Radioactivity

Question 1

What is radioactivity?

Answer 1

The phenomenon of spontaneous emission of highly penetrating substances by heavy elements is called radioactivity.

Question 2

Who discovered radioactivity?

Answer 2

Henry Becquerel found that uranium and some of its salts emit spontaneously some invisible radiations that penetrate through opaque substances and affect the photographic plate.

Question 3

What is the atomic number past which nuclei having more protons than neutrons are unstable?

Answer 3

83. However, some isotopes of the elements of less Z are also unstable.

Question 4

What is radioactive disintegration?

Answer 4

Unstable nuclei get their stability by emitting radiations like alpha, beta particles, and gamma rays. This process is called radioactive disintegration.

Question 5

What are the types of radioactivity?

Answer 5

There are two types of radioactivity: natural radioactivity and artificial radioactivity.

Question 6

What is a common thing about both natural and artificial radioactivity?

Answer 6

They are both spontaneous and can’t be controlled (but can be initiated) by any artificial means.

Question 7

What is natural radioactivity?

Answer 7

The phenomenon of spontaneous emission of highly penetrating radiation from heavy elements of atomic weights greater than about 206, occurring in nature is called natural radioactivity.

Question 8

What is artificial radioactivity?

Answer 8

Radioactivity induced in an element by bombarding it with alpha particles, neutrons, protons, and other particles or radiations is called artificial radioactivity.

Question 9

How are radioactive elements identified?

Answer 9

From a radioactive element, the rays coming are made to pass through the magnetic field. The magnetic force makes the rays separate in three directions, referring to the distinction in charges. Positive charges are of alpha particles, negative charges are of beta particles and Y has no charge. Refer to the book for the experiment.

Question 10

What are the five laws of radioactive disintegration?

Answer 10

1. Radioactivity is the spontaneous disintegration process of a nucleus and cannot be accelerated or retarded by any physical or chemical process.
2. In any radioactive transformation, either an alpha or a beta particle(never both or more than one of each kind) is emitted by the atom.
3. When a radioactive atom emits an alpha particle, a new atom is formed whose mass number is less by four units and whose atomic number is less than two units than those of the parent atom.
4. When a radioactive atom emits a beta particle, the new atoms formed have the same mass number but the atomic number is increased by one unit.
5. The rate of disintegration at any time, i.e. the number of atoms that disintegrate at the time, is directly proportional to the number of atoms present at that instant.

Question 10

Are alpha rays and beta rays actual radiations?

Answer 10

No, they are particles.

Question 11

What is the significance of the half-life period?

Answer 11

The atoms in a radioactive sample always take infinite time to disintegrate completely. However some radioactive substances are more active than others. To compare the activity of one radioactive element with that of another, the half-life is measured and used.

Question 12

What is the definition of half-life?

Answer 12

The half-life period of a radioactive substance is defined as the time during which half of the original radioactive atoms of the substance are disintegrated.

Question 13

What is the formula for half-life?

Answer 13

0.693 upon disintegration constant.

Question 14

Is the half-life characteristic property of the nucleus?

Answer 14

YES. But what does this mean?

Question 15

What is the radioactive decay rate?

Answer 15

It is defined as the number of radioactive disintegrations taking place in a sample per second.

Question 16

What is the formula for radioactive decay rate or activity?

Answer 16

negative of disintegration constant times the number of atoms present in the sample at that time.

Question 17

What is the mean life of a radioactive substance?

Answer 17

The mean life of a radioactive substance is defined as the ratio of the total lifetime of all the radioactive atoms to the number of such atoms.

Question 18

Why is the concept of the mean life of a radioactive substance important?

Question 19

What is successive disintegration?

Answer 19

When a radioactive substance decays, a new element is obtained. the new substance again being radioactive, may further disintegrate into other new substances an son on until a stable substance is formed. Such a chain of disintegration is called successive disintegration.

Question 20

What is radioactive equilibrium?

Answer 20

When the daughter product is formed at the same rate at which it decays, then the proportions of different radioactive atoms in the mixture do not change with time and the parent is said to be in radioactive equilibrium with its daughter.

Question 21

When is a radioactive substance said to be in equilibrium with its parent?

Answer 21

When the number of atoms of the radioactive substance in a radioactive chain becomes constant, it is said to be in equilibrium with its parent.

Question 22

What is secular or permanent equilibrium?

Answer 22

If the parent substance is long-lived in comparison to its daughter substance, then the daughter substance will disintegrate faster. Ultimately, they obtain a state if equilibrium known as secular equilibrium.

Question 23

What is transient equilibrium?

Answer 23

When the parent is longer lived than the daughter but the half-life period of the parent is not very long, the equilibrium attained is known as transient.