Abstract
In this thesis a new method for the unfolding of γ-ray spectra using Bayesian statistics has been investigated. The method in question goes by the name Fully Bayesian Unfolding. By making use of Bayes’ theorem the method samples from a likelihood function and prior distribution to achieve a posterior distribution for each energy-bin of the spectrum. The γ-ray spectra are obtained from experiments at the Oslo Cyclotron Laboratory with OSCAR an array of LaBr3 :Ce scintillator detectors and SiRi a particle telescope. The reaction chosen to test the method was the 28Si(p,p'γ) reaction. The new FBU method was compared to the iterative unfolding method that was developed and is currently used for unfolding in the Oslo nuclear physics group. In addition, the iterative unfolding method is a well known unfolding method used in nuclear physics research outside of the Oslo nuclear physics group. The motivation of the study is to extract the uncertainty from the unfolding method. These uncertainties can be propagated into further analysis such as the Oslo-Method or others. In addition the iterative unfolding method can suffer from negative fluctuations. Using Bayesian unfolding prevents this since the priors can have lower bounds set to zero, thus only the positive solutions are presented in the outcome. The Fully Bayesian Unfolding was found to deliver on these terms both giving reasonable uncertainty estimates and give a stable solutions for the γ-ray spectra tested in this work. The main source of discrepancy was found in the threshold region ([0, 160] keV), which in turn seems to have an effect on the re-distribution of counts to the γ-ray peaks. The discrepancy was decreased for the FBU when including the background into the unfolding. Since the raw spectra are zero in this region the only effect in this area can be from the response matrix. The response matrix was made under different conditions than the experiment tested in this thesis, and is still a work in progress. The total efficiency of OSCAR has not been fully established either and was estimated using the geometric efficiency. There is uncertainty in the total efficiency assumed in this thesis and it can also have an affect on the discrepancies seen in the unfolded spectrum.