Which of the following is not conserved in nuclear reaction ?

• Total energy

• Mass number

• Charge number

• Number of fundamental particles

312.

The number of $\mathrm{\alpha }$-particles and β-particles respectively emitted in the reaction ₈₈A¹⁹⁶ →  ₇₈B¹⁶⁴ are

• 8 and 8

• 8 and 6

• 6 and 8

• 6 and 6

The counting rate observed from a radioactive source at t = 0 was 1600 count/s and at t = 8 s it was 100 counts/s. The counting rate observed as counts per second at t = 6 s, will be

• 400

• 300

• 250

• 200

Which of the following statement is correct ?

• The rest mass of a stable nucleus is less than the sum of the rest masses of its separated nucleons.

• The rest mass of a stable nucleus is greater than the sum of the rest masses of its separated nucleons.

• In nuclear fission, energy is released by fusion two nuclei of medium mass (approximately 1O0 amu).

• In nuclear fission, energy is released by fragmentation of a very low nucleus.

What is the particle X in the following nuclear reaction ?

    ${}_4{}^9\mathrm{Be} + {}_2{}^4\mathrm{He} \stackrel{}{\to } {}_6{}^{12}\mathrm{C} + \mathrm{X}$

• Electron

• Proton

• Photon

• Neutron

At time t = O, a radioactive sample has a mass of 10 g. Calculate the expected mass of radioactive sample after two successive mean lives.

The energy released by the fission of one uranium atom is 200 MeV. The number of fissions per second required to produce 3.2 W of power is (Take, 1eV = 1.6 x 10^-19 J)

• 10⁷

• 10¹⁰

• 10¹⁵

• 10¹¹

A radioactive isotope X with half life 1.5x 10⁹ yr decays into a stable nucleus Y. A rock sample contains both elements X and Y in ratio 1 : 15. Find the age of the rock.

A radioactive nucleus of mass number A, initially at rest, emits an α-particle with a speed v. The recoil speed of the daughter nucleus will be

• $\frac{2\mathrm{v}}{\mathrm{A} - 4}$

• $\frac{2\mathrm{v}}{\mathrm{A} + 4}$

• $\frac{4\mathrm{v}}{\mathrm{A} - 4}$

• $\frac{4\mathrm{v}}{\mathrm{A} + 4}$

In the nuclear reaction ${}_7{}^{14}\mathrm{N} + \mathrm{X} \underset{}{\to } {}_6{}^{14}\mathrm{C} + {}_1{}^1\mathrm{H}$, the X will be

• ${}_{-1}{}^0\mathrm{e}$

• ${}_1{}^1\mathrm{H}$

• ${}_1{}^2\mathrm{H}$

• ${}_0{}^1\mathrm{n}$