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# Category Archives: Nuclear Physics

## Is it possible to stop a nuclear reaction once started?

Is it possible to stop a nuclear reaction,after starting it ( I’m not only talking about reactor, but in nuclear bombs too ). If it’s possible then which laws will fail or If It is impossible then Why? …………. have any country have prepared about It? (Asks George)

## Fission and Fusion again

Fusion gives more energy than fission right? When a uranium nucleus fissions into two daughter nuclei fragments, an energy of ~200 MeV is released. Whereas in a fusion of deuterium to give helium atom, only 18.3 MeV is released (which is the maximum?). Yes, the nucleus of uranium are heavier but the same deuterium fusion occurs in the stars and gives off a much larger amount of energy.

Ans:

If we consider energy released per reaction (fission or fusion), energy released is more in the case of fission.

If we consider energy released per unit mass (say one kg Uranium and 1 kg hydrogen), the energy released in fusion is very much larger than in the case of fission.

In fusion about 4 amu releases approx 20 MeV whereas in fusion about 236 amu releases approx 200 MeV

## Nuclear Fission and Fusion

which releases more energy?fusion or fission?

Ans:

per fission energy is more for fission, Per unit mass energy released is very much more for fusion

Mani again:

ok..bt our nuclear weapons are not powerful enough .. their energy is infinitesimally smaller than d energy released in natural process like earthquake volcano

Ans: Nuke weapons are targeted and sufficient to produce local destruction

## The problem of a rock thrown vertically up

A rock is thrown vertically upward from the ground with an initial speed 15m/s.

a. how high does it go
b. how much time is required for the rock to reach its maximum height?
c. what is the rock’s height at t=2.00s?

(Posted by Merhawi)

(a)

u=15m/s

a=-10m/s2

v=0 m/s (at the max height)

S=?

v2-u2=2aS

S=v2-u2/2a

=225/20

=11.25 m

(b) From the above case

using v=u+at

t=v-u/a=1.5s

(c) Use S = ut + 1/2 at2

put t=2s, u = 15m/s, a=-10m/s2

S=30 – 20 = 10 m

(If you use g = 9.8 m/s2 The answers will be slightly different)

## Mass Energy conversion and the Big Bang

Respected sir, in the famous theory of Albert Einstein which is of mass energy equivalence  he stated a formula E = mc2 .
sir does this mean that mass can be converted in to energy or the opposite will happen .
it is even stated in the big bang theory  that the universe was created with respect to the  above theory is that so?

The mass energy conversion and the equivalence is a widely discussed topic in relation to the creation of the universe or the Big Bang.

There is some energy missing in calculation when we consider the equivalence; this is called dark energy.

http://csep10.phys.utk.edu/astr162/lect/cosmology/hotbb.html

http://www.big-bang-theory.com/

http://ssscott.tripod.com/BigBang.html

## Formation of Heavier Elements

Question: Iron is the heaviest element that can be formed by nuclear reactions in a star.So how the heavier elements after iron were formed?And could there be further heavier elements out there in the cosmos?

Nuclear fusion inside a star is not the only process my which new elements are created. There are many others too.

During a supernova explosion many unpredictable nuclear transmutations occur, fusing elements and forming heavier elements.

But however, the amount of elements heavier than iron is less.

It’s a good idea to think back (say from the time of BigBang)

Every explosion has a consequent implosion resulting in creation of heavier elements

Remember that birth and death of stars are taking place everyday in some part or other of the universe. The earlier stars had relatively lighter elements in their core. As they die, the remains form part of other stars and other celestial bodies thereby forming heavier elements in the universe.

(I don’t claim that this is a complete answer. Visitors are requested to suggest amendments to this Answer via comments)

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