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The TUDA and TACTIC facilities at TRIUMF provide versatile experimental capabilities for the study of astrophysically important reactions using both direct and indirect techniques. The present work will outline the research programme to date, describe the experimental facilities and discuss recent developments. [ABSTRACT FROM AUTHOR]

The low-energy structures of the radioactive nuclei 20, 21Na have been examined using Coulomb excitation at the TRIUMF-ISAC radioactive ion beam facility. Beams of ∼ 5×106 ions/s were accelerated to 1.7MeV/A and Coulomb excited in a 0.5mg/cm^2 natTi target. Two TIGRESS HPGe clover detectors perpendicular to the beam axis were used for $ \gamma$ -ray detection, while scattered nuclei were observed by the Si detector BAMBINO. For 21Na , Coulomb excitation from the 3/2+ ground state to the first excited 5/2+ state was observed, while for 20Na , Coulomb excitation was observed from the 2+ ground state to the first excited 3+ and 4+ states. For both beams, B ( $ \lambda$ L) values were determined using the 2+ $ \rightarrow$ 0+ de-excitation in 48Ti as a reference. The resulting B( E2) ↓ value for 21Na is 137±9 e^2fm^4, while the resulting B( $ \lambda$ L) ↓ values for 20Na are 55±6 e^2fm^4 for the 3+ $ \rightarrow$ 2+ , 35.7±5.7 e^2 fm^4 for the 4+ $ \rightarrow$ 2+ , and 0.154±0.030 μ_ N^2 for the 4+ $ \rightarrow$ 3+ transitions. This analysis significantly improves the measurement of the 21Na B( E2) value, and provides the first experimental determination of B( $ \lambda$ L) values for the proton dripline nucleus 20Na .-1 [ABSTRACT FROM AUTHOR]

TACTIC (TACTIC web site: http://tactic.triumf.ca) is a new detector for low-energy nuclear reactions currently under development at TRIUMF. The cylindrical ionization chamber allows three-dimensional reconstruction of particle tracks by means of a two-dimensional anode array combined with a TOF measurement of the drift electrons. In addition, the integrated charge for each pulse provides information about the energy loss of the particle and therefore allows a better identification of the nuclear species producing the track. The geometry of TACTIC covers a large angular range permitting the measurement of differential cross-sections over a large solid angle. It will be ideal for investigations of nuclear processes pertinent to the field of nuclear astrophysics. [ABSTRACT FROM AUTHOR]

TheAl( n, p)Mg reaction has been studied using neutron spectra which closely resembled Maxwell-Boltzmann (M.-B.) distributions with thermal energies of kT=40 ×10, 31 and 71 keV and also for E=270-350 keV. These energies correspond to stellar temperatures T=4.6×10, 0.36, 0.82 and 3.1-4.1, where T is in units of 10 K. The partial cross sections for the p-( p-)transition are found to equal 26±10(1,850 ±150), 13±6(124±17), 16±13(84±14) and 21±8(72±15) mb for the above neutron spectra, respectively. The astrophysical reaction rate is determined for the combined p- and p-transitions to be N〈σν〉=(0.324±0.026, 20.5±2.7, 22.6±4.3 and 38.7±11.1) ×10 cm mole s. The results are compared with previous investigations and with statistical model calculations. [ABSTRACT FROM AUTHOR]

The capture reactionHe(C, γ)O ( E= 1.34-3.38 MeV) as well as the elastic scattering processHe(C,C)He ( E=1.44-3.38 MeV) have been investigated with the use of an intenseC beam and a windowless andHe recirculating gas target system. The measurements involved two large NaI(T1) crystals in close geometry to an extended gas target, whereby angle-integrated γ-ray yields were obtained. A large area plastic detector was used for the suppression of time-independent background. A search for cascade γ-ray transitions was carried out by coincidence techniques. The measurement of absolute cross sections is also reported. Theoretical fits of the excitation function for the groundstate γ-ray transition require E1 as well as E2 capture amplitudes, which are of equal importance at stellar energies. This result increases significantly the stellar burning rate ofHe(C, γ)O and leads toO as the dominant product at the end of helium burning in massive stars. The observed capture yield to the 6.92 MeV state is dominated by the direct capture mechanism and plays a small role at stellar energies. [ABSTRACT FROM AUTHOR]

The capture reactionHe(α, γ)Be has been investigated in the energy range of E =107 to 1,266 keV. TheHe orHe beams of up to 300 μA particle current were incident onHe orHe gas targets, respectively. The gas target systems were all of the windowless and recirculating type. Excitation functions have been obtained with the use of an extended-static gas target, while the measurements of γ-ray angular distributions involved a quasi-point supersonic jet system. The determination of absolute cross sections has been carried out with both types of gas target systems. The γ-ray yields in theHe( α, γ)Be reaction were detected using 80 cm Ge(Li) detectors. The data lead to a zero-energy intercept of the astrophysical S( E) factor of S(0)=0.30±0.03 keV-b. This result reduces the calculated solar neutrino rate by a factor of 1.76. [ABSTRACT FROM AUTHOR]

The reactionMg( p, γ)Al has been investigated at E(lab)=80-355 keV. The existence of the resonances at E=292 and 338 keV has been verified and new resonances were found at E=227 and 275 keV. Information on branching and mixing ratios, ωγ values, total widths, and J assignments for the observed resonances is given. Upper limits on the ωγ strengths for expected resonances in the energy range covered are presented. The astrophysical aspects of the data are discussed in the light of theMg(Al) isotopic anomaly. [ABSTRACT FROM AUTHOR]

The reactionMg( p,γ)Al has been investigated at E(lab)=80-350keV. The existence of the resonance at E=317keV has been verified and new resonances have been found at E=198, 255 and 304 keV. The E = 304keV resonance represents a new compound state inA1. Information on branching ratios, Ωγ values, total widths and J assignments for the observed resonances as well as upper limits on the my strengths for the expected resonances at E=97 and 134 keV are given. The astrophysical aspects of the data are discussed in the light of the renewed interest in the precise location ofA1 nucleosynthesis. [ABSTRACT FROM AUTHOR]

Nuclear levels ofMg near and above the proton threshold were investigated with high resolution. A new level has been identified at 7.643 MeV (66 keV above the proton threshold) with a possible J=(3/2, 5/2). Some other spin-parity and excitation-energy assignments are also made. These results enable the reaction rate estimate ofNa(p,γ)Mg with much smaller uncertainties, which is critical for the Ne-E problem in nuclear astrophysics. [ABSTRACT FROM AUTHOR]