| System | Specification |
| Telegraphy | Message in the form of codes are sent. |
| Television broadcast | Both sound as well as pictures are sent. |
| Telephony | It sends voice signal from one place to another by means of wire. |
| Radar | It means radio detection and ranging. It is used for determining the distance and direction of objects using microwave. |
| Teleprinting | Message can be typed and telegraphed to distant receivers |
| System | Specification | |||||||||||||||||||||||||||||||||||||||||||||
| Facsimile transmission (FAX) | This involves exact reproduction of more...
A basic communication system consists of an information source, a transmitter, a link and a receiver.
(1) Information : The idea/message that is to be conveyed is information. The message may be individual one or a set of messages. The message may be a symbol, code, group of words or any pre decided unit.
(2) Transmitter : In radio transmission, the transmitter consists of a transducer, modulator, amplifier and transmitting anteena.
Transducer : Converts sound signals into electric signal.
Modulator : Mixing of audio electric signal with high frequency radio wave.
Amplifier : Boosting the power of modulated signal.
Anteena : Signal is radiated in the space with the aid of an anteena.
(3) Communication channel : The function of communication channel is to carry the modulated signal from transmitter to receiver. The communication channel is also called transmission medium or link.
The term channel refers to the frequency range allocated to a particular service or transmission.
Different channels
The term communication refers to the transmitting, receiving
and processing of information by electronic means.
(1) In medicine
(i) For testing blood-chromium \[-51\]
(ii) For testing blood circulation - \[Na-24\]
(iii) For detecting brain tumor- Radio mercury \[-203\]
(iv) For detecting fault in thyroid gland - Radio iodine \[-131\]
(v) For cancer - cobalt \[-60\] (vi) For blood - Gold \[-189\]
(vii) For skin diseases - Phospohorous \[-31\]
(2) In Archaeology
(i) For determining age of archaeological sample (carbon dating) \[{{C}^{14}}\]
(ii) For determining age of meteorites \[-{{K}^{40}}\]
(iii) For determining age of earth-Lead isotopes
(3) In agriculture
(i) For protecting potato crop from earthworm- \[C{{O}^{60}}\] (ii) For artificial rains \[-Agl\] (iii) As fertilizers \[-{{P}^{32}}\]
(4) As tracers - (Tracer) : Very small quantity of radioisotopes present in a mixture is known as tracer
(i) Tracer technique is used for studying biochemical reaction in tracer and animals.
(5) In industries
(i) For detecting leakage in oil or water pipe lines
(ii) For determining the age of planets.
Suppose a radioactive element A disintegrates to form another radioactive element B which intern disintegrates to still another element C; such decays are called successive disintegration.
Rate of disintegration of \[A=\frac{d{{N}_{1}}}{dt}=-{{\lambda }_{1}}{{N}_{1}}\] (which is also the rate of formation of B)
Rate of disintegration of \[B=\frac{d{{N}_{2}}}{dt}=-{{\lambda }_{2}}{{N}_{2}}\]
\[\therefore \] Net rate of formation of B = Rate of disintegration of A - Rate of disintegration of B
\[={{\lambda }_{1}}{{N}_{1}}-{{\lambda }_{2}}{{N}_{2}}\]
Equilibrium
In radioactive equilibrium, the rate of decay of any radioactive product is just equal to it's rate of production from the previous member.
i.e.\[{{\lambda }_{1}}{{N}_{1}}={{\lambda }_{2}}{{N}_{2}}\Rightarrow \]\[\frac{{{\lambda }_{1}}}{{{\lambda }_{2}}}=\frac{{{N}_{2}}}{{{N}_{2}}}=\frac{{{\tau }_{2}}}{{{\tau }_{1}}}=\frac{({{T}_{1/2}})}{{{({{T}_{1/2}})}_{1}}}\]
(1) If the isotope that results from a radioactive decay is itself radioactive then it will also decay and so on.
(2) The sequence of decays is known as radioactive decay series. Most of the radio-nuclides found in nature are members of four radioactive series. These are as follows
Four radioactive series
|
(1) \[\alpha -\]decay : Nearly 90% of the 2500 known nuclides are radioactive ; they are not stable but decay into other nuclides
(i) When unstable nuclides decay into different nuclides, they usually emit alpha \[(\alpha )\] or beta \[(\beta )\] particles.
(ii) Alpha emission occurs principally with nuclei that are too large to be stable. When a nucleus emits an alpha particle, its N and Z values each decrease by two and A decreases by four.
(iii) Alpha decay is possible whenever the mass of the original neutral atom is greater than the sum of the masses of the final neutral atom and the neutral helium- atom.
(2) \[\beta -\]decay : There are different simple type of \[\beta -\]decay \[{{\beta }^{-}}\], \[{{\beta }^{+}}\] and electron capture.
(i) A beta minus particle \[({{\beta }^{-}})\] is an electron. Emission of \[{{\beta }^{-}}\] involves transformation of a neutron into a proton, an electron and a third particle called an antineutrino \[(\bar{\nu })\].
(ii) \[{{\beta }^{-}}\] decay usually occurs with nuclides for which the neutron to proton ratio \[\left( \frac{N}{Z}ratio \right)\] is too large for stability.
(iii) In \[{{\beta }^{-}}\] decay, N decreases by one, Z increases by one and A doesn't change.
(iv) \[{{\beta }^{-}}\] decay can occur whenever the neutral atomic mass of the original atom is larger than that of the final atom.
(v) Nuclides for which N/Z is too small for stability can emit a positron, the electron's antiparticle, which is identical to the electron but with positive charge. The basic process called beta plus \[{{\beta }^{+}}\] decay
\[p\to n+{{\beta }^{+}}+\nu \] (n = neutrino)
(vi) \[{{\beta }^{+}}\] decay can occur whenever the neutral atomic mass of the original atom is at least two electron masses larger than that of the final atom
(vii) The mass of n and \[\bar{\nu }\] is zero. The spin of both is \[\frac{1}{2}\] in units of \[\frac{h}{2\pi }.\] The charge on both is zero. The spin of neutrino is antiparallel to it's momentum while that of antineutrino is parallel to it's momentum.
(viii) There are a few nuclides for which \[{{\beta }^{+}}\] emission is not energetically possible but in which an orbital electron (usually in the k-shell) can combine with a proton in the nucleus to form a neutron and a neutrino. The neutron remains in the nucleus and the neutrino is emitted.
\[p+{{\beta }^{+}}\to n+\nu \]
(3) \[\gamma -\]decay : The energy of internal motion of a nucleus is quantized. A typical nucleus has a set of allowed energy levels, including a ground state (state of lowest energy) and several excited states. Because of the great strength of nuclear interactions, excitation energies of nuclei are typically
(2) For fusion high pressure (\[\approx {{10}^{6}}\] atm) and high temperature (of the order of \[{{10}^{7}}\,K\] to \[{{10}^{8}}\,K\]) is required and so the reaction is called thermonuclear reaction.
(3) Here are three examples of energy-liberating fusion reactions, written in terms of the neutral atoms. Together the reactions make up the process called the proton-proton chain.
\[_{1}^{1}H+\,_{1}^{1}H\to \,_{1}^{2}H+{{\beta }^{+}}+{{\nu }_{e}}\] \[_{1}^{2}H+\,_{1}^{1}H\to \,_{2}^{3}He+\gamma \]
\[\frac{_{2}^{3}He+\,_{2}^{3}He\to \,_{2}^{4}He+\,_{1}^{1}H\,+\,_{1}^{1}H}{4{{\,}_{1}}{{H}^{1}}{{\to }_{2}}H{{e}^{4}}+2\,{{\beta }^{+}}+2\gamma +26.73\,MeV}\]
(4) The proton-proton chain takes place in the interior of the sun and other stars. Each gram of the suns mass contains about \[4.5\times {{10}^{23}}\] protons. If all of these protons were fused into helium, the energy released would be about 130,000 kWh. If the sun were to continue to radiate at its present rate, it would take about \[75\times {{10}^{9}}\,years\] to exhaust its supply of protons.
(5) For the same mass of the fuel, the energy released in fusion is much larger than in fission.
(6) Plasma : The temperature of the order of \[{{10}^{8}}\,K\] required for thermonuclear reactions leads to the complete ionisation of the atom of light elements. The combination of base nuclei and electron cloud is called plasma. The enormous gravitational field of the sun confines the plasma in the interior of the sun.
The main problem to carryout nuclear fusion in the laboratory is to contain the plasma at a temperature of \[{{10}^{8}}\,K\]. No solid container can tolerate this much temperature. If this problem of containing plasma is solved, then the large quantity of deuterium present in sea water would be able to serve as in-exhaustible source of energy.
Nuclear bomb (Based on uncontrolled nuclear reactions)
