1.

Radiation is energy that comes from a source and travels through some material
or through space. Light, heat and sound are types of radiation. The kind
of radiation discussed in this presentation is called ionizing radiation because it can
produce charged particles (ions) in matter.

1.

Radioactivity refers to the particles which are emitted from nuclei as a result of
nuclear instability. Because the nucleus experiences the intense conflict between the
two strongest forces in nature, it should not be surprising that there are many nuclear
isotopes which are unstable and emit some kind of radiation.

In 1896 Henri Becquerel was using naturally fluorescent minerals to

study the properties of x-rays, which had been discovered in 1895
by Wilhelm Roentgen. He exposed potassium uranyl sulfate to
sunlight and then placed it on photographic plates wrapped in black
paper, believing that the uranium absorbed the suns energy and
then emitted it as x-rays. This hypothesis was disproved on the
26th-27th of February, when his experiment "failed" because it was
overcast in Paris. For some reason, Becquerel decided to develop his
photographic plates anyway. To his surprise, the images were strong
and clear, proving that the uranium emitted radiation without an
external source of energy such as the sun. Becquerel had
discovered radioactivity.
Becquerel used an apparatus similar to that displayed below to show
that the radiation he discovered could not be x-rays. X-rays are
neutral and cannot be bent in a magnetic field. The new radiation
was bent by the magnetic field so that the radiation must be
charged and different than x-rays. When different radioactive
substances were put in the magnetic field, they deflected in
different directions or not at all, showing that there were three
classes of radioactivity: negative, positive, and electrically neutral.

The term radioactivity was actually coined by Marie Curie, who

together with her husband Pierre, began investigating the
phenomenon recently discovered by Becquerel. The Curies extracted
uranium from ore and to their surprise, found that the leftover ore
showed more activity than the pure uranium. They concluded that
the ore contained other radioactive elements. This led to the
discoveries of the elements polonium and radium. It took four more
years of processing tons of ore to isolate enough of each element to
determine their chemical properties.
Ernest Rutherford, who did many experiments studying the
properties of radioactive decay, named these alpha, beta, and
gamma particles, and classified them by their ability to penetrate
matter. Rutherford used an apparatus similar to that depicted in Fig.
3-7. When the air from the chamber was removed, the alpha source
made a spot on the photographic plate. When air was added, the
spot disappeared. Thus, only a few centimeters of air were enough
to stop the alpha radiation.
Because alpha particles carry more electric charge, are more
massive, and move slowly compared to beta and gamma particles,
they interact much more easily with matter. Beta particles are much
less massive and move faster, but are still electrically charged. A
sheet of aluminum one millimeter thick or several meters of air will
stop these electrons and positrons. Because gamma rays carry no
electric charge, they can penetrate large distances through

materials before interactingseveral centimeters of lead or a meter

of concrete is needed to stop most gamma rays.
Types of radiation
Types of radiation

Radiation is a form of energy. There are two basic types of radiation. One kind is
particulate radiation, which involves tiny fast-moving particles that have both energy
and mass. Particulate radiation is primarily produced by disintegration of an unstable
atom and includes Alpha and Beta particles.
Alpha particles are high energy, large subatomic structures of protons and
neutrons. They can travel only a short distance and are stopped by a piece of paper or
skin. Beta particles are fast moving electrons. They are a
fraction of the size of alpha particles, but can travel
farther and are more penetrating.

Particulate radiation is of secondary concern to industrial radiographers. Since these

particles have weight and are relatively large, they are easily absorbed by a small
amount of shielding. However, it should be noted that shielding materials, such as
the depleted uranium used in many gamma radiography cameras, will be a
source of Beta particles if the container should ever develop a leak. If a leak were
to occur, the material could be transferred to the hands and other parts of a
radiographers body, causing what is known as particulate contamination. This is the
reason periodic leak and wipe tests are performed on equipment.

PROPERTIES OF RADIATION

Different radiations have different properties, as summarized below:

Radiation
Alpha
Beta
Gamma
Neutrons

Type of Radiation
Particle
Particle
Electromagnetic Wave
Particle

Mass (AMU)
4
1/1836
0
1

Charge
Shielding material
+2
Paper, skin, clothes
1
Plastic, glass, light metals
0
Dense metal, concrete, Earth
0
Water, concrete, polyethylene, oil

In summary, the most common types of radiation include alpha particles, beta and
positron particles, gamma and x-rays, and neutrons. Alpha particles are heavy and
doubly charged which cause them to lose their energy very quickly in matter. They
can be shielded by a sheet of paper or the surface layer of our skin. Alpha particles are
only considered hazardous to a persons health if an alpha emitting material is ingested
or inhaled. Beta and positron particles are much smaller and only have one charge,

which cause them to interact more slowly with material. They are effectively shielded
by thin layers of metal or plastic and are again only considered hazardous if a beta
emitter is ingested or inhaled.
Gamma emitters are associated with alpha, beta, and positron decay. X-Rays are
produced either when electrons change orbits within an atom, or electrons from an
external source are deflected around the nucleus of an atom. Both are forms of high
energy electromagnetic radiation which interact lightly with matter. X-rays and
gamma rays are best shielded by thick layers of lead or other dense material and are
hazardous to people when they are external to the body.
Neutrons are neutral particles with approximately the same mass as a proton. Because
they are neutral they react only weakly with material. They are an external hazard best
shielded by thick layers of concrete. Neutron radiation will be discussed in more detail
in the discussion of nuclear power.
The electromagnetic spectrum is the range of all possible frequencies of electromagnetic
radiation.[4] The "electromagnetic spectrum" of an object has a different meaning, and is instead the
characteristic distribution of electromagnetic radiation emitted or absorbed by that particular object.
The electromagnetic spectrum extends from below the low frequencies used for
modern radiocommunication to gamma radiation at the short-wavelength (high-frequency) end,
thereby covering wavelengths from thousands of kilometers down to a fraction of the size of
an atom. The limit for long wavelengths is the size of the universe itself, while it is thought that the
short wavelength limit is in the vicinity of the Planck length.[5] Until the middle of last century it was
believed by most physicists that this spectrum was infinite and continuous.
Most parts of the electromagnetic spectrum are used in science for spectroscopic and other probing
interactions, as ways to study and characterize matter.[6] In addition, radiation from various parts of
the spectrum has found many other uses for communications and manufacturing
(seeelectromagnetic radiation for more applications).

Class

Gamma rays

Freq-

Wave-

uency

length

300 EHz

1 pm

Energy

1.24 MeV

HX

SX

EUV

NUV

10 pm

124 keV

3 EHz

100 pm

12.4 keV

300 PHz

1 nm

1.24 keV

30 PHz

10 nm

124 eV

3 PHz

100 nm

12.4 eV

300 THz

1 m

1.24 eV

30 THz

10 m

124 meV

Hard X-rays

Soft X-rays

Extreme
ultraviolet

Near
ultraviolet

Visible
NIR

30 EHz

Near infrared

MIR

FIR

Mid infrared

3 THz

100 m

12.4 meV

300 GHz

1 mm

1.24 meV

30 GHz

1 cm

124 eV

3 GHz

1 dm

12.4 eV

300 MHz

1m

1.24 eV

30 MHz

10 m

124 neV

Far infrared

Microwaves

EHF

Extremely high
frequency

and
radio
waves
SHF

UHF

VHF

HF

Super high
frequency

Ultra high
frequency

Very high
frequency

High

frequency

MF

LF

VLF

VF / ULF

SLF

ELF

3 MHz

100 m

12.4 neV

300 kHz

1 km

1.24 neV

30 kHz

10 km

124 peV

3 kHz

100 km

12.4 peV

300 Hz

1 Mm

1.24 peV

30 Hz

10 Mm

124 feV

3 Hz

100 Mm

12.4 feV

Medium
frequency

Low
frequency

Very low
frequency

Voice frequency
/Ultra low frequency

Super low
frequency

Extremely low
frequency

a nuclear reaction is semantically considered to be the process in which twonuclei, or else a

nucleus of an atom and a subatomic particle (such as a proton, neutron, or high energy electron)
from outside the atom, collide to produce one or more nuclides that are different from the nuclide(s)
that began the process. Thus, a nuclear reaction must cause a transformation of at least
one nuclide to another. If a nucleus interacts with another nucleus or particle and they then separate
without changing the nature of any nuclide, the process is simply referred to as a type of
nuclear scattering, rather than a nuclear reaction

In this symbolic representing of a nuclear reaction,lithium-6 (6

3Li) and deuterium (2
1H) react to form the highly excited intermediate nucleus 8
4Be which then decays immediately into two alpha particles of helium-4 (4
2He). Protons are symbolically represented by red spheres, and neutrons by blue spheres.