Tag: nuclear reactor

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Multiple choice chemistry nuclear physics nuclear reactor the nuclear power station isotopes and nuclear chemistry

The most suitable material for moderator in a nuclear reactor is 

  1. $D _{2}$
  2. $Cd$
  3. $B$
  4. $ _{92}\textrm{U}^{235}$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation
In nuclear reactor, a neutron moderator is a medium that reduces the speed of fast neutrons, thereby turning them into thermal neutrons capable of sustaining a nuclear chain reaction.
Commonly used moderators include regular (light) water (roughly 75% of the world's reactors), solid graphite (20% of reactors) and heavy water.
Multiple choice chemistry nuclear physics nuclear reactor the nuclear power station isotopes and nuclear chemistry

The fission of $U^{238}$ is possible by 

  1. only fast neutrons

  2. only slow neutrons

  3. fast as well as slow neutrons

  4. fast protons
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Uranium-23, do not usually undergo fission when struck by slow neutrons, but do split when struck with neutrons of high enough energy. The fast neutrons produced in a hydrogen bomb by fusion of deuterium and tritium have even higher energy than the fast neutrons produced in a nuclear reactor. This makes it possible to increase the yield of any given fusion weapon by the simple expedient of adding layers of cheap natural (or even depleted) uranium. Fast fission of uranium-238 provides a large part of the explosive yield, and fallout, in many designs of hydrogen bomb.

Multiple choice chemistry nuclear physics nuclear reactor the nuclear power station isotopes and nuclear chemistry

What is the order of the temperature at which average kinetic energy of an atom in gaseous hydrogen becomes equal to the binding energy of the electron in hydrogen atom?

  1. $10^{4}$ K
  2. $10^{5}$ K
  3. $10^{3}$ K
  4. $10^{2}$ K
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Let the temperature be $T$.

So, the K.E. of an atom is gaseous hydrogen is $3kT/2$
where $k=1.38\times10^{-23}$ is the boltzmann constant.
Now the binding energy of the electron in hydrogen atom is $13.6eV=13.6\times1.6\times10^{-19}\ J$
Equating Binding energy and the kinetic energy we get, 
$T=1.004\times10^5\ K$
So temperature is of order of $10^5\ K$

Multiple choice chemistry nuclear physics nuclear reactor the nuclear power station isotopes and nuclear chemistry

The number of fissions of $^{235}U _{92}$ required to a produce a power of $1\ W$ is :

  1. $3.1\times 10^{10}$
  2. $3.1\times 10^{13}$
  3. $3.1\times 10^{19}$
  4. $3.1\times 10^{8}$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

1 Watt = 1 Joule/second. Energy per fission of U-235 is approx 200 MeV = 3.2 * 10^-11 J. Fissions per second = 1 / (3.2 * 10^-11) = 3.125 * 10^10.