Green and red scintillator crystals with plastic fiber optics were used to investigate their application as optical fiber dosimeters. In Part 1, the radiation beam is perpendicular to the system with 20x20cm2 half field. We have a linear response for both systems with doubling the MU starting from 1MU up to 1024MU. Here we define the SOBR (Signal to Optical Background Ratio) to be the response of total signal (crystal and fiber) divided by the background (fiber) signal. The SOBR of red and green with no filter were 16.58 and 17.74 respectively. When we added the filter, the SOBR for red and green became 11.03 and 66.72 respectively. In Part 2, we changed the field to X=1cm, Y1=5cm and Y2=1cm. The SOBR for red and green with no filter are 44.43 and 45.47. After we added the filter, the SOBR for red and green became 15.62 and 1684. This change in field shape gave us a higher SOBR, especially when the filter was added. In Part 3, we tested the angular response of our detector. Both systems increased their response when gantry angle reach 45° and -45° (315°). When the filter was added, a change of a factor of 2 in response remained. When the crystal was then rotated and pointed in the direction of the gantry, good response was obtained from range 90° to -90° (270°). The response of green system was within 2.5%. For the red system, a large step about 10% was observed. Conversion of the fiber fluorescence and Cerenkov radiation in the scintillator crystal and transmission to the detector is a problem in all optical fiber systems, including the dual fiber system, that remains to be addressed.

Green and red scintillator crystals with plastic fiber optics were used to investigate their application as optical fiber dosimeters. In Part 1, the radiation beam is perpendicular to the system with 20x20cm2 half field. We have a linear response for both systems with doubling the MU starting from 1MU up to 1024MU. Here we define the SOBR (Signal to Optical Background Ratio) to be the response of total signal (crystal and fiber) divided by the background (fiber) signal. The SOBR of red and green with no filter were 16.58 and 17.74 respectively. When we added the filter, the SOBR for red and green became 11.03 and 66.72 respectively. In Part 2, we changed the field to X=1cm, Y1=5cm and Y2=1cm. The SOBR for red and green with no filter are 44.43 and 45.47. After we added the filter, the SOBR for red and green became 15.62 and 1684. This change in field shape gave us a higher SOBR, especially when the filter was added. In Part 3, we tested the angular response of our detector. Both systems increased their response when gantry angle reach 45° and -45° (315°). When the filter was added, a change of a factor of 2 in response remained. When the crystal was then rotated and pointed in the direction of the gantry, good response was obtained from range 90° to -90° (270°). The response of green system was within 2.5%. For the red system, a large step about 10% was observed. Conversion of the fiber fluorescence and Cerenkov radiation in the scintillator crystal and transmission to the detector is a problem in all optical fiber systems, including the dual fiber system, that remains to be addressed.

Blowfish is a highly segmented neutron detector array consisting of 88 cells filled with BC-505 liquid scintillator. <p>The cells make up a spherical shape that covers approximately one quarter of the total solid angle of 4 pi steradians.<p> A high-priority measurement for Blowfish is the low energy contribution to the Gerasimov-Drell-Hearn (GDH) sum rule on the deuteron, which uses circularly polarized gamma rays. <p>The experimental data that needs to be collected are the absolute cross-sections when the gamma ray helicity and target polarization are parallel and anti-parallel. To extract absolute cross-sections from the data, it will be necessary to have characterized the efficiency of the detector.<p>Another measurement that would benefit from the efficiency calibration is the photodistegration of deuterium, which has already been performed. This measurement used linearly-polarized gamma rays at energies of 2.6, 3.5, 4.0 and 6.0 MeV. The relative cross-sections from this measurement provide much useful information, but to extract the absolute cross-sections the Blowfish efficiency calibration is needed. This thesis presents this efficiency calibration. <p> The efficiency calibration was done using a 252Cf source in a parallel plate ionization chamber over the energy range of 0 to 6 MeV. <p>To determine the absolute scale of the extracted efficiency curves, an efficiency analysis and simulation of a previously characterized BC-519 liquid scintillator cell needed to be performed along with a simulation of the Blowfish detector array. <p>The measured efficiencies were consistent with those predicted by the simulation over the desired energy range.

Blowfish is a highly segmented neutron detector array consisting of 88 cells filled with BC-505 liquid scintillator. <p>The cells make up a spherical shape that covers approximately one quarter of the total solid angle of 4 pi steradians.<p> A high-priority measurement for Blowfish is the low energy contribution to the Gerasimov-Drell-Hearn (GDH) sum rule on the deuteron, which uses circularly polarized gamma rays. <p>The experimental data that needs to be collected are the absolute cross-sections when the gamma ray helicity and target polarization are parallel and anti-parallel. To extract absolute cross-sections from the data, it will be necessary to have characterized the efficiency of the detector.<p>Another measurement that would benefit from the efficiency calibration is the photodistegration of deuterium, which has already been performed. This measurement used linearly-polarized gamma rays at energies of 2.6, 3.5, 4.0 and 6.0 MeV. The relative cross-sections from this measurement provide much useful information, but to extract the absolute cross-sections the Blowfish efficiency calibration is needed. This thesis presents this efficiency calibration. <p> The efficiency calibration was done using a 252Cf source in a parallel plate ionization chamber over the energy range of 0 to 6 MeV. <p>To determine the absolute scale of the extracted efficiency curves, an efficiency analysis and simulation of a previously characterized BC-519 liquid scintillator cell needed to be performed along with a simulation of the Blowfish detector array. <p>The measured efficiencies were consistent with those predicted by the simulation over the desired energy range.

No description available.

The SNO+ experiment is a multi-purpose neutrino detector which is under construction in the SNOLAB facility in Sudbury, Ontario. SNO+ will search for neutrinoless double beta decay, and will measure low energy solar neutrinos. This thesis will describe three main development activities for the SNO+ experiment: the measurement of the timing parameters for the liquid scintillator cocktail, using those timing parameters to estimate the ability of SNO+ to discriminate alpha and beta events in the detector, and a sensitivity study that examines how solar neutrino data can constrain a light sterile neutrino model. Characterizing the timing parameters of the emission light due to charged-particle excitation in the scintillator is necessary for proper reconstruction of events in the detector. Using data obtained from a bench-top setup, the timing profile was modelled as three exponential components with distinct timing coefficients. Also investigated was the feasibility of using the timing profiles as a means to separate alpha and beta excitation events in the scintillator. The bench-top study suggested that using the peak-to-total method of analyzing the timing profiles could remove >$99.9% of alpha events while retaining >$99.9% of beta events. The timing parameters measured in the test set-up were then implemented in a Monte Carlo code which simulated the SNO+ detector conditions. The simulation results suggested that detector effects reduce the effectiveness of discriminating between alpha and beta events using the peak-to-total method. Using a more optimal method of analyzing the timing profile differences, specifically using a Gatti filter, improved the discrimination capability back to the levels determined in the bench-top setup. One of the physics goals of SNO+ is the first precision measurement of the pep solar neutrino flux at the level of about 5% uncertainty. A study was performed to investigate how current solar neutrino data constrains the allowed parameters of a light 3+1 sterile neutrino model. The impact of adding a SNO+ pep solar neutrino measurement on the allowed parameters of the sterile model was then examined. / Thesis (Ph.D, Physics, Engineering Physics and Astronomy) -- Queen's University, 2014-04-28 20:52:42.41

Giant Resonances (GR) are the broad resonances that occur at excitation energies between 10 and 30 MeV. They correspond to the collective motion of nucleons within the nucleus. The GR modes can be classified according to their multipolarity L, spin S and isospin T quantum numbers. In the microscopic description, the GR modes can be understood as the collective particle-hole excitations characterized by certain values of the angular momentum and parity (Jπ), orbital momentum, spin, and isospin. The Giant Monopole Resonance (GMR) is interesting because its excitation energy is directly related to the incompressibility of the nucleus KA. KA can be used to derive the incompressibility of nuclear matter KNM, but this extrapolation from the data for real nuclei is not straightforward due to contributions from surface, Coulomb and asymmetry effects. Thus, improvements to the extrapolated KNM can be made by measuring the GMR for increasing (N-Z)/A. The incompressibility of nuclear matter is of importance in the nuclear equation of state (EOS) which describes a number of phenomena: collective excitations of nuclei, supernova explosions and radii of neutron stars. In order to study the Isoscalar Giant Monopole Resonance in unstable nuclei, a ΔE-ΔE-E decay detector composed of plastic scintillator arrays has been built and tested. The measurement of the ISGMR in unstable nuclei will be done using inverse kinematics, with a 40 MeV per nucleon beam of the unstable nucleus incident on a 6Li target. Xinfeng Chen studied the viability of this approach, taking data for elastic scattering and inelastic scattering to low-lying states and giant resonances of 240 MeV 6Li ions on 24Mg, 28Si, and 116Sn. Nuclei excited to the GMR region are particle unstable, and will decay by p, α or n decay shortly after excitation. To reconstruct the event it is necessary to measure the energy and angle of the decay particle and of the residual heavy ion. In many lighter nuclei a few nucleons off stability, and in light proton rich nuclei, the neutron threshold is above the region of interest.

The growing interest towards polysiloxane-based radiation detection systems is related with the several advantages that polysiloxanes offer in comparison with other state-of-the-art plastic materials used in scintillation, like polyvinyltoluene and polystyrene. In this respect, polysiloxane elastomers offer higher thermal stability, flexibility and radiation hardness than the traditional plastic counterpart. For this reason, the study of polysiloxane-based systems for the detection of several types of radiation such as neutrons, high-energy photons and charged particles has recently received increasing attention by the scientific community. In this thesis, we report the current advances on both organic and hybrid polysiloxane-based radiation detection systems for scintillation and passive dosimetry applications. In this framework, we will start from the recent advances on organic polysiloxane-based scintillators for the detection of fast neutrons, with particular emphasis on their pulse-shape discrimination capabilities, allowing for the distinction of neutrons from the γ-ray background. The other and main part of the thesis will be then dedicated to hybrid nanostructured polysiloxane-based radiation detection systems. In this context, latest progress on polysiloxane scintillators embedding 6LiF nanocrystals for thermal neutron detection will be presented, with particular focus on the role of the nanocrystal size and dispersion in the detection performances. Subsequently, polysiloxane/quantum dots nanocomposites will be investigated for their possible use in both scintillation and passive dosimetry. In this latter application, the optical properties of the samples are analyzed after irradiation, with the aim to correlate the radiation-induced effects with the radiation dose. Lastly, the role of the polymer matrix in the post-irradiation optical response of the nanocrystals will be investigated.

No description available.

This thesis is part of a project focusedon investigating the possibility ofmeasuring void distributions usingtransmission tomography with fastneutrons. The measurements are plannedto be conducted at thermal hydraulictest loops. The project, called STUNT,is carried out at Uppsala University atthe division for applied nuclearphysics.The purpose of this work was to designand optimize a detection system for thedetection of fast neutrons in the abovementioned environment. For this purpose,detector elements consisting of theplastic scintillator material EJ208 wasmodeled using the particle transportcode MCNPX.Both plate shaped elements and fibers ofdifferent dimensions where tested forperformance.Through a comparison utilizing severalfigures of merit and MATLAB, the plateshape was selected with an element widthof 2.6 mm. During the optimizationprocess a possible detector design with73 detector plates was chosen. At anenergy threshold of 11 MeV the followingdesign parameters were found; adetection efficiency of 3.0 %, a signalto background ratio of 15, a totalmeasurement time of 3600 s and a pixelresolution of 1.4 mm.A point spread function was produced andtwo projection tests where conductedusing a water filled steel cylinder asobject. / STUNT