1. RADIOCHEMICAL METHOD IN ACTIVATION ANALYSIS & ISOTOPIC DILUTION METHOD

2. Radiochemical Method…
Nuclei of some atoms are unstable and emit particles/radiation , the branch of chemistry which is concerned with the decay of unstable nuclei and the products of decay is Radiochemistry.
Analysis of stable nuclei using the radio chemicals/radioisotopes is called radiochemical methods.
Radiochemical methods of analysis depend on the specific properties of certain. These properties include the type and energy of the radiation
emitted, the half-life (t1/2), and the deecay schemes of that particular nuclide.
Furthermore, detection limits tend to be high for long-lived isotopes using radiochemical methods .
Fine Particle Technology of Radio Chemical Method of Analysis
12/7/2018

3. Fine Particle Technology of Radio Chemical Method of Analysis
Radioactive Decay…
Radioactive Decay
Alpha Decay
Beta Decay
X-Ray Emission
Gamma Decay
Fine Particle Technology of Radio Chemical Method of Analysis

4. Fine Particle Technology of Radio Chemical Method of Analysis
Radioactive Decay…
Radioactive Decay
Beta Decay
Alpha Decay
X-Ray Emission
Gamma Decay
Alpha () decay is a common radioactive process encountered with heavier isotopes. The alpha particle is a helium nucleus having a mass of 4 and a charge of +2.
Fine Particle Technology of Radio Chemical Method of Analysis

5. Fine Particle Technology of Radio Chemical Method of Analysis
Radioactive Decay…
Radioactive Decay
Gamma Decay
Beta Decay
Alpha Decay
X-Ray Emission
Beta () decay is a radioactive process in which, the atomic number changes but the mass number stays the same.
The high-energy electrons have greater range of penetration than alpha particles, but still much less than gamma rays.
Fine Particle Technology of Radio Chemical Method of Analysis

6. Fine Particle Technology of Radio Chemical Method of Analysis
Radioactive Decay…
Radioactive Decay
X-Ray Emission
Gamma Decay
Beta Decay
Alpha Decay
Gamma () rays are produced by nuclear relaxations. Gamma rays are more dangerous than radio waves
Fine Particle Technology of Radio Chemical Method of Analysis

7. Fine Particle Technology of Radio Chemical Method of Analysis
Radioactive Decay…
Radioactive Decay
Beta Decay
X-Ray Emission
Gamma Decay
alpha Decay
X-Ray emission are formed from electronic transitions in which outer electrons fill the vacancies created by the nuclear process.
Fine Particle Technology of Radio Chemical Method of Analysis

8. Radiochemical Methods
Radiochemical methods are both sensitive and
specific. There are three general types of radio-
analytical methods of analysis:
Radiometric analysis
Isotope dilution, and
Activation analysis

9. Radiometric Analysis
The process of analyzing a nonactive component by combination with a radioactive isotope is known as radiometric analysis For example, radioactive silver might be used to determine a small quantity of chlorine in a sample. The radioactive silver, Ag*, would combine with the chloride ions,
Ag*+ + Cl > Ag*Cl
to form active silver chloride. The silver chloride could be separated from the solution by centrifugation or by collection on a precipitate of ferric hydroxide.
The weight of silver used could be calculated from the specific activity, SAg, of the silver added and the activity, AAgCl, of the silver chloride:

10. Isotopic dilution
One of the most useful methods of analysis with radioactive materials is isotopic dilution. The method is based upon a comparison of the specific activity of a radioactive-labeled material before and after dilution with a nonactive form of the same material. Isotopic dilution is of particular advantage for the determination of a compound which is difficult to separate quantitatively from a sample.
The method may be illustrated by an example: (1) Assume a sample which contains an unknown A grams of X, (2) Mix B grams of X having a specific activity of SB counts per minute per gram into the sample, (3) Separate a portion of X in pure form, and (4) Determine the specific activity of SAB of this portion of X.
Then the various quantities may be related through the equation,
BSB = (A + B) SAB,
and A calculated by,
The technique may also be used to analyze an unknown radioactive sample.
In this case, the sample is diluted with a portion
of a nonactive form of the compound.
The specific activity before SA, and after, SAB.
dilution are measured. The equations involved are,

11. Neutron Activation Analysis
Samples of some materials may be analyzed by neutron activation (Taylor and Havens, 1950). The sample is placed in a flux of slow neutrons. Some of the atoms of the sample absorb neutrons and become radioactive isotopes. A determination of the half-life and energy of the radiation identifies the radioisotope present. The quantity of the original material present may be calculated.
The rate of production of the radioactive atoms is given by the difference between their rate of formation and their rate of decay:
where N*= number of active atoms, N = number of original inactive atoms,
a = atomic activation cross section, f = flux of neutrons, X = decay constant for
N*, and t = time.
Integration and substitution of the activity, A = N*ƛ, gives

12. Neutron Activation Analysis
where t1/2 = half-life of N*. When t is much greater than t1/2, the saturation activity in the sample is approached and the formula simplifies to
If the measurement of the activity is made at a time t1 after neutron irradiation is ended, the activity is related to the original activity in the following manner:
where At1: = the activity at time t1, and A = the activity at the end of neutron
irradiation. By substituting the expression for A in equation (3) into equation (4), we obtain
Now, if t is not much greater than t1/2, the formula needs to be corrected, since
the activity of the sample was not at saturation:

13. Neutron Activation Analysis
Now, if t is not much greater than t1/2, the formula needs to be corrected, since
the activity of the sample was not at saturation:
For accurate work, the absolute activity of the sample must be determined by comparison with a standard.
Standardization
Standardization is based on the determination of the proportionality factors F that relate the net peak areas in the gamma-ray spectrum to the amounts of the elements present in the sample under given experimental conditions:

14. Radiochemical Methods
Gamma ray spectrum of a sample after neutron induced radioactivity

15. Radiochemical Methods
The basic essentials required to carry out an analysis of samples by NAA are a source of neutrons, instrumentation suitable for detecting gamma rays, and a detailed knowledge of the reactions that occur when neutrons interact with target nuclei.

16. Radiochemical Methods
The sequence of events occurring during the most common type of nuclear reaction used for NAA, namely the neutron capture or (n, gamma) reaction, is illustrated in Figure 1. When a neutron interacts with the target nucleus via a non-elastic collision, a compound nucleus (metastable) forms in an excited state. The excitation energy of the metastable nucleus is due to the binding energy of the neutron with the nucleus. This nucleus will almost instantaneously de-excite into a more stable configuration through emission of one or more characteristic gamma rays.

17. Radiochemical Methods
Fig. 1. Diagram illustrating the process of neutron capture by a target nucleus followed by the emission of gamma rays. The above figure is from

18. Radiochemical Methods
In many cases, this new configuration yields a radioactive nucleus which also decays by emission of one or more characteristic delayed gamma rays, but at a much slower rate according to the unique half-life of the radioactive nucleus. Depending upon the particular radioactive species, half-lives can range from fractions of a second to several years.

19. Radiochemical Methods
Although there are several neutron sources such as reactors, accelerators, and radio isotopic neutron emitters, nuclear reactors with their high fluxes of neutrons from uranium fission offer the highest available sensitivities for most elements. Different types of reactors and different positions within a reactor can vary considerably with regard to their neutron energy distributions and fluxes due to the materials used to moderate the primary fission neutrons.

20. Radiochemical Methods
There are 3 types of neutrons, classified according to their energies:
1) thermal (low energy, < 0.5eV)
2) epithermal (mid energy, 0.5eV to 0.5MeV) , and
3) fast (> 0.5 MeV) An NAA technique that employs nuclear reactions induced by fast neutrons is called fast neutron activation analysis (FNAA).

21. J. Ruticka and J. Stary, Substoichiometry in Radiochemical Analysis,
REFERENCE
J. Ruticka and J. Stary, Substoichiometry in Radiochemical Analysis,
Pergamon Press, (1968)
D. Brune, B. Forkman, B. Person, Nuclear Analytical Chemistry, Chartwell-
Bratt Ltd., (1984)
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