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31.3 Substructure of the Nucleus
Photomultipliers use the photoelectric effect on the photocathode to convert the light output of a scintillator into an electrical signal.
The ejected electrons get more energy from each successive dynode.
The output current is easily detected by the number of electrons.
Semiconductors can not conduct current in one direction.
Current flows only when radiation is produced when a voltage is applied in that direction.
Since the amount of current in a solid-state detector is closely related to the energy deposited, it can have a high efficiency.
Information can be obtained from solid-state detectors.
Carbon dating is one of the different types of dating.
Understand how decay and half life work.
If you can match the percentage of the dating element that remains to the age of the object, you will win the game.
Natural questions like these have led to many fundamental discoveries.
Table 31.2 shows the mass of protons, neutrons, and electrons.
If you look past the third digit, you'll see that the neutron is more massive than the protons.
Both nucleons are much larger than an electron.
In fact, as noted in Medical Applications of Nuclear Physics.
Table 31.2 gives mass units that are more convenient than kilograms on the atomic and nuclear scale.
The mass of a neutral carbon atom is defined by this unit.
Mass is expressed in units.
When considering the conversion of mass into energy, these units are very convenient.
We find that cancels and comes out in MeV when we use and units of in.
The properties of a nucleus are determined by the number of protons and neutrons.
Ca for calcium is the symbol for the element X.
The element is redundant because it is known once.
It's always calcium and it always has.
The subscript is usually left out of the nuclide's notation.
The mass of an atom is nearly the same as that of its nucleus, so this is logical.
The mass of the nucleus is proportional to the mass of the protons and neutrons in it.
It's convenient to express mass in units of U.
The mass of an atom is close to 1 U.
In an oxygen nucleus with eight protons and eight neutrons, the mass is 16u.
The unified atomic mass unit is defined so that a neutral carbon atom has a mass of exactly 12.
Carbon was chosen because of its importance in organic chemistry.
There are a few examples of nuclides expressed in the notation.
The zero for no neutrons is the nucleus of the simplest atom, hydrogen.
The atomic number of hydrogen is 1.
The mass number is also 1.
If you are told that the nucleus of the particle has two protons and two neutrons, what do you think?
There is a rare form of hydrogen called deuterium, which is twice the mass of common hydrogen.
Sometimes the symbol for deuterated water is also used for deuterium.
The form of hydrogen called tritium has a single protons and two neutrons, and is written.
The three hydrogen varieties have almost the same chemistries, but the nuclei differ in mass, stability, and other characteristics.
There is more than one symbol in the symbols.
If the element is known, it can be found in a periodic table and the same for it.
We read this backwards, saying helium-4 for.
Should we need to know, we can determine that from the periodic table.
A variety of experiments show that a nucleus behaves like a tightly packed ball of nucleons and that it moves rapidly in very close contact.
In a collision with another nucleus, nucleus can be separated by a large force, but resist being pushed closer together.
The volume of a nucleus is related to the number of nucleons in it.
If there was no empty space between them, this would happen.
Nucleons are held together by nuclear forces and resist being pulled apart.
The volume of the nucleus is the sum of the volumes of the nucleons in it.
We need to convert density from units to.
We noticed that the nucleus is about in diameter, which is for lighter nuclei, consistent with the result of the discovery.
The typical atom has a diameter of the order of, but the nucleus is much smaller.
It's consistent with previous discussions that the nucleus is small and contains most of the atom.
Nuclear densities are much greater than water, which has a density of "only".
The mass of a cube of water is 61 km on a side, while the mass of a cube of nuclear matter is one square meter.
The nucleus is small and its protons exert repulsive forces on one another.
Two previously unknown forces hold the nucleus together and make it into a tightly packed ball of nucleons.
The weak and strong nuclear forces are what these forces are called.
Nuclear forces fall to zero strength when nucleons are separated.
They are attracted to one another when the nucleons are close to each other.
The repulsive EM force can't hold the nucleons together, but the strong nuclear force can.
Nuclear forces are very strong and that's why they emit large energies in nuclear decay.
Since work is force times the distance, a large force can result in a large emitted energy.
The strong nuclear force is responsible for decay, while the weak nuclear force is responsible for decay.
There is a plot of versus.
A simplified chart of nuclides.
Nuclear forces are revealed by the patterns of stable and unstable nuclides.
There is a dashed line.
Mass numbers are numbers along diagonals.
Figure 31.14 shows a pattern for those that are stable, even though a nucleus can have any combination of protons and neutrons.
There is a tendency to be nearly equal for low-mass nuclei.
The nuclear force is more attractive when it is attractive.
Nuclear forces are more stable when they are in pairs.
There are more protons in stable nuclei when the mass is higher.
The repulsion between protons is growing.
Since nuclear forces are short ranged and the Coulomb force is long ranged, an excess of neutrons keeps the protons a little farther apart.
The region of stability has decay modes that produce nuclides closer to it.
The closed shells are more stable than the open shells.
Nuclear energy levels, nuclear decay, and the greater stability of nuclei with closed shells have been explained by nuclear shell theory.
We have been making transuranic elements since the early 1940s.
There are predictions of relative stability for nuclei with high s.
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