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Title:Deep inelastic neutron scattering studies of condensed argon and neon
Author(s):Fradkin, Mark Aaron
Doctoral Committee Chair(s):Simmons, R.O.
Department / Program:Physics
Subject(s):deep inelastic neutron scattering
Abstract:The single-particle kinetic energy, , has been determined in condensed natural Ar over the temperature range 18.3 to 85 K by deep-inelastic-neutron scattering. The Low Resolution Medium Energy Chopper Spectrometer (LRMECS) at Argonne National Laboratory's Intense Pulsed Neutron Source (IPNS) was used to measured the neutron Compton profile over the range of wave-vector transfers 192 to 254 nm-1. From the neutron Compton profile the single-particle kinetic energy as a function of temperature, , is obtained. A new method, using the scattering from liquid Ar samples, has been used to account for spectrometer resolution and multiple scattering. The temperature dependence of is compared to expectations from theory, from thermodynamic measurements, and from previous inelastic neutron-scattering measurements of collective vibrational modes of the solid The self-consistent average phonon model (SCAP) is found to give excellent agreement with the measured over the entire temperature range examined. Path integral Monte Carlo calculations, using a Lennard-Jones potential, are also consistent with my results for . The groundstate value of , deduced from the results at finite temperature, is compared to the results of various theoretical calculations. The magnitude and neutron wave-vector-transfer dependence of final-state effects have been examined in natural liquid Neat 27 K for a molar volume of 16.7 cc/mole, (36.1 atoms per nm3). In this experiment, performed on the High Resolution Medium Energy Chopper Spectrometer (HRMECS) at IPNS, deviations from impulse approximation behavior in the wave-vector transfer region from 105 to 276 nm-1 have been investigated. At these values of the wave-vector transfer, any deviations from impulse approximation scattering are expected to arise solely from fimil-state effects. The series expansion of the neutron Compton profile proposed by V. F. Sears has been used in the analysis of the data. Instrument resolution and sample-dependent multiple scattering have been accounted for using a sophisticated Monte Carlo simulation developed by Blasdell. Good agreement is found between my results and predictions from Sears' theory. Therefore, for systems in which S(Q,ro) is analytic and the interatomic pair-potential and radial distribution function are known or can be accurately calculated, final-state effects can be accounted for in inelastic scattering data using Sears' theory.
Issue Date:1993
Genre:Dissertation / Thesis
Rights Information:1993 Mark Aaron Fradkin
Date Available in IDEALS:2012-01-20

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