Allison O’Brien Rose Hills
Characterizing Photomultiplier Tube Nonlinearity for Radiation Detection
In the radiological sciences, photomultiplier tubes (PMTs) are often used for measuring scintillation, light emitted from certain materials in the presence of radiation. For example, the neutron response of organic scintillating materials is currently being measured at LBNL using photomultiplier tubes. When incident neutron radiation strikes an organic scintillator, the fast neutrons interact with the nuclei present, primarily through elastic scattering. The recoiling nuclei move through the medium causing excitation and ionization of the scintillating molecules. These molecules de-excite through the emission of light and this light can then be measured with a PMT. Ideally, PMTs would behave linearly–where the current output they produce is proportional to the light input. However, in certain operating regimes, such as at low bias voltage, previous measurements have shown nonlinearity of the PMT response. Thus, to effectively use a PMT in radiation detection measurements, one must first understand its response. Given current limitations on lab work, my plan is to develop diagnostic software to further refine our nonlinearity measurement workflow using my existing data sets.