Transcript Interaction of Radiation with Matter

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An Atom can be defined as the smallest
quantity of an element which can enter into
a chemical reaction. All atoms of a
particular element are chemically alike but
they differ from the atoms of other
elements.
The atom is a basic unit of matter.
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Electrons(-) orbiting nucleus of protons(+)
and neutrons.
Same number of electrons as protons; net
charge = 0.
Atomic number (number of protons)
determines element.
Mass number (protons + neutrons) gives
mass in terms of 1/12th mass of Carbon
atom.
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An Element is a substance which cannot be
split up into two or more simpler
substances by the usual chemical methods
of applying Heat, Light or electric energy.
An is made up of atoms. All having same
atomic number.
Radiation is an energy in the form of electro-magnetic
waves or particulate matter, traveling in the air.
OR
The term radiation applies to the emission and
propagation of energy through space or a material.
Types of
Radiation
Ionizing
Non- Ionizing
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Three possible occurrences when x or gamma
photons in the primary beam pass through
matter:
◦ No interaction at all
 Known as transmission
◦ Absorption
◦ Scatter
 The latter two are methods of attenuation
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Forces: There are many interactions among
nuclei. It turns out that there are forces other
than the electromagnetic force and the
gravitational force which govern the
interactions among nuclei.
Einstein in 1905m showed 2 more laws:
energy/mass, and binding energy
• Electromagnetic
• Particular
X-rays (produced extra-nuclearly)
γ-rays (produced intra-nuclearly)
Electrons
Protons
α-Particles
Neutrons
Deuterons
Heavy charged particles
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The electromagnetic spectrum is the range of
all possible frequencies of electromagnetic
radiation.
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.
Like X-rays, radio waves, radar,
radiant heat, laser and visible light
are forms of electromagnetic
radiation. They have the same
velocity but different wavelengths.
For example, radio wave have
a wavelength of 300m; visible
light - 5x10-5; X-rays - 1x108cm.
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Electromagnetic
radiation
(EM
radiation or EMR) is a form of energy emitted
and absorbed by charged particles which
exhibits wave-like behavior as it travels
through space.
EMR has both electric and magnetic
field components.
In a vacuum, electromagnetic radiation
propagates at a characteristic speed, the speed
of light.
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no mass or physical form
travel at speed of light (c) in a vacuum (or
air)
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c = 3 x 108 m/s
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travel in a linear path (until interaction
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unaffected by
occurs)
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electric or magnetic fields
gravity
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obeys the wave equation
c=
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In Passing through the matter, the intensity is reduced
(attenuation), because of absorption & scattering.
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obeys the inverse square law
I1d12 = I2d22
Radiation intensity is inversely proportional to the square of the
distance from the source at any place.
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In passing through matter, the intensity of
the radiation is reduced (attenuation), both
because some radiation energy is taken
Up by material (absorption) and some is
deflected from its original path to travel in a
new direction (scattering).
It should be noted that any effect of
radiation on matter depends on how much
energy that matter receives (absorbs) from
the beam
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Two types of Radiation:
◦ Ionizing Radiation
◦ Non-ionizing Radiation
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Ionizing radiation is produced by unstable
atoms. Unstable atoms differ from stable
atoms because they have an excess of
energy or mass or both.
Unstable atoms are said to be radioactive.
In order to reach stability, these atoms give
off, or emit, the excess energy or mass.
These emissions are called radiation.
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They are electromagnetic waves incapable
of producing ions while passing through
matter, due to their lower energy.”
It has not enough energy to pull electron
from orbit, but can excite the electro.
Radiation that has enough energy to
move atoms to vibrate, but not
enough energy to remove electrons.
The process by which a neutral atom
acquires a positive or a negative charge
is known as Ionization.
Removal of an orbital electron leaves the
atom positively charged, resulting in an
ion pair.
• molecule with a net positive
charge
• free electron with a negative
charge
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Alpha Particles
Beta Particles
Gamma Rays (or Photons)
X-Rays
Neutrons
Radioactive Atom
Ionizing Radiation
alpha particle
X-ray
beta particle
gamma ray
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Alpha Particles: emitted from the nucleus of an atom
have 2 neutrons and 2 protons
They travel short distances, have large mass.
It is identical to the nucleus of a Helium atom,
without the electrons.
Only a hazard when inhaled.
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Beta Particles: Electrons or positrons having small
mass and variable energy.
Emitted from the nucleus of an atom.
Electrons form when a neutron transforms into a
proton and an electron.
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Gamma Rays (or photons): are Electromagnetic
waves / photons.
Releases energy, usually after an alpha, beta or
positron transition
Emitted from the nucleus (center) of an atom.
Have higher energy in MeV’s.
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X-Rays: are photons Electromagnetic waves and
photons.
Emitted from electron orbits.
X-rays have energy in KeV‘s.