Precision Neutron Cross Section Measurements at Reactor Neutron Filtered Beams

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Precision Neutron Cross Section Measurements at
Reactor Neutron Filtered Beams

• O. Gritzay, V. Kolotyi, O. Kalchenko, V. Libman
• Institute for Nuclear Research of NAS of Ukraine
• Prospekt Nauky, 47, Kyiv, Ukraine, 03680

Olena Gritzay Neutron Physics Department Ukrainian
Nuclear Data Center e-mail ogritzay_at_kinr.kiev.
ua
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2
Content

• Actuality
• Today situation Reason
• Ways of problem solving
• Short characteristics of the KRR
• Physical basis of NFT
• Essential principle of NFBT
• Merits Demerits of NFT
• Improvement of filter purity
• Set of filter components in the NPD
• Neutron filters used in NPD
• Components of some filters
• Procedure of neutron filter creation
• Fundamental investigations
• Main systems of experimental equipment
• Some experimental results
• New direction in NFBT (developing)
• Conclusion

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Actuality

• 
  scientific
• Up-to-date level of
  development demands
• 
  technology
• the high accuracy of neutron data
  

allows
to make progress in development of
nuclear simulation codes
generation of END libraries
THE BASIS FOR ANY TRANSPORT
CALCULATIONS
for operating future reactors
for nuclear technologies in
industry for
nuclear technologies in medicine, etc.
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Today situation

• The most difficult situation with the accuracy of
  NCS is in the energy range
• from several keV to several 100 keV
  

Reason
The lack of high flux installations for the
mentioned energy range from several keV to
several 100 keV
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Ways of problem solving

• 1) Construction of new facilities similar to
  ORELA or GELINA with very long flight paths
• Very expensive
  !!!
• 2) Use of the neutron filtered beam
• 
  technique at the existing research reactors

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Short characteristics of the KRR

• The WWR-M KRR is a light water moderated and
• cooled tank-type reactor with a beryllium
  reflector
• The reactor currently uses 36 enriched
  uranium-235 WWR-M2 fuel assemblies, each of which
  consists of an outer hexagonal tube and two inner
  cylindrical tubes
• (today replacement on 20 U235 fuel is
  started)
• The nominal thermal power is 10 MW
• Neutron flux in the core is about 1014n/cm2s
• Ten horizontal experimental channels (HEC)

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Physical basis of NFT
The general idea of NFT is
transmission of white spectrum through the thick
layers of materials, which nuclei have the deep
interference minima in their total neutron cross
sections

• Through these minima the neutrons transmit
• form rather narrow quasi-mono-chromatic filtered
  beams

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Essential principle of NFBT
Reactor (white) spectrum
Quasi-mono- energy line
1014 n/cm2s
105 - 108 n/cm2s
1 reactor core, 2 beryllium reflector 3
horizontal channel tube 4 beam shutter
disks 5 preliminary collimator 6
filter-assembles 7 filter components 8
outside collimator.
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Merits Demerits of NFT
Neutron filter technique at research reactors
allows to extract from white neutron reactor
spectrum a neutron line with certain energy
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Improvement of filter purity(ways of removing of
parasitic energy lines)
1) To take so thick layer of the material that
only neutrons, corresponding to the most deep
interference minimum, would be able to pass
through it
2) To use additional materials, for which
resonance maxima in their total neutron cross
sections coincide with interference minima for
filter material, with the exception of the most
deep interference minimum
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Set of filter components in the NPD

• The wide set of natural elements and high-pure
  isotopes are used as components for neutron
  filters
• Natural elements
• Si, Al, V, Sc, S, Mn, Fe, Ti, Mg, Co, Ce, Cr, Rh,
  Cu,
• B, Cd, LiF
• High-pure isotopes
• 52?r (99.3), 54Fe (99.92),56Fe (99.5),
• 57Fe (99.1), 58Ni (99.3), 60Ni (92.8 99.8),
  62Ni (98.0), 80Se(99.2), 10B(85), 7Li (90)

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Set of FC in the NPD (cont.)
The wide set of filter materials allows to modify
filter parameters (purity, intensity, width,
etc.) subject to the given research task
Through expensiveness of high enriched isotopes,
the natural elements or enriched isotopes
available in NPD are usually considered as
components of new or improved
filters New filter 7.5 keV (exist) main
component Cu New filter 275 keV (develop) main
component Mn
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Neutron filters used in NPD
275 keV
7.5 keV
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Components of some filters
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Procedure of neutron filter creation
1-th step modeling
calculation of neutron filtered spectra
using information from ENDF 2-nd step
creation of filter with components chosen
by calculation 3-rd
step experimental testing of
the created filter. If it is necessary the
sequence of these steps is repeated.
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Fundamental investigations

• High precision measurements (with accuracy
  better 1) of total neutron cross sections,
  averaged on filter spectrum
• Measurements (with accuracy 3-6) of neutron
  scattering cross sections, averaged on filter
  spectrum
• Measurements (with accuracy 5-6 ) of activation
  cross sections, averaged on filter spectrum
• To determine averaged resonance parameters
• To estimate self-shielding factor
• To feel resonance parameters of single
  resonance

Type of information
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Main systems of experimental equipment (may be
different in configuration and size )
1) System for forming of filtered neutron
beam 2) System of radiation shielding 3)
Sample management system 4) Neutron detector
and counting system
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Forming system of filtered neutron beam
includes the elements of beam collimation
neutron filtration

• Preliminary forming of beam - two iron and
  boron carbide collimators
• Further forming - in the 1-st three discs of
  shutter in outer collimator
• (in the order lead, textolite and mixture
  of paraffin with H3BO3)
• The collimation system provides beam narrowing
  to necessary diameter
• The elements of neutron filtration system - in
  the 1-st three disks of shutter
• 
  in the
  outer collimator
• To facilitate and quicken the procedure of
  filter changing, special steel containers for
  filters were made

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Neutron detector and counting system
neutron counter, electronic blocks, personal
computer and communication lines about 50 m long
between spectrometric installation and measuring
room
En lt 12 keV - helium-3 counters
(???-37, LND 2527) En gt
12 keV - hydrogen recoil counters
(CHM-38, LND 281)
ND for stot
ND for sel
58 helium-3 counters placed in five layers,
located just above the sample
Five assemblies of 7 He-3 counters ?H?-17 Set of
7 hydrogen counters LND-281 Set of 7 helium
counters LND-2527
ND for ds/dO
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Some experimental results
152.9 keV
The accuracy ?tot is between 0.3 and 1.7.
Concerning BNL-325 isotope 13C, part of which in
natural carbon makes only 1.1, has strong
p-resonance with energy 152.9 1.4 keV (J2,
?n3.7 0.7 keV, ??4.0 1.6 keV)
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Some experimental results (cont.)
52Cr
In energy region from 50 keV to 60 keV isotope
Cr-52 has 2 resonances with energies 50 keV
and 58 keV. How can we get information
about
resonance parameters?
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New direction in NFBT (developing)
How can we get information about resonance
parameters by NFBT?
1) Set of stot, averaged on filter spectra, the
main energy of which are shifted
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New direction in NFBT (cont.)
1) Shift of the main energy of filter owing to
dependence energy of scattering neutrons from
angle of scattering
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New direction in NFBT (cont.)
How can we get information about resonance
parameters by NFBT?
2) Set of the averaged stot using
filter the main energy line of which is
cutted into 2 or 3 parts
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Conclusion

• NFBT at research reactors allows to get
  experimental data with high accuracy in energy
  region from thermal to several hudreed keV
  stot lt 1 sel lt3-4 dsel/dO lt5-6 sn,?
  lt5-6
• New directions (shift cutting main filter line)
  will allow to get information about resonance
  parameters

to make progress in development of
nuclear simulation codes
generation of END libraries
THE BASIS FOR ANY TRANSPORT
CALCULATIONS
for operating future reactors
for nuclear technologies in
industry for
nuclear technologies in medicine, etc.
The X-th International School-Seminar "THE ACTUAL
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TOPICS
Conference chairman Ivan M. Vyshnevskyi
(Director of KINR) Scientific secretary Vitali
Yu. Denisov (KINR) E-mail npae-2010_at_kinr.kiev.u
a Website http//www.kinr.kiev.ua/NPAE-2010

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Thank You for your attention!
e-mail ogritzay_at_kinr.kiev.ua
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