Atom centers {nucleus, atom}| have protons and neutrons.
ratio
In the most-massive atoms, neutron number can be up to 1.5 times proton number. In light atoms, neutron number equals proton number.
alpha particles
Light nuclei have alpha particles.
layers
Nuclei lighter than aluminum have no interior and no special surface. Heavier nuclei have surface neutron layer.
shape
Most atomic nuclei are spherical, but some are ellipsoids. If outer shell fills, nucleus is spherical. If outer shell is half-filled, nucleus is ellipsoidal. Spherical and ellipsoidal nuclei can rotate, but other shapes oscillate.
force
Strong nuclear force holds protons and neutrons in nuclear orbits, against electric force repulsions.
force: particle speed
Protons and neutrons have speed 6 x 10^7 meters per second.
force: orbit
Protons have orbits, and neutrons have orbits. Orbits have shells, angular momenta, orientations, and spins.
models
Atomic nuclei can be like charged drops {liquid drop model}, with charge spread evenly throughout. Nuclei can be like radial fields from nucleus center {shell model}.
Nuclei with odd number of protons and odd number of neutrons can break apart {radioactivity}|. Nuclei with even numbers of both protons and neutrons are stable, because orbits are full. Bigger nuclei are less stable, because neutron number is more than proton number. Radioactive decay happens randomly. Temperature, pressure, and other substances do not affect it. However, it can increase above 10^6 K.
Radioactive material takes time {half-life, radioactivity}| to become half as radioactive. Half-life can be several hours to billions of years. Short-half-life isotopes emit high-velocity alpha particles. Long-half-life atoms emit low-velocity alpha particles.
Radioactive nuclei can lose clusters {alpha particle, radiation} with two protons and two neutrons. Paper can stop alpha particles.
Radioactive nuclei can lose electron {beta particle}|. Neutron to proton and electron conversion makes beta particles. Aluminum foil can stop beta particles.
Radioactive nuclei can lose high-energy radiation {gamma particle}|. Five meters of concrete can stop gamma particles.
Devices {Geiger counter} can measure inert-gas ionization in 2000-V potential. Ionization causes current cascade. Current is proportional to ionization.
Devices {proportional counter} can measure gas ionization in 1000-V potential. Current is sensitive to voltage change.
Devices {scintillation counter} can measure sodium-iodide, anthracene, or naphthalene fluorescence. Photomultiplier detects visible light.
Radioactivity detection can use tiny bubbles in saturated fluid {bubble chamber}.
Radioactivity detection can use condensation trails in saturated vapor {cloud chamber}.
Radioactivity detection can combine bubble and spark chamber {streamer chamber}.
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Date Modified: 2022.0225