2. Isotopes and Radioactive Decay
Presented to: Madam Bushra Khalid
Presented by: Sairah Akber
Sidra Butt
FatimaWaleed

3. Isotopes
What are isotopes ?
Any of two or more forms of a chemical element,
having the same number of protons in the
nucleus, but having different numbers of
neutrons in the nucleus.

4. History
• Henri Becquerel (1852-1908) discovered the
existence of multiple masses for the same
element when he realized a product of uranium's
radioactive decay, ionium, was unable to be
retrieved again by chemical means from the
element thorium.
• Because chemical uniqueness is a defining
characteristic of an element, it had to be
concluded that ionium was not a new
element, just a different variation of thorium.

5. History
• Frederick Soddy (1877-1956) was an English
scientist who worked along with Ernest Rutherford
on his research with radioactivity.
• They hypothesized in 1913 that elements existed
with different atomic masses that were chemically
inseparable.
• He concluded that these were all the same element
and should reside in the same place on the periodic
table.
• He coined these different atoms in the same element
isotopes.

6. Occurrence in nature
• All isotopes are not equally abundant in nature.
• For example, naturally occurring isotopes of
Hydrogen (Hydrogen-2 is the only common
isotope which has its own name, and is generally
called Deuterium).

7. Radioactive and Stable isotopes
Radioactive isotopes Stable isotopes
• Radioactive isotope or
radioisotope, natural or
artificially created isotopes of a
chemical element having an
unstable nucleus that
decays, emitting
alpha, beta, or gamma rays
until stability is reached.
• The stable end product is a
nonradioactive isotope of
another element, i.e., radium-
226 decays finally to lead-206.
• Stable isotopes are chemical
isotopes that may or may not
be radioactive, but if
radioactive, have half lives too
long to be measured.
• Only 90 nuclides from the first
40 elements are energetically
stable .
• there are 255 known stable
nuclides of the 80 elements
which have one or more stable
isotopes.

8. Radioactive and stable isotopes
• Diagram for radioactive isotopes:
• Diagram for stable isotopes: stable isotopes of
carbon

9. Uses of Radioactive isotopes
• In therapy, they are used to kill or inhibit specific
malfunctioning cells.
• Radioactive phosphorus is used to treat abnormal cell
proliferation, e.g., polycythemia and leukemia.
• Radioactive iodine can be used in the diagnosis of thyroid
function and in the treatment of hyperthyroidism.
• In research, radioactive isotopes as tracer agents make it
possible to follow the action and reaction of organic and
inorganic substances within the body.
• They also help to ascertain the effects of radiation on the
human organism.
• In industry, radioactive isotopes are used for a number of
purposes, including measuring the thickness of metal or
plastic sheets, testing for corrosion or wear, and monitoring
various processes.

10. Uses of Stable isotopes
• With growing demand for petroleum products
methods such as isotopic analysis is becoming more
common.
• Stable Isotopes can enhance prospecting as well as
production in a petroleum company.
• Stable isotopes have helped uncover migratory
routes, trophic levels, and the geographic origin of
migratory animals.
• They can be used on land as well as in the ocean and
have revolutionized how researchers study animal
movement.

11. Chemical and molecular properties
• Chemical behavior of an atom is largely determined
by its electronic structure, so different isotopes
exhibit nearly identical chemical behavior.
• The main exception to this is the kinetic isotope
effect: due to their larger masses, heavier isotopes
tend to react somewhat more slowly than lighter
isotopes of the same element.
• This is most pronounced for protium (1H) and
deuterium (2H).
• The mass effect between deuterium and the
relatively light protium also affects the behavior of
their respective chemical bonds.

12. Chemical and molecular properties
• However, for heavier elements, which have more
neutrons than lighter elements, the ratio of the
nuclear mass to the collective electronic mass is far
greater, and the relative mass difference between
isotopes is much less.
• For these two reasons, the mass-difference effects
on chemistry are usually negligible.
• In similar manner, two molecules that differ only in
the isotopic nature of their atoms (isotopologues)
will have identical electronic structure and therefore
almost indistinguishable physical and chemical
properties.

13. Nuclear properties and Stability
• Atomic nuclei consist of protons and neutrons bound
together by the residual strong force.
• Proton repel each other and neutron stabilize the atom
in two ways:
• Their copresent pushes protons slightly apart, reducing
the electrostatic repulsion between the protons, and they
exert the attractive nuclear force on each other and on
protons.
• For this reason, one or more neutrons are necessary for
two or more protons to be bound into a nucleus.
• As the number of protons increases, so does the ratio of
neutrons to protons necessary to ensure a stable nucleus
.

14. Application of isotopes
• Isotope analysis is the determination of isotopic
signature, the relative abundances of isotopes of a
given element in a particular sample. For biogenic
substances in particular, significant variations of
isotopes of C, N and O can occur.
• The identification of certain meteorites as having
originated on Mars is based in part upon the
isotopic signature of trace gases contained in them.
• Isotopic substitution can be used to determine the
mechanism of a chemical reaction via the kinetic
isotope effect.

15. Applications of isotopes
• Isotopic labeling, the use of unusual isotopes as
tracers or markers in chemical reactions. Normally,
atoms of a given element are indistinguishable from
each other.
• However, by using isotopes of different masses, even
different nonradioactive stable isotopes can be
distinguished by mass spectrometry or infrared
spectroscopy. For example, in 'stable isotope
labeling with amino acids in cell culture (SILAC)'
stable isotopes are used to quantify proteins.

16. Radioactivity
• Radioactivity
▫ emission of high-energy radiation from the nucleus of an atom
• Nuclide
▫ nucleus of an isotope
• Transmutation
▫ process of changing one element into another via nuclear decay
• The nuclei of some atoms are unstable. The nucleus of an
unstable atom will decay to become more stable by emitting
radiation in the form of a particle or electromagnetic radiation.

17. Radioactive Decay

18. Radioactivity
• Random process :
Random process means there is no way to
tell which nucleus will decay, and cannot predict
when it is going to decay.
• Spontaneous process :
A spontaneous process means the process
is not triggered by any external factors such as
temperature of pressure.

19. History
• Radioactivity was discovered in 1896 by the French scientist Henri
Becquerel, while working on phosphorescent materials.
• Rutherford and his Student where first to realize that many decay processes
resulted in transmutation
• Radioactive Displacement law of Fajjans And Soddy were Formulated to
Describe alpha and Beta Decay.

20. Radioactive Particles
• By the end of the 1800s, it was known that certain
isotopes emit penetrating rays. Three types of
radiation
were known:
•
1) Alpha particles (a)
2) Beta particles (b)
3) Gamma-rays (g)

22. Alpha decay(a)
• In alpha decay, the nucleus emits an alpha
particle; an alpha particle is essentially a helium
nucleus, so it's a group of two protons and two
neutrons. A helium nucleus is very stable.

23. Beta Decay(b)
• A beta particle is often an electron, but can also
be a positron, a positively-charged particle that
is the anti-matter equivalent of the electron. If
an electron is involved, the number of neutrons
in the nucleus decreases by one and the number
of protons increases by one.

24. Gamma Decay (g)
• The third class of radioactive decay is gamma
decay, in which the nucleus changes from a
higher-level energy state to a lower level. Similar
to the energy levels for electrons in the atom, the
nucleus has energy levels.

25. Properties of Radioactive Particles

26. Penetrating power
• The penetrating effect of alpha, beta and gamma
radiation depends on their ionizing power.
• Radiation which has a stronger ionizing power will have
a lower penetrating effect.
• The radiation emission loses some of its energy each
time an ion pair is produced.
• Alpha particles lose energy very quick as they move
through a medium. After a short distance in the
medium, the alpha particles would have lost almost all
energy. So alpha particles have the lowest penetrating
power.

28. Interaction with electrical field
• Alpha and beta particles are deflected in an electric field
because they are charged. The deflections are in opposite
direction because they carry opposite charges. The
deflection of beta is larger than alpha because mass of
beta < mass of alpha
• Gamma rays are not deflected because they do not carry
any charge.

29. Ionizing effect
• Radioactive emission has an ionizing effect
• The 3 types of radiation are highly energetic and
use their energy to remove electrons from the air
molecules when they pass through air.
• The ionization of an atom produces positive ion
and negative ion (electron)
• Due to their different charges and masses, they
have different ionizing abilities

30. Interaction with magnetic field
•Alpha particles and beta
particles are also deflected when
they pass through a magnetic
field while gamma rays are
unaffected.
•The direction of the deflection
of alpha particles in the
magnetic field can be found
using Fleming’s left-hand rule.

31. Radioactive Decay
• Radioactive decay is the process by which
unstable atomic nuclei emit subatomic particles
or radiation.
• When a radioactive nucleus decays, its nucleus
breaks up, emits an alpha particle or beta
particle and energy, and forms a new atom of a
different element.
• A parent nuclide X changes into a daughter
nuclide Y.

32. During radioactive decay, principles of conservation
apply. Some of these we've looked at already, but
the last is a new one:
• conservation of energy
• conservation of momentum (linear and
angular)
• conservation of charge
• conservation of nucleon number
Conservation of nucleon number means that the total
number of nucleons (neutrons + protons) must be
the same before and after a decay.

33. What Causes Radioactive Decay?
• As we know that a nucleus consists of protons and
neutrons, they are bound together by strong
interaction. The attractive force of strong interaction
and repulsive force of electrostatic force between
protons is responsible for the nature of the nucleus
in terms of its stability.
• Atoms which have low atomic number have
approximately same neutron and protons. As the
value of atomic number increases, the number of
neutrons inside the stable nucleus increases than
the number of protons. As a result, a point is
obtained where there is no stable nucleus.

34. Rate of Decay
 Beyond knowing the types of particles which are emitted
when an isotope decays, we also are interested in how frequently
one of the atoms emits this radiation.
 A very important point here is that we cannot predict when a
particular entity will decay.
 We do know though, that if we had a large sample of a radioactive
substance, some number will decay after a given amount of time.
 Some radioactive substances have a very high “rate of decay”,
while others have a very low decay rate.
 To differentiate different radioactive substances, we look to
quantify this idea of “decay rate”

35. Decay Rates
For a given element, the decay or disintegration rate is
proportional to the number of atoms and the
activity measured in terms of atoms per unit time. If "A"
represents the disintegration rate and "N" is number of
radioactive atoms, then the direct relationship between
them can be shown as below:
A proportional to N
Or mathematically speaking
A= λ N Equation 1
Where λ is constant of proportionality or decay constant.

36. Radioactive nuclei decay by first-order kinetics.
The rate of radioactive decay is therefore the
product of a rate constant (k) times the number
of atoms of the isotope in the sample (N).
Rate = kN

37. Danger of Radioactive Decay
• Alpha particles may be completely stopped by a sheet of
paper, beta particles by aluminum shielding. Gamma rays can
only be reduced by much more substantial mass, such as a
very thick layer of lead.
• The dangers of radioactivity and radiation were not
immediately recognized. Acute effects of radiation were first
observed in the use of X-rays when electrical engineer and
physicist Nikola Tesla intentionally subjected his fingers to X-
rays in 1896. He published his observations concerning the
burns that developed, though he attributed them to ozone
rather than to X-rays. His injuries later healed.
• The genetic effects of radiation, including the effect of cancer
risk, were recognized much later. In 1927, Hermann Joseph
Muller published research showing genetic effects, and in
1946 was awarded the Nobel prize for his findings.

38. Effect of Radioactive Decay

39. Unit of Radioactivity Decay
• The rate at which a radioactive isotope decays
is called the activity of the isotope. The most
common unit of activity is the curie (Ci), which
was originally defined as the number of
disintegrations per second in 1 gram of 226Ra.
The curie is now defined as the amount of
radioactive isotope necessary to achieve an
activity of 3.700 x 1010 disintegrations per
second.

41. Half-Life
• The half-life of a radioactive element is the time
that it takes for one half of the atoms of that
substance to disintegrate into another nuclear
form. These can range from mere fractions of a
second, to many billions of years. In addition,
the half-life of a particular radionuclide is
unique to that radionuclide, meaning that
knowledge of the half-life leads to the identity of
the radionuclide.