The TRI\(\mu\)P facility, under construction at KVI, requires the production and separation of short-lived and rare isotopes. Direct reactions, fragmentation and fusion-evaporation reactions in ...normal and inverse kinematics are foreseen to produce nuclides of interest with a variety of heavy-ion beams from the superconducting cyclotron AGOR. For this purpose, we have designed, constructed and commissioned a versatile magnetic separator that allows efficient injection into an ion catcher, i.e., gas-filled stopper/cooler or thermal ionizer, from which a low energy radioactive beam will be extracted. The separator performance was tested with the production and clean separation of \(^{21}\)Na ions, where a beam purity of 99.5% could be achieved. For fusion-evaporation products, some of the features of its operation as a gas-filled recoil separator were tested.
The isoscalar giant dipole resonance (ISGDR) has been investigated in 208Pb
using inelastic scattering of 400 MeV alpha particles at forward angles,
including 0deg. Using the superior capabilities of ...the Grand Raiden
spectrometer, it has been possible to obtain spectra devoid of any
"instrumental" background. The ISGDR strength distribution has been extracted
from a multipole-composition of the observed spectra. The implication of these
results on the experimental value of nuclear incompressibility are discussed.
Electron capture and beta decay play important roles in the evolution of pre-supernovae stars and their eventual core collapse. These rates are normally predicted through shell-model calculations. ...Experimentally determined strength distributions from charge-exchange reactions are needed to test modern shell-model calculations. We report on the measurement of the Gamow-Teller strength distribution in 58Co from the 58Ni(t,3He) reaction with a secondary triton beam of an intensity of ~10^6 pps at 115 MeV/nucleon and a resolution of \~250 keV. Previous measurements with the 58Ni(n,p) and the 58Ni(d,2He) reactions were inconsistent with each other. Our results support the latter. We also compare the results to predictions of large-scale shell model calculations using the KB3G and GXPF1 interactions and investigate the impact of differences between the various experiments and theories in terms of the weak rates in the stellar environment. Finally, the systematic uncertainties in the normalization of the strength distribution extracted from 58Ni(3He,t) are described and turn out to be non-negligible due to large interferences between the dL=0, dS=1 Gamow-Teller amplitude and the dL=2, dS=1 amplitude.
The strength distribution of the isoscalar giant dipole resonance (ISGDR) in \(^{58}\)Ni has been obtained over the energy range 10.5--49.5 MeV via extreme forward angle scattering (including ...0\(^{\circ}\)) of 386 MeV \(\alpha\) particles. We observe a ``bi-modal'' \({E1}\) strength distribution for the first time in an A \(<\) 90 nucleus. The observed ISGDR strength distribution is in good agreement with the predictions of a recent QRPA calculation.
We investigated the feasibility of quantum-correlation measurements in nuclear physics experiments. In a first approach, we measured spin correlations of singlet-spin (1S0) proton pairs, which were ...generated in 1H(d,2He) and 12C(d,2He) nuclear charge-exchange reactions. The experiment was optimized for a clean preparation of the 2He singlet state and offered a 2pi detection geometry for both protons in the exit channel. Our results confirm the effectiveness of the setup for theses studies, despite limitations of a small data sample recorded during the feasibility studies.
Charge-exchange reactions are an important tool for determining weak-interaction rates. They provide stringent tests for nuclear structure models necessary for modeling astrophysical environments ...such as neutron stars and core-collapse supernovae. In anticipation of (t,3He) experiments at 115 MeV/nucleon on nuclei of relevance (A~40-120) in the late evolution of stars, it is shown via a study of the 26Mg(t,3He) reaction that this probe is an accurate tool for extracting Gamow-Teller transition strengths. To do so, the data are complemented by results from the 26Mg(3He,t) reaction at 140 MeV/nucleon which allows for a comparison of T=2 analog states excited via the mirror reactions. Extracted Gamow-Teller strengths from 26Mg(t,3He) and 26Mg(3He,t) are compared with those from 26Mg(d,2He) and 26Mg(p,n) studies, respectively. A good correspondence is found, indicating probe-independence of the strength extraction. Furthermore, we test shell-model calculations using the new USD-05B interaction in the sd-model space and show that it reproduces the experimental Gamow-Teller strength distributions well. A second goal of this work is to improve the understanding of the (t,3He) and (3He,t) reaction mechanisms at intermediate energies since detailed studies are scarce. The Distorted-Wave Born Approximation is employed, taking into account the composite structures of the 3He and triton particles. The reaction model provides the means to explain systematic uncertainties at the 10-20% level in the extraction of Gamow-Teller strengths as being due to interference between Gamow-Teller dL=0, dS=1 and dL=2, dS=1 amplitudes that both contribute to transitions from 0+ to 1+ states.
Phys.Lett.B502:1-8,2001 Decay via proton emission of isobaric analog states (IAS's) in $^{91}{Nb}$
was studied using the $^{90}{Zr}(\alpha,t)$ reaction at $E_\alpha$=180 MeV.
This study provides ...information about the damping mechanism of these states.
Decay to the ground state and low-lying phonon states in $^{90}{Zr}$ was
observed. The experimental data are compared with theoretical predictions
wherein the IAS `single-particle' proton escape widths are calculated in a
continuum RPA approach. The branching ratios for decay to the phonon states are
explained using a simple model.
Phys.Rev.Lett.85:4442-4445,2000 Discrete Gamow-Teller (GT) transitions, 176Yb-->176Lu at low excitation
energies have been measured via the (3He,t) reaction at 450 MeV and at 0
degrees. For 176Yb, ...two low-lying states are observed, setting low thresholds
Q(neutrino)=301 and 445 keV for neutrino capture. Capture rates estimated from
the measured GT strengths, the simple two-state excitation structure, and the
low Q(neutrino) in Yb--Lu indicate that Yb-based neutrino-detectors are well
suited for a direct measurement of the complete sub-MeV solar electron-neutrino
spectrum (including pp neutrinos) where definitive effects of flavor conversion
are expected.
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