Reports
Determining DRAGON's acceptance: a Microscopic view
DRAGON measures the resonance strengths of nuclear reactions using beams from the ISAC facility, this resonance strength is fundamental in calculating the rates at which elements are created and destroyed in the interior of stars and during explosions like supernovae and novae. A key component of the resonance strength is the yield mea- surement. For an accurate measurement of the yield, various efficiency fractions must be known including the efficiency of the DRAGON mass spectrometer. This report presents measurements taken with a 148Gd α-source mounted in the gas target of DRAGON, this simulates a reaction with a cone angle of ≈ 20 mrad. A collimator is used that allows a microscopic view of particle transmission in DRAGON. Results suggest that the gas target box axis is lower than the separator axis by ≈ 2 mm, Q1’s ’standard’ setting is high by ≈ 5%, there is a possible quadrupole misalignment between the two electric dipoles of DRAGON which decreases the transmission of particles emitted to the left (looking upstream), and finally there is a possible misalignment that causes a x − y correlation at the final slits. Simulations with GEANT have been performed to test these conclusions with mixed results. Conclusions and recommendations are presented.
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DRAGON summer research report: charge state distributions after radiative capture
DRAGON Measurements of the charge-state distribution (CSD) of a 1.068 MeV/u C beam in He, and of the 6+:5+ charge-state population ratio in the recoils of the 12C(α,γ)16O reaction are reported. A computer simulation was developped to model the CSD of both beam and recoil par- ticles in inverse kinematics experiments. The code was used to model this reaction, and the results are compared to data from DRAGON and from ERNA. The simulation was in good agreement with the DRAGON data and with recoil data from ERNA. The results suggest that, for this fu- sion reaction on the Jπ=4+ resonance at Ebeam = 1.064 MeV/u, the recoil ions contain only the nucleons and not the electrons of the target He atom.
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DRAGON summer research report: differential pumping system
Constraints on the differential pumping system of the DRAGON are discussed, as are the weak- nesses in the current design. An attempt is made to improve the system, so as to allow for a 30 mrad acceptance half-angle with a 4 mm beam spot size, and the production of recoils up to 1 cm upstream from the target center. Three new designs are presented. The new systems use either the same number of pumps as the exising one or require the purchase of 1-2 new turbo pumps. The new pumping systems are around 45 cm shorter than the existing one; this extra space could be used to incorporate another magnetic quadrupole doublet or a post-stripper gas cell into the DRAGON.
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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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The 26gAl(ρ,γ)27Si Reaction at DRAGON
The astrophysically important 26gAl(p,γ)27Si radiative proton capture reaction was recently investigated using the ISAC-DRAGON facility at TRIUMF. In this experiment, an intense radioactive 26gAl beam produced at the ISAC radioactive beam facility was used in conjunction with a windowless H2 gas target at the DRAGON facility to investigate narrow resonances which are believed to dominate the rate of this reaction in explosive stellar environments such as novae and supernovae explosions. The 188 keV resonance in 27Si was investigated over a 3 week running period, during which approximately 250 runs were taken. From the data collected, the thick target yield of the reaction will be determined, which will then be used to calculate an experimental value for the resonance strength, a value that can be used in astrophysical models attempting to describe the reactions occurring in explosive stellar nucleosynthesis. The purpose of this project was to work on determining two quantities critical to the calculation of the thick target yield and resonance strength: the normalized beam particles on target over the run, and the BGO gamma array detection efficiency. Two methods of beam normalization were used and refined in the analysis of the experimental runs, and validated one another, showing agreement within 8%. BGO efficiency was evaluated using GEANT simulations for a number of different angular distributions and thresholds, to provide averaged efficiency values. Further work on incorporating angular distributions of emitted gamma radiation into the GEANT simulation is ongoing, and will improve the accuracy of efficiency calculations.
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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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