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)