Principles of NAAPrinciples of NAA

Mohamed Abdullah Mohamed El SAIEDMohamed Abdullah Mohamed El SAIED

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

Pulsed fast reactor IBR-2 Dubna

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

Ch1-Ch4 –irradiation channels, S- intermediate storage, DCV- directional control valves,L- loading unit, RCB- radiochemical glove-cell, U- unloading unit, SU- separate unit, SM- storage magazine, R- repacking unit, D- Ge(Li) detector, AA- amplitude analyser, CB- control board, CC- CAMAC controller, R1-R3- the rooms where the system is located

Neutron energy spectra in irradiation channels CH1() and CH2 (curve)

The main characteristics of the irradiation channels at 1.5 MW

10-2 10-1 100 101 102 103 104 105 106 10710-210-110010110210310410510610710810910101011101210131014

E (eV)

n(E

), n/

(s.c

m2)

Neutron energy spectra and irradiation channels

Thermal Resonance FastCh1 Cd-coated 3.31 4.32 70 28 260Ch2 1.23 2.96 4.1 60 28 260Ch3 Gd-coated 7.5 7.7 30-40 30 400Ch4 4.2 7.6 7.7 30-40 30 400

Channel length,

mmIrradiation site T

0C

Neutron flux density (n/cm2 s) 10

12 Channel diam., mm

Sampling

Sample Preparation

Irradiation

Measurements

Data Analysis

Calculations

Steps of Neutron Activation Analysis

Sample preparation for NAA

Irradiation:

A: number of decay per second (activity)

N: number of atom of target isotopes; decay time

Tirr: irradiation time , activation cross section , neutron Flux

After delayed time td :

For a counting time tc :

Measurements:

Using semiconductor detector :HPGe

Analysis of gamma-ray spectra :

Using Gamma-ray Counts to Calculate Element Concentration

irradiate the unknown sample and a comparator standard containing a known amount of the element of interest together in the reactor. If the unknown sample and the comparator standard are both measured on the same detector, then one needs to correct the difference in decay between the two

OR

Advantages:

No sample digestion, extraction, volume loss, or dilution required. No potential for contamination due to handling or laboratory chemicals. One simple procedure can analyze 30+ elements simultaneously. High sample volume capabilities. Cost effective & affordable for small and large sample quantities. Quick turnaround – standard results available within 5-10 working days. Faster turnarounds possible – 24 hrs to 3 days. Limited sample volume capability – gram, milligram and microgram in many cases. High precision – reproducibility of quality controls over long periods of time (years) is often better than 2% relative standard deviation (RSD). Primary analytical method used by the National Institute of Standards & Technology (NIST) to certify elemental concentrations in Standard Reference Materials (SRMs).

Applications:

Polymers, resins, adhesives, and organic solids .Pharmaceutical materials .Semiconductor and high-purity .Fine chemicals, solvents, and organic liquids .Catalysts.Environmental.Nutritional & epidemiological .Forensic.Archeological.Development of performance standards .

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