What is a proton?
A: A proton is a stable subatomic particle.
One or more protons are present in the nucleus of every
They provide the attractive electrostatic central force
which binds what?
A: The atomic electrons.
The number of protons in the nucleus is the defining
property of a what?
A: An element, and is referred to as the atomic number (represented by the symbol Z).
Since each element has a unique number of protons, each
element has its own unique what?
A: Atomic number.
The atomic number determines the number of atomic
electrons and consequently what?
A: The chemical characteristics of the element.
The word proton is Greek for what?
A: "First", and this name was given to the hydrogen nucleus by Ernest Rutherford in 1920.
In previous years, Rutherford had discovered what?
A: That the hydrogen nucleus (known to be the lightest nucleus) could be extracted from the nuclei of nitrogen by atomic collisions.
Protons were therefore a candidate to be what?
A: A fundamental or elementary particle, and hence a building block of nitrogen and all other heavier atomic nuclei.
Although protons were originally considered elementary
particles, in the modern Standard Model of particle physics, protons are now
known to be what?
A: Composite particles, containing three valence quarks, and together with neutrons are now classified as hadrons.
The rest masses of quarks contribute how much of a
A: Only about 1%.
The remainder of a proton's mass is due to quantum
chromodynamics binding energy, which includes the kinetic energy of what?
A: The quarks and the energy of the gluon fields that bind the quarks together.
Because protons are not fundamental particles, they
possess a what?
A: A measurable size; the root mean square charge radius of a proton is about 0.84–0.87 fm (or 0.84×10−15 to 0.87×10−15 m).
How do free protons occur occasionally on Earth?
A: Thunderstorms can produce protons with energies of up to several tens of MeV.
At sufficiently low temperatures and kinetic energies,
free protons will bind to what?
A fast proton moving through matter will slow by
interactions with electrons and nuclei, until it is what?
A: Captured by the electron cloud of an atom.
The result is a protonated atom, which is a what?
A: A chemical compound of hydrogen.
In a vacuum, when free electrons are present, a
sufficiently slow proton may pick up a single free electron, becoming what?
A: A neutral hydrogen atom, which is chemically a free radical.
When free hydrogen atoms react with each other, they
form neutral hydrogen molecules (H2), which are the most common molecular
component of what?
A: Molecular clouds in interstellar space.
Free protons are routinely used for accelerators for
proton therapy or various particle physics experiments, with the most
powerful example being what?
A: The Large Hadron Collider.
In 1917 (in experiments reported in 1919 and 1925),
Rutherford proved that the hydrogen nucleus is present in other nuclei, a
result usually described as what?
A: The discovery of protons.
Rutherford had noticed that, when alpha particles were
shot into air (mostly nitrogen), his scintillation detectors showed what?
A: The signatures of typical hydrogen nuclei as a product.
After experimentation Rutherford traced the reaction to
A: The nitrogen in air and found that when alpha particles were introduced into pure nitrogen gas, the effect was larger.
In 1919 Rutherford assumed that the alpha particle did
A: It merely knocked a proton out of nitrogen, turning it into carbon.
After observing Blackett's cloud chamber images in
1925, Rutherford realized what?
A: That the alpha particle was absorbed.
After capture of the alpha particle, what is ejected?
A: A hydrogen nucleus is ejected, so that heavy oxygen, not carbon, is the result.
This was the first reported what?
A: Nuclear reaction, 14N + α → 17O + p. Rutherford at first thought of our modern "p" in this equation as a hydrogen ion, H+.
The free proton (a proton not bound to nucleons or
electrons) is a stable particle that has not been observed to what?
A: Break down spontaneously to other particles.
Free protons are found naturally in a number of
situations in which energies or temperatures are high enough to do what?
A: To separate them from electrons, for which they have some affinity.
Free protons exist in plasmas in which temperatures are
too high to allow them to what?
A: Combine with electrons.
Free protons of high energy and velocity make up 90% of
A: Cosmic rays, which propagate in vacuum for interstellar distances.
Free protons are emitted directly from atomic nuclei in
some rare types of what?
A: Radioactive decay.
Protons also result (along with electrons and
antineutrinos) from the radioactive decay of what?
A: Free neutrons, which are unstable.
The spontaneous decay of free protons has never been
A: Observed, and protons are therefore considered stable particles according to the Standard Model.