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 Although a variety of irradiation types have been introduced in activation analysis, the nuclear reactor is still the most important source of irradiation. Scheme of irradiation facility REGATA at the IBR-2 Reactor with irradiation positions: Ch1 Cadmium Coated Ch2 conventional channel Pulsed fast reactor IBR-2 Dubna

Steps of Neutron Activation Analysis 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 is the 2200 ms-1 cross-section Φth is the thermal neutron flux Φepi is the epithermal neutron flux per unit ln E I 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: 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 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

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: 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: 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: 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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