In 1895, Wilhelm Roentgen
discovered X-rays. This accidental discovery took place when he was studying
cathode rays using an evacuated glass tube. X-Rays are electromagnetic
radiations having a wavelength between 10A to 0.01A. In Free Space they travel
in a straight line with a velocity of 3 ×10 (power) 8 meters per second and they are
Invisible to human Eye.
Formation: When cathode rays strike against a metal of high atomic
weight, a new form of radiation called X-rays, are produced. X-rays are
generated when a stream of electrons travelling from tungsten filament
(cathode) is suddenly stopped by its impact on anodic tungsten target .
Properties of X Rays
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(i) X-rays are electromagnetic waves and part
of the electromagnetic spectrum. They are electromagnetic waves heaving
extremely short wave length about a thousand times shorter than those of
visible rays (1 to 3 AU).
(ii) X-rays
carry no charge on them. X-rays diverge from the source and cannot be focused
to a point.
(iii) X-rays
travel along straight line like cathode rays.
(iv) They produce
fluorescence on certain substances which they strike, such as rock salt.
(v) They can ionise gases due to high velocity and KE associated
with them. They have a very short wavelength (about the same size as the
diameter of an atom. They cause ionisation (adding or removing electrons in
atoms and molecules)
(vi) they can
cause photoelectric emission
(vii) They can be
reflected and refracted but not through ordinary plane surface.
(viii) They
produce interference and diffraction phenomenon.
(ix) They cannot be
deflected by electric and magnetic fields.
(x) They can
produce secondary X-rays when they strike metals.
(xi) X Electrical
and magnetic fields fluctuate perpendicular to the direction of X-rays and at
right angles to each other.
(xii) They have
the properties of Attenuation, Absorption & Scattering.
(xiii) Chemical
Properties: X-Ray induces colour changes
of several substances or their solutions. X-Rays bring about chemical changes
in solution because X-Rays produce highly active radical OH ions in water,
which react with the solutes.X-Rays cause destruction of the fermenting powers
of Enzymes
(xiv) Biological Properties: The excitation property of X-Rays are used
in treatment of malignant lesions. X-Rays
also have a germicidal or bactericidal effect. Somatic Effect-This ranges from simple Sun Burn to Severe
dermatitis or to change in blood supply to malignancy.
(xv) Physiochemical
Property: X-rays are capable of
producing an image on a photographic film
Applications of X Rays in
Various Fields:
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(i) In medical
science and in surgery for detection of:
(a) Fractures.
(b) Foreign
matters.
(c) Diagnosis of
tumors, ulcers, tuberculosis, stones in kidneys etc.
(d) Ionising effect of X-rays: The
ionising properties of X-rays mean that they can damage the DNA in cells. The
ionising effect of X-rays is more damaging to actively dividing cells in the
body.
Low doses of X-rays may cause cancer - whereas high doses
may kill cancerous cells.
(f) Cancer treatment: Cancer is a disease
in which cells divide uncontrollably because of changes in their DNA, forming
tumours. One method of treating cancer is to direct high energy X-rays at the
tumours. This causes so much damage to the cancerous cells that they die. This
treatment is called radiotherapy.
(ii) In detective department: Solid materials like gold and
jewellery carried by smugglers can be detected at the check outposts. Similarly
the banned materials concealed in packages can be detected by passing X-rays
through them.
(iii) In
technology : Any minute crack inside the solid material can be detected.
(iv) In industry:
For examination of rubber tyres, golf balls, wireless valves, testing homogeneity
of timber and uni-formality of insulating materials, detecting the presence of
pearls, etc.
(v) Digital
X-rays porperties are, inspection is becoming more and more important for
quality assurances in food industry .A typical application is inspection of
food for foreign bodies.
(vi) They are
also used in the field of archeology for restoration of objects of historical
importance.
(vii) Hard
properties of X-rays have shorter wavelength with high penetration power and
are used in diagnostic radiology
(viii) Soft X-rays
have longer wavelength and less penetration power and are used in radiation
therapy.
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