Nuclear Energy - Study Guide

Nuclear Energy Subtopics: The Nature of Nuclear Reactions Nuclear Stability Learning Outcome: Contrast chemical Write and balance reactions and nuclear equations for nuclear reactions reactions Discuss the main types of Deter...

Nuclear Energy Subtopics: The Nature of Nuclear Reactions Nuclear Stability Learning Outcome: Contrast chemical Write and balance reactions and nuclear equations for nuclear reactions reactions Discuss the main types of Determine whether a radiation – α particles, β nucleus is stable – particles, γ rays, positron neutron/proton ratio emission; electron capture. Topic The study of nuclear energy is interdisciplinary, involving physics, engineering, chemistry, biology, environmental science, policy analysis, and Overview: international relations.  It addresses critical energy needs, environmental Topic concerns, and global security challenges, making it a complex and essential field of study with far- Overview: reaching implications for society and the future of energy production. Chemical Reaction making and breaking of chemical bonds the manner in which atoms are connected changes but the number of atoms of each type is the same on both sides of the chemical equation “atoms are neither created nor destroyed” Nuclear Reactions reactions in which the nuclei of atoms undergo change (Transformation of atomic nuclei) changing the identities of the atoms involved involve changes in the nucleus of an atom The Nature of Nuclear Reactions Involvement of Nucleus: ❑Nuclear reactions primarily affect the atomic nucleus, ❑contains protons and neutrons. ❑Electrons, which orbit the nucleus in electron clouds, are generally not directly involved in nuclear reactions. The Nature of Nuclear Reactions Changes in Nuclear Composition: ❑the number of protons and neutrons in the nucleus changes ❑transformation of one element into another ❑For example, in nuclear fission, the nucleus of a heavy atom, like uranium-235, splits into two smaller nuclei, releasing energy and neutrons. This process transforms uranium into other elements. The Nature of Nuclear Reactions Energy Release: ❑release a tremendous amount of energy ❑due to the conversion of a small amount of mass into energy, as described by Albert Einstein's famous equation, E=mc2 ❑The energy generated in nuclear reactions is millions or billions of times greater than that produced in chemical reactions. The Nature of Nuclear Reactions Nuclear Stability: ❑achieve a more stable configuration of atomic nuclei ❑Nuclei can be unstable due to an imbalance of protons and neutrons, and nuclear reactions seek to correct this imbalance. The Nature of Nuclear Reactions Radioactive Decay: ❑emission of radiation, such as alpha particles (composed of two protons and two neutrons), beta particles (electrons or positrons), or gamma rays. ❑This emission of radiation is associated with the unstable nature of certain atomic nuclei, which seek to achieve greater stability. The Nature of Nuclear Reactions High Energy Requirements: ❑Nuclear reactions often require high energy conditions to initiate and sustain. ❑For example, nuclear fusion, requires extremely high temperatures and pressures to overcome the electrostatic repulsion between positively charged nuclei. The Nature of Nuclear Reactions Applications: ❑including nuclear power generation, ❑medical diagnostics and treatments, ❑radiocarbon dating, and ❑scientific research. ❑also play a role in nuclear weapons The Nature of Nuclear Reactions Radioactivity and Nuclear Equations Recall: two types of subatomic particles reside in the nucleus: protons and neutrons - nucleons all atoms of a given element have the same number of protons - element’s atomic number The atoms of a given element can have different numbers of neutrons - different mass numbers; the mass number is the total number of nucleons in the nucleus Atoms with the same atomic number but different mass numbers are known as isotopes. The Nature of Nuclear Reactions Radioactivity and Nuclear Equations Recall: Different isotopes of an element are distinguished by their mass numbers. For example, the three naturally occurring isotopes of uranium are uranium-234, uranium- 235, and uranium-238, where the numerical suffixes represent the mass numbers. also written as where the superscript is the mass number and the subscript is the atomic number The Nature of Nuclear Reactions Radioactivity and Nuclear Equations Different isotopes of an element have different natural abundances. For example, ❑99.3% of naturally occurring uranium is uranium-238, ❑0.7% is uranium-235, and ❑only a trace is uranium-234. Different isotopes of an element also have different stabilities. The Nature of Nuclear Reactions Radioactivity and Nuclear Equations A nuclide is a nucleus containing a specified number of protons and neutrons. Nuclides that are radioactive are called radionuclides, and atoms containing thesenuclei are called radioisotopes. Nuclear Equations Radionuclides are unstable and spontaneously emit particles and electromagnetic radiation. Emission of radiation for an unstable nucleus - transformed into a more stable nucleus with less energy. The emitted radiation is the carrier of the excess energy. For example: ▪ Uranium-238, is radioactive, undergo a nuclear reaction ▪ Emits helium-4 nuclei. ▪ Helium-4 particles are known as alpha (A) particles, and a stream of them is called alpha radiation. Nuclear Equations When a nucleus loses an alpha particle, the remaining fragment has an atomic number of 90 and a mass number of 234. The element with atomic number 90 is Th, thorium. Therefore, the products of uranium-238 decomposition are an alpha particle and a thorium-234 nucleus. The nuclear equation is represented as: Such spontaneous decomposition - have decayed or have undergone radioactive decay. Involvement of alpha particle in the nuclear reaction, the process is described as alpha decay. Nuclear Equations the sum of the mass numbers is the same on both sides of the equation (238 = 234 + 4) the sum of the atomic numbers on both sides of the equation is equal (92 = 90 + 2) Mass numbers and atomic numbers must be balanced in all nuclear equations. Sample Exercise 1. What product is formed when radium-226 undergoes alpha decay? Solution: Analyze We are asked to determine the nucleus that results when radium-226 loses an alpha particle. Plan We can best do this by writing a balanced nuclear reaction for the process. Solve The periodic table shows that radium has an atomic number of 88. The complete chemical symbol for radium-226 is therefore An alpha particle is a helium-4 nucleus, and so its symbol is The alpha particle is a product of the nuclear reaction, and so the equation is of the form  where A is the mass number of the product nucleus and Z is its atomic number. Mass numbers and atomic numbers must balance, so 226 = A + 4 and 88 = Z + 2 Hence, A = 222 and Z = 86 From the periodic table, the element with Z = 86 is radon (Rn). The product, therefore, is and the nuclear equation is  Types of Radioactive Decay Table 1. Properties of Alpha, Beta, and Gamma Radiation Types of Radioactive Decay Types of Radioactive Decay Types of Radioactive Decay Radioactive Decay Types of Radioactive Decay Types of Radioactive Decay  Table 2. Particles Found in Nuclear Reactions  Table 3. Types of Radioactive Decay Sample Problem 1: Writing Equations for Nuclear Reactions  Write nuclear equations for (a) mercury-201 undergoing electron capture; (b) thorium-231 decaying to protactinium-231. Sample Problem Solution: 2: Writing Nuclear Analyze We must write balanced nuclear equations Equations in which the masses and charges of reactants and products are equal. Plan We can begin by writing the complete chemical symbols for the nuclei and decay particles that are given in the problem. Solve a) The information given in the question can be summarized as The mass numbers must have the same sum on both sides of the equations: 201 + 0 = A Thus, the product nucleus must have a mass number of 201. Similarly, balancing the atomic numbers gives 80 - 1 = Z Thus, the atomic number of the product nucleus must be 79, which identifies it as gold (Au): b) In this case we must determine what type of particle is emitted in the course of the radioactive decay: From 231 = 231 + A and 90 = 91 + Z, we deduce A = 0 and Z = -1. According to Table 2, the particle with these characteristics is the beta particle (electron). We therefore write Patterns of Nuclear Stability Why is it that some nuclides are stable but others that may have only one more or one fewer neutron are not? No single rule to predict whether a particular nucleus is radioactive and, if it is, how it might decay. Several empirical observations to predict the stability of a nucleus. Neutron-to-Proton Ratio like charges repel each other large number of protons can reside within the small volume of the nucleus a strong force of attraction, called the strong nuclear force, exists between nucleons Neutrons are involved in this attractive force. All nuclei other than contain neutrons. As the number of protons in a nucleus increases, there is an ever-greater need for neutrons to counteract the proton–proton repulsions. Neutron-to-Proton Ratio Stable nuclei with atomic numbers up to about 20 have approximately equal numbers of neutrons and protons. For nuclei with atomic number above 20, the number of neutrons exceeds the number of protons. The number of neutrons necessary to create a stable nucleus increases more rapidly than the number of protons. Thus, the neutron-to-proton ratios of stable nuclei increase with increasing atomic number Neutron-to-Proton Ratio For Example: the most common isotopes of carbon, manganese and gold Figure 1. Stable and radioactive isotopes as a function of numbers of neutrons and protons in a nucleus. The stable nuclei (dark blue dots) define a region known as the belt of stability.  The plot goes above the line for 1:1 neutron-to-proton for heavier elements. The dark blue dots in the figure represent stable (nonradioactive) isotopes. The region of the graph covered by these dark blue dots is known as the belt of stability. The belt of stability ends at element 83 (bismuth), which means that all nuclei with 84 or more protons are radioactive. For example, all isotopes of uranium, Z = 92, are radioactive.  Three general situations: Neutron-to- proton ratio 1. Predicting Modes of Nuclear Decay 1. Predicting Modes of Nuclear Decay 1. Predicting Modes of Nuclear Decay 2. Predicting the Modes of Nuclear Decay 2. Predicting the Modes of Nuclear Decay 3. Predicting Nuclear Stability Predicting Nuclear Stability