Concept of Nuclear chemistry

Radioactivity and Nuclear Chemistry

THE DISCOVERY OF RADIOACTIVITY

In 1896, a French physicist named Henri Becquerel discovered that uranium consisting crystals emitted rays that could expose and fog photographic plates. He found that these rays were able to make changes within the atomic nuclei of the Uranium atoms. He proposed that the uranium atoms were unstable. Particles and energies were emitted to become more stable. These emissions he called uranic rays. , Marie Curie carried out her further experiments to determine if other elements were able to emit uranic rays. She discovered two elements, which was later named polonium and radium, which emitted high levels of radioactivity. The name of uranic rays were changed to radioactivity (or radioactive decay) by her. Nobel prize in physics was shared with Becquerel and her husband, Pierre Curie.They combinedly discovered radioactivity.

Atomic Notation (or Nuclear Symbol):

For keeping track of protons and neutrons in the nucleus

A number of neutron + a number of proton = mass number = A

A number of proton = atomic number = Z

E= Symbol of Element

Atomic notation of common particles: electron: proton: neutron:

TYPES OF RADIOACTIVITY: ALPHA, BETA, AND GAMMA DECA

Alpha (α) particle: a helium nucleus ( or ) without electrons → positively charged – largest particle emitted by radioactive nuclei possessest he highest charge

Beta (β) particle: a beta particle (β ) is an electron emitted by radioactive decay,

Positron: the antiparticle of an electron/beta particle,

Or – The same size as an electron but with a positive charge

gamma (γ) rays:They are like high-energy rays (like X-rays) The Electromagnetic Spectrum shows the different forms of electromagnetic radiation. The cosmic and gamma rays have the highest frequency and the highest energy and make them potentially the most dangerous threat to humans.

Different Types of Radioactivity

The different types of radioactivity are mentioned below:

Alpha (α) emission: a helium nucleus is emitted

Beta (β) emission: a beta particle (or electron) is emitted

Gamma (γ) emission: high-energy rays (like X-rays), are emitted

Positron emission: a positron (the antiparticle of an electron), or , is emitted

NATURAL RADIOACTIVITY AND HALF-LIFE

Decaying of radioactive sample emits particles. The rate of the radioactive decay does not vary by just changing temperature, pressure, or any other factors. Hence, a radioactive sample continues to decay. When much amount of the radioactive particle is present, the activity is higher & vice versa.

Half-Life (t ): The amount of time required for the radioactive particle to decay half.

INDUCED NUCLEAR REACTIONS

It can also be induced to decay by the bombardment of high energy particles (e.g. neutrons, electrons, and other nuclei) – These kinds of nuclear reaction are called nuclear transmutation.

Nuclear Binding Energy: Energy required to break up a nucleus into its component nucleons .Usually, stable nuclei have mass numbers of about 40-80.

Nuclear fission: Heavier nuclei (those with mass numbers > 80), They are capable to split into smaller, more stable nuclei.

Nuclear fusion: Smaller nuclei (those with mass numbers < 40) combine with other smaller nuclei to form more stable nuclei.

THE DISCOVERY OF FISSION AND THE ATOMIC BOMB AND NUCLEAR FISSION: A heavy nucleus is divided to form smaller, more stable nuclei, resulting in the release of large amounts of energy.

The Fission Process: Heavy element's isotopes undergo fission if bombarded by high-energy neutrons. Two isotopes of uranium, and , have practical applications.

There must be enough present, so the neutrons produced can collide with them to cause more fission reactions

Fission Energy: The energy released is 8.4×107 kJ/g of , about equal to the explosion of 30 metric tons.

NUCLEAR FUSION: Smaller nuclei combine to form larger, more stable nuclei. The energy produced is greater than energy given by fission reactions.

Advantages of Nuclear Fusion:

• Produces more energy per gram of materials.
• Light isotopes needed for fusion reactions are more abundant than heavy isotopes needed for fission reactions.
• Fusion products are not radioactive.

Disadvantages of Nuclear Fusion:

High energies are required to control this reaction. For example, the fusion reaction shown above needs the high temperature of around 40 million Kelvin initiates the fusion process, but no known structural material can handle that high temperature.

Radioactive isotope & their uses

The isotope which shows radioactivity is called radioactive isotope.s

Characteristics

• Each and every radioisotope has its own half-life period. Shorter half-life indicates the faster disintegration rate.
• Chemical properties of each isotope of the same element are similar.

Uses of radioisotope

• They are used to trace the root of that element and study the mechanism of the reaction.
• They are used as medicine to cure cancer disease & leukemia.
• Radio dating of mineral and rocks helps to find their age mostly carbon dating technic is used.

Reference:

poulse,tracy.Introduction to chemistry.u.s.a:flexbook, 2010.

Pathak, Sita Karki. The Text Book of Chemistry. kathmandu: Vidhyarthi Pustak Bhandar, 2012.