Transcript Document

I WELCOME YOU ALL
TO HAVE A CUP OF
PHYSICS WITH SMILE
Discovery
The discovery of X-rays was by a German
physicist called Wilhelm Roentgen. In 1895 Roentgen
discovered X-rays almost by accident. Whilst doing some
experiments in which he passed an electric current
through Crook's tubes (special tubes containing a
cathode and electrode from which the air has been
removed), Roentgen noticed that photographic plates
nearby began to grow fogged. To discover why this
occurred he placed black paper on the tube and then
switched on the current. Nearby a screen coated with
barium began to glow. This caused Roentgen to believe
that unknown rays produced inside the tube were passing
through the paper to make this fluorescent substance give
out light. These he named X-rays since x is a scientific
number for anything that is unknown.
What are X-rays?
X-rays are electromagnetic waves like radio
and light waves. These all travel at the speed of
light, which is 300 000km per second. The
wavelength of an X-ray however is one hundredth
that of the light rays that you can see, at around
10¯¹ºm. This means that they have a lot more
energy. X-ray fluorescence is the emission of Xrays from excited atoms produced by the impact of
high-energy electrons, other particles or a primary
beam of other X-rays. Atoms of all the elements
emit a characteristic X-ray spectrum when they are
bombarded with electrons.
USES OF X-RAYS
The main use of X-rays is in medicine. A common
application is in the form of X-ray machines, which
take photos of a patient’s body. If an arm or leg were
broken for example, then this limb would be put in
front of the X-ray with a piece of photographic film
behind. The X –ray is turned on briefly and goes
through to the film. The rays go through the skin and
flesh easily, showing up as dark areas on the film, but
with more difficulty through bone. They are slowed
down and so these areas are much lighter. X-rays can
also be used to kill cancer cells, but also kill healthy
cells, so must be used with much care.
Properties of x-rays
X-rays were discovered in 1895 by the German
physicist Wilhelm Conrad Röntgen - in some
languages x-rays are called Röntgen-rays - and xray diffraction was discovered in 1912.
The X-rays used in diffraction experiments all have
a wavelength of 0.5-2.5 Å. The intensity of a beam of
x-rays is the rate of transport of energy flow
through a unit area perpendicular to the direction of
propagation.
Making X-rays
Where do x-rays come from?
An x-ray machine, like that used in a doctor's or a
dentist's office, is really very simple. Inside the
machine is an x-ray tube. An electron gun inside the
tube shoots high energy electrons at a target made of
heavy atoms, such as tungsten. X-rays come out
because of atomic processes induced by the energetic
electrons shot at the target.
BETA RAYS:
Beta decay can occur in two ways. As shown
on the left, a neutron turns into a proton by
emitting an antineutrino and a negatively
charged beta particle. As shown on the right,
a proton turns into a neutron by emitting a
neutrino and a positively charged beta
particle. Positive beta particles are called
positrons and negative beta particles are
called electrons..
ALPHA RAYS:
Alpha Particles
An alpha particle consists of two protons and
two neutrons that act as a single particle. It
is identical to the nucleus of a helium atom.
When an alpha particle is emitted from an
unstable radioactive nucleus, the atom is
transmuted into a different element.
GAMMA RAYS
Gamma Rays
Gamma rays, or high-energy photons, are
emitted from the nucleus of an atom when it
undergoes radioactive decay. The energy of the
gamma ray accounts for the difference in
energy between the original nucleus and the
decay products. Gamma rays typically have
about the same energy as a high-energy X-ray.
Each radioactive isotope has a characteristic
gamma-ray energy
MAY I FLY AWAY FROM MY PROJECT
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