Fundamentals of ENAAFundamentals of ENAA

Ahmed Ashry Abdel AalAhmed Ashry Abdel Aal

Egyptian Atomic Energy Authority-Egypt Second Research Reactor ETRR-2Egyptian Atomic Energy Authority-Egypt Second Research Reactor ETRR-2

Department of Neutron Activation Analysis, Frank Laboratory of Neutron Department of Neutron Activation Analysis, Frank Laboratory of Neutron Physics Joint Institute for Nuclear Research, Dubna, RussiaPhysics Joint Institute for Nuclear Research, Dubna, Russia

Supervisor Dr. Supervisor Dr. Marina FRONTASYEVAMarina FRONTASYEVA

Theory of NAA:Theory of NAA:

Neutron capture by a target nucleus followed by the emission of gamma rays

Sources of IrradiationSources of Irradiation Although a variety of irradiation types have been introduced in Although a variety of irradiation types have been introduced in

activation analysis, activation analysis, the nuclear reactorthe nuclear reactor is still the most important is still the most important source of irradiation.source of irradiation.

C h3 C h4

C h0

C dS

C h1 C h2BS

DC VLR C BU

SU

SM

32

R

d28

d28

D

R 1

d16

R 2

BS

D D

C B

A A C C IBMPC

R 3

Scheme of irradiation facility REGATA at the IBR-2 Reactor with irradiation positions:

(1) Ch1 Cadmium Coated

(2) Ch2 conventional channel

Pulsed fast reactor IBR-2 Dubna

Sampling

Sample Preparation

Irradiation

Measurements

Data Analysis

Calculations

Steps of Neutron Activation Analysis

Rate of neutron capture for thermalRate of neutron capture for thermal and epithermal neutrons and epithermal neutrons

R = R = ΦΦthth σσ00 + + ΦΦepiepi ( I + 0.44 ( I + 0.44 σσ00 ) ) σσ00 is the 2200 msis the 2200 ms-1 -1 cross-section cross-section

ΦΦthth is the thermal neutron fluxis the thermal neutron flux ΦΦepiepi is the epithermal neutron flux per unit ln Eis the epithermal neutron flux per unit ln E I I is resonance integral defined as follows: is resonance integral defined as follows:

Where Where σσ(E)(E) is the activation cross section as a function of neutron is the activation cross section as a function of neutron energy, excluding the 1/v contribution.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 The epithermal activation properties of a nuclide can be conveniently expressed by means of the can be conveniently expressed by means of the cadmium ratio:cadmium ratio:

RCd = th 0 + epi (I + 0.44* 0)

epi (I + 0.44* 0)

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 nuclideD is for the nuclide experimenter is searching

More than 20 trace elements in silicate rocks

have Fa > 20A table of advantage factors for various isotopescan be found in Steinnes, Epithermal NeutronActivation Analysis of Geological Material

Table 1: epithermal activation possibilities for elements which can be Table 1: epithermal activation possibilities for elements which can be determined by reactor Neutron Activation Analysis. The calculated determined by reactor Neutron Activation Analysis. The calculated Advantage Factor are based on RAdvantage Factor are based on RCdCd

AUAU= 3.00, corresponding to R= 3.00, corresponding to RCdCd=72 =72

for a nuclide following 1/v Law.for a nuclide following 1/v Law.

Advantages of ENAA: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

Limitations of ENAA:Limitations of ENAA:

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:Sources of uncertainty:

Possible interference from (n, αPossible interference from (n, α ) and (n,) and (n,PP) reactions will be ) reactions will be more serious in the case of ENAA.more serious in the case of ENAA.Interference from the second order reactions of the typeInterference from the second order reactions of the type

In the In the determination of element No. Z, will in general not be the determination of element No. Z, will in general not be the same as in the case of thermal neutron irradiation.same as in the case of thermal neutron irradiation.If a sample contains a significant amount of light nuclides such If a sample contains a significant amount of light nuclides such as as 11H, moderation of neutrons within the sample might H, moderation of neutrons within the sample might introduce error due to distortion of of the epithermal spectrum.introduce error due to distortion of of the epithermal spectrum.The epithermal neutron energy spectrum may be interfered by The epithermal neutron energy spectrum may be interfered by resonance absorption either by surrounding materials or in the resonance absorption either by surrounding materials or in the sample itself.sample itself.

Applications:Applications: The technique could be used in the 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.

References: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-Planetary-Sciences/12-

091January--IAP--2005/82FA55AA-76A0-4A23-B1E7-1550E587E246/0/enaa.pdf

http://archaeometry.missouri.edu/naa_overview.html http://www.wpi.edu/Academics/Depts/ME/Nuclear/Reactor/Labs/R-naa.html 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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