The Concept of Radioactivity Dr. (Mrs.) Ndukwe, Nelly Acha MOUNTAIN TOP UNIVERSITY CHM 101 The Concept of Radioactivity Dr. (Mrs.) Ndukwe, Nelly Acha           The Concept of Radioactivity by Dr. (Mrs.) Ndukwe, Nelly Acha is licensed under a Creative Commons Attribution-Non Commercial 4.0 International License.

Radioactivity Principle The chemistry of radioactivity originates from the interaction of subatomic particle. All the mass of an atom are concentrated in the positively charged (+) Nucleus. While, Electrons have Negatively charged (-). Electrostatic force is the force required to attract the electrons to the nucleus of the atom.

Atomic Nuclear structure The nuclear structure is largely made up of Atomic number (Z) , which is defined as the no. of protons, or also the no. of electrons in a neutral atom. Mass number which is defined as the no. of protons plus the no. of neutrons. The lightest atomic nucleus is the hydrogen atom and is 1830 times more massive than an electron. The size of a nucleus is around 10−15 m.

Interaction of the Atomic Nuclear structure Nuclei contain positively charged Protons and uncharged Neutrons Protons and neutrons are held together by an attraction force (strong interaction). An electrostatic repulsion occurs between the protons inside the nucleus The balance of the two forces; the attraction and repulsion forces control some basic important features of atomic nuclear stability

Nuclear structure The lighter nuclei are generally stable with approximately equal no. of protons and neutrons, examples are O16 and C12. The heavier ones have higher proportion of neutrons as pb208. As atomic number Z increases the electro static repulsion comes to be dominate. There is a limit to the number of stable nuclei. All elements beyond Bi (z=83) are considered as being radioactive.

The Stability of Atomic Nuclei Magic number The nuclei with even no. of either protons or neutrons ( or both) are generally more stable than ones with odd no. O16 and Pb208 are example of nuclei with magic no. certain magic numbers of protons or neutrons, which give extra atomic stability. Eg: 2 8 20 28 50 82 126

The Influence Isotopes on Radioactivity of Atomic Nuclei    Isotopes are atoms of the same element that have a different number of neutrons, isotopes have the following characteristics: Isotopes have the same atomic number (same number of protons), but a different atomic mass number (a different number of neutrons). Isotopes behave the same chemically, as they are of the same element.  The only difference is that one is heavier than the other because of the additional neutrons. For example, carbon-12 and carbon-14 are both isotopes of carbon.  Carbon-12 has 6 neutrons; carbon-14 has 8 neutrons.

The Influence Isotopes on Radioactivity of Atomic Nuclei Some elements have: only one stable isotope (e.g. 19F, 27Al, 31P). others may have several (e.g. 1H and 2H, the latter also being called deuterium, 12C and 13C). Molar mass is also known as Relative atomic mass (RAM) is determine by the Proportions of mixture of the isotopes of an element.

Isotopes and Nuclear magnetic Resonance NMR (nuclear magnetic resonance ) technique depend on NMR of H1 and C13. All elements have unstable radioactive isotopes, some of these occur Naturally and the other can be made artificially.

Radioactive Decay: Radioactive decay: It is a process whereby unstable atomic nuclei change into more stable ones by emitting atomic particles of different kinds. These atomic particles include; Alpha, beta and gamma (α, β and γ) radiation

Radioactivity Is the emission of subatomic particles or high- energy electromagnetic radiation by atomic nuclei. Such atoms/isotopes are said to be radioactive in nature. Example of alpha decay: 23892U  23490Th + 42He

Alpha Decay The alpha decay has largest ionizing power and the ability to ionize molecules & atoms due to largeness of -particle. But has lowest penetrating power as with the ability to penetrate matter Skin, even air, protect against human beings and animals from -particle radiation.

Beta decay 13755Cs  13756Ba + 0-1e- Beta () particle = e- How does nucleus emit an e-?  neutron changes into proton & emits e-  10n  11p + 0-1e Daughter nuclide = parent nuclide atomic number plus 1 13755Cs  13756Ba + 0-1e-

Beta Decay Beta decay has a lower ionizing power than alpha particle, but higher penetration power. Requires sheet of metal or thick piece of wood to arrest penetration. Therefore, more damage outside of body, but less in (alpha particle is opposite).

Gamma Ray Emission Is an electromagnetic radiation with high-energy photons; 00 It has no charge, no mass Usually emitted in conjunction with other radiation types Lowest ionizing power, highest penetrating power  requires several inches lead shielding

Radioactivity Decay Gamma radiation is high energy electro magnetic radiation accompanies alpha and beta decays. Half-life is the time taken for half of a sample to decay. It can vary from a fraction of a second to billions of years. All elements beyond Bi (z=83) are radioactive and non beyond U(z=92) occur naturally on Earth. Spontaneous fission: this occurs for heavy elements where the nucleus splits into two fragments of similar mass.

The Concept of Radioactivity by Dr. (Mrs The Concept of Radioactivity by Dr. (Mrs.) Ndukwe, Nelly Acha is licensed under a Creative Commons Attribution-Non Commercial 4.0 International License