Introduction to neutron scattering for MENA3100 Part 1: - Geir - - PowerPoint PPT Presentation

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Introduction to neutron scattering for MENA3100 Part 1: - Geir - - PowerPoint PPT Presentation

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Introduction to neutron scattering for MENA3100 Part 1: - Geir Helgesen The neutron Neutron production Interactions between neutrons and matter Neutron detection What can be studied using neutrons Small-angle neutron

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SLIDE 1
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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
  • Introduction to neutron scattering for MENA3100

07.03.2018

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SLIDE 3

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
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SLIDE 4

The neutron

  • production and properties
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James Chadwick 1891-1974 Nobel prize 1935

Discovery of the neutron - 1932

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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 1.91N ~ 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)

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SLIDE 7

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

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SLIDE 8

The JEEP-II reactor

250 kg UO2 D2O moderated 2 MW thermal power

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SLIDE 9

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

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SLIDE 10

Neutron, x-ray, and electron penetration depths

(intensity reduced to 1/e = 37% of original)

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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%: cm t     

Intensity: I(t) = I0 exp(-t)

t = tickness

  linear absorption coeffisient

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SLIDE 12

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

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SLIDE 13

Neutron-detection and neutron scattering

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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

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SLIDE 15
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Neutron detection processes

Two main detection techniques:

3He gas

  • r BF3

6Li

  • r 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

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Detector example: Moving the neutron beam away from the reactor:

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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
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WANS SANS

Bragg peaks, atomic positions Size/shape of scatterers Properties of interfaces SANS WANS

After R. Lund, UiO

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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

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SLIDE 21
  • Nanoscale lengths are probed.

Adapted from A.V. Belushkin, Dubna

Small-angle neutron scattering (SANS) instrumentation

spectrum of 

  • ne 
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SLIDE 22

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

  • r concrete

Lead

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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

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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

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ESS construction site on 05.03.2018

  • seen toward target station

https://europeanspallationsource.se/page/construction-site-webcams

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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)