Nuclear radiations
2nd Year Physics Notes
karachiboardnotes.blogspot.com
NUCLEAR RADIATIONS
What do you know about Wilson and Cloud Chamber?
WILSON CLOUD CHAMBER
Introduction
Wilson Cloud Chamber is used to observe the path of ionizing particles.
It helps to examine the mechanism of ionization of various ionizing
radiations and the product of their interaction with material inside the
chamber.
Construction
It consist of a closed cylindrical chamber with transparent glass top
"I" and a movable piston on the bottom. On the sides near the top the
cylindrical is provided with a glass window for light and for the
ionizing particles or radiations. The piston can be moved up or down by a
lever attached to it. Before making the enclosed space above the piston
arright, enough quantity of a low boiling point liquid such as water or
alcohol is introduced in the space to produce its saturated vapours. A
small quantity of the liquid stay on the piston.
Working
The vapours of the liquid usually condense at its dew point but the
condensation never takes place in the absence of some particles, dust
particles or ions, which are essential to form the nuclei (centres) of
condensation. In particle free space the saturated vapour may cool much
below the dew point. Then they are called Super Saturated Vapours.
Paths, additional information about the charged and uncharged nature,
the magnitude of the charge, the charge to mass ration (e/m), etc of the
incident particle or the particle found by their interaction with the
atoms can be obtained. By this very method a number of particles have
been discovered.
Explain the construction and working of Gelger Counter.
Definition
Gelger counter is a portable device which is widely used for the detaction of ionizing particles or radiations.
Construction
It consists of a hollow metal cylinder, one end of which is closed by an
insulating cap. At the centre of the cap is fixed a stiff straight wire
along the axis of the cylinder. A thin mica or glass disc closes the
other end which also serves as all entrance window for the ionizing
particles or radiations. The sealed tube usually contains a special
mixture (air, argon, alcohol etc) at a low pressure of 50 to 100
millimetres of mercury. A potential difference of the order of one
thousand volts is applied between the metal cylinder and difference is
only slightly less than than, necessary to start a discharge between the
wire and a cylinder.
Working
When an ionizing particle enter the tube under this condition if a
charged particle pass through the chamber it produces ionization along
its track. The condensation of vapours takes place on ion in the form of
tiny droplets of fog, which can be photographed.
1. α-Particle
An α-particle is highly ionizing the ions produced are so numerous that its trade is a thick and continuous line.
2. β-Particle
β-Particle is much less ionizing its track is therfore, a thin and broken line.
3. γ - Rays
γ - Rays are photons emitted in a widening cone of some angle. They
produce ionization by photoelectric effect distributed on a wide space.
Some of the photoelectrons ejected by them give tiny line tracks in
directions like the β- Particles and scattered dots are produced. The γ -
rays not produce well-defined line track
Tags:
2nd Year Physics Notes