material investigation

1. NEUTRON
SCATTERING
prep. by: Ishfaq

2. Outlines
 Introduction
 Application
 Why neutron
 Neutron VS X ray
 Types of neutron scattering
 Theory
 Instrumentation
 Fitting
 Data
 Pros and Cons

3.  Scattering of free neutrons by matter reffer
to.
 Physical process or experimental
technique which uses this process for
material investigation
 As physical process
 Primordial importance in neuclear
engineering
 As exeprimental technique used in
 Crystallography
Neutron
scattering

4. Application of Neutron
diffraction
 Used for determination of structure
 Locating Light atoms
 Heavy atoms that absorb x-ray strongly
 Similar atomic no /Isotopes
 Magnetic properties
 Single crystal studies analysis
 Inelastic scattering Used for study of atomic
vibration and other excitations

5. Neutrons
 Neutron Are Wave
 Beam of neutrons incident on sample
 Distribution of radiation scattered from sample
measured
 This is determined by interaction potential and
momentum transfer b/w the beam and sample

6. Why neutrons ?
• No charge
• High energy
• Strong magnetic interaction
• Scatter strongly from light nuclei

7. Neutron Vs X-ray
Neutron X-ray
Highly penetrating due to their 0
charge. Therefore can probe the
internal structure of materials
No charge, and provides data on the
surface structure mainly
Interacts with nuclei, and therefore
scatters strongly from light atoms,
as well as heavy atoms, and can
differentiate easily between
isotopes
Interacts with the electron clouds,
and therefore scatters strongly from
heavier elements with larger
electron clouds.
Neutrons are spin- ½ particles, and
carry a magnetic moment (good to
study magnetism over short ranges)
Can be used to study magnetism,
through electromagnetic radiation,
but provide less information.
Expensive!!!! Less expensive
Requires the use of high energy
synchrotron rings
Can be done in house

8. Types of neutron experiment
 Diffraction/ elastic scattering
-no energy transfer to/from sample
- crystal structure ,atomic correlation in liguid
/glass
 Inelastic scattering
-energy transfer to/from sample
- Measurment of lattice vibration (phonons),atomic
difusion,molecular modes
 Small angle scattering
-diffraction at small angle
-measure large molecule protein ,colloid,
nanoparticle etc
 Reflectrometry
Diffraction from surface speculars or off specullar
Measure depth profile of thin film ,membrane
 Imaging

9. Theory
 Scattering of neutrons at small angles gives
information about their structure and size, giving a
scattering pattern
 This pattern is subjected to Fourier Transformation,
and described in terms of a momentum transfer
vector (Q), instead of a diffraction angle.
 Q is scattering in reciprocal space, rather than actual
(d) space.
 Small Q values look at long distances, large Q values
look at short distances.
 Q values of 0.006 to 0.28 Å-1 probes distances of
about 10 to 1000 Å ( 1 to 100 nm ).

10. Sample preparation
 All samples need to be made in D20.
 Samples can be contrast matched, allowing for
parts of the sample to become invisible to the
neutron beam.
 Contrast variation involves matching the density
of part of the sample, with ratios of D2O and H2O.
 All samples need to be placed in clean quartz
cuvettes, and placed in the instrument.

11. Instrumentation
1. Neutron generator
Deutrium
+Tritiumneutron(14.1MeV)+He
D+D n+He3
2. Vacum pump
3. Sample holder
quartz cuvvet
4. Detector

12. Fitting
 Many fitting programmes available:
 SASview
 Fish
 SASfit
 Fitting based on prior knowledge about
system, and uses other experimentally
determined values

13. The data
• The data generated provides info on the shape and
structure (but needs to be fitted).
• Changes in Q (the wiggles) define a change in scatering
length density
• From this, the data can be fitted to different models,
which can provide information on the size of the particle,
interactions, radius of rotation, structure, shape etc…

14. Pros and Cons
Pro’s Con’s
Powerful technique to characterise
internal and external structural features
Requires previous knowledge on
system from other techniques
Contrast matching can make parts of
the system “invisible”
Requires knowledge on the density of
different parts of the system
Very good at looking at probing size
and structural effects in “smart”
systems
Looking at samples in different
conditions is time consuming. Only a
limited amount of beam time is available
Good in characterisation of simple
systems (e.g. sphecircal
particles/polymers), up to very complex
systems in complicated sample
environments (e.g. temperature
responsive nanoparticles in a
supercritical environment)
Data fitting gets more complicated as
more parameters are added to a system,
which requires more previous
knowledge
Looks very good in papers, and
increases the impact of the article
Need to apply for beam time
Can be used for many types of particle
in many different environments
Specific fields requires more expertise
in the area e.g. biological samples.