http://www.primeonlinetutor.com/pd8 Transmutation is the process responsible for transforming one element into another. There are two fundamentally different processes whereby transmutations occur: nuclear decay and nuclear fusion. Nuclear decay occurs when there is the emission of an alpha or beta particle from the nucleus. These are known as alpha and beta decay respectively when they occur naturally. Natural transmutations involve the emission of alpha or beta particles from the nucleus of a radioactive atom. In the early days of studying radioactive decay, one of the first devices invented was the Wilson cloud chamber by Scottish scientist Charles Wilson. The penetration of the alpha or beta particle through a saturated vapour in a sealed chamber results in a cloud-like track of condensation. If the particle is an alpha particle, the track is usually quite thick and penetrating. The length of the track may indicate the energy of emission. Longer tracks indicate a higher energy of emission. A beta particle track is usually quite a lot finer and often shorter than an alpha particle track, but again the length of the track is an indication of the energy of the particle at emission. In the process of nuclear fusion, a nucleus combines with a colliding particle that fuses into the nucleus to form a new element of higher atomic mass. The most familiar example of fusion occurring close to Earth is the fusion of hydrogen atoms to form helium on the Sun. This process provides the Sun with its radiant energy. In artificial transmutations, a particle such as an alpha particle may be captured by a nucleus to form a larger atomic number nucleus. This capture often results in the release of another particle from the nucleus. In all transmutation reactions, both the atomic mass and number on both sides of the nuclear equation are conserved. Hemi Becquerel discovered that uranium was radioactive. Later it was shown that the radiation was emitted from the nucleus of unstable isotopes. There are three types of radiation emitted by radioactive substances: alpha, beta and gamma radiation. The least penetrating radiation (alpha) was found to produce the most ionisation, and the most penetrating radiation (gamma) was found to produce the least ionisation. The following table sets out the main properties of these radioactive emissions. Alpha decay occurs in large nuclei because the strong nuclear force has a very short range, and hence only operates between adjacent nuclei, while the electrostatic force of repulsion between protons acts between all the protons in the nucleus. Clearly when a large nucleus undergoes an alpha decay it will change into a different element because it loses two neutrons and two protons. This changing of a parent nucleus into a daughter product through radioactive decay is called natural transmutation. transmutes the uranium-232 into thorium-228. The uranium nucleus is unstable because the mass of the uranium-232 nucleus is greater than the sum of the masses of the thorium-228 and the alpha particle. As with all natural systems the lowest energy state is preferred and the uranium atom will spontaneously undergo alpha decay. The kinetic energy of the alpha particle can be calculated from the mass lost in the decay, and measurements of the kinetic energy of emitted alpha particles have verified this. Beta decay that involved the emission of a high energy electron from the nucleus was initially quite puzzling because the wave nature of the electron meant it could not be found in a region as small as the atomic nucleus. To explain the appearance of the electron, physicists assumed that the electron must be created at the time of its emission by a neutron changing into a proton and an electron in the nucleus. A beta decay therefore transmutes the parent element to an element with the same number of nucleons but with one extra proton and one less neutron. For example, beta decay in carbon-14 produces a beta particle and an atom of nitrogen-14. Beta decay occurs in atoms which have too many neutrons to be stable. All fundamental particles have mirror images with opposite properties called anti-particles and that the neutral particle emitted in beta decay is actually an anti-neutrino. The nucleus has energy levels similar to the energy levels of the atomic electrons, and when a nucleus moves to a lower energy it emits a gamma ray. Because the energy gaps in the nucleus are much greater than those between the allowed electron orbitals, the electromagnetic quanta emitted from the nucleus have much higher frequencies than those emitted from the electron states. Gamma rays are often emitted from nuclei after an alpha emission because the nucleus is left in an excited state after the emission. The nucleus returns to its ground state by emitting electromagnetic radiation in the form of a gamma ray. Unlike alpha and beta decay, no transmutation occurs in gamma decay. http://youtu.be/FF3YX3rETdg PD8312

• published: 07 Mar 2014
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