Development of an alpha-particle imaging detector based on a low radioactivity micro-time-projection chamber

Abstract An important issue for rare-event-search experiments, such as the search for dark matter or neutrinoless double beta decay, is to reduce radioactivity of the detector materials and the experimental environment. The selection of materials with low radioactive impurities, such as isotopes of the uranium and thorium chains, requires a precise measurement of surface and bulk radioactivity. Focused on the first one, an alpha- particle detectorhas been developed based on a gaseous micro- time-projection chamber. A low- α μ -PIC with reduced alpha-emission background was installed in the detector. The detector offers the advantage of position sensitivity, which allows the alpha-particlecontamination of the sample to be imaged and the background to be measured at the same time. The detector performance was measured by using an alpha-particlesource. The measurement with a sample was also demonstrated and the sensitivity is discussed.