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Part 1: - Geir Helgesen
• The neutron
• Neutron production
• Interactions between neutrons and matter
• Neutron detection
• What can be studied using neutrons
• Small-angle neutron scattering
• Radiation protection
Part 2: - Magnus Sørby
• Neutron powder diffraction
Visit to the JEEP-II reactor:
• Uses of the reactor
• Uses of the neutron instrumentation
Part 3:
• Analysis of neutron powder data
• Some examples
Introduction to neutron scattering for MENA3100
07.03.2018
Institute for Energy Tecnology - IFE
• Located at Kjeller near Lillestrøm
• Operating the two nuclear research reactors in Norway
(Kjeller og Halden)
• More than 600 employees
The neutron
- production and properties
James Chadwick
1891-1974
Nobel prize 1935
Discovery of the neutron - 1932
Neutron:
• Uncharged elementary particle
• With an inner electric charge distribution
• Slightly heavier than a proton
• Lifetime 615 s p + e
• Spinn S= ½
• Magnetic moment 1.91N ~ B/1836
• Can behave both as particle and wave
v ~ 2km/s
= wave length
k= wave number (vector || v), k=2/
Proton - p:
2u + 1d quarks
charge= 2*(+2/3)+1*(-1/3)
Neutron – n:
1u + 2d quarks
charge= 1*(+2/3)+2*(-1/3)
A1) Fission
B) Spallation
Neutron production
A2) Neutron
moderation
Energy spectra –
Maxwell-Boltzmann distribution
liquid H2 > 5 Å
~ 1.8 Å
25 meV
Water or heavy water
The JEEP-II reactor
250 kg UO2
D2O moderated
2 MW thermal
power
Interactions of neutron and x-ray beams with matter
• Absorption – reduces beam intensity
• Refraction – bending beam when passing
• Scattering – almost all intensity transmitted in certain spatial
directions dependent on the sample structure and orientation
Neutron, x-ray, and electron penetration depths (intensity reduced to 1/e = 37% of original)
X-rays Neutrons
Element Z Density
(g/cm3) / (cm2/g) t1/2 / (cm2/g) t1/2
B 5 2.53 2 1.4 mm 24 114 m
Al 13 2.70 40 64 m 0.003 86 cm
Cd 48 8.65 200 4.0 m 14 57 m
Gd 64 7.9 330 2.7 m 73 12 m
Pb 82 11.34 240 2.5 m 3*10-4 2.04 m !!
Absorption
1/ 2
ln(2)Intensity reduced by 50%: cmt
Intensity: I(t) = I0 exp(-t) t = tickness
linear absorption coeffisient
Why are materials so transparent to neutron
beams?
Cross-sections are tiny – most of an atom is empty
space for a neutron
Ex.: Assume atomic nucleus has size of a golf ball
neutron
Neutron-detection
and
neutron scattering
Scattering of neutrons
• Happens in the atomic nucleus
• Wave length of thermal neutrons ~ 1 Å = 0.1 nm = 10-10 m
• Range of nuclear force ~ 1 fm = 10-15 m
neutron is scattered from point source
• Strength of scattering measured in the cross section in unit of barn – 1 barn = 10-28 m2
• -values are measured experimentally
– impossible to calculate in practice
• dependent on:
i) atomic element
ii) isotope of same element
iii) nuclear spin state
Ex: Hydrogen isotopes
Neutron detection processes
Two main detection techniques:
3He gas
or BF3
6Li
or ZnS
He-3: Scint. counter:
- high efficiency (75%) - high countrate
- low g-sensitivity - can be big
n
The only way to detect a
neutron is to destroy it
neutron absorption with
energy release
Detector
example:
Moving the neutron beam away from the reactor:
What can we learn from
neutron scattering?
• Material structure
• crystal structure
• disordered materials, alloys
(grain size, form ….)
• structural defects
• liquid structure
(molecular distances and orientations)
• Dynamics
• molecular rotations (NH2-, CH3-, …)
• vibrations
• sound waves – phonons in solids
• magnetization waves – magnons in
magnetic matter
• diffusion
WANS
SANS
Bragg peaks,
atomic positions
Size/shape of
scatterers
Properties of
interfaces
SANS
WANS
After R. Lund, UiO
Small angle scattering – basic principle
Larger particles
smaller scattering angle ( 1 – few 100 nm)
1. Carbon nanotubes
2-3. Microemulsions
4. Silver nanoparticles
5. Magnetic nanoparticles
6. Silicates (clay)
Example of SANS patterns:
Measures: Size and shape
• Nanoscale lengths are probed.
Adapted from A.V. Belushkin, Dubna
Small-angle neutron scattering (SANS) instrumentation
spectrum of one
Radiation protection
Dosimetry badges GM counter
Regulations
ICRP (International Commission on Radiological
Protection) decides international regulations
Statens Strålevern – Norwegian regulations +
check IFE standards etc.
Radiation doses – unit of Sievert (Sv)
1 Sv big dosis!!
Allowed dosis:
Radiation workers: max 20 mSv/year
Ordinary population: max 1 mSv/year
Compare:
background radiation ~ 3-4 mSv/year
or concrete
Lead
NcNeutron – Norwegian Center for Neutron Research
• National research center – in operation from January 2016
• New powder diffractometer ODIN in operation 2017
• New source for cold, long wavelength neutrons
• Three new instruments under construction 2017-2020
• Neutron reflectometer – FREYJA, for thin film analysis
• Neutron imaging and tomography – NIMRA,
3-dim. look into solid materials
• Residual stress instrument – NEST, measure stress/strain in alloys,
engine parts etc.
• Total upgrade cost about 31 MNOK
• Access for all academic and industrial
users in Norway
ODIN
SANS
DIFF
R2D2
NEST
FREYJA NIMRA
PUS
The European Spallation Source – ESS in Lund The neutron source for the future (2022 =>)
Total cost about 15 billions NOK - 50% of costs covered by Nordic countries
ESS construction site on 05.03.2018
- seen toward target station
https://europeanspallationsource.se/page/construction-site-webcams
Some references:
Online:
1. NIST Neutron Techniques – http://www.ncnr.nist.gov/summerschool/ss15/materials.html
2. Neutron Scattering Reference – www.neutron.anl.gov/reference.html
3. Introduction to Neutron Powder Diffractometry – www.iucr.org/iucr-top/comm/cteach/pamphlets/19/
4. Introduction to Neutron and X-Ray Scattering by S.K. Sinha – www.dep.anl.gov/nx/lectrnotes.pdf
5. European Neutron Portal – http://www.neutron-eu.net/
6. Exploring Matter with Neutrons (from ILL):
https://www.ill.eu/fileadmin/users_files/img/instruments_and_support/support_facilities/computing_for_
science/Computing_for_Science/CS_Software/NeutronEncyclopedia/NeutronEncyclopedia.swf
Books:
1. ”Experimental Neutron Scattering” by B.T.M. Willis and C.J. Carlile (Oxford University Press, 2009)
2. ”Neutron and Synchrotron Radiation for Condensed Matter Studies”, vol. 1-3
(Springer/EDP, 1993 – ISBN 2-86883-185-0)
3. ”Introduction to the Theory of Thermal Neutron Scattering” by G.L. Squires
(Cambridge Univ. Press, 1978)
4. ”Neutron Scattering”, Los Alamos Science, no. 19, 1990
(http://library.lanl.gov/cgi-bin/getfile?number19.htm)