Development of Cryogenic Detector for Radioactivity Measurement

Abstract

Cryogenic detectors, which measure the temperature change due to absorption of energy at low temperatures typically below 100 mK, have made breakthroughs in particle detections in many aspects of science. In spite of their outstanding sensitivities and versatile performances, cryogenic detection technique has not yet well established in Korea. In the present thesis, an effort of developing cryogenic detectors particularly using a metallic magnetic calorimeter (MMC) is introduced. The temperature sensor of an MMC is made of dilute concentration of paramagnetic material in a metallic host. Its magnetization is a function of temperature in an applied magnetic field. The change of magnetization resulted from absorption of energy is measured by a dc-SQUID. A small piece of Au:Er was used as the sensor material. The first MMC result in Korea was measured with a use of an 55Fe X-ray source. An energy resolution of 26 eV in FWHM was achieved for 5.9 keV X-rays, which is nearly one order of magnitude better than that of a conventional Si(Li) detector. Moreover, the absolute measurement of 241Am activity was carried out with the source entirely enclosed by gold foils forming a 4π-geometry and the MMC attached to the foil. The absolute radioactivity of two different 241Am was measured. The energy resolution was 93 keV in FWHM for 5486 keV alpha particles.