting neutron stars. The thermonuclear runaway is fueled by the alpha p process that describes a sequence of (alpha,p) reactions triggered by the Ne-18(alpha,p)Na-21 breakout reaction from the hot CNO cycles. We studied the level structure of the compound nucleus Mg-22 by measuring the Mg-24(p,t)Mg-22 reaction at the Grand Raiden spectrometer at Research Center for Nuclear Physics, Osaka. A large number of alpha-unbound states was identified and precise excitation energies were determined. Based on shell model and alpha-cluster model calculations we predict the level parameters for determining the stellar reaction rate of Ne-18(alpha,p)Na-21 for a wide temperature range. x-ray burst simulations have been performed to study the impact of the reaction on the x-ray burst luminosity.

Gamow-Teller transitions studied in the high-resolution {sup 64}Ni({sup 3}He,t){sup 64}Cu reaction

To study the Gamow-Teller (GT) transitions to the pf-shell nucleus Cu-64, the Ni-64(He-3,t)Cu-64 experiment was performed at the Research Center for Nuclear Physics (RCNP) Ring Cyclotron, Osaka, using a He-3 beam of 140 MeV/nucleon. The outgoing tritons were momentum analyzed by the Grand Raiden spectrometer at 0(degrees). A high energy resolution of 32 keV (full width at half-maximum) allowed the separation of individual levels in the excitation-energy region from 0 to 3.5 MeV. In addition to the ground state (gs), known to be a J(pi)=1(+) GT state, many low-lying states showed L=0 nature, suggesting that they are candidates for GT states. Because the GT strength B(GT) for the gs transition is known from the beta-decay measurement, the strengths for the excited states could be determined using the proportionality between the B(GT) and the reaction cross section extrapolated to q=0 momentum transfer. At higher excitation energies, the level density becomes high and the so-called GT giant resonance dominates the spectrum. The lower and the upper limits of the strength contained in this energy region were estimated. Our results show that less than 55% of the strength predicted by the Ikeda sum rule is located in the excitation-energy region from 0 to 17 MeV..

Distribution of the GT strength starting from the ground state of 14N

Two charge‐exchange reactions were performed at intermediate energies in order to investigate the Gamow‐Teller strength distribution starting from 14Ng.s. in β+ and β− directions: 14N(d,2He)14C and 14N(3He,t)14O. We describe here a few delicate details of the experimental techniques used in these investigations.

M1and Gamow-Teller transitions inT=1/2nuclei23Naand23Mg

The magnetic dipole

Looking for the isoscalar giant dipole resonance in 208Pd using inelastic a scattering at and near O

(M1)

Non-spin-flip (3He, t) charge-exchange and isobaric analog states of actinide nuclei studied at and 200 MeV

operator consists not only of the usually dominant isovector (IV) spin

High-resolution study of Gamow-Teller transitions via the Fe-54(He-3, t)Co-54 reaction

(\ensuremath{\sigma}\ensuremath{\tau})