RADIO ACTIVITY

Radioactivity is a process through which atoms emits energetic particles or rays

known as radiation. Nuclear radiation occurs as a result of alteration in the
nuclear structure or composition and this process occurs in a nucleus that is
unstable and hence radioactive.
Radioactivity can either be natural (spontaneous) emitting radiation on its
own or artificial by altering the nucleus of the element

TYPES OF RADIATION
Radioactive radiation that is emitted from an unstable nuclei are of three types
with different penetrating powers which include the following: - alpha, beta,
and gamma radiations.

THE ALPHA PARTICLE (RAYS);- These are fast moving streams of positively
charged particles each with having a mass number of four and an atomic
number of two. Each alpha particle is identical to nucleus of Helium atom (He)
or an Helium ion (He2+) which is represented as 42He or 42He2+.
Since alpha particles are positively charged and heavy, they are slightly
deflected towards the negative plate in the electromagnetic field and they
have a very low penetrating power. They travel on a few centimeters in air and
are stopped by a thin sheet of paper or aluminum foil that is 0.1mm thick and
they exerts very powerful ionizing effect upon any gas they pass through. They
also cause fluorescence in some materials eg ZnSO4 .

BETA PARTICLES (RAYS) :- Beta rays are fast moving streams of electrons and
negatively charge with relatively low mass compare to alpha rays. They are quit
deflected to the positively charged plate in the electromagnetic field. Each
particle has amass number of zero and a charge of -1and are represented by
the symbol -1oe . Beta particle has more penetrating power than alpha particle
and move the distance of about 3m in air and about 4mm in aluminium. They
also can cause flourescencein some materials or some substaces.
GAMMA RAYS :- This is not a particle but a part of electromagnetic wave
similar to a visible light and an X-rays but with a very short wave length. They
travel at the speed of light and not affected by the electromagnetic field and
they have a very high penetrating power which can penetrate about 100m in
air and pass through 0.5m of iron or lead. It is a pure energy and has no
proton, neutron, or electron. It is only represented by the symbol ꙋ.
X-RAYS :- these are electromagnetic wave like visible light but with a shorter
wavelength produced by allowing a fast moving streams of electrons to
bombard metals such as tungsten. The fast moving electron knocks electrons
out of the inner shells of the metal atoms and dislodge electrons are replaced
by electrons moving inn from the outer shells. This movement of electrons is
accompanied by the emission of X-rays.
X-rays can easily penetrate through substances which are opaque to visible
light such as metals, woods, flesh and papers.
There are two types of X-rays which are the hard and soft X-rays with the hard
type having a higher penetrating power than the soft type. Soft X-rays pass
through the flesh and are absorbed by the dense bones that is why it is used in
medicine to photograph human body parts while the hard X-rays are used to
destroy cancer cells in the body when carefully controlled.

MAJOR PROPERTIES OF ALPHA BETA AND GAMA RADIATIONS

NAME/SYMBOL IDENTITY CHARGE MASS VELOCITY PENETRATION
Alpha (α) Helium +2 4.0026 5-10% Low
nucleus speed of
light
Beta (β) Electron -1 0.000549 Up to 90% Medium
speed of
light
Gamma (ꙋ) Radiant 0 0 Speed of High
energy light
 RADIO ACTIVE DECAY
Radioactive decay is the spontaneous disintergration of certain quantity of
radioactive material or element. During this process atoms emits either alpha
or beta particles when the nucleus of the parent material undergo change in
atomic number and become the nucleus of another element. The new nucleus
is called a daughter nucleus and the process is known as transmutation of an
atom. Basically there are two types of radioactive decay that is the alpha and
beta decay.
1. ALPHA DECAY:- when the nucleus of an atom loses an alpha particle
during disintegration, the atomic number of the atom is reduced by two
(2) units and its mass number by four (4) units which results into a new
element with an atomic number and mass number different (smaller)
than those of the generating or originating atom by two and four units
respectively.
When we consider the decay of one isotope of uranium 238 to thorium
and an alpha particle, the loss of alpha particle in this process is called
alpha decay eg.
238 234 4
92U → 90 Th + 2He

2. BETE DECAY:-When the nucleus of an atom emits beta particle, it is

equal to the splitting of a neutron in the nucleus to form electron which
is the beta particle and a proton which remains in the nucleus which
result in increase in atomic number by one unit but the mass number
remains unaltered and thus resulting into new element with similar
properties to the parent element.
If a thorium nucleus changes to protactinium (23491Pa) with the same
mass number but different atomic which is increase by one unit. Eg.
234 234 0
90 Th 91Pa + -1e

HALF LIFE
Radioactive elements decay at varying rates and this decay is usually
express in terms of half life of the radioactive element.
The half life of a radioactive element is the time taken for half of the
total number of atoms in a given sample of element or isotope to decay
or undergo a change. The half life of an isotope may vary from split of
seconds to millions of years. The stability of an isotope is determine by
the isotopes half life. Isotopes with short half life decays rapidly and are
 very unstable eg. Polonium 212 half life is 3.0 x 10-7 seconds. On the
other hand, carbon 14 half life is 5.76 x 103 years while uranium 238 is
4.51 x 109 years.

NUCLEAR FISSION AND NUCLEAR FUSSION

NUCLEAR FISSION ;- this is the process in which the nucleus of a heavy
element is split into two nuclei of nearly equal mass with the release of energy
and radiation.
In all cases of nuclear fission, the total mass of all the fragment and the
neutrons release, differs from the total mass of the original atom of the
element and the mass of the bombarding neutron this is because mass is
converted to energy during fission.
236
92 U ----------> 9436 Kr + 141
56 Ba + 3 01n + energy
NUCLEAR FUSION ;- this is the process in which two or more lighter nuclei
combine to form a heavier nucleus with the release of energy and radiation.
This energy is due to slight loss in mass when the heavier nuclei is formed by
the fusion of the lighter nuclei. Fusion occurs at extremely high temperature of
1.5 x 107o c in a process known as thermo-nuclear reaction. This is because
large energies have to be given to the positively charged nuclei to overcome
the repulsion between them.
2
1 H + 31H -----> 4
2 He + 1 0n + energy.

MEDICAL APPLICATION OF RADIOACTIVITY

The use of radiation in the treatment of various forms of cancer as well as the
newer area of nuclear medicine and the use of radio isotopes in diagnosis has
become wide spread in recent times. Examples include :-
1. CANCER THERAPY :- when a high energy radiation such as gamma
radiation pass through a cell, it may collide with one of the molecules in
the cell and cause it to lose one or more electrons, causing a series of
events that result in the production of ion pairs eg. Ionizing radiation.
 Ions produce in this format or process may damage biological molecules
and cause changes in their cellular biochemical process which may alter
call function and in extreme cases even death of the cell.
Tumor cells are more susceptible to the effects of gamma radiations
than normal cells. Therefore exposing the tumor area to a carefully
controlled dosage of high energy gamma radiation from cobalt 60 will
kill high percentage of the abnormal cells than the normal cells. If the
dosage is given correctly, good number of cancer cells will die leaving
good number of normal cells which will maintain the function of the
affected organ.
Exposure of normal cells to a gamma radiation equally cause cancer but
radiation therapy for cancer requires unusual care and sophistication.
2. NUCLEAR MEDICINE :- The diagnosis of disease of the human body has
been made routine through the use of radioactive tracers. Tracers are
small amounts of radioactive substance use as probes to study internal
organs.
A small amount of tracers usually from an isotope of an element that is
known to be attracted to the organ of interest is administered to the
patient. Because the isotope is radioactive and its path can be traced or
followed by using a suitable device. When the picture of the organ is
obtained, it gives a far detailed information than a conventional x-rays.
Such techniques are none invasive ie surgery may not be required to
study or investigate the condition of the internal organs.
The radioactive isotope used for tracer studies has exactly the same
chemical behavior as any isotope of the same element eg. Iodine-127 is
the most abundant nonradioactive isotope of iodine which concentrate
in the thyroid gland. The rate of uptake of radioactive isotope gives a
valuable information regarding the under-activity or over-activity of the
thyroid gland.

ISOTOPES COMMONLY USED IN MEDICINE

 S/ AREA OF BODY ISOTOPE USES
N
1 Blood Chromium- Detects volume of blood
51
2 Coronary Thallium- Detects location of obstruction in
artery 201 coronary arteries
3 lungs Xenon-133 Locates region of reduced
ventilation and tumors
4 thyroid Iodine-131 Detects rate of iodine uptake by
the thyroid gland
5 Bone Barium -501 Detects active sites of
rheumatoid arthritis
6 Heart Technetium- Detects cardiac output
99
7. Kidney Technetium- Detects renal function
99

EFFECTS OF RADIATION
In working with radioactive substance, the chosen protocol is base on
the understanding of the effects of radiation, dosage levels and
tolerance levels and the basic precepts of radiation safety. Base on this,
the following factors must be considered :-

1. TIME OF EXPOSURE :- The effects of radiation are cumulative ie

potential damage is directly proportional to the time of exposure.
Workers expose to moderately high level of radiation on a job may be
limited in the time that they can perform that particular task to
reduce the effects of radiation and radiation related ailments.
2. DISTANCE FROM RADIATIO SOURCE :- the intensity of radiation varies
inversely with the square of the distance from the radiation source.
Doubling the distance from the source decrease the intensity by the
factor of four. The use of robot manipulators is of great advantage
which allows a greater distance between the operators and the
radioactive source.
3. SHIELDING :- Alpha and beta particles with relatively low penetrating
powers requires low level of shielding. A lab coat and gloves are
 relatively sufficient protection from these low penetrating radiation.
On the other hand, shielding made from concrete lead or block or
both are required for x-rays and gamma which are high energy
radiations. Extensive emission and manipulation of gamma emitters
are often accomplished in the laboratory by the use of robotic
control.
4. MAGNITUDE OF HALF LIFE :- In considering safety, isotopes with
short half life are of advantage and disadvantage. On one hand short
half life isotopes produce a large amount of radioactivity per unit
time than a long half life substance. Equal time of exposure will result
into a higher level of radiation for substance with short half life and a
lower level of radiation with substance with long half life.