Nuclei(23 Jan) - Free MCQ Practice Test with solutions, JEE

The nuclide (nucleus) consists of neutrons and protons (when combined called nucleons).
Thus,
No. of protons in 92U²³⁸ = 92,
No. of neutrons = 146 (238 – 92)
No. of nucleons = 238 (146 + 92)

Most nuclei are approximately spherical. The average radius of a nucleus with A nucleons is R = R₀A^1/3, where R⁰ = 1.2*10^-15 m. The volume of the nucleus is directly proportional to the total number of nucleons. This suggests that all nuclei have nearly the same density.

R∝A^1/3
A(mass no.)=n+p
R/x=(10/80)^1/3
R/x=(1³/2³)^1/3
R/x=1/2
X=2R

Binding energy per nucleon is the ratio of the binding energy of a nucleus to the number of the nucleons.

Binding energy per nucleon = (Total binding energy) / (Number of nucleon)

Measure of stability of the nucleus: Larger the binding energy per nucleon, the greater the work that must be done to remove the nucleon from the nucleus, the more stable the nucleus.

The atomic number or proton number (symbol Z) of a chemical element is the number of protons found in the nucleus of every atom of that element. The atomic number uniquely identifies a chemical element. It is identical to the charge number of the nucleus

James Chadwick set up an experiment to test his hypothesis. Chadwick put a piece of beryllium in a vacuum chamber with some polonium. The polonium emitted alpha rays, which struck the beryllium. When struck, the beryllium emitted the mysterious neutral rays.

A moderator is used in nuclear reactors in order to slow down the speed of neutrons.
In nuclear engineering, 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 involving uranium-235 or a similar fissile nuclide.
Clearly, an obvious way to make a reactor work, and to make use of this characteristic of the 235U(n,f) cross-section, is to slow down the fast, fission neutrons. This can be accomplished, for example, when the neutrons collide with nuclei and scatter in some substance (a moderator).

Nucleus of hydrogen has only one proton. Hence its binding energy will be zero. The nuclear binding energy is the energy it takes to separate all the nucleons in a nucleus from each other. Since there is only the one nucleon, it's already separated from any other nucleons.

The fusion of hydrogen into helium is more likely to take place at high temperature and high pressure, like the sun.

Packing fraction: - It tells about the stability of a nucleus.
Packing fraction=isotonic mass=molecular mass (atomic mass)/atomic mass
p.f.=M-A/A