First Semester Notebook

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Learning Goal for this section: Explain and compare nuclear reactions (radioactive decay, fission, and fusion), the energy changes associated with them and their associated safety issues. Notes Section: For beta particles, there are negative and positive "electrons". They have the same they don't come from the nucleus. This is converting from a neutron to a proton. Go up from 1 to get to a new element. Everytime it undergoes this process, it gives off energy. As the helium leaves, it gives off energy and that is what is radioactive about it. Boron has 5 protons. It is essential when talking about carbon decay. Gamma is not a particle, gamma energy is associated with some types of alpha or beta particle or radiation. Gamma radiation is very high frequency whereas alpha and beta particles aren't as much, gamma basically goes through everything. It doesn't just decay, it becomes something else aka element change. Take a substance and each time take half of the amount of grams it has. Fission is to take apart. Fusion is to come together. TRANSMUTATION: the change of one chemical element into another by a nuclear reaction 54
The Nucleus A typical model of the atom is called the Bohr Model, in honor of Niels Bohr who proposed the structure in 1913. The Bohr atom consists of a central nucleus composed of neutrons and protons, which is surrounded by electrons which “orbit” around the nucleus. Protons carry a positive charge of one and have a mass of about 1 atomic mass unit or amu (1 amu =1.7x10- 27 kg, a very, very small number). Neutrons are electrically “neutral” and also have a mass of about 1 amu. In contrast electron carry a negative charge and have mass of only 0.00055 amu. The number of protons in a nucleus determines the element of the atom. For example, the number of protons in uranium is 92 and the number in neon is 10. The proton number is often referred to as Z. Atoms with different numbers of protons are called elements, and are arranged in the periodic table with increasing Z. Atoms in nature are electrically neutral so the number of electrons orbiting the nucleus equals the number of protons in the nucleus. Neutrons make up the remaining mass of the nucleus and provide a means to “glue” the protons in place. Without neutrons, the nucleus would split apart because the positive protons would repel each other. Elements can have nucleii with different numbers of neutrons in them. For example hydrogen, which normally only has one proton in the nucleus, can have a neutron added to its nucleus to from deuterium, ir have two neutrons added to create tritium, which is radioactive. Atoms of the same element which vary in neutron number are called isotopes. Some elements have many stable isotopes (tin has 10) while others have only one or two. We express isotopes with the nomenclature Neon-20 or 20 Ne 10, with twenty representing the total number of neutrons and protons in the atom, often referred to as A, and 10 representing the number of protons (Z). Alpha Particle Decay Alpha decay is a radioactive process in which a particle with two neutrons and two protons is ejected from the nucleus of a radioactive atom. The particle is identical to the nucleus of a helium atom. Alpha decay only occurs in very heavy elements such as uranium, thorium and radium. The nuclei of these atoms are very “neutron rich” (i.e. have a lot more neutrons in their nucleus than they do protons) which makes emission of the alpha particle possible. After an atom ejects an alpha particle, a new parent atom is formed which has two less neutrons and two less protons. Thus, when uranium-238 (which has a Z of 92) decays by alpha emission, thorium-234 is created (which has a Z of 90). Because alpha particles contain two protons, they have a positive charge of two. Further, alpha particles are very heavy and very energetic compared to other common types of radiation. These characteristics allow alpha particles to interact readily with materials they encounter, including air, causing many ionizations in a very short distance. Typical alpha particles will travel no more than a few centimeters in air and are stopped by a sheet of paper. 55
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