1.Write nuclear reaction equations for

2.A radioactive isotope has a half-life of T years. How long will it take the activity to reduce to (a) 3.125%, (b) 1% of its original value?

3.Obtain the amount of necessary to provide a radioactive source of 8.0 mCi strength. The half-life of is 5.3 years.

                         R = 8.0 x 10^-3 Ci

                             = 8.0 x 10^-3 x 3.7 x 10¹⁰ dis s^-1

                             = 2.96 x 10⁸ dis s^-1

                       t_1/2 = 5.3 years = 5.3 x 365 x 24 x 3600 s

                             = 1.67 x 10⁸ s

Rate of disintegration is given by

4.Why carbon dating is unable to provide accurate estimates of very old materials?

The amount of carbon - 14 left in very old materials is extremely small and detection cannot be accomplished with a high degree of accuracy.

5.What are the essential conditions for a sustained chain reaction?

For chain reaction to be sustainable, firstly the reproduction factor or multiplication factor should be always 1. Reproduction factor K is defined as the ratio of number of neutrons in any one generation to other number of neutrons in the preceding generation. This is because the neutrons in one generation may not be able to induce reaction in the next generation due to leakage of neutrons through the surface of system or non fission capture. Thus there is a critical size for the system. Critical size of a system containing fissile material is defined as the minimum size for which the number of neutrons produced in the fission process just balance those lost by leakage and non fission capture. The neutrons produced in one generation are thermal neutrons with high energy. For fission to occur, the neutron should be slow neutrons. This can be attained by providing moderators between generations. If the above said conditions are maintained, the chain reaction becomes self sustaining.

6.The half-life of  is 28 years. What is the disintegration rate of 15 mg of this isotope?

7.What is the significance of energy level diagram?

The significance of energy level diagram lies in the ease with which the transitions responsible for the spectrum of atom, can be visualised. Also the energy of a photon involved in a particular transition can be easily obtained from the energy level diagram.

8.Obtain approximately the ratio of the nuclear radii of the gold isotope

We know that

9.What is the whole number rule?

According to the whole number rule, atomic masses of different elements should be integral multiples of the mass of hydrogen atom.

10.Find the Q-value and the kinetic energy of the emitted

11.When is monochromatic line emitted in the Balmer series of hydrogen atom?

A monochromatic line is emitted in the balmer series of hydrogen atom when electron transits from an outer orbit to the second orbit.

12.The radionuclide ¹¹C decays according to

The maximum energy of the emitted positron is 0.960 MeV.

Given the mass values :

Calculate Q and compare it with the maximum energy of the positron emitted.

, where Q is the kinetic energy released in the decay process. The Q of this decay process is given by

; the masses used in the equation are nuclear masses.

Now, if we express the Q value in terms of atomic masses we have to subtract the 6m_e from the atomic mass of carbon and 5 m_e from carbon atomic mass to get the corresponding nuclear masses. Therefore, we have

Now, using the atomic mass data, we get

        Q = 0.961 MeV

13.The nucleus decays by β^-emission. Write down the β-decay equation and determine the maximum kinetic energy of the electrons emitted. Given that :

14.What are the properties of a neutron?

1.It is a fundamental particle that exist in all nuclei except that of hydrogen.

2.Inside the nucleus a neutron is highly stable.

3.Out side the nucleus a neutron is highly unstable with an average life of 11.4 minutes.

4.It has no charge.

5.The mass of a neutron is slightly greater than that of the proton.

6.Neutrons are very attractive in bombarding experiments with nucleus.

                   (since they have no charge and mass)

7.A neutron when bombarded with its anti particle called anti neutron, it gets anihilated and releases energy.

8. A neutron may be split into proton, electron and anti neutrino resulting pair production.

9. They are not deflected by electric and magnetic fields.

10.They have high penetrating power.

11.Neutrons produces intense biological effects.

15.What do you meant by radioactivity?

The self disintegrating activity exhibited by the nuclei of several elements whose mass number is greater than 206 is called radioactivity. It was first discovered by Becquerel in 1896 during the study of fluorescence of phosphorescence exhibited by certain uranium salts. During radioactivity a complex types of radiations is emitted. By studying these radiations, a lot of information about the nucleus can be obtained.

Most of the isotopes of elements with A > 206 are naturally radio active. Similarly lighter nuclei like C14, K40 etc are also radioactive. The nuclei having 2,8,20,50,82 and 126 protons or neutrons are more stable than the other nuclei. These numbers are called magic numbers.

Properties :

1.It is a self disintegrating activity.

2.It is independent of external conditions like temperature, pressure etc.

3.It is purely a nuclear phenomena.

4.By studying radioactivity a lot of information about the nucleus can be collected.

5.Radio activity is independent of chemical or physical composition of matter.

16.What are the properties of Alpha rays?

1.They are positively charged particles.

2.Measurements showed that alpha particles are equivalent to helium nucleus.

3.They travel in straight lines.

4.Velocity of alpha particles is not a constant and it depends on the nucleus from where it is emitted.

5.They affect photographic plates.

6.They produce fluorescence and phosphorescence.

7.They are deflected by electric and magnetic fields.

8.They have low penetrating power.

9.They have high ionizing power.

10.The distance travelled by an alpha particle through the air medium before coming to rest is defined as the range of the alpha particle.

17.What are the properties of beta particles ?

1.Beta particles are negatively charged particles.

2.Measurement proved that beta particles are electrons.

3.They travel with very high velocity ( but less than the velocity of light).

4.They have very low ionizing power.

5.They have high penetrating power.

6.They affect photographic plates.

7.They produce fluorescence and phosphorescence.

8.They are deflected by electric and magnetic fields.

9.They travel in straight lines.

10.They produce artificial radioactivity in certain elements and can produce nuclear reactions.

18.What are the properties of gamma radiations?

1.Gamma rays are electromagnetic radiations of very short wavelength.

2.They travel with the same velocity of light.

3.They affect photographic plates.

4.They are not affected by electric and magnetic fields.

5.They produce fluorescence and phosphorescence.

6.They ionise the gas through which they pass.

7.They have very high penetrating power.

8.Gamma rays can induce certain nuclear reaction.

9.Gamma rays produce intense biological defects.

10.Gamma rays are used in radio therapy.

19.Define (i) Artificial transmutation

                 (ii) Artificial radioactivity

(i)The process by which one stable element is converted to another stable element by artificial means is termed as artificial transmutation.

Example : When ₇N¹⁴ is bombarded with an alpha particle, it gets converted to ₈O¹⁷ releasing a proton.

                         ₇N¹⁴ + ₂He⁴ → ₈O⁷ + ₁H¹

(ii)The process by which one stable element is converted to a radioactive isotope by artificial means is called artificial radioactivity. Here the unstable radioactive isotope become stable by emitting a particle. The half life of such radio isotopes are very small.