Progress in Electron Volt Neutron Spectroscopy Workshop

 

A workshop on “Progress in Electron Volt Neutron Spectroscopy” will be held on the Sunday (April 24th) preceding the ICANS-XVII meeting. The workshop will be held from 2:00 p.m. to 6:00 p.m., at the Bishops Lodge Resort & Spa (the same location as the ICANS-XVII meeting), in the Thunderbird Room. The observational window provided by high-energy (many electron volt) neutrons offers unique possibilities for the exploration and understanding of condensed matter systems. This special workshop will review the progress of the field from its beginnings, discuss the most recent experiments measuring momentum distributions of light ions in a variety of systems, alternative means for doing the measurements, and the possibilities that the latest instrument developments provide for measuring the spectrum of electron volt excitations.

For more information on the Electron Volt Neutron Spectroscopy Workshop, please contact Dr. George Reiter (greiter@uh.edu, 713-743-3527)


 

Provisional Workshop Program
200pm

Meeting Begins
 

Welcome Jim Rhyne, (LANSCE)
   
 

Session 1. Introduction to Deep Inelastic Neutron Scattering
(Neutron Compton Scattering)
  Session Chair Roger.Pynn (Los Alamos)
   
205pm

Neutron Compton Scattering: History of the Experimental Technique
Jack Carpenter (Argonne National Laboratory)
 

 
225pm

Description of the Inverted Geometry Spectrometer for Electron Volt Spectroscopy and its Capabilities.
Jerry Mayers (ISIS Facility, UK)
   
255pm What Can Be Measured with Neutron Compton Scattering and What is it Good For?
George Reiter (University of Houston, USA)

 
325pm Momentum Distribution in He-3- He-4 Mixtures
Roberto Senesi (Univ. Di Roma Tor Vergata, Italy)
 

 
355pm

Break (15 mins)
   
 

Session 2. Instrumentation Issues and Other Uses for Electron Volt Neutrons
   
410pm

Direct and Indirect Geometry Machines for eV Spectroscopy
Paul Sokol (Univ of Pittsburgh, USA)
   
440pm

High Energy Inelastic Neutron Scattering on VESUVIO
Carla Andreani (Universita' di Roma Tor Vergata, Italy)
 

 
500pm

Gamma detectors for High Energy Inelastic Scattering(HINS)
Erik Schoneveld (ISIS Facility, UK)
 

 
520pm

Topic to be announced
Masatoshi Arai (KEK, Japan)
 

 
540pm

Prospects for the Future/Panel Discussion
   
600pm End

 

Abstracts

 

TITLE:

 Momentum Distribution in He-3- He-4 Mixtures
Roberto Senesi (Universita' di Roma Tor Vergata, Italy)
ABSTRACT:









 Dilute solutions of 3He atoms in liquid 4He form a prototype quantum liquid as an example of an interacting boson-fermion mixture. Indeed the presence of 3He affects the condensate fraction, the superfluid fraction of 4He, the individual momentum distributions, n(p),and the single-atom mean kinetic energy of the two isotopes. Deep Inelastic Neutron Scattering measurements on liquid 3He-4He mixtures in a wide concentration range in the normal phase have been performed on the VESUVIO spectrometer at the ISIS pulsed neutron source.
The results are compared with previous measurements on eV and chopper instruments on pure liquids and mixtures and current theoretical estimates. The talk will focus on the light 3He fermion component in the mixtures which shows a departure from the density dependence of kinetic energy which is found in the pure 3He and all other quantum fluids and solids.
   
TITLE:

 High energy Inleastic Neutron Scattering on VESUVIO
Carla Adreani (Universita' di Roma Tor Vergata, Italy)

ABSTRACT:













 In recent years novel instrumentation concepts have been proposed on the VESUVIO spectrometer at the ISIS spallation neutron source aiming to extend the dynamical range of neutron spectroscopy at eV energies towards both high and low momentum transfer, q. The scientific interest is to study: (a) short time single particle dynamics in quantum and molecular systems and (b) high energy excitations in materials, i.e. electronics transitions in rare earth metals and compounds, vibrational levels in insulators, semiconductors and magnetic materials. This talk revises the concepts of the High energy Inelastic Neutron Scattering (HINS) proposed on VESUVIO to measure high energy excitations in materials.
The HINS measurements are performed using a Very Low Angle Detector Bank (VLAD) device, equipped with gamma detector, which operates in the resonant detector (RD) configuration in the angular range 1°<2 theta<5° . This technique extends the dynamical (q,w) range accessible for eV neutron spectroscopy on the instrument towards low momentum transfers, i.e. ( q<10 Å-1) and high energy transfer w>0.35meV. The principal components of the
resolution function for HINS measurements on VESUVIO will be revised. Instrument performances, test experiment and examples of future applications for neutron scattering processes at high energy transfer and at low momentum transfer are discussed.
   
TITLE:


 Description of the Inverted Geometry Spectrometer for Electron Volt Spectroscopy and its Capabilities.
J Mayers Rutherford Appleton Laboratory, Chilton, Didcot,OX110QX, UK.
ABSTRACT:

The spectrometer eVS, (recently renamed VESUVIO) operating on the ISIS pulsed neutron source has pioneered Deep Inelastic Neutron Scattering measurements of the momentum distribution of light atoms in condensed matter systems. Inelastic neutron scattering at eV neutron energies, is measured using time of flight, combined with the filter difference technique in inverse geometry. In the simplest applications, VESUVIO is used to measure the kinetic energies of atoms as a function of temperature, pressure and sample composition - for example in liquid and solid He4, liquid neon and He4-He3 mixtures. An unexpected and puzzling result, which has attracted much interest, is the cross-section deficit observed in hydrogen containing systems. More recently measurements of the line shape have allowed reconstruction of the atomic momentum distribution and proton wave function in hydrogen bonded systems. An outline of the operation of the spectrometer, together with examples of measurements performed will be presented.
   
TITLE: What Can Be Measured with Neutron Compton Scattering, and What Is It Good For?
George Reiter, University of Houston

ABSTRACT:

 

 We will discuss the level of precision and accuracy of momentum distribution measurements with Vesuvio. The unique capabilities of this technique as a local probe to detect spatial coherence and to make possible the reconstruction of local structure will be illustrated with the examples of KDP, a superprotonic conductor, bulk ice and water, water with acid and base solutes, and water in nanotubes.