Nuclear Chemistry

Group 8 Nuclear Chemistry Discovery of radioactivity Radioactivity – is the spontaneous emission of particles and rays from the nucleus of the atom. Persons behind the discovery of radioactivity Wilhelm Roentgen – he discovered the X-rays when he observed that a vacuum discharge tube enclosed in a thin, black board box caused a nearby piece of paper with the salt barium platinocyanide to glow with brilliant phosphorescence. Antoine Henri Becquerel – showed the relationship between X-rays and the phosphorescence of uranium salts. Marie and Pierre Curie – coined the name “Radioactivity” - Discovered the two new elements polonium and radium, both are radioactive. Ernest Rutherford – discovered the two particles alpha and beta particles. Paul Villard – discovered the gamma ray, a third type of emission from the radioactive materials similar to an X-ray. 2. Symbolism and notation of element Example the element Uranium

This represents a uranium isotope with an atomic

number of 92 and a mass number of 238.

Nucleons – the term used for the collective protons and neutrons. Nuclide – the term used in nuclear chemistry to mean any isotope of any atom. Radionuclide – nuclide that spontaneously emit radiation. Nuclear Reactions Evidences: 1. Involves change in atom molecules. 2. Different behavior for different isotopes of element in nuclear reactions. 3. Rate unaffected by changes in T and P 4. Reaction of an atom same regardless of whether combined or uncombined. 5. Energy involved in change is very large.

Alpha particles • Alpha particles (named after and denoted by the first letter in the Greek alphabet, α) consist of two protons and two neutrons bound together into a particle identical to a helium nucleus; hence, it can be written as He2+ or 42He2+. They are a highly ionizing form of particle radiation, and have low penetration. The alpha particle mass is 6.644656×10-27 kg, which is equivalent to the energy of 3.72738 GeV. The charge of an alpha particle is equal to +2e, where e is the magnitude of charge on an electron, e=1.602176462x10-19C. • Alpha particles are emitted by radioactive nuclei such as uranium, thorium, actinium, or radium in a process known as alpha decay. This sometimes leaves the nucleus in an excited state, with the emission of a gamma ray removing the excess energy. In contrast to beta decay, alpha decay is mediated by the strong nuclear force. In classical physics, alpha particles do not have enough energy to escape the potential of the nucleus. However, the quantum tunneling effect allows them to escape. Beta particle • •

History Henri Becquerel, while experimenting with fluorescence, accidentally found out that Uranium exposed a black paper wrapped photographic plate with some unknown radiation that could not be turned off like Xrays. Ernest Rutherford continued these experiments and discovered two different kinds of radiation: alpha particles that did not show up on the Becquerel plates because they were easily absorbed by the black wrapping paper (actually just about any sheet of paper fully absorbs alpha particles) beta particles which are 100 times more penetrating that alpha particles. He published his results in 1899. Beta particles are high-energy, high-speed electrons or positrons emitted by certain types of radioactive nuclei such as potassium-40. The beta particles emitted are a form of ionizing radiation also known as beta rays. The production of beta particles is termed beta decay. They are designated by the Greek letter beta (β). There are two forms of beta decay, β− and β+, which respectively give rise to the electron and the positron.

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Gamma rays Gamma rays (denoted as γ) are a form of electromagnetic radiation or light emission of frequencies produced by sub-atomic particle interactions, such as electron-positron annihilation or radioactive decay. Gamma rays are generally characterized as electromagnetic radiation having the highest frequency and energy, and also the shortest wavelength (below about 10 picometers), within the electromagnetic spectrum. Gamma rays consist of high energy photons with energies above about 100 keV. Gamma rays were discovered by Paul Villard, a French chemist and physicist, in 1900, while studying uranium.

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Nuclear fission Nuclear fission is the splitting of the nucleus of an atom into parts (lighter nuclei) often producing free neutrons and other smaller nuclei, which may eventually produce photons (in the form of gamma rays). The fragment are called fission Product as the atom split , it releases energy and two or three neutrons, each of which can cause another nuclear fission the 1st instance was reported by the German scientist Otto Hahn (1879-1968) and fritz strassmann (1902-1980). Detecting isotopes of barium, krypton, cerium and lanthanum

Characteristic of nuclear fission 1. upon absorption of a neutron, a heavy nuclide splits into two or more smaller nuclides 2. The mass of the nuclides formed range from about 70-60 amu 3. Two or more neutron are produced from the fission of each atom 4. Large quantities of energy are produced as a result of the conversion of a small amount of mass into energy 5 most nuclides produced are radioactive and continue to decay until they are stable nucleus Structure of nuclear fission

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An atom's nucleus can be split apart. When this is done, a tremendous amount of energy is released. The energy is both heat and light energy. This energy, when let out slowly, can be harnessed to generate electricity. When it is let out all at once, it makes a tremendous explosion in an atomic bomb. The word fission means to split apart. Chain reaction

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A chain reaction is a sequence of reactions where a reactive product or by-product causes additional reactions to take place example, every step of H2 + Cl2 chain reaction consumes one molecule of H2 or Cl2, one free radical H· or Cl· producing one HCl molecule and another free radical In which the product cause the reaction to continue or magnify, Nuclear Fusion

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Another form of nuclear energy is called fusion. Fusion means joining smaller nuclei (the plural of nucleus) to make a larger nucleus. Fusion is a nuclear process in which two light nuclei combine to form a single heavier nucleus. An example of a fusion reaction important in thermonuclear weapons and in future nuclear reactors is the reaction between two different hydrogen isotopes to form an isotope of helium. Fusion reactions have been going on for billions of years in our universe. In fact, nuclear fusion reactions are responsible for the energy output of most stars, including our own Sun. Scientists on Earth have been able to produce fusion reactions for only about the last sixty years. At first, there were small scale studies in which

only a few fusion reactions actually occurred. However, these first experiments later lead to the development of thermonuclear fusion weapons (hydrogen bombs). • Fusion is the process that takes place in stars like our Sun. Whenever we feel the warmth of the Sun and see by its light, we are observing the products of fusion. We know that all life on Earth exists because the light

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generated by the Sun produces food and warms our planet. Therefore, we can say that fusion is the basis for our life. When a star is formed, it initially consists of hydrogen and helium created in the Big Bang, the process that created our universe. Hydrogen isotopes collide in a star and fuse forming a helium nucleus. Later, the helium nuclei collide and form heavier elements. Fusion is a nuclear reaction in which nuclei combine to form a heavier nucleus. It is the basic reaction which drives the Sun. Lighter elements fuse and form heavier elements. These reactions continue until the nuclei reach iron (around mass sixty), the nucleus with the most binding energy. When a nucleus reaches mass sixty, no more fusion occurs in a star because it is energetically unfavorable to produce higher masses. Once a star has converted a large fraction of its core's mass to iron, it has almost reached the end of its life. The fusion chain cannot continue so its fuel is reduced. Some stars keep shrinking until they become a cooling ember made up of iron. However, if a star is sufficiently massive, a tremendous, violent, brilliant explosion can happen. A star will suddenly expand and produce, in a very short time, more energy than our Sun will produce in a lifetime. When this happens, we say that a star has become a supernova Atomic bomb

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an extremely destructive type of bomb, the power of which results from the immense quantity of energy suddenly released when a very rapid chain reaction of nuclear fission is set off by neutron bombardment in the atoms of a charge of plutonium (primarily Pu-239) or uranium (U-235): first used in warfare (1945) by the United States against the Japanese cities of Hiroshima and Nagasaki Is a fission bomb; it operates on the principles of a very fast chain reaction that releases a tremendous amount of energy. On August 2, 1939, just before the beginning of World War II, Albert Einstein wrote to then President Franklin D. Roosevelt. Einstein and several other scientists told Roosevelt of efforts in Nazi Germany to purify uranium-235, which could be used to build an atomic bomb. It was shortly thereafter that the United States Government began the serious undertaking known then only as "The Manhattan Project." Simply put, the Manhattan Project was committed to expediting research that would produce a viable atomic bomb. The hazards of atomic bomb The hazard of atomic bomb explosion includes not only shock waves from the explosive pressure and tremendous heat, but also intense radiation in the form of beta particle, alpha particle, gamma rays. and ultraviolet rays, gamma rays and x-ray can penetrate deeply into the body, causing burns, sterilization and gene mutation, which can be adversely effect future generations If the bomb explode trough the ground , many tons of dust lifted to the air this called as fallout, is the spread by air current over wide areas of the land and constitutes a lingering source of radiation hazard