BELIEVE ME NOT!   A SKEPTIC's GUIDE
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Einstein's association of the term m c^{2} with a REST MASS ENERGY
E_{0} naturally led to a great deal of speculation
about what might be done to convert mass into useable energy,
since for a little mass you get a lot of energy!
Let's see just how much: in S.I. units 1 J
1 kgm^{2}/s^{2}
so a 1 kg mass has a rest mass energy of
(1 kg)
m/s
J  i.e.,

(24.10) 
which is a lot of joules. To get an idea how many, remember that
one WATT is a unit of power equal to one joule per second,
so a JOULE is the same thing as a WATTSECOND.
Therefore a device converting one millionth of a gram
(1 g) of mass to energy every second would release
approximately 90 megawatts [millions of watts] of power!
Contrary to popular belief, the first conclusive demonstration of
massenergy conversion was in a controlled nuclear reactor.
However, not long after came the more unpleasant manifestation
of massenergy conversion: the fission bomb. An unpleasant
subject, but one about which it behooves us to be knowledgeable.
For this, we need a new energy unit, namely the KILOTON [kt],
referring to the energy released in the explosion of one thousand
tons of TNT [trinitrotoluene], a common chemical
high explosive. The basic conversion factor is

(24.11) 
which, combined with Eq. (10), gives a restmass equivalent of

(24.12) 
That is, one KILOTON's worth of energy is released in the conversion
of 0.04658 grams [46.58 mg] of mass.
Thus a MEGATON [equivalent to one million tons of TNT or 10^{3} kt]
is released in the conversion of 46.58 grams of mass; and the largest
thermonuclear device [bomb] ever detonated, about 100 megatons'
worth, converted some 4.658 kg of mass directly into raw energy.
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Jess H. Brewer 
Last modified: Mon Nov 23 11:15:06 PST 2015