Thermal vacancies and phase separation in bcc mixtures of helium-3 and helium-4

Thesis/Dissertation · Tue Jan 01 00:00:00 EST 1980

DOI:https://doi.org/10.2172/5583333· OSTI ID:5583333

Fraass, Benedick Andrew ^[1]

---

1. Univ. of Illinois, Urbana-Champaign, IL (United States). Dept. of Physics

Thermal vacancy concentrations in crystals of ³He-⁴He mixtures have been determined. A new x-ray diffractometer-position sensitive detector system is used to make measurements of the absolute lattice parameter of the helium crystals with an accuracy of 300 ppM, and measurements of changes in lattice parameters to better than 60 ppM. The phase separation of the concentrated³He-⁴He mixtures has been studied in detail with the x-ray measurements. Vacancy concentrations in crystals with 99%, 51%, 28%, 12%, and 0% ³He have been determined. Phase separation has been studied in mixed crystals with concentrations of 51%, 28%, and 12% ³He and melting pressures between 3.0 and 6.1 MPa. The phase separation temperatures determined in this work are in general agreement with previous work. The pressure dependence of T_c, the phase separation temperature for a 50% mixture, is found to be linear: dT_c/dP = -34 mdeg/MPa. The x-ray measurements are used to make several comments on the low temperature phase diagram of the helium mixtures.

• Research Organization: Univ. of Illinois at Urbana-Champaign, IL (United States)
• Sponsoring Organization: USDOE Office of Science (SC)
• DOE Contract Number: EY-76-C-02-1198
• OSTI ID: 5583333
• Report Number(s): DOE/ER/01198-1296; TRN: 80-005106
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
HELIUM
LATTICE PARAMETERS
PHASE TRANSFORMATIONS
VACANCIES
CALIBRATION
HELIUM 3
HELIUM 4
POSITION SENSITIVE DETECTORS
SOLIDS
STRAIN GAGES
THERMODYNAMIC PROPERTIES
THERMOMETERS
CRYOGENIC FLUIDS
CRYSTAL DEFECTS
CRYSTAL STRUCTURE
ELEMENTS
EVEN-EVEN NUCLEI
EVEN-ODD NUCLEI
FLUIDS
HELIUM ISOTOPES
ISOTOPES
LIGHT NUCLEI
MEASURING INSTRUMENTS
NONMETALS
NUCLEI
PHYSICAL PROPERTIES
POINT DEFECTS
RADIATION DETECTORS
RARE GASES
STABLE ISOTOPES
360102* - Metals & Alloys- Structure & Phase Studies