Science
Analysis of the CCD camera
There are only a few methods in determining the current of the incoming beam throughout a run. The primary method being used involves analyzing the data received from the elastic monitors and observing how the counts fluctuate with time. As the elastic monitors have been known to be unreliable, alternative methods of determining beam current are needed. A CCD camera has recently been installed in DRAGON, which looks upstream towards the gas target. The reaction between the incoming beam and the gas target creates a small light output, which the camera is able to capture. The main function of the camera has been to help ensure that the beam is centered through the target, but as the camera also produces data that represents light intensity, it can be used to track the current of the incoming beam.
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Calibration of the DRAGON DSSSD end detector
The double sided silicon strip detector, or DSSSD, a position sensitive, segmented semi-conductor diode detector, is one of the options commonly used as an end detector at the DRAGON facility1. This detector, often used in conjunction with another detector, such as an MCP (micro-channel plate) can offer a wealth of information during experiments, including the number and energy of particles detected, as well as positional information, and when used in tandem with another detector, local timing information.
The DSSSD consists of 16 front strips orthogonal to 16 back strips, which creates a pixilated detection surface, allowing position information to be extracted for each particle incident on the detector. However, since each strip uses its own electronics, an important step before the detector can be used in an experiment is calibration to ensure all channels (adc and tdc channels) are gain and offset matched, as well as energy calibrated.
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GEANT Simulations of DRAGON and the 12C(12C, γ)24Mg Reaction
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.
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Gamma radiation spectroscopy and the 12C(α,γ)16O reaction with DRAGON
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.
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