Chapter II: Radioactivity PDF
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UniversitΓ© Ferhat Abbas SΓ©tif 1
A. Hamma
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This document discusses radioactivity, the emission of radiation by unstable nuclei. It explores natural radioactivity, including alpha, beta, and gamma decay, and artificial radioactivity, including fission and fusion reactions. It also touches upon transmutation and radioactive decay laws.
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Chapter II Radioactivity Chapter II Radioactivity...
Chapter II Radioactivity Chapter II Radioactivity π¨ CHAPTER II: RADIOACTIVITY ππΏ is called the parent nuclide (le nuclΓ©ide parent) π¨ π π ππ is called the daughter nuclide (le nuclΓ©ide fille) In the previous chapter, we discussed the binding energy per nucleon and its relation to The previous nuclear reaction occurs and carry out a gamma energy (photon of light) symbolized the stability of the atomic nucleus. We remind that the nucleus is more stable when its EBn is π ππΈ. greater. For the existing elements of the periodic table, the binding energy per nucleon is increasing with the increase of the atomic mass till a maximum reached with the Iron-56 isotope. This nuclear reaction is frequent for chemical elements with a heavy nucleus having The later possesses the most stable nucleus among all elements. A=Z+N>200. In stable nuclides, the nucleus do not undergoes change. However, in an unstable one, the Example: nucleus spontaneously undergoes change. This change involves emission of radiation from the nucleus, a process by which the unstable nucleus can become more stable. The radiation emitted Bismuth-211 decay to give Thallium-207: from unstable nuclei is called radioactivity. πππ π πππ π πππ π πππ πππ©πβ ππ―π + πππ»π+ ππΈ πππ©πβ ππ―π + πππ»π II.1. DEFINITION Uranium-238 decay to give a daughter nuclide Thorium-234: The radioactivity is the emission of radiations by the nucleus that is changing from a higher πππ π πππ π energy level to a lower energy level. The released energy is emitted as a radiation. The πππΌβ ππ―π + πππ»π+ ππΈ radioactivity is a result of the decay of an unstable isotope. As we can see for 211Bi or 238U, the number of protons is important (Z>83). Thus, the ratio (N/Z) is 1.54 and 1.59, respectively. In both nuclides, the repulsive electrostatic force II.2. TYPES (rising from the repulsion of protons) in the nucleus is more important than the strong nuclear II.2.1. Natural Radioactivity (Main types of radiation) force. The latter is not enough to counter the repulsion force, thus the nucleus search to reach a Some naturally occurring isotopes of certain elements have nuclei that spontaneously more stable level. This is achieved by breaking down the nucleus into less heavy one by rejecting disintegrate (breakdown), and we have no control over these processes. These include most some neutrons and protons. The estimation of the mass defect in both cases will reveal realizing isotopes with atomic numbers greater than 83 (Z>83). Each of these disintegrations occurs with of a quantity of energy in form of gamma rays. emission of one of the three types of nuclear radiation: alpha, beta particles and gamma ray as well as a considerable quantity of energy. II.2.1.2. Beta particles II.2.1.1. Alpha particles ( πππ―π, πππΆ) The beta particles are realized when a nucleus has an excess of protons or neutrons. Therefore, two types of Beta particles can arise: The particles are identical to a Helium-4 nucleus, which has 2 protons and 2 neutrons. Alpha particle has a mass number A=4, an atomic number Z=2 and a charge βe=2+β. a- Beta negative ( πππ·) or ( πππ )or (Ξ²-) The Beta negative particle has a charge and mass identical to those of an electron (high In short the alpha particles can be represented as Ξ±, 4Ξ±, πππΆ , 4He, or πππ―π energy electron e= -1 and A=0.00055 amu). The general equation representing the alpha particle decay of a nuclide π¨ππΏ to give new The beta particle forms because of breakdown of a neutron into proton and electron as stable one π is: π¨ π follow: π¨ ππΏ β π ππ + πππ―π + πππΈ π π π π π π Parent Nuclide Daughter Nuclide Alpha particles Energy ππβ ππ + ππ or ππβ ππ + ππ· The resulting proton remains in the nucleus and the energy will be released as beta Note: (The nuclear reaction must be balanced against the atomic number and mass particles. In short, the beta negative particles can be represented as Ξ²-, πππ· or πππ. number) Prepared by A. HAMMA Prepared by A. HAMMA 18 19 Chapter II Radioactivity Chapter II Radioactivity The general equation representing the Beta negative particle decay of a parent nuclide We notice that nuclear reactions release different quantities of energy or gamma rays. π¨ ππΏ to give a daughter nuclide of a new element π is: Example: π¨ π¨ π π ππΏ β π ππ + ππ· + ππΈ Technetium-99m is the unstable isotope of Technetium (m indicate that is metastable or Nuclide parent Nuclide daughter Beta negative Energy exited). By emitting energy in the form of gamma rays, the nucleus become more stable. πππ ππ π πππ»πβ πππ»π+ ππΈ Example: Same for Tin-119: πππΊπβ πππ ππππ π πππΊπ+ ππΈ Beryllium decay to give Boron: ππ π ππ π II.2.2. Artificial Radioactivity ππ©πβ ππ· + ππ©+ ππΈ The artificial radioactivity is produced by bombarding some stable and nonradioactive isotopes, Thorium decay to give Palladium: πππ π πππ π with high-speed particles (a particle projectile that can be a protons, neutrons or small nuclei). πππ»πβ ππ· + πππ·π+ ππΈ When one of these particles is absorbed, the stable nucleus is converted to a radioactive isotope b- Beta positive or Positron ( πππ·) or (πππ+) or (Ξ²+) and usually some types of radiation particles. The Beta positive particle is a particle that is charged positively and has no mass. The The general nuclear reaction which could represent the artificial radioactivity is : positron forms as a result of breakdown of a proton into neutron and electron as follows: π¨ π¨π π¨ π¨π ππΏ + ππ π· β ππ + ππ π· π π ππβ ππ + πππ or π π ππβ ππ + πππ· Target nucleus Projectile New Nucleus Radiation π¨ π¨ The resulting neutron remains in the nucleus and the energy will be realized as beta positive The abbreviated writing of the nuclear reaction is : π¨ππΏ ( πππ π·, πππ π·) π¨π π particles. In short, the beta positive particles or positron can be represented as Ξ²+, πππ· or πππ. II.2.2.1. Fission In the nuclear fission reaction, a heavy nucleus (A>200) is bombarded by neutrons and The general equation representing the Positron emission of a parent nuclide π¨ππΏ to give a became unstable. The later splits and gives rise to a lowest nuclei (72 we replace it in the decay law: N = N. e => π π = ππ. π 8- Mass of the source at this life-time: π΄ = π. π => π =... m = m.e ο¨ m = 4.8742 β 10.e. = 9.7489 β 10 Example: Cesium-137 ( πΆπ ) is a radioactive isotope undergoing Ξ²- decay. The initial activity of a radioactive sample source containing this isotope is A0= 1.5*105 Bq. The cesium has a half- life of 30.2 years. 1- Write the corresponding nuclear reaction. Prepared by A. HAMMA Prepared by A. HAMMA 26 27