1. By : Yash Jain
Grade 9
DISCOVERY OF RADIOACTIVITY
& ADVANCES IN THE FIELD

3. WHAT IS RADIOACTIVITY ?
The atoms making up matter are
stable, but some of them are
spontaneously transformed by
emitting radiations which release
energy. This is called
radioactivity.

4. There are three types of radiations corresponding to three types of
radioactivity.
alpha radioactivity corresponds to the emission of a helium nucleus, a
particularly stable structure consisting of two protons and two neutrons, called
an a particle.
beta radioactivity corresponds to the transformation, in the nucleus:
- either of a neutron into a proton, beta- radioactivity, characterised by the
emission of an electron e-
- or of a proton into a neutron, beta+ radioactivity, characterised by the emission
of an anti-electron or positron e+. It only appears in artificial radioactive nuclei
produced by nuclear reactions.

5. CONTD.
 gamma radioactivity unlike the other two,
is not related to a transmutation of the
nucleus. It results in the emission, by the
nucleus, of an electromagnetic radiation, like
visible light or X-rays, but more energetic.
 gamma radioactivity can occur by itself or
together with alpha or beta radioactivity

6. ALPHA DECAY
Alpha decay means that a twice positive
charged heliumion (helium atomic nucleus) is
emited from the atomic nucleus .We find two
protons and two neutrons less in this atomic
nucleus, so it is lighter. The alpha radiation is
the most dangerous of the three types of
radiation, but a sheet of paper is enough to
protect oneself. The skin protects us also
from alpha radiation

7. BETA DECAY
There are two types of the beta decay. The one is the
beta minus decay and the other is the beta plus
decay. The beta minus decay a neutron decays into
a proton, an electron and an antineutrino. The
electron and the antineutrino are emitted. The
radioactive particle is the electron. The number of
nucleons do not change, but we have got one
proton more than before the decay. 2 or 3 cm of
wood are enough to protect oneself.

9. GAMMA DECAY
 When we talk about the gamma decay high-
energy electromagnetic waves are emited
from the atomic nucleus. This waves are
photons, which have got a higher frequency
and less wave long than light. A gamma
decay can happen after an alpha decay or a
beta decay, because the atomic nucleus is
very energitic

10. RADIATION PENETRATION
Radiation is absorbed by the material through which it passes. During radioactive decay the alpha
or beta particles, and the gamma rays that are given off can all penetrate matter, although alpha-
particles can be stopped by a piece of paper or the human skin, whereas beta-particles require a
few millimetres of metal to absorb them. Gamma-rays, on the other hand, are very penetrating and
require lead shields or a metre of concrete to stop them. The dose of radiation received is the
amount of energy absorbed per unit mass of matter. Exposure to ionizing radiation can be harmful
as the radiation can cause cancers in the living population and genetic changes that may produce
heritable defects in future generations

11. Alpha particles can usually be stopped by a very thin barrier. Radioisotopes emitting alpha
particles are usually not hazardous outside the body, but they can cause damage if ingested.
Betas (streams of electrons) can pass through a hand, but are usually stopped by a modest
barrier such as a few millimeters of aluminum, or even a layer of clothing. As with alphas,
beta particles are more hazardous if inhaled or ingested.
Gammas can be very penetrating and can pass through thick barriers. Several feet of concrete
would be needed to stop some of the more energetic gammas. A natural gamma source found
in the environment (and in the human body) is 40K, an isotope of potassium.
Neutrons are also very penetrating. Some elements, like hydrogen, capture and scatter
neutrons. Water is commonly used as a neutron radiation shield.

12. CARBON DATING
The rate at which 14C decays is absolutely constant. Given any set of 14C
atoms, half of them will decay in 5730 years. Since this rate is slow relative
to the movement of carbon through food chains (from plants to animals to
bacteria) all carbon in biomass at earth's surface contains atmospheric levels
of 14C. However, as soon as any carbon drops out of the cycle of biological
processes - for example, through burial in mud or soil - the abundance of 14C
begins to decline. After 5730 years only half remains. After another 5730
years only a quarter remains. This process, which continues until no 14C
remains, is the basis of carbon dating

13. THANK YOU !!!