Physics of Atom Lecture Notes PDF

Al-Salam University College Department of Radiology Techniques Physics of atom Lecture No: 2 Prepared by : Assist.Lect. Safa Sami Dr. saad Thabet Radioactive Decay It is the phenomenon of the emission of...

Al-Salam University College Department of Radiology Techniques Physics of atom Lecture No: 2 Prepared by : Assist.Lect. Safa Sami Dr. saad Thabet Radioactive Decay It is the phenomenon of the emission of nuclear particles) α, β, γ( from some excited nuclei. The phenomenon of radioactivity is described as random and subjective. It is random because the number of decaying nuclei per unit of time is not constant, and subjective because it cannot be affected by any external influence such as temperature, pressure, humidity, etc. 1-Alpha decay: Occurs mainly for very heavy nuclei which are not stable against alpha emission Alpha particle α = 4He  2-Beta Decay: β decay is the emission of an electron e- or positron e+ to convert a neutron to a proton or a proton to a neutron inside the nucleus. Beta Decay β + β− This type of decay occurs in proton rich This type of decay occurs in neutron nuclei only One proton converts to neutron rich nuclei. one neutron converts to and positron, then the positron (Beta plus proton and electron, then the electron particle) will be ejected from the radioactive (beta particle) will be ejected from the nucleus. radioactive nucleus. 3-Gamma decay: involves the emission of gamma photons to allow nuclides to reach a lower energy state. Gamma decay usually co-occurs with alpha and beta decays as they produce nuclides in excited states. Nuclides with excessive energy reach a lower energy state through emission of gamma photons. Gamma decay is exothermic. Unlike other types of radioactive decay, gamma decay does not change the nuclear composition of the nuclide. 𝐴 ∗ 𝑍𝑋 → 𝐴𝑍𝑋 + 𝛾 137 137 56𝐵𝑎 → 56𝐵𝑎 + 00𝛾 Radioactive Decay Law: When a radioactive material undergoes α, β or γ-decay, the number of nuclei undergoing the decay, per unit time, is proportional to the total number of nuclei in the sample material. 𝑵𝒕 = 𝑵𝟎 𝒆−𝝀𝒕 𝑁𝑡 = number of undecayed nuclei at a certain time t 𝑁0 = the initial number of undecayed nuclei (when t = 0) λ=decay constant t = time interval (s)  The number of nuclei can be substituted for other quantities For example, the activity A is directly proportional to N, so it can also be represented in exponential form by the equation: A = A0 e–λt Where: A = activity at a certain time t (Bq) A0 = initial activity (Bq Half-Life or previously known as Half-Life Period is one of the common terminologies used in Physics to describe the radioactive decay of a particular sample or element within a certain period of time. t1/2 = 0.693/λ Example: What is the remaining mass of a sample of 100 g of U -232 after 250 years? If you know that the half-life of uranium-232 is 68.9 years. Answer: A(t) = A0.e-λt A(t) = 100.e-(0.693/68.9)/250 A(t) = 100.e-0.01/250 , A(t) = 100.e-2.5 A(t) = 100 ×0.082 A(t) = 8.2 gm