Neutron Activation Analysis

1. Neutron Activation Analysis References: Alfassi, Z.B., 1994, Determination of Trace Elements,(Rehovot: Balaban Publ.) Alfassi, Z.B., 1994b, Chemical Analysis by Nuclear Methods, (Chichester: Wiley) Alfassi, Z.B., 1990, Activation Analysis, (Boca Raton: CRC Press), p. 161. Balla, M., Ke�mley G., Moln�r Zs., 1998, Neutron Activation Analysis in V�rtes, A., Nagy S., S�vegh K., Nuclear Methods in Mineralogy and Geology (New York: Plenum), chapter 2, pp.115-143. Handbook of Nuclear Chemistry

2. Contents Principle of activation analysis (AA) Different types of AA Neutron Activation Analysis (NAA) - different types of NAA (prompt - delayed, instrumental-radiochemical) - neutron sources used for NAA - measuring equipment used for NAA - quantification of NAA (absolute, relative and comparator techniques) - properties of INAA (sensitivities, and non-destructive multielement character) - radiochemical separations in NAA INAA - application examples RNAA � application examples

3. Principle of activation analysis

4. Steps of analysis: sample preparation (homogenization, weighing) optional: pre-irradiation chemistry irradiation cooling (different times) optional: post-irradiation chemistry measurement by gamma spectrometry evaluation

5. History Hevesy and Levi 1936: principle of NAA Neutron sources became available in the fifties Low resolution detectors (proportional counters, NaI scintillator) High resolution semiconductor detectors Alternative non-nuclear methods (AAS, ICP-OES, ICP-MS)

6. Various types of AA Charged particle activation analysis Photon activation analysis Neutron activation analysis (NAA) Thermal neutron activation analysis Epihermal neutron activation analysis (ENAA) Fast neutron activation analysis (FNAA) Neutron capture prompt gamma activation analysis (PGAA)

7. Neutron sources used for NAA

8. Research reactors as neutron sources: thermal power: 100 kW-10 MW thermal neutron flux: 1012-1014 neutrons cm-2 s-1 thermal epithermal +resonance fast neutrons <0.05 eV 0.1eV<E<1 eV 0.5 Mev<E 1eV<E<1 keV mean:0.04 eV 2200 m/s (n,?) (n,?) (n,p),(n,a),(n,2n) cold neutron beam Measuring systems used for NAA Gamma spectrometers: scintillation detector Ge(Li) detector HP Ge detector

9. Quantification N: number of interacting isotopes ?s??(E): cross-section [cm2] at neutron energy of E [eV] f??(E): neutron flux per unit of energy interval [1/cm2/s/eV] R: reaction rate In reactors the integral is replaced:

11. Combining the last 2 equations, the mass of the unknown element can be calculated:

12. Standardization Absolute method Based on the expression of �m� Parameters to be measured: Np, tm, ti, td Parameters to be determined by calibration: e, fth, fe Parameters derived from tables (nuclear+additional): sth, I0, f?, fi, ?, NAv, M

13. Comparator method: �k� method All elements are measured related to a single element, the comparator. Calibration phase: k factors are determined for each element compared to the comparator element (irradiation together) * refers to comparator element � refers to analyte in calibration procedure Measurement phase: Sample is irradiated together with the single comparator, sample and comparator are measured ** refers to comparator element during measurement phase

14. k factors are constant under constant irradiation and measurement conditions (including the same geometry):

15. K0 values were experimentally determined/checked according to the following equation:

16. Properties of INAA Advantages Sensitive, trace elements are determined Multi-element method Matrix dependence is often small Non-destructive Disadvantages Neutron source and gamma spectrometer are needed Expensive and �nuclear� method

17. Application of INAA Geological samples: NAA at INT-TU Budapest - 1 minute irradiation,15 min cooling times: (28Al decays) Ti, V, (Cu), Mn, Cl, Dy and Ca are determined. - 8 hour irradiation in a thermal channel of the reactor measurment twice: one week, one month - usually 25-30 elements can be determined Epithermal NAA - gross activity due to 24Na, 56Mn, 46Sc, 28Al: low Io/sth - analytes (Rb, Sr, Ba, Ga, As, Mo, Ag, In, Sn, Sb, Sm, Tb, Ho, Ta, W, Au, Th, U): high Io/sth - epithermal AA in Cd wrapping ? high sensitivity.

18. Disturbing nuclear reactions - The same radionuclide is produced from two different elements: e.g. 28Al : 27Al(n,?)28Al 28Si(n,p)28Al. thermal n fast n - samples can be activated twice, with and without cadmium filter, in order to determine both Al and Si Studies on lanthanides to derive concentrations relative to standard condrites volcanic activities Biological samples - Analysis of Na, K, Al, Se in brain samples to study deseases e.g. Alzheimer Archaeological samples Provenance studies on Roman ceramics Provenance studies on the jars storing the Dead Sea Scrolls Gold in fibres of the royal gown See the home page for details!

19. Types of radiochemical NAA Post-irradiation chemistry (RNAA) no contamination hazard addition of carriers � no radiocolloids yield determination shielded, remote-controled devices separations: matrix separation group separation single element separation Pre-irradiation chemistry (PC NAA): pre-concentration contamination hazard Pre- and post-irradiation chemistry (PC RNAA) extremely high sensitivites e.g. 129I determination in environment Chemical AA (Ch NAA): separation for speciation purposes pre-irradiation (irradiation may change the chemical conditions)

20. Application of RNAA in material sciences Separation of the matrix Analysis of impurities in high purity Al 27Al(n,a)24Na Na separation by HAP Analysis of Ni based alloys separation of Ni by DMG Analysis of Mo/W coumpounds Mo and W separation by anion exchangers Separation of single elements Si analysis in Mo: 32Si is short-lived, can be counted by beta detector, Si is separated P analysis in semiconductors: 32P is pure beta emitter separation with AMP

21. Application of RNAA for the analysis of biological, environmental and geological samples Matrix removal: matrices are: Na, K, P, Br, Cl removal: HAP TiO2 Al2O3 volatilization Single element separations: - Se:toxic/micro-nutrient separation by extraction or precipitation of elemental Se with ascorbic acid - I: essentiel element separation: I2 extraction + AgI - Hg: toxic element separation by volatilization or extraction + precipitation as HgI2 or HgS or Hg - Sr: major interest as natural carrier for 90Sr separation by co-precipitation with Ca - Th and U: radioactive elements Th:separation of 233Pa by co-precipitation with MnO2 and BaSO4 Th:PC RNAA of Th: pre-conc of Th by ion exchange separation of 233Pa by ion exchange or extraction U, Th: separation of 239Np and 233Pa by TBP

22. Single group separations Pt group elements:Ru, Rh, Pd, Os, Ir, Pt. history of rocks environmental concern: catalysts in cars, medicines - RNAA: OsO4 + RuO4 /CCl4 extraction, anion exchange of chlorides - PC NAA: fire assay/NiS preconcentration Rare earth elements (REE): - co-precipitation with ferric hydroxide - others: ion exchange, extraction Several elements and various groups separations �historic significance Pietra method: 50 elements in biological materials separation by all types of analytical methods (volatilization, ion exchange, sorption�)

23. Application of RNAA for the determination of radionuclides 129I PC RNAA: volatilization, extraction of I2, precipitation of PdI2 237Np 99Tc Application of NAA for speciation studies ChNAA Non-protein bound Al or protein bound Al in urine: role in osteomalacia separation by cation exchange Iodine speciation in sea water separation by anion exchange

24. Nem nukle�ris elemanalitikai m�dszerek T�megspektrometria: SS MS TI MS ICP MS GD MS R�ntgenfluoreszcencia: WD XRF ED XRF TR XRF SR XRF PIXE EPMA Optikai m�dszerek: abszorpci�s: AAS (l�ng, l�mpa) emisszi�s: OES (=AES) ICP OES Elektrok�miai m�dszerek: Voltammetria Coulombmetria Polarogr�fia

25. Elem-analitikaim�dszerek�rz�kenys�ge�ssze-hasonl�t�s