DISCOVERY OF RADIOACTIVITY& ADVANCES IN THE FIELD

By : Yash Jain Grade 9

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.

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.

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

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

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.

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

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

                                                                                    

           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.

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

THANK YOU !!!