These slides briefly introduce the concepts of Radio-chemistry including nuclear stability, half life, nuclear emissions and their detection, and then highlight 02 radio chemical methods namely isotopic dilution methods and radio-chemical titrations.

1. Radiochemical Methods of
Analysis
Dr. Sajjad Ullah
Institute of Chemical Sciences
University of Peshawar, Pak
Dr. Sajjad Ullah, ICS, University of Peshawar

2. Nuclear Chemistry--- The Wonders Land
Nuclear
Research
Can the power of the nucleus be harnessed for our benefit Or are the Risks too great?
Mystery
&
Wonder
Enormous potential
Dr. Sajjad Ullah, ICS, University of Peshawar

3. We should remember that there are nations
which meet more than 30 to 60% of their
power requirements through the nuclear
power system.
A. P. J. Abdul Kalam
Nuclear power will help provide the electricity that our
growing economy needs without increasing emissions. This is
truly an environmentally responsible source of energy.
Michael C. Burgess
A nuclear power reactor is just a fancy way of boiling water.
Leslie Dewan
Nuclear power plants must be prepared to withstand
everything from earthquakes to tsunamis, from fires to
floods to acts of terrorism.
Ban Ki-moon
We have a legal and moral obligation to rid our world of
nuclear tests and nuclear weapons.
Ban Ki-moon
All the waste in a year from a nuclear power plant can be
stored under a desk.
Ronald Reagan
Dr. Sajjad Ullah, ICS, University of Peshawar

4. Radiochemistry
Radiochemistry deals with the study of the decay of unstable nuclei (radionuclide) and products
(particle or radiation) of the decay.
It studies unstable nuclei (radioactive nuclei) which spontaneously emit or stable nuclei from
which emission can be induced through different mechanisms.
Each type of unstable nucleus has a characteristic rate (from fraction of s to billions of years) of
radioactive decay.
Qualitative analysis: Energy of the emitted particle/radiation is measured
Quantitative analysis: Magnitude of the emission is measured
Radioisotope: An isotope of an element that emits a particle or EMR
Radionuclide: A nucleus that emits.
Radioactive: A substance which spontaneously emit radiation or particle or which undergoes fission.
Fission: The process by which a radionuclide decays into at least two pieces which have atomic number
greater than 2
Density of nucleus = 1014g/mL
Dr. Sajjad Ullah, ICS, University of Peshawar

5. Components of Nucleus: Terms and Notions
Mass number
Atomic number
for nuclide
Symbol for particles/nuclide
Proton = 1
1p or 1
1H
Electron = -1
0e
Neutron = 0
1n
No. of neutrons (N)= A - Z
Alpha particles = α or 2
4H
Beta particles = β or -1
0β or +1
0β
Gamma rays = ɤ or 0
0ɤ
Dr. Sajjad Ullah, ICS, University of Peshawar

6. Neutron/ Proton ratio
The ability of a nuclide to spontaneously emit is
a function of the ratio of neutrons to protons (N/Z).
Neutron/Proton (N/Z) ratio =
𝐴−𝑍
𝑍
For lighter elements (Z< 20), one neutron for each proton (N/Z ~1)
Is enough to provide stability: 2
4He, 6
12C, 8
16O and 10
20Ne
For heavier nuclides to be stable, the number of neutrons must
exceed the number of protons (N/Z >1)
If N/Z ratio is either too HIGH or NOT HIGH enough, the nuclide is
unstable and decay.
The N/Z ratio of stable nuclides increases with increase in Z
No stable nuclides exists with N/Z =1 for Z > 20. Thus, Fe, Ag and W
all have N/Z > 1)
All nuclides with Z > 83 are unstable. Bi-209 is the heaviest stable
nuclide.
Very Few nuclides exists with N/Z < 1 (the only are 1
1H and 2
3He)
Neutron vs. Protons plot
For stable nuclides
Dr. Sajjad Ullah, ICS, University of Peshawar

7. Dr. Sajjad Ullah, ICS, University of Peshawar

8. p  n + e+
n  p + e-
Dr. Sajjad Ullah, ICS, University of Peshawar

9. Dr. Sajjad Ullah, ICS, University of Peshawar

10. Alpha (α or 4
2He) Particles
• Alpha particles are dense, positively charged particles identical to helium nuclei
• Heavier (greater mass, m) than other nuclear emission and thus have lesser mean
velocity (v) than other emission of the same kinetic energy (KE= 1/2mv2)
• Larger size, so lesser penetration than other emissions
• After emission of α particles from the parent nuclide, the daughter nuclide contains
two lesser p and n.
• α particles emitted from a particular nuclide possess discrete kinetic energy
and they rapidly lose KE as they penetrate into matter (thus they are highly
ionizing). They thus have shallow penetration depth (µm range).
• α particles interact with e in matter causing ionization. Eventually, these α
particles captures e and convert into
He atoms Dr. Sajjad Ullah, ICS, University of Peshawar

11. Beta (β or -1
0β) Particles
• Beta particles are charged particles identified as high-speed electrons.
• Both positively (1
0β or positron) and negatively (-1
0β or negatron) charged electrons can be emitted
• In nucleus, electrons are formed (and ejected from nucleus) either by decay of neutron to yield a proton
• and a negatron (equation 1) Or by decay of a proton to yield a neutron and position. (equation 2)
n  p + e-
p  n + e+
0
1n  1
1p + -1
0βor
1
1p  0
1n + +1
0βor
-----(1)
-----(2)
71
176Lu  72
176Lu + -1
0β
19
40K  18
40K + +1
0β
• Beta particles are lighter than alpha particles, so they are less effective in ionization of matter than alpha
particles
• For the same reason, their penetration depth is 500 times more than alpha particles of the same energy.
• The maximum energy (Emax) which a beta particle can posses is determined by the energetic loss by the
Emitting atom. It is characteristic of a particular nuclear reaction and can be used for qualitative analysis.
• Beta particles loss energy by ionizing the medium or exciting the target atoms (interaction with e-) and
through Bremsstrahlumg Emission (a shock wave of EMR caused by rapid deceleration of e)
• Annihilation: e+ + e- (in matter)  2 ɤ (0.511 MeV) (remember E= mc2)Dr. Sajjad Ullah, ICS, University of Peshawar

12. Neutron (n or 0
1n)
• They have no charge so exhibit 10 times deeper penetration depth than e-.
• They are primarily used in chemical analysis to induced radioactivity in a bombarded sample.
• Bombarding neutron either transfer energy to the target nucleus (which gets energetically excited)
or are captured by the nucleus (change N/Z ratio and induced radioactivity)
• Measurement of the nuclear emissions (particles or ɤ rays) emitted simultaneously can be used for
chemical analysis
• Neutron Activation Analysis: Analytical technique in which neutrons are used to produce an
unstable nucleus ( to de discussed later)
Dr. Sajjad Ullah, ICS, University of Peshawar

13. Gamma (ɤ) Rays
• Any excess energy produced during nuclear
reactions may be released as ɤ-rays
• Photons emitted from nucleus are called ɤ-
rays
• ɤ-rays are like x-rays except fro the source:
They are formed during relaxation of the
nucleus.
• The E of emitted ɤ-rays is characteristic of the
change in nuclear energetic levels for a
particular nuclide. Emission occurs at discrete
energies (Qualitative Analysis)
• Qualitative analysis: Compare ɤ-rays
spectrum of sample with those of known
nuclides.
• ɤ-rays-Matter interaction: Photoelectric effect,
Compton scattering and pair production Dr. Sajjad Ullah, ICS, University of Peshawar

14. Radiochemical Decay and Activity
Radiochemical decomposition of an unstable nuclide does not require
A collision with any other body, the process occurs by a first-order
mechanism
Activity: The rate at which radiochemical decay occurs is the Activity (A)
of the nuclide and is given by first-order rate law:
where, A= change in number of nuclei (N) divided
by the change in time (t)
λ = first order rate constant (1/s) or decay
constant. The larger the value
of λ, the higher is the decays rate
N = number of parent nuclei present at time t
The number (N) of parent nuclei present at time t is given by:
N0 = initial number of parent nuclei
present at time t0
This equation can be used to determine nuclear decay constant λ for a reaction from measurement of the half life.
The SI unit of radioactivity is Becquerel (Bq).
It is defined as one disintegration (decay of a
single nuclide) per second (d/s)
1 Bq= 1 d/s
Curie (Ci): A much larger unit.
1 curie equals the no. of nuclei disintegration
each second in 1 g of Radiuam-226:
1 Ci= 3.7 x 1010 d/s = 3.7 x 1010 Bq
Smaller units (mCi, µCi) are generally used.
Specific Activity = decay rate per unit substance
SA= Bq/g, Bq/mL, mCi/g, µCi/mL, , µCi/mmol
A α N or A = λN =
The number decaying per unit time is
Proportional to the number present
Dr. Sajjad Ullah, ICS, University of Peshawar

15. The half time t1/2 of a radiochemical decay is defined as the time
at which one half of the nuclides have decayed as is given by:
Half-life of Radioactive Decay
Note that first-order chemical change, the half-life in not dependent on
the number of nuclei and is inversely related to the decay constant (λ).
Lager λ, smaller t1/2 smaller λ, larger t1/2
6
14C  7
14N + -1
0β
Half-life in terms of mass
Initial amount of C = 1g
C left after fist half life= 0.5 g
C left after 2nd second half life = 0.25 g
A depends on N present, so A become ½
after each half-life
The decay constants and half lives of radionuclides vary
over an extremely wide range, even for nuclide of the a
given element (Table 24.5)
Since t1/2 is constant for a particular radionuclide and
since the t1/2 values vary between radionuclides, they can
sometimes be used to identify the nuclides.
Dr. Sajjad Ullah, ICS, University of Peshawar

16. Half lives= fraction of seconds to billions of years
Radionuclides that have half-lives between a fraction
of min and several thousands years could be used
for chemical analysis (see Table 20-2)
Dr. Sajjad Ullah, ICS, University of Peshawar

17. Instrumentation
(Radiochemical methods of analysis)
Source of nuclear particles
(to induce radioactivity)
Detectors
(monitor emission from the sample)
Cell
(to hold the sample)
The simplest apparatus that is used for radiochemical analysis
consists solely of a detector to monitor emission from the sample
Gas-ionization Scintillation) Semiconductive )
Ionization
Chamber
(α particle)
Geiger-Muller
Counter
(portable, total β activity)
Proportional
Counter
(β+ α particle)
Solid Liquid state
(Cocktail)
Proportional, scintillation, and semiconductive are energy
dispersive when operated with a multichannel analyser.
Dr. Sajjad Ullah, ICS, University of Peshawar

18. Gas Ionization Detector
Dr. Sajjad Ullah, ICS, University of Peshawar

19. Gas Ionization Detector
• Easily ionized gas (Ar, Kr, Xe and CH4) and two electrodes
• Cathode (metallic casing grounded)
• Anode: A rod in middle of the detector (positive potential)
• 5 cm thick Lead (Pb) shielding around the apparatus to lower background
count from environmental alpha, beta, gamma, cosmic rays)
• Responds unequally to alpha and beta particle
• Detector is more sensitive to alpha particles when operated in saturation
or proportional region
• Same response for alpha and beta particle in Geiger region
Sealed
(Be or mica)
window
Incident nuclear
emission
Dr. Sajjad Ullah, ICS, University of Peshawar

20. Proportional Counter (PC) Detector
A gas ionization detector operated in proportional
region
Can handle counting rates that approach 1 MHz
Sealed PC and flow-through PC
Filler Gas: 90% Ar and 10% CH4
Dr. Sajjad Ullah, ICS, University of Peshawar

21. Scintillation Counter
• Monitors the amount of emitted visible radiation from a phosphor powder (ZnS, calcium tungstate)
after excitation by incident radiation
• Modern detectors use a singe crystal rather than powder for such conversion.
• Mostly used to monitor β-particles (of E < 0.2 eV) and gamma radiation. For E> 0.2 eV, GM counter
or proportional counter are used
• Consists of a scintillator and one or two PMTs
• The radioactive emission strikes the scintillator and induces emission of visible radiation which is
monitored by PMT.
• Thallium (1 mol%) doped crystals of sodium iodide
(NaI(Tl)) detector is a common scintillation detector.
• Incident radiation excite the I atoms which transfer
some of their excess energy to thallium atoms which
subsequently emit 410 nm radiation (monitored)
• High sensitivity and thousands time amplification factor
Dr. Sajjad Ullah, ICS, University of Peshawar

22. Scintillation Cocktail
• Some detectors contain Scintillation solutions
• Sample and Scintillator are dissolved ins same solvent
• Some Liquid Scintillators: Anthracene, 2,5-diphenyloxazole (PPO),
p-terphenyl
• If primary scintillator (PPO) emit in the UV region, a second
scintillator (POPOP) is used to convert this UV light into visible light
(measured with PMT)
2,5-diphenyloxazole (PPO)
p-terphenyl
https://en.wikipedia.org/wiki/Scintillator
Anthracene
1,4-bis(5-phenyloxazol-2-yl) benzene (POPOP)
Dr. Sajjad Ullah, ICS, University of Peshawar

23. Semiconductive Detectors
• Lithium-drifted silicon (Si(Li)) , Lithium-drifted germanium Ge(Li), intrinsic Ge
detectors
• Used to monitor gamma or x-rays
• Detection based on the increase in conductivity when struck by radiation
• The detector has three regions:
- n-type region contains Li atoms in Si,
- p-type region
- intrinsic central region: contains Li ions in Si and has higher resistance
than the other two regions (this portion is sensitive to radiations)
Lithium-drifted silicon detector
• X-rays or gammas rays enter the intrinsic region and excites electrons to a conduction band and the
resistance in this region decreases, allowing a flow of current through the device.
• A large current pulse is generated from each incident x-ray photon.
• The output of the detector is directly proportional to the E of the incident radiation.
• Operational Temperature (77 K, liquid nitrogen bath): Decrease thermal noise, increase reslaution
Dr. Sajjad Ullah, ICS, University of Peshawar

24. Dr. Sajjad Ullah, ICS, University of Peshawar

25. Fission: The process by which a radionuclide decays into at least two pieces which have atomic number greater than 2
Dr. Sajjad Ullah, ICS, University of Peshawar

26. Dr. Sajjad Ullah, ICS, University of Peshawar

27. Dr. Sajjad Ullah, ICS, University of Peshawar

28. Dr. Sajjad Ullah, ICS, University of Peshawar

29. Isotopic Dilution Methods
BS 7 (Chemistry)
Dr. Sajjad Ullah, ICS-UoP
Nov 2018

30. Isotopic Dilution Methods:
(1) Direct Isotopic Dilution Analysis (DIDA)
(2) Inverse Isotopic Dilution Analysis (IIDA)
(1) Direct Isotopic Dilution Analysis (DIDA):
The Method of quantitative analysis which relies upon addition of a radioactive component to the sample (non-radioactive) is
DIDA
In this technique, a known amount of radioactive material (m*) is homogenously mixed with a nonradioactive analyte (m)
The added radioactive component is as nearly identical to the analyte as possible. That is, it must behave identically to the
analyte during the separation portion of the assay.
The analyte and the radioactive component are chemically separated, as pure compounds, from the remainder of the
sample.
A weighed portion of the separated component (mM) is measured for it radioactivity and the result is used to calculate
The amount of the analyte in the original sample (see below).

31. During DIDA, it is convenient to use the Specific Activity (SA) of the components
For DIDA, Specific activity is the ratio of the activity to a unit mass of substance. For instance, for the radioactive
component:
As = SAs . m*
ORSAM =
𝐴 𝑀
𝑚 𝑀
AM = SAM . mM
ORSAs =
𝐴 𝑠
𝑚∗
SAs = specific activity of radioactive component
As = activity of radioactive component
m* = mass of radioactive component
SAM = specific activity of the separated mixture of the
radioactive component and the analyte
mM= mass of the mixture (radioactive component + analyte)
i.e., mM = m* + m
AM= activity of the mixture
Similarly, the specific activity (SAM) of the separated mixture of the radioactive component and
the analyte is given by:
AM = SAM . (m + m*)
The number of radionuclides in the pure radioactive component is identical to the number in the mixture.
Consequently, the activity of pure radionuclide (As) and the activity of the mixture (AM) must be identical (As= AM)
SAs . m* = SAM . (m + m*)
m =
𝑚∗(𝑆𝐴𝑠−𝑆𝐴𝑀)
𝑆𝐴 𝑀
This equation allows calculation of mass (m) of the analyte
OR

32. (2) Inverse Isotopic Dilution Analysis (IIDA
The Method of quantitative analysis which relies upon addition of a nonradioactive nuclide to the
radioactive analyte (to be quantified) of the same element is IIDA.
IIDA is used to determine the mass of radionuclide after dilution with a non-radioactive nuclide of the same
element.
The principle of IIDA is the same as that of DIDA.
AM = SAM . (m + m*)
SAM =
𝐴 𝑀
𝑚 𝑀
Setting SAM =
𝐴 𝑀
𝑚 𝑀

33. Radiometric Titrations
• In a Radiometric Analysis, a radioactive substance is used in a chemical reaction with a nonradioactive
Substance for the purpose of quantitatively assaying the nonradioactive substance
• The radioactive substance can be used in a titration with the non-radioactive substances.
• A radiometric titration curve is obtained by plotting the radioactivity as function of titrant volume.
• The Endpoint of the titration is located from a titration curve.
• Can be applied to precipitation (most common), complexometric and redox titration. It can be used when the
titrant gives an insoluble precipitate or compound can be extracted easily, and when one of the reaction
partners can be labeled
• Standard solution of radiometric compound is prepared and used as titrand or titrant
110Ag+ + Cl-  AgCl(s)
The activity of solution is measured. Before end point, AgCl precipitates out and Activity is low.
After end point, excess Ag+ added to solution causes an increase in activity and
titration curve: Plot A vs added AgNO3 amount
1102Ag+ + CrO4
2-  Ag2CrO4(s)
Ca2+ + 2F-  CaF2
Ag+ + Br-  AgBr(s)

34. During the titration, the reagent is added in different quantities and the activity of the precipitate or the filtrate is
measured, or in case of extraction the activity of one phase is determined.
There are three methods, depending the way of labeling:
1. The titrant is labeled with its radioactive isotope: the activity of the solution decreases to the equivalent point, and
then it remains constant.
2. The reagent is labeled: the activity of the solution increases after the equivalency.
3. Both reaction partners are labeled: the activity of the solution has a minimum.