Explain why Light elements like hydrogen and deuterium are effective in shielding against neutrons while heavy elements like lead are effective in case of gamma rays.

$ in keV units if E is in the range 7 meV.

Write a brief scientific note on Elementary particles and their classification.

Give an example of nuclear fusion and explain how energy is released in the process. In nature fusion reactions are often brought about by height temperatures. Explain the role of high temperature and the relevance of quantum effect in this.

Radium has a half-life of 1600 years and the daughter nucleus Radon also decays with a half-life of 3.82 days. In an enclosure containing radium and radon gas, the amount of radon appears to be constant for observations extending over a week. Explain this and calculate the ratio of the numbers of radium nuclei. Will the amount of radon remain the same even after 400 years?

State the laws followed in \alpha-decay by different radioactive nuclei and outline the theory which explained \alpha-decay

Two isotopes of oxygen have nuclear masses 15.990523 a.m.u. and 17.994768 a.m.u. Calculate the binding energy per nucleon in the two cases in MeV. What do you expect about the relative abundances of the two isotopes?

Write a brief scientific note on Linear particle accelerators.

Explain why a cyclotron is used for accelerating particles like Protons and deuterons but is not used for accelerating electrons. Mention the advantages and disadvantages of a linear accelerator compared to cyclic accelerators like the cyclotron.

Given a rough sketch showing the variation of binding energy per nucleon with mass number of nuclei and hence explain how an enormous amount of energy is emitted in uranium fission. How it is that two blocks containing uranium of mass number 235 may remain quiet when separated but may explode when brought together into a single block? Explain the function of a moderator in a nuclear reactor.

Discuss briefly the three types of interaction between elementary particles, and explain the relative strength of the various kinds of interaction between elementary particles.

What is alpha decay? Deduce an expression for the potential barrier penetrability for alpha particle in a nucleus. Show how the penetrability is related to the alpha decay constant.

What is deuterium? Is deuterium the same as hydrogen? Hon can you obtain deuteron from deuterium? Calculate the frequency of the oscillating potential applied to a cyclotron as to accelerate deuterons when the magnetic induction has a constant value of 2.5\text{ Wb/m}^{2}.

Interpret the nuclear process described by the equation _{92}U^{235} + _{0}n^{1} \rightarrow _{92}n^{236} \rightarrow _{56}Ba^{141} + _{36}Kr^{92} + 3 _{0}n^{1} + Q The products of this kind of reaction vary widely, but the average Q is found to be 180 MeV. Compute the consumption rate of U^{235} per year if power generation is to be an average 100 MW. (Take efficiency = 1).

Schematically draw the binding energy cone for atomic nuclei defining the parameters used. Explain how it indicates release of energy on fission of some nuclei and on fusion of other. Could one of these processes be the origin of solar energy?

Some amount of a radioactive substance (half-life=30\text{ days}) spread inside a room and consequently the level of radiation becomes 50 times the permissible level for normal occupancy of the room. After how many days the room would be safe for occupation?

Write a brief note (about 200 words) on parity violation

The number of alpha particles emitted per gm of radium each second is 3.71 \times 10^{10}. Atomic weight of radium is 226. Calculate its half-life in years.

Which of the following reactions are forbidden and why? \begin{aligned} p &\longrightarrow n + e^+ + u_e \\\\ \pi^+ &\longrightarrow \mu^+ + u_\mu \\\\ \text{H}^2 &\longrightarrow \text{He}^3 + e^- + e \end{aligned}

How many types of neutrinos exist? How do they differ in their masses?