By : Yash Jain Grade 9DISCOVERY OF RADIOACTIVITY& ADVANCES IN THE FIELD
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 ofradioactivity.alpha radioactivity corresponds to the emission of a helium nucleus, aparticularly stable structure consisting of two protons and two neutrons, calledan a particle.beta radioactivity corresponds to the transformation, in the nucleus:- either of a neutron into a proton, beta- radioactivity, characterised by theemission of an electron e-- or of a proton into a neutron, beta+ radioactivity, characterised by the emissionof an anti-electron or positron e+. It only appears in artificial radioactive nucleiproduced 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 DECAYAlpha 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 DECAYThere 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 PENETRATIONRadiation is absorbed by the material through which it passes. During radioactive decay the alphaor 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 afew millimetres of metal to absorb them. Gamma-rays, on the other hand, are very penetrating andrequire lead shields or a metre of concrete to stop them. The dose of radiation received is theamount of energy absorbed per unit mass of matter. Exposure to ionizing radiation can be harmfulas the radiation can cause cancers in the living population and genetic changes that may produceheritable defects in future generations
Alpha particles can usually be stopped by a very thin barrier. Radioisotopes emitting alphaparticles 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 modestbarrier 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 concretewould be needed to stop some of the more energetic gammas. A natural gamma source foundin the environment (and in the human body) is 40K, an isotope of potassium.Neutrons are also very penetrating. Some elements, like hydrogen, capture and scatterneutrons. Water is commonly used as a neutron radiation shield.
CARBON DATINGThe rate at which 14C decays is absolutely constant. Given any set of 14Catoms, half of them will decay in 5730 years. Since this rate is slow relativeto the movement of carbon through food chains (from plants to animals tobacteria) all carbon in biomass at earths surface contains atmospheric levelsof 14C. However, as soon as any carbon drops out of the cycle of biologicalprocesses - for example, through burial in mud or soil - the abundance of 14Cbegins to decline. After 5730 years only half remains. After another 5730years only a quarter remains. This process, which continues until no 14Cremains, is the basis of carbon dating