All about Radiations, Different energy particles- starting from Basics to New methods of analysis also includes DIfferent applications related to it. Medha Thakur (M.Sc Chemistry)

1. RADIOCHEMICAL
METHOD OF
ANALYSIS
Presented by : Medha Thakur
MSc Chemistry,
S.N.D.T university

2. Contents
• Introduction
• Types of Radiations
• Alpha, Beta, Gamma, X-ray,
Neutrons
• The Decay law
• Carbon Analysis
• Isotopic Dilution Analysis
• Direct isotopic Dilution
Analysis (DIDA)
• Indirect isotopic Dilution Analysis
(IIDA)
• Applications
• Neutron Activation Analysis (NAA)
• Classification of NAA
• Destructive & Non- Destructive
Method
• Application of NAA

3. Introduction
• Radiochemical method of analysis employ radioactivity to obtain
qualitative and quantitative information about the composition of
materials.
• The fundamental difference between this method of analysis and all
other is that, in this method one is either induces radioactivity in the
sample or adds radioactive substance to the sample.
• Radioactive substance can also be employed as tracers to study
various physicochemical processes.

4. Fundamentals Of Radioactivity
• All atomic nuclei are made up of protons and neutrons (except H). Atoms of the same
element contain number of protons. However, atoms of the same element may have a
different number of neutrons and therefore a different mass number. such atoms
having same Z and different A are referred to as isotopes.
• Radioactive isotopes are either artificial (manmade e.g. 60Co) or natural (such as 40K).
Isotopes
Stable
do not undergo spontaneous
radioactive disintegration
Radioactive
spontaneous
disintegration

5. Types of Radiations
• When radioactive isotopes
disintegrate they produce energetic
particles are electromagnetic
radiations.
• Following are some of the types of
particles and radiations. that are
encountered in radiochemical studies.

6. a) Alpha Particles
• These usually result from the disintegration of
isotopes possessing high atomic number.
• e.g.
𝟗𝟐
𝟐𝟑𝟖
𝑼 → 𝟗𝟎
𝟐𝟑𝟒
𝑻𝒉 + 𝟐
𝟒
𝑯𝒆 (α particle)
• highly effective in producing ion pairs within
the matter through which they pass.
• because of their heavy mass, they have low
penetrating power.
• The general alpha decay reaction is
𝒁
𝑨
𝑿 → 𝒁−𝟐
𝑨−𝟒
𝒀 + 𝛂 𝒑𝒂𝒓𝒕𝒊𝒄𝒍𝒆

7. b) Beta Particles
• produced within a nucleus by the spontaneous
transformation of a neutron to a proton or a proton to a
neutron.
• The particle is an electron (negatron) in the former case
and a positive electron (positron) in the latter case. e.g.
• 𝟔
𝟏𝟒
𝑪 → 𝟕
𝟏𝟒
𝑵 + 𝒆−
+ 𝝑−
• 𝟑𝟎
𝟔𝟓
𝒁𝒏 → 𝟐𝟗
𝟔𝟓
𝑪𝒖 + 𝒆+
+ 𝝑
• not as effective as α particle in producing ion pairs in
matter because of its small mass (1/7000 times that of
an alpha particle).
• its penetrating power is very much greater than that of
the α particle. The general decay reactions are
• 𝒁
𝑨
𝑿 → 𝒁+𝟏
𝑨
𝒀 + 𝜷+
+ 𝝑
• 𝒁
𝑨
𝑿 → 𝒁−𝟏
𝑨
𝒀 + 𝜷+
+ 𝝑

8. c) Gamma ray emission
• The γ ray emission spectra is characteristic for each nucleus
and is thus useful for identifying radio isotopes.
• γ radiation is highly penetrative. Upon interaction of scatter γ
rays lose energy by 3 mechanisms.
1. Low energy = a photoelectric effect takes place. that is an
electron is ejected from a high atomic weight target atom.
2. Medium energy = Compton effect takes place, that is an
elastic collision between a photon and an electron takes
place. the γ photon energy diminishes and this photon
ultimately causes photoelectric effect.
3. Very higher energy = 1.02 MeV pair production can occur.
Here, the photon is converted into a positron and an
electron (in the field surrounding a nucleus).

9. d) X-ray emission
• Two types of nucleus processes, electron capture and internal
conversions are followed by the emission of X- ray photons.
• Electron capture process = the nucleus captures an orbital electron
(usually K electron) which creates an orbital vacancy. The vacancy is
then filled by electrons from higher energy levels. This transfer of
electrons may result in emission of rays.
• Internal conversion = an excited nucleus loses its excited energy by
ejecting an electron from one of the orbitals near the nucleus. This
results in the emission of x-ray photon.
• x-rays and γ rays differ in only their source. x-rays arise from
electronic transitions γ rays from nuclear events.

11. e) Neutrons
• Since neutrons possess no charge, they are effective bombarding particles.
they do not have to overcome electrostatic charge barriers, surrounding a
target nucleus.
• Slow (thermal) neutrons are more reactive than high energy neutrons.
• neutrons can interact with matter in several ways, the product depends on
the energies of bombarding neutrons.
• Irradiation of a stable isotope with thermal neutron is most likely to give
rise to a highly excited isotope with mass number. The product achieves
stability through emission of γ ray photon. The process can be represented
as
𝒁
𝑨
𝑿 + 𝟒
𝟏
𝒏 → [ 𝒁
𝑨+𝟏
𝑿]∗ → 𝒁
−𝑨+𝟏
𝑿 + 𝛄

12. The Decay Law
• The decay behavior of a large collection
of like nuclei can be described by the
expression.
•
−𝒅𝑵
𝒅𝒕
= 𝝀𝑵
• N = number of radioactive nuclei
t = time & 𝜆 = decay constant.
•
−𝑑𝑁
𝑁
= 𝜆𝑑𝑡
• integrating between t = o to t = t during
N0 to N1 we get,
• 𝑁0
𝑁 𝑑𝑁
𝑁
= 𝜆 0
𝑡
𝑑𝑡
• ln
𝑁
𝑁0
= −𝜆𝑡
• ∴ 𝑵 = 𝑵 𝟎 𝒆−𝝀𝒕
• The half-life of a radioactive isotope is
defined as the time required for number of
atom to decrease to half its original quantity
that is for N0 to become N0/2.
• Therefore, 𝒕 𝟏/𝟐 =
𝟎.𝟔𝟗𝟑
𝝀

13. Carbon Dating:
• The radioactive isotope of Carbon C14 is used to determine
the date at which an animal or plant had died. This method
of “dating” a sample of carbon material is called dating with
C14.
• The C14 isotope is formed in the upper regions of the
atmosphere by the action of neutrons (produced by cosmic
rays) on N,
7
14
𝑁 + 0
1
𝑛 → 6
14
𝐶 + 1
1
𝐻

14. C14 Activity
• C14 has a half life of 5720 years. it gets converted into CO2 & is
assimilated by plants during photosynthesis & also become a part of
animal when they eat plant. C14 in living plants & animals decay but is
made up again.
• A state of equilibrium is ultimately attained & a living being on an
average gives 15.3 dpm/gm,
• when a plant is cut or an animal dies, the intake of C14 stops & that
which is present decays, if the C14 activity of a living & dead plant of an
animal is compared the date on which the plant or animal died can be
found out.

15. Isotopic Dilution Analysis (IDA)
Isotopic Dilution
Analysis
DIRECT IDA
(DIDA)
INVERSE IDA
(IIDA)

16. 1) DIDA or IDA USING RADIOACTIVE
(RA) ISOTOPE
• In DIDA, a RA form of the component of interest is added to the sample and the
inactive forms initially present determined.
• Determination of an inactive compound by Dilution with an Active compound.
• THEORY:
Component of
Interest (N gm)
w gm of Active
Component (NA )
SPECIFIC
ACTIVITY
So = A / w
After
Mixing
Pure
Component (g
gm) isolated
Contain both
Active & inactive
form
Has
Activity B
S = B / g.

17. Theory Of DIDA
• Now, the total amount of activity
(dpm) must be the same after
mixing as before mixing.
• 𝑆 𝑜. 𝑤 = 𝑆 (𝑊 + 𝑤)
• (𝑆 𝑜. 𝑤 / 𝑆) – w = W ------(1)
• We can also calculate the amount
of the component of interest in
terms of total activity.
• Since total activity before and after mixing
in equal,
• A = B/g (W + w)
• (A. g / B) – w =W ------(2)
• W = (g. A/B) – w ------(3)
• If the material added is highly active, w
can be very small relative to W.
• therefore eq (1) reduces to
• W = g. A / B

18. 2) IIDA or IDA using STABLE ISOTOPES:
[ IIDA]
• A method similar to DIDA,where in a quantity of an inactive form of the component of interest
is added to the sample. A part of the Analyte mixture is then isolated and the amount of the
recovered component and its activity are measured.
• From this, the quantity of the RA substance initially present in the sample is calculated. This
method is referred to as IIDA.
• THEORY:
Wt. (w) & Activity
(A) of Radioactive
Subs.
Sample
SPECIFIC
ACTIVITY
So = A / w
W gm of
inactive form
of component
g gm of Pure
component
Has
Activity B
S = B / g
1
2

19. Theory of IIDA
• The total activity before and after
analysis is equal.
• therefore,
• wSo = S (W + w)
∴ w(So – S) = SW
∴ w = SW / (So – S)
• The amount of an substance can
be calculated in terms of total
activity.
• total activity before and after
analysis is equal.
• A = B / g (W + w) or A = S (w + W)
• ∴ (A / B) g = W + w
• ∴ [(A / B) g] – W = w
• The method of IIDA is not as widely
applied as that of DIDA.

20. UNITS OF RADIOACTIVITY
• The CURIE is the fundamental unit of radioactivity. It is defined as,
the quantity of Nuclide in which 3.7 × 10-10 dps occur. Milli and Micro
curie are frequently much more convenient units.

21. APPLICATIONS OF ISOTOPIC
DILUTION (ID) METHOD:
• The IDA technique has been employed for the determination of 33
elements in a variety of substances.
• The ID procedures have also been used for the determination of
organic and Biochemical compounds such as VIT D, VIT B12, Sucrose,
Insulin, penicillin, various Amino acid, Thyroxine, etc.
• IDA has been used for non chemical applications.
• Though the application of IDA has decreased since the advent of
activation method, it is still used since it requires relatively simple
instruments.

22. NEUTRON ACTIVATION ANALYSIS (NAA):
• The radiochemical method in which the sample to be analyzed is
bombarded with Nuclear radiation or particles and the radiation emitted
from the sample are measured is referred to as Activation Analysis.

23. Classification of NAA
Type of radiation
employed for
excitation of
sample
Type of radiation
emitted &
measured in final
step of analysis
As being
destructive or
Non destructive
of the sample

24. • In NAA the sample is bombarded with thermal neutrons and the RA
induced is measured. The most important advantage of NAA is its
high sensitivity, concentration determinations in the pp range are
common.
Destructive
Method
Non
destructive
method
The Irradiated sample is dissolved &
activity of element of interest is couple
after it has been isolated by suitable
chemical or physical means.
this activated sample is
counted
without preparatory treatment
Are more accurate and reliable

25. DESTRUCTIVE METHOD
• Involve dissolution of a known amount of the
irradiated sample followed by separation of the analyte
from interference.
• the isolated material is then counted for its beta or
gamma activity.
• NAA involves irradiation of std containing a known
mass of the activity that results are proportional to the
mass and the other components of the sample do not
produce detectable Radioactivity, then the wt,
• wx of the element in the sample is given by,
wx = (Ax / As) × ws ------(1)
• where Ax and As are the activities of the sample and
std. respectively.

26. Continue…
• Generally, the bombardment generates activity in
elements other than the analyte. Thus chemical
isolation of the analyte from a solution of the
sample is necessary before measuring of induced
activity.
• if the analyte is present in traces. the separation
is difficult
• Its difficulty is overcome by introducing a known
weight wx as a carrier after irradiation of sample.
• Separation of the carrier and the irradiated
sample (wx + Ws) is then done by some analytical
method.

27. NON DESTRUCTVE METHODS:
• In this method, a γ ray spectrometer is used to measure the activities
of the sample and the std immediately after irradiation. The wt. of the
analyte is then calculated directly from eqn
• wx = (Ax / As) × Ws
• Method is successful only if the spectrometer is able to isolate the γ
ray signals produced by the Analyte from signals arising from the
other components.
• At present destructive methods are being followed because they are
more selective, sensitive, simple, and fast.

28. APPLICATION OF NAA:
• NAA can be used to determine about 69 elements.
• NAA has been used to determine toxic, trace elements in natural H2O
and environmental samples, certifying percentage and art concepts,
studying impurities in conductor materials, in determining trace
elements abundance in meteorites, lunar samples etc. in Forensic
chemistry etc.

29. ACCURACY
The principle errors that arise in
Activation analysis are
• 1) Unequal Neutrons flux at sample and
std.
• 2) Counting uncertainties
• 3) errors in counting due to scattering,
absorption, etc.
• 4) difference in the geometry of sample
and std.
• These errors can be reduced to a large
extent.

30. SENSITIVITY:
• Sensitivity varies from element to element. As little as 10-5 μg of
several elements can be detected
• e.g. For Fe, the sensitivity is 50 mg and for Eu its 10-6.
• Sensitivity depends on a number of variables.
They are associated with
• 1) Properties of the particular nucleus
• 2) The Irradiation process
• 3) The efficiency of the counting apparatus
• 4) The efficiency of chemical recovery (If required)

31. • The effect of a number of these variables on the activity A produced in
a sample after irradiation for a time t is given by the expression.
• A = N σ ϕ [1 - e-λt ]
• where, A = given COUNTS per sec
• N = no. of TARGET NUCLEI.
• σ = neutron capture cross section in cm-2 per nucleus
• ϕ= neutron flux in units of neutrons per cm-2 per second
• t = irradiation time &
• λ = decay constant of the product.