UNIT 1 ATOMIC STRUCTURE . RADIOACTIVE DECAY NCCS 1.1.4. Radioactive Decay. Radioactive decay is the spontaneous disintegration of a nucleus into a slightly lighter nucleus, accompanied by emission of particles, electromagnetic radiation, or both.
Radioactive decay is the spontaneous disintegration of a nucleus into a slightly lighter nucleus, accompanied by emission of particles, electromagnetic radiation, or both.
Nuclear radiation is particles or electromagnetic radiation emitted from the nucleus during radioactive decay.
An unstable nucleus that undergoes radioactive decay is a radioactive nuclide.
All of the nuclides beyond atomic number 83 are unstable and thus radioactive.
Protons and neutrons are called nucleons.
An atom is referred to as a nuclide.
A nuclide’s type and rate of decay depend on the nucleon content and energy level of the nucleus.
Below are some examples of the type of radioactive decay that can occur.
Gamma rays () are high-energy electromagnetic waves emitted from a nucleus as it changes from an excited state to a ground energy state.
What type of particle is emitted?
Identify the product that balances the following nuclear reaction.
This is an alpha emission type of reaction
mass number: 212 − 4 = 208 atomic number: 84 − 2 = 82
2. The nuclide has a mass number of 208 and an
atomic number of 82,
3. The balanced nuclear equation is
Sample Problem B
Phosphorus-32 has a half-life of 14.3 days. How many
milligrams of phosphorus-32 remain after 57.2 days if
you start with 4.0 mg of the isotope?
Sample Problem B Solution
Given:original mass of phosphorus-32 = 4.0 mg
half-life of phosphorus-32 = 14.3 days
time elapsed = 57.2 days
Unknown:mass of phosphorus-32 remaining after 57.2 days
Step 1: find number of half lives
Step 2:find amount of phosphorus remaining after time has lapsed
Step 1: 57.2 days = 4 half lives
Step 2: 4 mg x ½ x ½ x ½ x ½ = .25 mg
OR 4 mg (1/2) 4 = .25 mg
FORMULA: (original amount of substance) x (1/2 life) (number of ½ lifes)
Fission isa reaction when the nucleus of an atom, having captured a neutron, splits into two or more nuclei, and in so doing, releases a significant amount of energy as well as more neutrons. These neutrons then go on to split more nuclei and a chain reaction takes place.
Fusion is a process where nuclei collide and join together to form a heavier atom, usually deuterium and tritium. When this happens a considerable amount of energy gets released at extremely high temperatures: nearly 150 million degrees Celsius. At extreme temperatures, electrons are separated from nuclei and a gas becomes a plasma—a hot, electrically charged gas.
The difference between the mass of an atom and the sum of the masses of its protons, neutrons, and electrons is called the mass defect.
Nuclear Binding Energy
The binding energy per nucleon is the binding energy of the nucleus divided by the number of nucleons it contains
Elements with intermediate atomic masses have the greatest binding energies per nucleon and are therefore the most stable. The elements with an atomic number of 82 or less have stable isotopes
The graph has a plot of stable elements, this part is called band of stability. At the higher end of the band of stability lies alpha decay, below is positron emission or electron capture, above is beta emissions and elements beyond the atomic mass of 83 are unstable radioactive elements.
Alpha decay is located at the top of the plotted line, because the alpha decay decreases the mass number of the element in order to keep the isotope stable. This is done by using the element helium (He). An unstable isotope's protons are decreased by 2 and its neutrons are decreased by 4, and because the isotope was originally unstable before it went through alpha decay, the elements are still considered unstable.
Beta decay accepts protons so it changes the amount of protons and neutrons. the number of protons increase while neutrons decrease. To make things easier to understand think of the ratio of the isotope: there are too many neutrons compared to the number of protons therefore it is above the band of stability.
Positron emission and electron capture is when the isotope gains more neutrons. Positron emission and electron capture are below the band of stability because the ratio of the isotope has more protons than neutrons, think of it as there are too few protons for the amount of neutrons and that is why it is below the band of stability.
The band of stability can be explained by the relationship between the nuclear force and the electrostatic forces between protons.
Stable nuclei tend to have even numbers of nucleons.
This is referred to as the even-odd rule
According to the nuclear shell model, nucleons exist in different energy levels, or shells, in the nucleus.
The numbers of nucleons that represent completed nuclear energy levels—2, 8, 20, 28, 50, 82, and 126—are calledmagic numbers.
Magic numbers are natural occurrences in isotopes and are stable. Below is a list of numbers of protons and neutrons; isotopes that have these numbers occurring in either the proton or neutron are stable. In some cases there the isotopes can consist of magic numbers for both protons and neutrons; these would be called double magic numbers. But the double numbers only occur for isotopes that are heavier, because the repulsion of the forces between the protons.
The magic numbers:
proton: 2, 8, 20, 28, 50, 82, 114
neutron: 2, 8, 20, 28, 50, 82, 126, 184
Also, there is the concept that isotopes consisting a combination of even-even, even-odd, odd-even, and odd-odd are all stable. There are more nuclides that have a combination of even-even than odd-odd. (See chart.)
Nuclear radiation can transfer the energy from nuclear decay to the electrons of atoms or molecules and cause ionization.
The roentgen (R) is a unit used to measure nuclear radiation exposure; it is equal to the amount of gamma and X ray radiation that produces 2 109 ion pairs when it passes through 1 cm3 of dry air.
Aremis a unit used to measure the dose of any type of ionizing radiation that factors in the effect that the radiation has on human tissue.