{"id":{"repo_id":"uiuc","oai_identifier":"oai:www.ideals.illinois.edu:2142/23861"},"canonical_url":"https://search.dev.ndltd.org/etd/uiuc/oai:www.ideals.illinois.edu:2142/23861","repository":{"repo_id":"uiuc","name":"University of Illinois - Urbana-Champaign","base_url":"https://www.ideals.illinois.edu/oai-pmh"},"display":{"title":"Thermal vacancies in hcp helium-4","abstract":"Activation energies of thermal vacancies have been determined in hcp 4He as a function of molar volume. A sensitive strain gauge was used to measure the temperature dependence of the pressure in twenty crystals between 18.17 and 20.9 cm3/mole. Absolute lattice parameters at low temperatures were measured for many of these crystals. The temperature dependence of the relative lattice parameter was measured in selected crystals. This provided lower bounds on the vacancy activation energy. The activation energies determined here agree at all reported molar volumes with those from previous measurements of pressure in hcp 4He. The lower bounds on the activation energies from the relative lattice parameter measurements are consistent with those determined from the pressure. Below 20 cm3/mole the activation energies reported here are in disagreement with those from ion mobility, NMR, and plastic deformation experiments. The determination of vacancy activation energies from the measured pressure requires knowledge of the phonon pressure. Difficulties with the present understanding of the phonon pressure are discussed.","abstract_html":"Activation energies of thermal vacancies have been determined in hcp 4He as a function of molar volume. A sensitive strain gauge was used to measure the temperature dependence of the pressure in twenty crystals between 18.17 and 20.9 cm3/mole. Absolute lattice parameters at low temperatures were measured for many of these crystals. The temperature dependence of the relative lattice parameter was measured in selected crystals. This provided lower bounds on the vacancy activation energy. The activation energies determined here agree at all reported molar volumes with those from previous measurements of pressure in hcp 4He. The lower bounds on the activation energies from the relative lattice parameter measurements are consistent with those determined from the pressure. Below 20 cm3/mole the activation energies reported here are in disagreement with those from ion mobility, NMR, and plastic deformation experiments. The determination of vacancy activation energies from the measured pressure requires knowledge of the phonon pressure. Difficulties with the present understanding of the phonon pressure are discussed.","abstract_has_math":false,"creators":["Thorpe, John Clifton"],"institution":null,"degree_name":"Ph.D.","degree_level":"Dissertation","degree_discipline":"Physics","degree_department":null,"school":null,"contributors":["Simmons, R.O."],"advisors":[],"committee_chairs":[],"committee_members":[],"year":2011,"date_issued":"2011-05-10T14:58:46Z","date_published":"2011-05-10T14:58:46Z","updated_at":"2026-07-22T22:25:22Z","subjects":["thermal vacancies","hcp helium","phonon pressure"],"languages":["en"],"rights":["1991 John Clifton Thrope"],"rights_urls":[],"identifier_entries":[{"key":"dc:identifier","label":"Identifier","values":["3476222"],"render_values":[{"text":"3476222","href":null,"code":true}]}]},"links":{"outbound_url":"http://hdl.handle.net/2142/23861","outbound_label":"Handle","outbound_source":"dc:identifier"},"metadata_groups":[{"id":"people","label":"People","entries":[{"key":"dc:contributor","label":"Contributor","values":["Simmons, R.O."]},{"key":"dc:creator","label":"Author","values":["Thorpe, John Clifton"]}]},{"id":"academic_context","label":"Academic Context","entries":[{"key":"dc:date","label":"Dc Date","values":["2011-05-10T14:58:46Z","10000-01-01","1991"]},{"key":"dc:type","label":"Dc Type","values":["Dissertation / Thesis","text"]},{"key":"thesis:degree_discipline","label":"Discipline","values":["Physics"]},{"key":"thesis:degree_level","label":"Degree Level","values":["Dissertation"]},{"key":"thesis:degree_name","label":"Degree Name","values":["Ph.D."]}]},{"id":"subjects_keywords","label":"Subjects and Keywords","entries":[{"key":"dc:subject","label":"Dc Subject","values":["thermal vacancies","hcp helium","phonon pressure"]}]},{"id":"language_rights","label":"Language and Rights","entries":[{"key":"dc:language","label":"Dc Language","values":["en"]},{"key":"dc:rights","label":"Dc Rights","values":["1991 John Clifton Thrope"]}]},{"id":"identifiers","label":"Identifiers","entries":[{"key":"dc:identifier","label":"Identifier","values":["3476222","http://hdl.handle.net/2142/23861"]}]},{"id":"additional","label":"Additional Metadata","entries":[{"key":"dc:description","label":"Description","values":["Activation energies of thermal vacancies have been determined in hcp 4He as a function of molar volume. A sensitive strain gauge was used to measure the temperature dependence of the pressure in twenty crystals between 18.17 and 20.9 cm3/mole. Absolute lattice parameters at low temperatures were measured for many of these crystals. The temperature dependence of the relative lattice parameter was measured in selected crystals. This provided lower bounds on the vacancy activation energy. The activation energies determined here agree at all reported molar volumes with those from previous measurements of pressure in hcp 4He. The lower bounds on the activation energies from the relative lattice parameter measurements are consistent with those determined from the pressure. Below 20 cm3/mole the activation energies reported here are in disagreement with those from ion mobility, NMR, and plastic deformation experiments. The determination of vacancy activation energies from the measured pressure requires knowledge of the phonon pressure. Difficulties with the present understanding of the phonon pressure are discussed.","Submitted by Carolyn Mead (cmead2@illinois.edu) on 2011-05-10T14:58:46Z No. of bitstreams: 1 1991_thorpe.pdf: 5929111 bytes, checksum: dc81626d472c121dc925a216a8b19a4c (MD5)","Made available in DSpace on 2011-05-10T14:58:46Z (GMT). No. of bitstreams: 1 1991_thorpe.pdf: 5929111 bytes, checksum: dc81626d472c121dc925a216a8b19a4c (MD5) Previous issue date: 1991","Item marked as restricted to the 'UIUC Users [automated]' Group (id=2) by Carolyn Mead (cmead2@illinois.edu) on 2011-05-10T14:58:46Z Item is restricted indefinitely.","Restriction data tranferred 2014-07-01T11:12:34-05:00 Original Data Group with Access UIUC Users [automated] Release Date: none Reason: Thesis","Thesis","U of I Only"]},{"key":"dc:title","label":"Title","values":["Thermal vacancies in hcp helium-4"]}]}],"canonical_facts":{"dc:contributor":["Simmons, R.O."],"dc:creator":["Thorpe, John Clifton"],"dc:date":["2011-05-10T14:58:46Z","10000-01-01","1991"],"dc:description":["Activation energies of thermal vacancies have been determined in hcp 4He as a function of molar volume. A sensitive strain gauge was used to measure the temperature dependence of the pressure in twenty crystals between 18.17 and 20.9 cm3/mole. Absolute lattice parameters at low temperatures were measured for many of these crystals. The temperature dependence of the relative lattice parameter was measured in selected crystals. This provided lower bounds on the vacancy activation energy. The activation energies determined here agree at all reported molar volumes with those from previous measurements of pressure in hcp 4He. The lower bounds on the activation energies from the relative lattice parameter measurements are consistent with those determined from the pressure. Below 20 cm3/mole the activation energies reported here are in disagreement with those from ion mobility, NMR, and plastic deformation experiments. The determination of vacancy activation energies from the measured pressure requires knowledge of the phonon pressure. Difficulties with the present understanding of the phonon pressure are discussed.","Submitted by Carolyn Mead (cmead2@illinois.edu) on 2011-05-10T14:58:46Z No. of bitstreams: 1 1991_thorpe.pdf: 5929111 bytes, checksum: dc81626d472c121dc925a216a8b19a4c (MD5)","Made available in DSpace on 2011-05-10T14:58:46Z (GMT). No. of bitstreams: 1 1991_thorpe.pdf: 5929111 bytes, checksum: dc81626d472c121dc925a216a8b19a4c (MD5) Previous issue date: 1991","Item marked as restricted to the 'UIUC Users [automated]' Group (id=2) by Carolyn Mead (cmead2@illinois.edu) on 2011-05-10T14:58:46Z Item is restricted indefinitely.","Restriction data tranferred 2014-07-01T11:12:34-05:00 Original Data Group with Access UIUC Users [automated] Release Date: none Reason: Thesis","Thesis","U of I Only"],"dc:identifier":["3476222","http://hdl.handle.net/2142/23861"],"dc:language":["en"],"dc:rights":["1991 John Clifton Thrope"],"dc:subject":["thermal vacancies","hcp helium","phonon pressure"],"dc:title":["Thermal vacancies in hcp helium-4"],"dc:type":["Dissertation / Thesis","text"],"thesis:degree_discipline":["Physics"],"thesis:degree_level":["Dissertation"],"thesis:degree_name":["Ph.D."]},"updated_at":"2026-07-22T22:25:22Z"}