Скачать или смотреть ICSE PHYSICS || Class 10 || Radioactivity|| Unit A || Types Of Nuclei ||

The three constituents of an atom are electrons, protons and neutrons.
(a) Atomic number (Z) — The atomic number of an atom is equal to the number of protons in it's nucleus (which is same as the number of electrons in a neutral atom). i.e.,
Z = number of protons in the nucleus of an atom.

(b) Mass number (A) — The mass number of an atom is equal to the total number of nucleons (i.e., the sum of the number of protons and the number of neutrons ) in it's nucleus. i.e.,
A = number of protons + number of neutrons in the nucleus of an atom.

The atoms of the same element, having same atomic number Z, but different mass number A, are called isotopes.

The atoms of different elements which have the same mass number A, but different atomic number Z are called isobars.

Radioactivity is a nuclear phenomenon. It is the process of spontaneous emission of α or β and γ radiations from the nucleus of atoms during their decay.

Uranium and Polonium are radioactive substances.

There will be no change in the nature of radioactivity when a radioactive substance is oxidized because radioactivity is a nuclear phenomena.

α and β radiations are charged particles (i.e., α radiation is positively charged and β radiation is negatively charged) therefore, they are deflected in an electric or magnetic field. γ radiations are uncharged particles hence, they do not show deflection in an electric or magnetic field.

‘Radioactivity is a nuclear phenomenon’.GIVE REASON:
Any physical change (such as change in pressure and temperature) or chemical change (such as excessive heating, freezing, action of strong electric and magnetic fields, chemical treatment, oxidation etc.) does not change the rate of decay and the nature of radiation emitted by the substance.

This clearly shows that the phenomenon of radioactivity cannot be due to the orbital electrons which could easily be affected by such changes. Therefore the radioactivity should be the property of the nucleus. Thus, radioactivity is a nuclear phenomenon.

(i) Atomic number

When an α particle is emitted atomic number decreases by 2.
When a β particle is emitted atomic number increases by 1.
When γ radiation is emitted there is no change in atomic number.
(ii) Mass number

When an α particle is emitted mass number decreases by 4.
When a β particle is emitted there is no change in the mass number.
When a γ radiation is emitted there is no change in the mass number.

The isotopes of some elements with atomic number (Z) less than 82 are found to be radio active. They are called the radio isotopes.
State the medical use of radioactivity.

Answer

Many diseases such as leukemia, cancer, etc., are cured by radiation therapy. γ radiations from cobalt-60 are used to treat cancer by killing the cells in the malignant tumor of the patient.
The salt of weak radioactive isotopes such as radio-sodium chloride, radio-iron and radio-iodine are used for diagnosis. Such radio isotopes are called the tracers. These tracers are used to detect the suspected brain tumors and blood clots before they become dangerous.
γ rays emitted by the radio isotopes are used to sterilize bandages, dressings, syringes and other equipments to make them free from germs.