X-RAYS
X-rays are produced by bombarding a target of heavy metal with high energy electron.
NECTA 1984/2/8
The emission of X-rays may be regarded as the inverse of photo electric effect.Explain
SOLUTION
X-Rays which are waves are produced by bombarding a hard metal with electrons(particles)where as in photoelectric effect electron(particles) are liberated from ametal surface by incident radiation(waves)
MODERN X-RAY TUBE
Electron are obtained from the filament by thermionic emission and are accelerated to the anode having small target of high melting point such as tangstem.
X-RAY QUANTITY
Refers to the intensity of X-rays which increases with the number of electrons limiting the target.This depends on the cathode temperature controlled by the heating current
X-RAY QUALITY
Refer to the penetrating power of X-ray and determined by velocity whith which electrons strikes the target.
SOFT X-RAY:
Are those which can penetrate soft objects such as flesh
Are those which can penetrate soft objects such as flesh
HARD X-RAY
Are those which can vibrate much more solid material
Are those which can vibrate much more solid material
PROPERTIES OF X-RAY
1.They travel in a straight line.
2.They readily penetrate matter.
3.They affect photographic plates
4.They are not deflected by electric or magnetic field,because they have no charge
They are wave of wavelength 10A
X-RAY SPECTRA
CONTINUOUS SPECTRUM
Explained by electromagnetic theory.
It is due to electrical interaction between the bombarding electrons and the nuclei of the target atom
An electron approaching a positively charged nucleus is accelerated and according to electromagnetic theory accelerated motion is accompanied by emission of radiations in this case x-ray
DISCRETE SPECTRA
These are explained by quantum theory.They are produced when the incident electron interact with electron close to nucleus of the target atom.The bombarding electrons knock off electron in their orbits and the created gaps are filled by electrons in the high energy levels,when they moves in these gaps they produce x-ray photon.
The cut off wavelength or short wave limit(λ min)
This is the minimum wavelength of x-radiations which corresponds to the maximum energy of the X-rays produced by electrons which have given out all their K.Æ on a single encounter with the target nucleus
ENERGY OF X – RAY:
Energy of an electron striking the atom of the target is eV where e = electronic charge.
V = p.d across the X-ray tube.
If a direct collision is made with a target atom and the energy is absorbed then on quantum theory X-rays produced hence a maximum energy hV
Therefore
eV = 1/2mV2 = hV
eV = hc/ λ minimum
λmin = hc/eV
NECTA 1989/1/18
Calculate the wavelength of most energetic X-rays produced by a tube operating at 1.0 x 105V.
USES OF X – RAYS
1.in investigation of suspected bone fractures
2.Detection of lung tuber culosis (feased tissue is denser than a heatthy one).
3.Treatment of cancer (cancer cells are killed by X-rays)
4.Casting and welding joints can be inspected for internal imperfection.
5.It is used in the study of crystal structure refer to Bragg’s law.
NUCLEAR FISSION FUSSION
Nuclear fission is a splitting disintegrating of heavy nucleus such as uranium into two other lighter nuclei (with several neutrons)
Example:
Nuclear fusion
This is the combination of light nuclei to form a heavier nucleus.
Example:
NECTA 1990/2/8
(1)Both fission and fusion are source of energy
Explain.
SOLUTION:
Fission-During disintegration of heavy nucleus such as uranium, energy is released which is
transformed into K.E of fragments.
Fussion-When light nuclei are fused together a large amount of energy is released in term of heat.(eg
in the sun)
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