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Tuesday, August 19, 2014

What is a relay?

A relay is an electromagnetic switch. An actuating current passed in a coil operates one or more galvanically separated contacts. In fact it is a remote controlled switch capable of switching multiple circuits, either individually, simultaneously or in sequence.    

The most widely used type of relay is electromechanical relay. In electromechanical relays the switching element is a mecahncial contact, actuated by an electromagnet. This is the msot widely used type of relay design. The principal internal functions of the electromechanical relay are:

  1. Conversion of electrical current into  magnetic field
  2. Conversion of magnetic field into a mechanical force
  3. This Mechanical force operates the contacts
  4. Contacts switch and conduct electrical current
Applications of Relay

Typical applications of relays are as follows:
  • Laboratory instruments
  • Telecommunication systems
  • Domestic appliances
  • Traffic control
  • Control of motors & solenoids
  • Air conditioning & heating

Natural Radioactivity in Soil (Bq.Kg-1)


Country
Type of Radioactive Isotope

K-40
U-238
Ra-226
Th-232
India
400
29
29
64
China
440
33
32
41
Japan
310
29
33
28
USA
370
35
40
35
Russia
520
19
27
30
Spain
470
NA
32
33

Mean values are given from wide range of values
Courtesy: UNSCEAR, 2000

Natural Background Radiation in Various Cities of India


City
µGy.yr-1
Cosmic
Terrestial
Total
Mumbai
280
204
484
Kolkata
280
530
810
Delhi
310
390
700
Chennai
280
510
790
Bangalore
440
385
825


As one shifts from Mumbai to Delhi, he is going to get 216 µGy additional natural radiation dose which is 10 times more than that from a nuclear power plant.

WE LIVE IN NATURALLY RADIOACTIVE WORLD

We are exposed to radiation from the sun and outer space, also from the naturally occurring radioactive materials present in the earth, the house we live in, the buildings where we work, the food and drink we consume.

Where we live in
The houses are made up of materials which contain radioactivity. Gamma radiation from walls, floor & ceiling, and Radon and Thoron progeny are major sources of radiation exposure. Especially in closed rooms, Radon is the significant dose contributing factor.

Natural Radioactivity (Bq.Kg-1) in Building Materials used in India
Material
Type of Radioactive isotope
K-40
Ra-226
Th-232
Cement
5-385
16-377
8-78
Brick
130-1390
21-48
26-126
Stone
48-1479
6-155
5-412
Sand
5-1074
1-5047
4-2971
Granite
76-1380
4-98
103-240
Clay
6-477
7-1621
4-311
Fly Ash
6-522
7-670
30-159
Lime stone
6-518
1-26
1-33
Gypsum
70-807
7-807
1-152

We are always in natural background radiation*
Cosmic-from the sun and outer space – 0.4mSv.Yr-1
Terrestrial – from the earth’s crust – 0.5mSv.yr-1
Radon – from decay of Uranium/radium – 1.2mSv.yr-1
Internal sources in the body(eg:  40K)  --- 0.3mSv.yr-1

Total Dose from Natural Sources: ----2.4 mSv.Yr-1

What we drink
Radioactivity in milk  is over 200 times more than in drinking water and 3 times that in beer. 

From a cup of milk , 180 beta particles of Ptassium-40 are emitted per minute

From a cup of tea, 91 beta particles of Potassium-40 are emittd per minute from tea leaves(excluding milk and water)

What we eat

Food stuff
K-40 (Bq.Kg-1)
Rice
40-90
Leafy vegetables
80-220
Brinjal
90-140
Carrot
60-120
Beetroot
90-120


Radiation Doses from Cosmic Rays

Distance above Ground
Dose Rate in µSv. h-1
~ 15 Km above ground
10
~ 10 Km above ground
5
~ 8 Km above ground
2
~ 2 Km above ground
0.1
Sea Level
0.03

Courtesy: Radiation Safety, IAEA (1996), NRPB, UK

Comparison Between Wastes From A Nuclear Reactor & Coal Based Thermal Power Plant [1000 Mwe Each]



Thermal Power Plant

Nuclear Power Plant

Ash:
320,000 tonnes

High Level:
27 tonnes spent fuel or 3 Cu.m after reprocessing
CO2:
6.5 Million tonnes

SO2:
44,000 tonnes

Intermediate level:
310 tonnes
NO2:
22,000 tonnes

Low Level:
460 tonnes

Tuesday, August 12, 2014

Units of Radioactivity

------------------------------------------------------------------------------------------------------------
        Physical Quantity                               SI Unit                                 Non-SI Unit
------------------------------------------------------------------------------------------------------------
             Activity                                       Becquerel                                Curie (Ci)

        Absorbed Dose                                 Gray                                        RAD

        Dose Equivalent                                Sievert                                     REM

        Exposure                                         Coulomb/Kg                              Roentgen
------------------------------------------------------------------------------------------------------------

BF3 Properties


  1. Molecular Weight  : 67.82
  2. Density of gas       : 3.06 gm / litre at 0 deg C, 760mm of Hg 
  3. Density of Liquid  : 1.68 gm/cc @ -128 deg C
  4. Density of solid     : 1.87 gm/cc
  5. Melting Point        : -128 deg C
  6. Boiling Point         : -100 deg C
  7. Triple Point          : - 123 deg C