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Chapter 17
Radioactivity and Nuclear Chemistry

17-01
Title
Radiation comes from the nucleus
Caption
Radioactivity is the emission of tiny, energetic, invisible particles by the nuclei of certain atoms.
Notes
Just as the electrons undergo certain processes (i.e., bonding) to get to lower energy, nuclei likewise undergo certain processes (decay with emission of radiation) to get to lower energy.
Keywords
radiation, radioactivity, nucleus, atom
17-03
Title
Becquerel’s experiment
Caption
Becquerel placed a sealed package of photographic film near a sample of potassium uranyl sulfate. Even when kept in darkness, the film became exposed. How could Becquerel explain this observation?
Notes
Becquerel originally believed that the uranium compound phosphoresced. But he had to change his hypothesis when he determined that the photographic plate was exposed even when the plate was kept in the dark: Phosphorescence cannot occur without a light source. Becquerel finally proposed that the film was exposed by rays coming from within the potassium uranyl sulfate.
Keywords
radiation, radioactivity, nucleus, atom, Becquerel
17-04
Title
Alpha radiation
Caption
Alpha radiation occurs when an unstable nucleus emits a particle composed of 2 protons and 2 neutrons. What happens to the atomic number of an element upon emission of an alpha particle?
Notes
The atom giving up the alpha particle has its atomic number reduced by two. Of course, this results in the atom becoming a different element. For example, Rn undergoes alpha decay to Po.
Keywords
radiation, radioactivity, nucleus, atom, alpha, helium
17-04-01un
Title
An alpha particle
Caption
Alpha radiation occurs when an unstable nucleus emits a particle composed of 2 protons and 2 neutrons. What happens to the atomic number of an element upon emission of an alpha particle?
Notes
An alpha particle is the nucleus of a helium atom. When this nucleus picks up two electrons from its surroundings, it becomes a free helium atom. Most helium available on Earth comes from natural gas wells located near rock containing alpha emitters. For example, natural gas around Amarillo, TX, is up to 10% helium. Alpha radiation has high ionizing power, but low penetrating power.
Keywords
radiation, radioactivity, nucleus, atom, alpha, helium
17-04-02d
Title
Nuclear equation showing alpha decay of uranium
Caption
Alpha radiation occurs when an unstable nucleus emits a particle composed of 2 protons and 2 neutrons. In this example, a U-238 atom emits alpha radiation to become a Th-234 atom.
Notes
The parent/daughter designation is obvious, but note that the alpha particle is considered a daughter nuclide. This is because the alpha particle also forms an atom. Alpha particles form helium atoms.
Keywords
radiation, radioactivity, nucleus, atom, alpha, parent, daughter, nuclide, nuclear equation
17-04-02d1
Title
Deducing the mass number and atomic number of daughter nuclide
Caption
To the extent expressed by A-X-Z notation, the Law of Conservation of Mass applies in these nuclear equations. Therefore, the sum of protons should be the same on each side of the arrow. Likewise, the sum of neutrons should be the same.
Notes
Einstein's famous equation, E = mc2 tells us that mass is converted to energy, but the amount of mass converted will be too small to detect in these A-X-Z calculations.
Keywords
radiation, radioactivity, nucleus, atom, alpha, parent, daughter, nuclide, nuclear equation, mass number, atomic number
17-05
Title
Beta radiation
Caption
Beta radiation occurs when an unstable nucleus emits an electron. As the emission occurs, a neutron turns into a proton. What happens to the atomic number of an element upon emission of a beta particle?
Notes
The atom giving up the beta particle has its atomic number increased by one. The process can be thought of as the conversion of a neutron to a proton. Of course, this results in the atom becoming a different element. For example, C undergoes beta decay to N.
Keywords
radiation, radioactivity, nucleus, atom, beta, electron
17-05-01f
Title
A beta particle is simply a high-energy electron
Caption
Beta radiation occurs when an unstable nucleus emits an electron. As the emission occurs, a neutron turns into a proton. According to the quantum-mechanical model of the atom, an electron's probability is zero in the nucleus, so the electron will be emitted as soon as it forms.
Notes
The atom giving up the beta particle has its atomic number increased by one. The process can be thought of as the conversion of a neutron to a proton. Of course, this results in the atom becoming a different element. For example, C undergoes beta decay to N. Beta radiation has intermediate ionizing power and intermediate penetrating power.
Keywords
radiation, radioactivity, nucleus, atom, beta, electron
17-05-03h
Title
Gamma radiation is high-energy electromagnetic radiation
Caption
Gamma radiation occurs when an unstable nucleus emits electromagnetic radiation. The radiation has no mass, and so its emission does not change the element. However, gamma radaition often accompanies alpha and beta emission, which do change the element's identity.
Notes
Gamma rays have the lowest ionizing power, but the highest penetrating power.
Keywords
radiation, radioactivity, nucleus, atom, gamma, electromagnetic radiation
17-06
Title
Positron emission
Caption
Positron emission occurs when an unstable nucleus emits a positron. As the emission occurs, a proton turns into a neutron. What happens to the atomic number of an element upon positron emission?
Notes
The atom giving up a positron has its atomic number decreased by one. The process can be thought of as the conversion of a proton to a neutron. Of course, this results in the atom becoming a different element. For example, P undergoes positron emission to Si. When the positron encounters an electron, both particles are immediately and completely converted to energy.
Keywords
radiation, radioactivity, nucleus, atom, electron, positron
17-06-01j
Title
A positron has the charge of a proton and the mass of an electron
Caption
Positron emission occurs when an unstable nucleus emits a positron. As the emission occurs, a proton turns into a neutron.
Notes
The atom giving up the positron has its atomic number decreased by one. The process can be thought of as the conversion of a proton to a neutron. Of course, this results in the atom becoming a different element. For example, P undergoes positron emission to form Si. Like beta radiation, positron emission has intermediate ionizing power and intermediate penetrating power.
Keywords
radiation, radioactivity, nucleus, atom, beta, electron
17-07
Title
Half-life: the concentration of a radioactive isotope decays with time
Caption
Number of Th-232 atoms in a sample initially containing 1 million atoms as a function of time. Th-232 has a half-life of 14 billion years.
Notes
The half-life is the time required for half of a radioactive sample to decay. The half-life is constant, but is different for each isotope.
Keywords
radiation, radioactivity, nucleus, atom, concentration, isotope, half-life
17-08
Title
Uranium-238: an example of an unstable nucleus decaying to form other unstable nuclei
Caption
Uranium-238 is radioactive, undergoing alpha decay. But, the daughter nuclide is also radioactive, undergoing beta decay, to produce yet another radioactive nuclide, which decays. The atom goes through a rather involved sequence of radioactive decays (both alpha and beta), until a stable isotope—lead-206—is reached.
Notes
The concentration of each nuclide is a function of its half-life: The shorter the half-life, the lower the concentration.
Keywords
radiation, radioactivity, nucleus, atom, concentration, isotope, radioactive decay series
17-08-01l
Title
Radon: a radioactive gas in the U-238 decay series
Caption
One of the daughters in the U-238 decay series is radon. Radon is an alpha emitter that presents an environmental hazard because it is a gas, capable of seeping to the Earth's surface and contaminating living spaces. Inhalation of radon and its daughters can ionize lung cells enough to increase the risk of lung cancer.
Notes
The health risk of radon depends on its concentration; the concentration in turn depends on the concentration of uranium and other radioactive elements deep in the ground. Ventilation to disperse the radon is the best practice for reducing its risk.
Keywords
radiation, radioactivity, nucleus, atom, concentration, isotope, radioactive decay series, radon, lung cancer
17-09-04p
Title
A fission reaction
Caption
Collision of a neutron with a U-235 nucleus can cause the nucleus to split, creating two smaller nuclides and three free neutrons. The three neutrons may travel outward from the fission, colliding with nearby U-235 nuclei, causing them to split as well. Each split (fission) is accompanied by a large quantity of energy.
Notes
If sufficient neutrons are present, we may achieve a chain reaction.
Keywords
radiation, radioactivity, nucleus, atom, isotope, fission, neutron, chain reaction
17-10
Title
Fission chain reaction
Caption
The neutrons produced by the fission of one uranium nucleus induce fission in other uranium nuclei to produce a self-amplifying reaction. Why is it necessary that each fission event produce more than one neutron for the chain reaction to amplify?
Notes
Collision of a neutron with a U-235 nucleus can cause the nucleus to split, creating two smaller nuclides and three free neutrons. The three neutrons may travel outward from the fission, colliding with nearby U-235 nuclei, causing them to split as well. Each split (fission) is accompanied by a large quantity of energy. If sufficient neutrons are present, we may achieve a chain reaction. If only one neutron were produced with each fission, no chain reaction would occur, because some neutrons would be lost through the surface of the uranium sample.
Keywords
radiation, radioactivity, nucleus, atom, isotope, fission, neutron, chain reaction
17-12
Title
Radiation exposure by source
Caption
The pie chart shows that human beings are exposed to radiation from a number of sources, both natural and man-made.
Notes
Some of these sources can be controlled; many cannot.
Keywords
radiation, radioactivity, nucleus, atom, isotope
17-14-01v
Title
Decay of sodium-20: Chapter 17, Problem 95
Caption
What other nuclide would form when sodium-20 decays?
Notes
The Law of Conservation of Mass applies here: sodium-20 has 11 protons and nine neutrons. If an alpha particle is removed, nine protons and seven neutrons remain; the missing nuclide would be F-16.
Keywords
radiation, radioactivity, nucleus, atom, isotope, radioactive decay, proton, neutron, alpha
17-14-02w
Title
Decay of fluorine-21: Chapter 17, Problem 96
Caption
What other nuclide would form when fluorine-21 decays?
Notes
The Law of Conservation of Mass applies here: fluorine-21 has 9 protons and 12 neutrons. If a beta particle is removed, 10 protons and 11 neutrons remain; the missing nuclide would be Ne-21.
Keywords
radiation, radioactivity, nucleus, atom, isotope, radioactive decay, proton, neutron, beta
17-14-03x
Title
Decay of carbon-10: Chapter 17, Problem 97
Caption
What other nuclide would form when carbon-10 decays?
Notes
The Law of Conservation of Mass applies here: carbon-10 has 6 protons and 4 neutrons. If a positron is removed, 5 protons and 5 neutrons remain; the missing nuclide would be B-10.
Keywords
radiation, radioactivity, nucleus, atom, isotope, radioactive decay, proton, neutron, positron

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