3. Radioactivity refers to the particles which are
emitted from nuclei as a result of nuclear
instability. Because the nucleus experiences the
intense conflictbetween the two strongest forces
in nature, it should not be surprising that there
are many nuclearisotopes which are unstable
and emit some kind of radiation. The most
common types of radiation are called alpha,
beta, and gamma radiation, but there are
several other varieties of radioactive decay.
Radioactive decay rates are normally stated in terms of their
half-lives, and the half-life of a given nuclear species is
related to its radiation risk. The different types of radioactivity
lead to different decay paths which transmute the nuclei into
other chemical elements. Examining the amounts of the decay
products makes possibleradioactive dating.
Radiation from nuclear sources is distributed equally in all
directions, obeying theinverse square law.
4. Radioactivity is the process whereby unstable atomic nuclei release
energetic subatomic particles. The word radioactivity is also used to refer
to the subatomic particles themselves. This phenomenon is observed in
the heavy elements, like uranium, and unstable isotopes, like carbon-14.
Radioactivity was first discovered in 1896 by the French scientist Henri
Becquerel, after which the SI unit for radiation, the Becquerel, is named.
Becquerel discovered that uranium salts were able to blacken a
photographic plate placed in the dark, even through a paper barrier.
Subsequent experiments distinguished three distinct types of radiation --
alpha particles, beta particles, and gamma rays. These are positively
charged, negatively charged, and neutral, respectively. In the United
States, human exposure to radioactivity is measured in rads, where one
rad represents 0.01 joule of energy absorbed per kilogram of tissue.
Radioactivity is a random process, meaning that it is physically impossible
to predict whether or not a given atomic nucleus will decay and emit
radiation at any given moment. Rather, radioactivity is quantified using
half-life, which is the period of time it takes for half of the given nuclei to
decay. Half-life applies to a sample of any size, from a microscopic
quantity to all the atoms of that type in the universe. Half-life varies widely,
from a couple seconds (Astatine-218) to billions of years (Uranium-238).
6. French physics Professor Antoine Henri Becquerel discovered that
uranium compounds produced rays that blacked photographic plates.
Elements that spontaneously emit energetic particles and rays from their
atomic nuclei have radioactive property or undergo radioactivity. These
emitted particles or rays are called radiation. An elemental material
(such as uranium) that emits radiation is called radioactive material.
Most, but not all, atomic nuclei are stable i.e. not radioactive.
Radioactivity is a naturally occurring process that occurs when an
unstable nucleus goes through a transformation, moving to a lower
energy state accessible to the nucleus. The nucleus splits apart releasing
energy in order to become stable.
Radiation emitted from a nucleus can be particles, such
as alpha particles (2 protons, 2 neutrons), beta particles (electrons) as
well as neutrons, and the electromagnetic gamma rays and x-rays.
A radioactive material can be in solid, liquid or gaseous form. They are
found naturally in our environment and commonly used in society. Natural
sources of radiation in the environment, such as the continuous shower of
cosmic rays from space and radioactive material in the ground and air
(some of which is a result of atmospheric atomic bomb testing, and
Chernobyl), create a "background" radiation exposure that we are all
7. Alpha Radioactivity Composed of two protons and two neutrons,
the alpha particle is a nucleus of the
element helium. Because of its very large
mass (more than 7000 times the mass of
the beta particle) and its charge, it has a
very short range. It is not suitable for
radiation therapy since its range is less than
a tenth of a millimeter inside the body. Its
main radiation hazard comes when it is
ingested into the body; it has great
destructive power within its short range. In
contact with fast-growing membranes and
living cells, it is positioned for maximum
Alpha particle emission is modeled as a
barrier penetration process. The alpha particle is the
nucleus of the helium atom and is the nucleus of
9. Radioactivity Decay Professionals often specialize in a certain area
of study, such as radioactivity, decay, fusion, or atomic interactions.
Using established scientific methods, nuclear chemists and physicists
design highly-detailed, controlled experiments.
Radioactivity is a random process, meaning that it is physically
impossible to predict whether or not a given atomic nucleus
will decay and emit radiation at any given moment.
Rather, radioactivity is quantified using half-life, which is the period of
time it takes for half of the given nuclei to decay.
At the start of the testing procedure, patients swallow the
radioactive iodine and wait for a period of six to 24 hours before returning to
have the thyroid's radioactivity assessed. During the
radioactive iodine uptake test, which only takes a few minutes, the patient
sits upright in a chair while a probe is positioned several inches in front of the
Patients normally refrain from eating and drinking for a couple of hours after
treatment, and are then encouraged to take plenty of fluids to
flushradioactivity from the body. As one of the effects of
radioactive iodine ablation is to make patients a little radioactive, patients are
required to stay in a room by themselves after treatment.
11. Tritium Radioactivity
In small doses, radioactivity is a useful
process that can be harnessed by man.
For example, nuclear reactors
exploit radioactivity to generate heat.
Phosphorescent materials sometimes
include small quantities of radioactive
atoms. Radioactivity Effects :
Materials containing carbon-14 can be In small doses, radioactivity is a useful
placed in geological time using a process that can be harnessed by man.
process known as radiocarbon dating, in For example, nuclear reactors
which the amount of carbon-14 in the exploit radioactivity to generate heat.
material is used to determine its age. Phosphorescent materials sometimes
Terrestrial radiation is the second major include small quantities of radioactive
source of natural radioactivity. This atoms.
radiation comes from isotopes of carbon A request to borrow a car may, in fact,
and potassium, as well as thorium and go no further than the objective
uranium, which may be found in soil, explicitly stated. The claimed cause
rocks, or water. and effect relationship simply does not
13. WHAT IS RADIOISOTOPES?
Radioisotopes are isotopes that are
unstable and release radiation.
A radioisotopes is an atom with an unstable nucleus,
characterized by excess energy available to be
imparted either to a newly created radiation particle
within the nucleus or via internal conversion. During
this process, the radionuclide is said to undergo
radioactive decay, resulting in the emission of
gamma ray and subatomic particles such as alpha or
beta particles. These emissions constitute
ionizing radiation. Radioisotopes occur naturally, or can
be produced artificially.
Radioisotopes are often referred to by chemists and
physicists as radioactive isotopes or radionuclide.
Radioisotopes with suitable half-lives play an important
part in a number of technologies (for example,
nuclear medicine). Radioisotopes can also present both
real and perceived dangers to health..
14. Radioisotopes produced with nuclear reactors exploit the high flux of neutrons
present. These neutrons activate elements placed within the reactor. A typical
product from a nuclear reactor is thallium-201 and iridium-192. The elements that
have a large propensity to take up the neutrons in the reactor are said to have a
high neutron cross-section.
They are radioactive isotopes
An element has a characteristic number of protons (P) in its nucleus.
Atoms of the element may have various numbers of neutrons (N) in the nucleus,
typically close to P. For each element, we can gather naturally occurring samples
and measure the number of neutrons N found in the nuclei, and find the average.
The mass of each atom in the sample is roughly P+N.
In the sample, one value of N will be predominant, with other numbers (other
atomic masses) being less common, and typically heavier. They are less common
because they are less stable, and are likely to break down (emitting radioactive
particles) into other isotopes. If two atoms of an element have different atomic
masses (different N's), then we call them isotopes of the element. The most
stable isotope of an element (the longest-lived isotope) will be the one mostly
commonly occurring in nature, as other isotopes will tend to break down and
A radioisotope is an unstable isotope of an atom with a short enough half-life to
cause measurable amounts of radioactive particles to be emitted.
15. Uses Of Radioactivity
Sterilization of medical instruments and food is another common
application of radiation. By subjecting the instruments and food to
concentrated beams of radiation, we can kill microorganisms that
cause contamination and disease. Because this is done with high
energy radiation sources using electromagnetic energy, there is no
fear of residual radiation. Also, the instruments and food may be
handled without fear of radiation poisoning.
Radiation sources are extremely important to the manufacturing
industries throughout the world. They are commonly employed by
nondestructive testing personnel to monitor materials and
processes in the making of the products we see and use every day.
Trained technicians use radiography to image materials and
products much like a dentist uses radiation to x-ray your teeth for
cavities. There are many industrial applications that rely on
radioactivity to assist in determining if the material or product is
internally sound and fit for its application.
16. Uses of Radioisotopes
Radioisotopes are also a method of treatment in
hemopoietic forms of tumors; the success for
treatment of solid tumors has been limited. More
powerful gamma sources sterilise syringes and other
In biochemistry and genetics, radionuclides label
molecules and allow tracing chemical and physiological
processes occurring in living organisms, such as
DNA replication or amino acid transport.
In food preservation, radiation is used to stop the
sprouting of root crops after harvesting, to kill
parasites and pests, and to control the ripening of
stored fruit and vegetables.
In industry, and in mining, radionuclides examine
welds, to detect leaks, to study the rate of wear,
erosion and corrosion of metals, and for on-stream
analysis of a wide range of minerals and fuels.