Fundamental Physics Flashcards
What is the electromagnetic spectrum?
Photons travel as electromagnetic waves, described by the electromagnetic spectrum. This spectrum defines regions based on their energy (and hence wavelength or frequency). From lowest energy (and lowest frequency, highest wavelength) the spectrum starts with radio waves, then microwaves, infrared, visible, ultraviolet, X-rays, and gamma rays.
What is the binding energy of an electron?
The electron binding energy is determined by the Coulomb attraction between the nucleus (protons) and orbital electrons (e−). The electron binding energy increases as Z increases and decreases as the distance from the nucleus increases. The binding energy of an electron is the minimum energy required to knock the electron out of the atom.
Arrange the following forces (weak force, strong force, gravitational force, and electromagnetic force) in order from weakest to strongest and describe their basic responsibilities.
The weakest is the gravitational force which is the force that attracts masses, but on the scale of the atomic world it is negligible. Next, the weak force is responsible for nuclear decay. The electromagnetic force exists between all particles which have an electric charge. The strong force is responsible for binding nuclei and exists over a very short range.
What is an isotope, isotone, isobar, and isomer?
An element is defined by its atomic number Z, which represents the number of protons, and gives the element its chemical properties. The same element can have differing numbers of neutrons but the same number of protons, these are referred to as isotopes. An isotone is the opposite, they are nuclei with the same number of neutrons, but different numbers of protons. Isobars are nuclei that have the same number of nucleons (eg, seven protons and eight neutrons, or six protons and nine neutrons), that is the same atomic number. A helpful guide is istoPes have equal number of Protons, isotoNes have equal Neutrons, and isobArs have same atomic weight (A). An isomer is the same nucleus (the same number of protons, neutrons, and the same atomic number) but is an excited, usually unstable state of the nucleus.
What is a characteristic X-ray?
If an atom is ionized, a vacancy may be created in an inner electron orbital. An electron in an outer orbital will then fill the vacancy and a photon with energy equal to the difference in energy of the two orbitals is created. This energy is characteristic of the particular element involved (hence the name).
What is an Auger electron?
An Auger electron is an alternative and competing process to characteristic X-rays that can sometimes occur. Here, instead of a characteristic X-ray escaping the atom, it hits another orbiting electron, which is ejected from the atom. This is known as an Auger electron.
What is the difference between an X-ray and a gamma ray?
X-rays and gamma rays are both photons and forms of electromagnetic energy but gamma rays are defined as being of nuclear origin, and X-rays of atomic origin.
What are the two competing mechanisms by which the nucleus can release excess energy in isomeric transition?
An isomeric transition means the nucleus is changing energy states, without changing the number of protons and neutrons within it. One way the nucleus can release energy is called gamma emission.
In gamma emission, the nucleus releases excess energy by the direct emission of one or more gamma rays from the nucleus. An alternative method of releasing energy is internal conversion where one or more of the orbital electrons is emitted. If an inner shell electron is emitted, shell filling will occur and will result in characteristic X-rays and/or Auger electrons being released.
Describe the type of equilibrium that can occur with radioactive decay when the decay constant of the daughter is much greater than the parent decay constant?
This type of equilibrium is called secular equilibrium. This is characterized by a gradual buildup of activity of the daughter until it reaches the level of the parent. After secular equilibrium has been established, the activity of the daughter is approximately equal to the activity of the parent. This is the case for Radium and its daughter Radon. The decay constant is inversely proportional to the half-life, so for secular equilibrium, the daughter half-life must be much shorter than the parent. If the decay constant of the daughter is greater than the decay constant of the parent but not much greater, then transient equilibrium is achieved. In transient equilibrium, there is an initial buildup of the daughter until it eventually exceeds the activity of the parent. After that point, the activity of the daughter follows the activity of the parent, always exceeding the parent by a small amount. This is exemplified by Mo-99 (molybdenum) and its daughter Tc-99m (Technetium).
What are the two types of decay that tend to occur in nuclei that have a low neutron to proton (n/p) ratio?
Radionuclides that have a low n/p ratio tend to increase the ratio by converting a proton into a neutron. In beta plus decay or positron emission, the proton converts into a neutron emitting a positive electron (positron or beta plus) and a neutrino.
A competing process with beta plus decay is electron capture. Here, one of the inner orbital electrons (usually K shell) is captured by the nucleus. The nucleus rearranges and transforms a proton into a neutron to reach a new stable state. After an electron is captured by the nucleus in electron capture decay, characteristic X-rays or Auger electrons will be produced.
Describe the differences in the neutron to proton ratio (n/p) with respect to the atomic number of the nucleus?
For atomic elements where Z is less than or equal to 20, the ratio of neutrons to protons is 1. If Z is greater than 20, the ratio increases with Z. The additional neutrons are needed to help keep the nuclei stable and to compensate for electrostatic repulsion between the protons.
What is isomeric transition?
Isomeric transition occurs when a previous radioactive decay leaves the daughter nucleus in a metastable state which then transitions to the ground state. The daughter nucleus stays in an excited state for a short period of time. The only difference between the metastable state and the final stable ground state is an energy difference, thus the two states are called isomers. An example of this is technetium-99m. Molybdenum-99 decays via beta decay to Tc-99m. In this metastable state, it has a half-life of 6 hours. It then decays via gamma emission, releasing a photon of 141 keV, which is used for imaging in single-photon emission computed tomography (SPECT).
What is isobaric decay?
Isobaric decay is any radioactive decay in which the original (or parent) nucleus and the new (or daughter) nucleus contains the same number of total nucleons (protons + neutrons). When this occurs, the parent nucleus and the daughter nucleus are referred to as isobars of one another. Both types of beta decay are isobaric.
What is the nuclear binding energy?
The nucleus is made up of protons and neutrons, but the mass of the nucleus will always be less than the sum of the individual masses of the protons and neutrons which constitute it. The deficiency of mass is called the mass defect, and the energy that is required to separate the nucleus into its constituent particles is called the binding energy of the nucleus and is given by Einstein’s famous equation: E = ∆mc2. The ∆m is the mass difference of the nucleus and its constituent particles (protons + neutrons).
What are the two types of beta decay? Describe beta decay in general.
The two types of beta decay are beta minus decay and beta plus decay. Beta decay is the process by which a radioactive nucleus ejects either a negatively charged electron (beta minus or β−) or positively charged positron (beta plus or β+). An electron that is ejected is differentiated from an orbital electron by using the β− term instead of “e” which refers to an orbital electron. Both forms of beta decay are isobaric as the total atomic number does not change.
