A cryogenic phonon detector to search for dark matter particles

Thesis/Dissertation · Tue Jan 01 04:00:00 EST 1991

OSTI ID:7067202

Wang, Ning

The systematic investigation of the thermal and electrical properties of neutron transmutation doped (NTD) Ge at low temperatures and the development of a detector to search for weakly interacting massive particles (WIMP's), predicted by some theories to make up to 90 percent of the matter in the universe, is presented. We have fabricated NTD Ge phonon sensors operated on a dilution refrigerator near 20 mK. The thermal and electrical properties of NTD Ge were investigated first. The zero bias resistance was found to be governed by variable range hopping, but the nonlinearity of the current-voltage characteristics indicated significant hot electron effects near 20 mK. A detailed investigation of hot-electron effects in NTD Ge is described. NTD Ge sensors were found to be very sensitive to high energy phonons generated by interactions of Ge with alpha-particles and photons. The mean absorption length of the high energy phonons in NTD Ge was found to be about 500 microns. In order to use these phonon sensors in conjunction with a target crystal, we developed a bonding technique using a Au-Ge eutectic. The bonds were found to be mechanically strong, thermally cyclable, and more transparent to high energy phonons than conventional silver-filled epoxies. The eutectic bonding technique was also found to leave the thermal and electrical properties of NTD Ge unchanged. We describe ionization signals observed in pure Ge target crystals, generated by the interaction of Ge with alpha-particles and photons; these ionization signals were observed simultaneously with phonon signals from the NTD Ge sensors. Such simultaneous signals can be used to reject unwanted background events, which is an important requirement for a WIMP detector. Finally, we describe the design and testing of a 60 g Ge detector to which six phonon sensors were attached. Simultaneous phonon and ionization signals were observed when irradiating the crystal with photons from Am-241.

• Research Organization: California Univ., Berkeley, CA (United States)
• OSTI ID: 7067202
• Country of Publication: United States
• Language: English

Related Subjects

440200* -- Radiation Effects on Instrument Components
Instruments
or Electronic Systems
46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND TECHNOLOGY
662000 -- Physics of Elementary Particles & Fields-- (1992-)
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS
ALPHA PARTICLES
BONDING
BOSONS
CHARGED PARTICLES
ELECTRICAL PROPERTIES
ELEMENTARY PARTICLES
ELEMENTS
EUTECTICS
FABRICATION
GE SEMICONDUCTOR DETECTORS
GOLD
JOINING
MASSLESS PARTICLES
MEASURING INSTRUMENTS
METALS
NUCLEAR REACTIONS
PHONONS
PHOTONS
PHYSICAL PROPERTIES
QUASI PARTICLES
RADIATION DETECTORS
SEMICONDUCTOR DETECTORS
SILVER
TEMPERATURE DEPENDENCE
TEMPERATURE RANGE
TEMPERATURE RANGE 0000-0013 K
THERMODYNAMIC PROPERTIES
TRANSITION ELEMENTS