G. Ruprecht

Measurement of two-halo neutron transfer reaction p(

The p(\nuc{11}{Li},\nuc{9}{Li})t reaction has been studied for the first time at an incident energy of 3

^{11}

A

Li,

MeV delivered by the new ISAC-2 facility at TRIUMF. An active target detector MAYA, build at GANIL, was used for the measurement. The differential cross sectionshave been determined for transitions to the \nuc{9}{Li} ground andthe first excited states in a wide range of scattering angles. Multistep transfer calculations using different \nuc{11}{Li} model wave functions, shows that wave functions with strong correlations between the halo neutrons are the most successful in reproducing the observation.

^{9}

The p(\nuc{11}{Li},\nuc{9}{Li})t reaction has been studied for the first time at an incident energy of 3

Li)t at 3

A

A

MeV delivered by the new ISAC-2 facility at TRIUMF. An active target detector MAYA, build at GANIL, was used for the measurement. The differential cross sectionshave been determined for transitions to the \nuc{9}{Li} ground andthe first excited states in a wide range of scattering angles. Multistep transfer calculations using different \nuc{11}{Li} model wave functions, shows that wave functions with strong correlations between the halo neutrons are the most successful in reproducing the observation.

MeV

The 15 O(α, γ) 19 Ne reaction plays a role in the ignition of type I x-ray bursts on accreting neutron stars. The lifetimes of states in 19 Ne above the 15 O+α threshold of 3.53 MeV are important inputs to calculations of the astrophysical reaction rate. These levels in 19 Ne were populated in the 3 He( 20 Ne , α) 19 Ne reaction at a 20 Ne beam energy of 34 MeV. The lifetimes of six states above the threshold were measured with the Doppler-shift attenuation method. The present measurements agree with previous determinations of the lifetimes of these states and in some cases are considerably more precise.

Measurement of the Two-Halo Neutron Transfer ReactionH1(Li11,Li9)H3at3AMeV

The decay rate of 22Na implanted in aluminium has been measured at room temperature and at 10 K. The rate should increase by 40% according to Rolfs (2006 Public Lecture for SLENA (Kolkata, India)) and by about 6% according to Limata et al (2006 Eur. Phys. J. A 28 251). In the latter publication, an increase of only 1.2 ± 0.2% has been measured and the deviation has been assigned to an incomplete implantation of 22Na in the palladium sheet. Contrary, the source used for our measurements has been made by a 70 MeV proton beam penetrating an aluminum sheet, therefore the 22Na was produced deep inside the metal and the full effect should be visible when cooling the sample. We did not see an enhanced decay rate within the precision limit (0.04%) of our measurement.

Lifetimes of states in 19Ne above the 15O+α breakup threshold

The deuteron-emission channel in the beta decay of the halo nucleus (11)Li was measured at the Isotope Separator and Accelerator facility at TRIUMF by implanting postaccelerated (11)Li ions into a segmented silicon detector. The events of interest were identified by correlating the decays of (11)Li with those of the daughter nuclei. This method allowed the energy spectrum of the emitted deuterons to be extracted, free from contributions from other channels, and a precise value for the branching ratio B(d)=1.30(13)x10(-4) to be deduced for E(c.m.)>200 keV. The results provide the first unambiguous experimental evidence that the decay takes place essentially in the halo of (11)Li and that it proceeds mainly to the (9)Li+d continuum, opening up a new means to study the halo wave function of (11)Li.

On the possible influence of electron screening on the lifetime of radioactive nuclei

Directly measuring nuclear astrophysics reactions presents unique challenges. Low energy reaction products and small reaction cross sections are just two of the issues that the TACTIC detector addresses. TACTIC is the TRIUMF Annular Chamber for Tracking and Identification of Charged-particles detector being developed by TRIUMF and the University of York, UK. TACTIC is a cylindrical, active-target TPC providing high detection efficiency; a shielding cathode traps the ionization created by the beam and allows for higher intensities than typical TPCs. The 480 anode signals are collected through custom preamplifiers, digital electronics and acquisition systems. Acquisition and analysis software is also undergoing extensive development. Amplification of the small signals is accomplished using a Gas Electron Multiplier (GEM). The fill gas, He-CO2, provides both particle detection and a homogeneous, variable-thickness target for studying reactions on αs, such as 8Li(α,n)11B. A preliminary study of this flagship reaction was carried out in June 2009 and the results are providing feedback into the development of the final detector and infrastructure.