title: Dual spectrum neutron radiography: identification of phase transitions between frozen and liquid water.
abstract: In this Letter, a new approach to distinguish liquid water and ice based on dual spectrum neutron radiography is presented. The distinction is based on arising differences between the cross section of water and ice in the cold energy range. As a significant portion of the energy spectrum of the ICON beam line at Paul Scherrer Institut is in the thermal energy range, no differences can be observed with the entire beam. Introducing a polycrystalline neutron filter (beryllium) inside the beam, neutrons above its cutoff energy are filtered out and the cold energy region is emphasized. Finally, a contrast of about 1.6% is obtained with our imaging setup between liquid water and ice. Based on this measurement concept, the temporal evolution of the aggregate state of water can be investigated without any prior knowledge of its thickness. Using this technique, we could unambiguously prove the production of supercooled water inside fuel cells with a direct measurement method.
authors.affiliation: Electrochemistry Laboratory (ECL), Paul Scherrer Institut (PSI), 5232 Villigen PSI, Switzerland.
authors.forename: J
authors.initials: J
authors.lastname: Biesdorf
authors.affiliation: Electrochemistry Laboratory (ECL), Paul Scherrer Institut (PSI), 5232 Villigen PSI, Switzerland.
authors.forename: P
authors.initials: P
authors.lastname: Oberholzer
authors.affiliation: Electrochemistry Laboratory (ECL), Paul Scherrer Institut (PSI), 5232 Villigen PSI, Switzerland.
authors.forename: F
authors.initials: F
authors.lastname: Bernauer
authors.affiliation: Neutron Imaging and Activation Group (NIAG), Paul Scherrer Institut (PSI), 5232 Villigen PSI, Switzerland.
authors.forename: A
authors.initials: A
authors.lastname: Kaestner
authors.affiliation: Neutron Imaging and Activation Group (NIAG), Paul Scherrer Institut (PSI), 5232 Villigen PSI, Switzerland.
authors.forename: P
authors.initials: P
authors.lastname: Vontobel
authors.affiliation: Neutron Imaging and Activation Group (NIAG), Paul Scherrer Institut (PSI), 5232 Villigen PSI, Switzerland.
authors.forename: E H
authors.initials: EH
authors.lastname: Lehmann
authors.affiliation: Neutron Imaging and Activation Group (NIAG), Paul Scherrer Institut (PSI), 5232 Villigen PSI, Switzerland.
authors.forename: T J
authors.initials: TJ
authors.lastname: Schmidt
authors.affiliation: Electrochemistry Laboratory (ECL), Paul Scherrer Institut (PSI), 5232 Villigen PSI, Switzerland and Neutron Imaging and Activation Group (NIAG), Paul Scherrer Institut (PSI), 5232 Villigen PSI, Switzerland.
authors.forename: P
authors.initials: P
authors.lastname: Boillat
mesh_terms: D001608:Beryllium / Q000737:chemistry; D005615:Freezing; D007053:Ice; D033363:Neutron Diffraction / Q000295:instrumentation / Q000379:methods*; D014867:Water / Q000737:chemistry*
chemical_list: D007053:Ice; D014867:Water; D001608:Beryllium