Substructure of the Nucleus Quiz

PDF page 1495: cesium in this ampule (c) even less stable than the uranium, decaying in far less than 1/1,000,000 the time? What is the reason uranium and cesium undergo different types of decay ( and , respectively)? (credits: (a) Bresson Thomas, Wikimedia Commons; (b) U.S. Department of Energy; (c) Tomihahndorf, Wikimedia Commons) We have already identified protons as the particles that carry positive charge in the nuclei. However, there are actually two types of particles in the nuclei—the proton and the neutron, referred to collectively as nucleons, the constituents of nuclei. As its name implies, the neutron is a neutral particle ( ) that has nearly the same mass and intrinsic spin as the proton. Table 31.2 compares the masses of protons, neutrons, and electrons. Note how close the proton and neutron masses are, but the neutron is slightly more massive once you look past the third digit. Both nucleons are much more massive than an electron. In fact, (as noted in Medical Applications of Nuclear Physics and .

PDF page 1495: cesium in this ampule (c) even less stable than the uranium, decaying in far less than 1/1,000,000 the time? What is the reason uranium and cesium undergo different types of decay ( and , respectively)? (credits: (a) Bresson Thomas, Wikimedia Commons; (b) U.S. Department of Energy; (c) Tomihahndorf, Wikimedia Commons) We have already identified protons as the particles that carry positive charge in the nuclei. However, there are actually two types of particles in the nuclei—the proton and the neutron, referred to collectively as nucleons, the constituents of nuclei. As its name implies, the neutron is a neutral particle ( ) that has nearly the same mass and intrinsic spin as the proton. Table 31.2 compares the masses of protons, neutrons, and electrons. Note how close the proton and neutron masses are, but the neutron is slightly more massive once you look past the third digit. Both nucleons are much more massive than an electron. In fact, (as noted in Medical Applications of Nuclear Physics and .

PDF page 1495: This unit is defined so that a neutral carbon atom has a mass of exactly 12 u. Masses are also expressed in units of . These units are very convenient when considering the conversion of mass into energy (and vice versa), as is so prominent in nuclear processes. Using and units of in , we find that cancels and comes out conveniently in MeV. For example, if the rest mass of a proton is converted entirely into energy, then 31.2 It is useful to note that 1 u of mass converted to energy produces 931.5 MeV, or 31.3 All properties of a nucleus are determined by the number of protons and neutrons it has. A specific combination of protons and neutrons is called a nuclide and is a unique nucleus. The following notation is used to represent a particular nuclide: 31.4

PDF page 1495: This unit is defined so that a neutral carbon atom has a mass of exactly 12 u. Masses are also expressed in units of . These units are very convenient when considering the conversion of mass into energy (and vice versa), as is so prominent in nuclear processes. Using and units of in , we find that cancels and comes out conveniently in MeV. For example, if the rest mass of a proton is converted entirely into energy, then 31.2 It is useful to note that 1 u of mass converted to energy produces 931.5 MeV, or 31.3 All properties of a nucleus are determined by the number of protons and neutrons it has. A specific combination of protons and neutrons is called a nuclide and is a unique nucleus. The following notation is used to represent a particular nuclide: 31.4

PDF page 1495: This unit is defined so that a neutral carbon atom has a mass of exactly 12 u. Masses are also expressed in units of . These units are very convenient when considering the conversion of mass into energy (and vice versa), as is so prominent in nuclear processes. Using and units of in , we find that cancels and comes out conveniently in MeV. For example, if the rest mass of a proton is converted entirely into energy, then 31.2 It is useful to note that 1 u of mass converted to energy produces 931.5 MeV, or 31.3 All properties of a nucleus are determined by the number of protons and neutrons it has. A specific combination of protons and neutrons is called a nuclide and is a unique nucleus. The following notation is used to represent a particular nuclide: 31.4

PDF page 1495: where the symbols , , , and are defined as follows: The number of protons in a nucleus is the atomic

PDF page 1495: number , as defined in Medical Applications of Nuclear Physics. X is the symbol for the element, such as Ca for

PDF page 1496: of protons and neutrons, 31.5

PDF page 1496: where is also called the mass number. This name for is logical; the mass of an atom is nearly equal to the mass

PDF page 1496: where is also called the mass number. This name for is logical; the mass of an atom is nearly equal to the mass

PDF page 1496: and other characteristics. Nuclei (such as those of hydrogen) having the same and different s are defined to be

PDF page 1496: isotopes of the same element.

PDF page 1496: Let us look at a few examples of nuclides expressed in the notation. The nucleus of the simplest atom, hydrogen, is a single proton, or (the zero for no neutrons is often omitted). To check this symbol, refer to the periodic table—you see that the atomic number of hydrogen is 1. Since you are given that there are no neutrons, the mass number is also 1. Suppose you are told that the helium nucleus or particle has two protons and two neutrons. You can then see that it is written . There is a scarce form of hydrogen found in nature called deuterium; its nucleus has one proton and one neutron and, hence, twice the mass of common hydrogen. The symbol for deuterium is, thus, (sometimes is used, as for deuterated water ). An even rarer—and radioactive—form of hydrogen is called tritium, since it has a single proton and two neutrons, and it is written . These three varieties of hydrogen have nearly identical chemistries, but the nuclei differ greatly in mass, stability,

PDF page 1496: Let us look at a few examples of nuclides expressed in the notation. The nucleus of the simplest atom, hydrogen, is a single proton, or (the zero for no neutrons is often omitted). To check this symbol, refer to the periodic table—you see that the atomic number of hydrogen is 1. Since you are given that there are no neutrons, the mass number is also 1. Suppose you are told that the helium nucleus or particle has two protons and two neutrons. You can then see that it is written . There is a scarce form of hydrogen found in nature called deuterium; its nucleus has one proton and one neutron and, hence, twice the mass of common hydrogen. The symbol for deuterium is, thus, (sometimes is used, as for deuterated water ). An even rarer—and radioactive—form of hydrogen is called tritium, since it has a single proton and two neutrons, and it is written . These three varieties of hydrogen have nearly identical chemistries, but the nuclei differ greatly in mass, stability,

PDF page 1496: determined (first find ; then, ). Thus the simpler notation for nuclides is 31.6 which is sufficient and is most commonly used. For example, in this simpler notation, the three isotopes of hydrogen are and while the particle is . We read this backward, saying helium-4 for , or uranium-238 for . So for , should we need to know, we can determine that for uranium from the periodic table, and, thus, . A variety of experiments indicate that a nucleus behaves something like a tightly packed ball of nucleons, as illustrated in Figure 31.11. These nucleons have large kinetic energies and, thus, move rapidly in very close contact. Nucleons can be separated by a large force, such as in a collision with another nucleus, but resist strongly being pushed closer together. The most compelling evidence that nucleons are closely packed in a nucleus is that the radius of a nucleus, , is found to be given approximately by 31.7 where and is the mass number of the nucleus. Note that . Since many nuclei are spherical, and the volume of a sphere is , we see that —that is, the volume of a nucleus is proportional to

PDF page 1497: the number of nucleons in it. This is what would happen if you pack nucleons so closely that there is no empty space between them.