Reports

The ²¹Ne(p, γ) reaction has been carried out a few times at the DRAGON facility with the intent of calculating the resonant strength of the reaction. Two known resonant center of mass energies have been used for this reaction, that of 731.5 keV and 258 keV, but only the latter energy will be discussed here. This reaction was analyzed in Sabine Engel’s thesis, but a few problems were discovered that lead to the need to re-examine the data. These problems will be discussed later. This report will begin with the analysis of the most recent runs carried out with this reaction, and then will re-examine some old data that was analyzed in Sabine’s thesis.

kathrynreport1.pdf

Author: Oraas, K.

Journal:

The ²⁶Al(ρ,γ)²⁷Si reaction has begun at DRAGON, the Detector of Recoils And Gammas Of Nuclear reactions. The experiment is done in inverse kinematics, meaning an aluminum ion produced and accelerated is incident on a hydrogen gas target. The resulting mix of beam ions and ²⁷Si then moves through the DRAGON, which separates the two, allowing silicon recoils to hit the end detectors.

In order to suppress the leaky beam incident of the end detectors, a coincidence measurement is made. For the ²⁶Al(ρ,γ) experiment, however, futher methods of suppression were examined. An ion chamber was used to aid in element separation, and suppression were examined. In order to understand these options, a number of simulations were completed. Also of importance to the experiment was an understanding of the composition of the incoming beam. Certain contaminents of mass 26 were expected to be present in the beam, notably magnesium, sodium and a metastable state of aluminum which would not react in the same way as the ground state. New hardware and analysis was required to look for these contaminents. Also, some programs were written in FORTRAN to aid with the data analysis.

The reaction is of astrophysical interest as ²⁶Al decays via a characteristic gamma-ray which can be readily observed. The ²⁶Al(ρ,γ)²⁷Si reaction is the only direct ²⁶Al destruction process besides β-decay. The reaction rate is currently known to within a factor of four, far from the 20% uncertainties required for consistent astrophysical modelling. Of increasing interest is the extent of ²⁶Al in explosive stellar environments, such as novae and supernovae, environments which the DRAGON facility was made to examine.

In this report, a brief overview of DRAGON will be given, then the results of the various simulations and contamination measurements, and, finally, some preliminary results from the experiment.

mikea.pdf

Author: Andeson, M.

Journal:

GEANT simulations of DRAGON and the radiative capture 12C(12C,γ) reaction were performed to understand the acceptance efficiencies and BGO response. Significant changes to both the real DRAGON and the simulated DRAGON had to be made: target cell changes for the solid target experiments, and collimator and pumping tube changes for better recoil detection. A new HBOOK ntuple, GAMMAHIT, was added to existing DRAGON simulations for more detailed analysis. Recoil acceptance was calculated to be 42.8% and 8.6% for cascade decays of two 10 MeV gammas and single decays of one 20 MeV gamma, respectively. Differentiating between the two decay paths will be possible with the BGO detector array.

joshreport.pdf

Author: Slater, J.

Journal:

The astrophysically important ¹²C(α,γ)¹⁶O reaction was recently re-enacted at TRIUMF using DRAGON. In this reaction a 12C nuclei fuses with an alpha particle to form ¹⁶O. Gamma rays are produced during the 16O decay, and these were detected by an array of 30 hexagonal BGO scintillation detectors. The purpose of this project was to devise a method of identifying and quantifying the discrete components of the gamma radiation using the resulting gamma spectra. The devised method involves identifying potential ¹⁶O decay paths and the discrete set of gamma energies associated with these paths, generating detector response functions for gamma radiation of these energies, and fitting a linear combination of these response functions to the experimental spectra. The fit coefficients represent the relative strengths of the contributions of each discrete component to the total spectrum. The method was tested on data taken at the 10.356 MeV resonance, at which ¹⁶O is known to decay solely through the 6.917 MeV state. Knowing this, two potential decay paths were assumed, these being cascade decay through the 6.917 MeV and decays through closely spaced states. The test was not successful, and the conclusion is that the method is very sensitive to detector gains and, lacking more accurate information about these gains, the devised methos cannot be used to distinguish between gammas so close in energy. The next step in this project must be an effort to better determine detector gains.

galt_report.pdf

Author: Galt, C. J.

Journal:

A facility for measuring cross-sections (resonance strengths) for reactions of astrophysical importance involving short-lived, radioactive reactants has been designed, built and installed at the new TRIUMF-ISAC Radioactive Beams Laboratory in Canada. Named DRAGON (Detector of Recoils And Gammas of Nuclear reactions), it has been successfully commissioned with stable and radioactive heavy ion beams from ISAC. This report presents the main components of the facility, namely, the windowless gas target, the surrounding ϒ detector array, the subsequent electromagnetic recoil mass separator, the focal plane detectors for recoils, the detection system for elastics, and the modular electronics and computer software used for the data acquisition. Examples of the operation of the facility for both stable beam reactions and the first radioactive beam reaction study, ²¹Na(ρ,ϒ)²²Mg are also presented, along with future plans for the program.

hutcheon.pdf

Author: Hutcheon, D. A. et al.

Journal: Nuclear Instruments and Methods in Physics Research A