Transcript COMPARISON PULSE AND CONTINUOUS SOURCES FOR …

COMPARISON BETWEEN PULSED AND
CONTINUOUS SOURCES FOR SMALL
ANGLE NEUTRON SCATTERING (SANS)
Tjatji Tjebane, Dolly Langa, Lolan Naicker,
Daphney Singo
Supervisor: Aleksander Kuklin
Joint Institute for Nuclear Research, Dubna – South African StudentS Summer Practice 2008
OUTLINE

Introduction

SANS Principles

Contrast Variation Method

Neutron Sources

IBR-2 and ILL Fission Reactors

SANS Equipment

Main Parameters of YuMO and D22 Instruments

Typical SANS Application

Remarks

Acknowledgements
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INTRODUCTION
 Neutron scattering is the process of collision between neutrons emitted by a
source and a target which is the studied sample.
 When the scattering angles of these collisions are very small (the emerging
beam is very close to the axis of the emitted neutrons), it is referred to as
Small Angle Neutron Scattering (SANS)
 Why Neutrons?
 No charge, very penetrating, and non destructive to samples
 Neutron wavelengths are comparable to atomic sizes and inter-distance
spacing
 Neutron interactions with hydrogen and deuterium are widely different
making the deuterium labeling method an advantage
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SANS PRINCIPLE
d
I
I0


I ( , )  I ( ) ( )T  d d
0
 d 
Where I  ,   Scattered neutron flux
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I ( )  Incident flux
0
 ( )  Detector efficiency,
T  Sample transmission
d  Sample differential cross - section
d
  Solid angle
d  Sample thickness
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CONTRAST VARIATION METHOD

Contrast is the difference in the scattering length density () values between that part of
the sample of interest (p), and the surrounding media or matrix (m), i.e.
  p  m

When the contrast is zero, the scattering bodies are said to be at contrast matching.

For example, a sample containing three compounds. Using contrast matching,
the contrast between the two parts could be erased, allowing analysis of the third
compound.
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NEUTRONS SOURCES
 Spallation source
• High energy incoming particle (typically
protons)
• Heavy metal target (Ta, W, U, e.t.c)
• Neutrons cascade
• >10 neutrons per incident proton
• Low power load per outgoing neutron (~ 55 MeV)
 Fragmentation Source
• 2.5 neutrons per event
•1 neutron consumed in sustaining reaction
• 0.5 absorbed
• High power load per neutron (~ 180 MeV)
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 Radioactive Sources
• Californium-252
A typical Cf-252 neutron source emits between 1×107 to 1×109 neutrons per second
 Nuclear Explosions
It results from a rapid release of energy from an intentionally high-speed nuclear reaction.
The driving reaction may be nuclear fission, nuclear fusion or a multistage cascading
combination
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IBR-2 and ILL Fission Reactors
IBR-2
ILL
Pulsed Beam Reactor
Continuous Beam Reactor
Power output ~ 2 MW
Power output ~ 58 MW
1 X 1016 neutrons/(cm2.s)
1.5 x 1015 neutrons/(cm2.s)
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SANS EQUIPMENT AT FLNP (JINR) AND ILL
(Grenoble)
YuMO
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MAIN PARAMETERS OF
YUMO AND D22 INSTRUMENTS
Name of parameter
YuMO
D22
1
Flux at sample
~ 107  x 107 n.cm2.s1
~ 1.2 x 108 n.cm2s1
2
Q-Range
7x103  0.5 Å-1
4 x 104 to 0.44 Å1
3
Dynamic Q-Range
7x103  0.5 Å1
_____
4
Used wavelength
0.5A to 8A
4.5 to 40 Å
5
Calibration standard
Vanadium (during the experiment)
H20 (Placed in sample position)
6
Resolution
5  10 %
5  10 %
7
Pulse repetition frequency
5 Hz
Continuous
Specific features
Two detector systems:
 filled, home made , 8 independent
wires.
Direct beam: 6Li-convertor (home made
preparation)
One large area detector system (1m2)
movable (
He3
8
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TYPICAL SANS APPLICATIONS INCLUDE
 Biology
• Organization of biomolecular complexes in solution
• Mechanisms and pathways for protein folding
 Polymers
• Conformation of polymer molecules in solution
• Structure of microphase for separated block polymers
 Chemistry
• Structure and interactions in colloid suspensions
• Mechanisms of molecular self-assembly in solutions
 Materials Engineering
• Analysis of ferrofluids
•Crystalline structure investigations
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REMARKS
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ACKNOWLEDGEMENT
The authors would like to acknowledge the following:
 Kuklin Aleksander
 Murugova Tat’yana
 Kovalev Yurii
 Raul Erhan
All of the above from the YuMO Group, Condensed Matter
Department

We would also like to extend our regards to the organizer of
the Summer Student Practice and all members of the JINR
involved in this project.
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THANK YOU!!!
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