Contents
Physics Topics are often described using mathematical equations, making them precise and quantifiable.
What are the Characteristics of Radioactive Substances?
Uranium and thorium: Henry Becquerel first observed in 1896 that photographic plates preserved in opaque black paper get affected, when kept close to a compound, uranium potassium sulphate and also found that no external energy source was required to initiate the chemical reaction. Becquerel also observed similar property in other compounds of uranium and named it as radioactivity. Scientist Madam Marie Curie of Poland, discovered radioactivity in element thorium too.
Polonium and radium: Marie Curie and Pierre Curie extracted radioactive elements polonium and radium from the uranium ore ‘pitchblend’. Polonium and radium exhibit radioactivity 103 and 106 times more than that exhibited by uranium.
Characteristics of radioactivity:
i) Elements of mass number 210 or more, generally exhibit radioactivity.
ii) All radioactive substances emit highly penetrating radiations (rays) that can easily penetrate thin metal sheets and similar substances:
iii) Radioactivity is a continuous and spontaneous activity.
iv) Radioactive rays affect photographic plates.
v) Radioactivity is not affected by physical changes brought about by light, heat, electric or magnetic fields.
vi) Chemical change of radioactive element cannot influence the amount of radioactivity. Hence, radioactivity of an element and that of its compound, is the same.
vii) A chemical change cannot influence radioactivity of an element and that chemical change involves electrons outside the nucleus. It led to the conclusion that radioactivity is entirely a nuclear phenomenon that happens due to internal changes in the nucleus.
viii) Radioactivity brings about transmutation of elements where one element changes into another.
Some useful definitions:
Radioactivity or radioactive decay or radioactive disintegration: The phenomenon of spontaneous emission of rays from an unstable nucleus or due to a nuclear reaction is called radioactivity or radioactive decay or radioactive disintegration. Radioactive rays are highly penetrating and originate due to change in nuclear structure.
Radioactive elements: Elements which exhibit radioactivity spontaneously are called radioactive elements. Generally nucleus of a radioactive element is unstable. The nature of stability varies from element to element.
Example: uranium, radium, thorium.
Parent and daughter atom: Radioactive element or atom that exhibits radioactivity is called parent atom. The atom that is left behind after the emission of radioactive radiation is called daughter atom, which may or may not be radioactive. If it is radioactive then it will be parent atom for next decay.
Radioactive sample: Radioactive sample is a specimen of the material that emits radioactive radiation. From medicine making to paper manufacture, radioactive samples are in wide use. The entire mass of any naturally occurring radioactive substance is not radioactive. Because radioactive decay starts from its beginning. so some part of radioactive substance transforms into stable non-radioactive part. For example, any radioactive sample of uranium also contains some non-radioactive lead.
Radioactive isotopes or radioisotopes: Radioactivity is not a characteristic of an element. One isotope of an element may be radioactive like C14 whereas the other isotope C12 is non-radioactive. Hence, radioisotopes are radioactive isotopes of elements. Example: The radioactive nature of two uranium isotopes U238 and U235 are different. Again, Pb206, Pb208 are non-radioactive but Pb210 called RaD is radioactive.