Transcript Fundamentals of ENAA

Egyptian Atomic Energy Authority-Egypt Second Research Reactor ETRR-2
Department of Neutron Activation Analysis, Frank Laboratory of Neutron
Physics Joint Institute for Nuclear Research, Dubna, Russia
Fundamentals of ENAA
Ahmed Ashry Abdel Aal
Supervisor Dr. Marina FRONTASYEVA
Theory of NAA:
Neutron capture by a target nucleus followed by the
emission of gamma rays
Sources of Irradiation
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Although a variety of irradiation types have been introduced in
activation analysis, the nuclear reactor is still the most important
source of irradiation.
C h4
C h3
C h0
BS
C h2
C h1
Cd
S
BS
RCB
U
SM
DC V
L
32
SU
d28
R
d28
R1
d16
D
D
D
R2
AA
CC
IBM
PC
CB
R3
Scheme of irradiation facility REGATA at the
IBR-2 Reactor with irradiation positions:
Pulsed fast reactor IBR-2 Dubna
(1) Ch1 Cadmium Coated
(2) Ch2 conventional channel
Sampling
Sample Preparation
Irradiation
Steps of Neutron
Activation Analysis
Measurements
Data Analysis
Calculations
Rate of neutron capture for thermal
and epithermal neutrons
R = Φth σ0 + Φepi ( I + 0.44 σ0 )
σ0
Φth
Φepi
I
is the 2200 ms-1 cross-section
is the thermal neutron flux
is the epithermal neutron flux per unit ln E
is resonance integral defined as follows:
Where σ(E) is the activation cross section as a function of neutron
energy, excluding the 1/v contribution.
An example of Gamma-spectra of rock material recorded 6 days after 2
days’ irradiation:
A – pile neutron activation;
B – epithermal neutron activation
(from Epithermal Neutron Activation Analysis of Geological Material, 1971)
Cadmium ratio:
The epithermal activation properties of a nuclide
can be conveniently expressed by means of the
cadmium ratio:
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RCd = th 0 + epi (I + 0.44* 0)
epi (I + 0.44* 0)
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This ratio is used To compare ability to activate
nuclide by epithermal activation compared to
thermal
Advantage Factor
Effectiveness of ENAA
Fa = (RCd)d / (RCd)D
d is for interference nuclide
D is for the nuclide experimenter is searching
More than 20 trace elements in silicate rocks
have Fa > 20
A table of advantage factors for various isotopes
can be found in Steinnes, Epithermal Neutron
Activation Analysis of Geological Material
Table 1: epithermal activation possibilities for elements which can be
determined by reactor Neutron Activation Analysis. The calculated
Advantage Factor are based on RCdAU= 3.00, corresponding to RCd=72
for a nuclide following 1/v Law.
Advantages of ENAA:
Provides improvement in the precision and
sensitivity in instrumental activation analysis
 Reduction of high activity levels caused by
more numerous major and minor elements
 Thermal fission interference of U-235 reduced,
would have produced radioactive daughter
products, gamma rays, and fast neutrons
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Limitations of ENAA:
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May cause fast fission interference with
Thorium-232
Highly active Cadmium which gives off gamma
rays.
Needs to be near the core for epithermal flux, Cd
lower the neutron flux which nuclear reactor
operators may not want.
Cd can melt
Cd burnup, becomes less effective over long
periods of use
Time needed to take off Cd foil prevents the
detection of short-lived nuclids (half-lives < 20 s).
Sources of uncertainty:
Possible interference from (n, α ) and (n,P) reactions will
be more serious in the case of ENAA.
Interference from the second order reactions of the type
In the determination of element No. Z, will in general not
be the same as in the case of thermal neutron irradiation.
If a sample contains a significant amount of light nuclides
such as 1H, moderation of neutrons within the sample
might introduce error due to distortion of of the
epithermal spectrum.
The epithermal neutron energy spectrum may be
interfered by resonance absorption either by surrounding
materials or in the sample itself.
Applications:
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The technique could be used in the Determination of Au,
As, Sb in plants.
Determination of l, In, Br, Sr, U, Th and Si in geological
samples.
Determination of contents of iodine in non-thyroid tissues
and serum.
Determination of I, Br and Sr in biological samples.
In the determination of Si, the thermal neutron activation
cross section of the reaction Si30(n,) Si31 is small (0.108
b).
Moss Biomonitoring of long-lived radionuclides near
Chernobyl
Determination of Halogens in Soils and Mosses.
Foodstuff Quality.
NAA in Assessment of the Condition of Natural
Ecosystems.
Biotechnologies.
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References:
An Overview of Neutron Activation Analysis by Michael D. Glascock,
University of Missouri Research Reactor (MURR)
Epithermal neutron activation analysis of Geological materials by
E.Steinnes, Institute of Atomenergi, isotope laboratories, Norway.
Instrumental and organizational aspects of a neutron activation
analysis laboratory by Peter Bode, Interfaculaire reactor institute
Delft university of technology.
Epithermal Neutron Activation Analysis at the IBR-2 Reactor of the
Frank Laboratory of Neutron Physics at the Joint Institute for
Nuclear Research (Dubna) M. V. Frontasyeva, Joint Institute for
Nuclear Research, Dubna, Russia.
Epithermal Neutron Activation Analysis and its Application in the
Miniature Neutron Source Reactor by XIAOLIN HOU,* KE WANG,**
CHIFANG CHAI**
 More information...
http://ocw.mit.edu/NR/rdonlyres/Earth--Atmospheric--and-PlanetarySciences/12-091January--IAP--2005/82FA55AA-76A0-4A23-B1E71550E587E246/0/enaa.pdf
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http://archaeometry.missouri.edu/naa_overview.html
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http://www.wpi.edu/Academics/Depts/ME/Nuclear/Reactor/Labs/
R-naa.html
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http://www.reak.bme.hu/Wigner_Course/WignerManuals/Budapest/NEUTRON_
ACTIVATION_ANALYSIS.htm.
http://www.jeffreycreid.com/Analytical_Methods/NAA_theory.html
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Thank you for your Attentions