Atomic Physics Lecture No 1 PDF

Al-Salam University College Department of Radiology Techniques Atomic physics Lecture No: 1 Prepared by : Assist.Lect. Safa Sami Dr. saad Thabet -The Basic Composition of an Atom: An atom consists of...

Al-Salam University College Department of Radiology Techniques Atomic physics Lecture No: 1 Prepared by : Assist.Lect. Safa Sami Dr. saad Thabet -The Basic Composition of an Atom: An atom consists of a central nucleus that contains comparatively larger particles known as protons and neutrons. There are smaller particles orbited central nucleus known as electrons. The number of electrons orbiting a nucleus equals the number of protons in the nucleus when an atom or molecule gains or loses electrons, it becomes an ion. Ions can be either positively or negatively charged. A positively charged ion results from the removal of one or more electrons, while a negatively charged ion results from gaining extra electrons. -The Atom: An atom is defined as the smallest particle into which an element can be divided without losing the chemical properties, it is composed by the atomic nucleus and by the electrons. -The Atomic Nucleus: It is composed by protons and neutrons, thus denominated nucleons, with a positive charge equal to the negative charge of the electrons, in such a way that the total electric charge of the atom is neutral (protons have positive charge and neutrons have no electric charge). -Atomic Number (Z): The number of protons present in the atomic nucleus, which characterizes a chemical element and determines its position on the periodic table, which also coincides with the number of electrons. -Mass Number (A): The total number of nucleons (protons plus neutrons) in the atomic nucleus (A = Z + N, where N= number of neutrons). -Mass Defect : The difference in the sum of masses of all the nucleons present in the nucleus and the nuclear mass is known as the mass defect (Δm). Can be represented by the following equation: Δm = Mp + Mn- M )D)  1amu=931.49 Mev -Nuclear Binding Energy: Is the energy required to separate an atomic nucleus completely into its constituent protons and neutrons Can be represented by the following equation: B.E  [Zmp  NmN  M(A,Z)]𝐶 2  1amu = 1.49239×𝟏𝟎−𝟏𝟎 J Example: The mass of deuteron nucleus is 2.014103 amu. If the masses of proton and neutron are respectively 1.007825 amu and l.008663 amu, find the mass defect? Solution: Mass defect ΔM= mp +mn -md =1.007825 + l.008663 - 2.014104 =0.002385 amu. ΔM = 0.002383 x 931.49 MeV = 2.22 MeV Example: Calculate the binding energy of α- particle and express it in Mev and joules. Given mp =1.00758 amu. mn=1.00897amu, and mHe = 4.0028 amu. Solutiom: Binding enegy (BE) = (Zmp +Nmn - mHe) amu BE = (2 * 1.00758 + 2 * 1.00897 - 4.0028) amu = 0.0293 amu 1 amu = 931.49 MeV BE = 0.0293 x 931.49 MeV = 27.29 MeV Therefore, the binding enegy of α- particle = 27.29 MeV 1 amu = 1.49239 x10−10 J BE = 0.0293 * 1.49239 x 10−10 J = 4.37 * 10-12 J