Definitions [10]
Radioactivity can be induced in elements, by bombarding them with a-particles, ne1,1trons, protons etc. and is called artificial radioactivity
Decay constant of a radioactive substance is defined as the ratio of its instantaneous rate of disintegration to the number of atoms present at that time. N = N0 e-λt.
The method of determining the age of organic materials by measuring the amount of radioactive carbon-14 present in them.
One curie is defined as the quantity of any radioactive substance which undergoes 3. 7 × 1010 disintegrations per second.
Conversion of nucleus of one element into nucleus,of another element is called transmutation.
The nuclear transmutations represented by means of equations similar to chemical reactions are called nuclear reactions.
Exposure is defined as the amount of ionisation produced in a unit mass of dry. air at standard pressure (STP). The S.I unit of radiation dosage is called gray (Gy).
One grey corresponds to one joule of energy absorbed per kilogram of target material.
The spontaneous emission of highly penetrating radiations (a particle, f3-particle, and y-rays) from heavy elements, of atomic weight greater than 206 is called "natural radioactivity".
The unit for measuring activity is Curie (Ci).
“The energy that is absorbed or released in a nuclear reaction is called the disintegration energy or the Q-value of the reaction.”
Key Points
- Biological dose is measured in rem (roentgen equivalent man) and is equal to:
rem = rad × RBE factor; 1 millirem = one thousandth of a rem. - Radiation effects increase with dose: below 25 rem, no visible effects, but doses above 500 rem can cause death within a week.
| No. | Property | α-particle | β-particle | γ-rays |
|---|---|---|---|---|
| 1 | Identification | Nuclei of helium | Fast-moving electrons | Electromagnetic waves of short wavelength |
| 2 | Electric charge | Positive charge (+2e) | Negative charge (−e) | No charge |
| 3 | Rest mass | Equal to that of a helium nucleus | Equal to the rest mass of an electron | Zero rest mass |
| 4 | Speed | About (1/10)ᵗʰ the velocity of light (c) | 0.99 c | Equal to c |
| 5 | Penetrating power | Smaller than that of β-particles | 100 times that of an α-particle | 100 times that of a β-particle |
| 6 | Ionising power | Higher than that of a β-particle | (1/100)ᵗʰ of α-particle | (1/100)ᵗʰ of β-particle |
| 7 | Behaviour in E and B fields | Deflected in electric and magnetic fields | Deflected | Not deflected |
| 8 | Photographic plate | Affect the photographic plate | Affect | Affect |
| 9 | Fluorescence | Produce fluorescence | Produce | Produce |
