Discovery and History
– The nucleus was discovered in 1911 by Ernest Rutherford through his experiments with alpha particles.
– J. J. Thomson’s plum pudding model of the atom was disproven by Rutherford’s experiment.
– Rutherford’s experiment involved directing alpha particles at a thin sheet of metal foil.
– Many alpha particles were deflected at large angles, indicating the presence of a concentrated point of positive charge.
– Rutherford’s discovery led to the development of the nuclear model of the atom.
– The term ‘nucleus’ is derived from the Latin word ‘nucleus,’ meaning the kernel inside a watery fruit.
– Michael Faraday first used the term in 1844 to refer to the central point of an atom.
– Ernest Rutherford proposed the modern atomic meaning of the term in 1912.
– The term ‘kernel’ is used for nucleus in German and Dutch.
– Initially, the term ‘kernel’ was also used by Gilbert N. Lewis in his atomic theory.
Composition and Structure
– The nucleus consists of neutrons and protons, which are composed of quarks.
– The nuclear strong force binds the neutrons and protons together against the repulsive electrical force.
– The nucleus holds the negatively charged electrons in their orbits around it.
– The number of protons in the nucleus determines the chemical identity of an atom.
– Neutrons contribute to the mass of the nucleus and help reduce electrostatic repulsion.
– Protons and neutrons are fermions, with different values of the strong isospin quantum number.
– Two protons and two neutrons can share the same space wave function since they are not identical quantum entities.
– In certain cases, two protons, two neutrons, or a proton and neutron can exhibit bosonic behavior when they become loosely bound in pairs.
– Hypernuclei, which contain a hyperon, are extremely unstable and not found on Earth except in high-energy physics experiments.
– The neutron has a positively charged core surrounded by a compensating negative charge, while the proton has an exponentially decaying positive charge distribution.
– The diameter of the nucleus ranges from 1.70 fm for hydrogen to about 11.7 fm for uranium.
– The dimensions of the nucleus are much smaller than the diameter of the atom itself.
– The nuclear force has a very short range and drops to zero just beyond the edge of the nucleus.
– The negatively charged electrons orbit around the positively charged nucleus.
– The stable electron configurations around the nucleus determine the chemical properties of an atom.
Forces and Stability
– Nuclei are bound together by the residual strong force (nuclear force).
– The residual strong force is a minor residuum of the strong interaction which binds quarks together to form protons and neutrons.
– The nuclear force is highly attractive at the distance of typical nucleon separation, allowing nuclei to exist.
– The residual strong force has a limited range and decays quickly with distance.
– Nuclei larger than a certain size are unstable and tend to be increasingly short-lived.
– Halo nuclei, such as lithium-11 or boron-14, have neutron or proton collections orbiting at distances of about 10fm.
– Halo nuclei are not maximally dense and are all unstable with short half-lives.
– Halos represent an excited state with nucleons in an outer quantum shell with unfilled energy levels.
– Nuclei with single or two-neutron halos exhibit specific behaviors and are called Borromean nuclei.
– Proton halos are expected to be more rare and unstable than neutron halos.
Nuclear Models
– The standard model of physics is widely believed to describe the composition and behavior of the nucleus.
– Predictions from theory are more difficult in the nucleus due to limited computational and mathematical approaches.
– Computational power and mathematical approaches need further improvement to accurately compute properties of heavy or highly unstable nuclei.
– Experimental data on nuclear structure cannot be completely explained by existing models.
– The nuclear radius is considered one of the basic quantities any model must predict.
– The cluster model describes the nucleus as a collection of proton-neutron groups with valence neutrons occupying molecular orbitals.
– The nucleus is viewed as a molecule-like structure.
– Alpha particles can be considered as proton-neutron groups within the cluster model.
– The cluster model explains the behavior of certain nuclei based on their composition.
– Valence neutrons play a role in the stability and properties of the nucleus.
– Early models of the nucleus viewed it as a rotating liquid drop.
– Long-range electromagnetic forces and short-range nuclear forces cause behavior similar to surface tension in liquid drops.
– The semi-empirical mass formula is successful in explaining many phenomena of nuclei.
– The formula accounts for the changing amounts of binding energy as the size and composition of nuclei change.
– The special stability of nuclei with magic numbers of protons or neutrons is not explained by the liquid drop model.
– Nucleons occupy orbitals, similar to atomic orbitals in atomic physics theory.
– Nucleons can be sizeless point particles in potential wells or probability waves in the optical model.
– Nucleons may occupy orbitals in pairs due to being fermions, explaining even/odd effects.
– Nuclear shells differ from electron shells due to the different potential well in which nucleons move.
– Some light nuclei, like helium-4 and lithium-6, achieve stability without a closed orbital shell.
– Atomic nuclei exhibit both ordinary particle physical rules and non-intuitive quantum mechanical rules.
– Nucleons in nuclei have wave-like nature and lack standard fluid properties.
– Nuclei made of fermions do not exhibit Bose-Einstein condensation.
– Properties of particles with volume and wave-like behavior explain many nuclear properties.
– Nuclei exhibit bulk properties consistent with Bose-Einstein condensation, similar to superfluid helium.
Additional Information
– Giant resonance
– List of particles
– James Rainwater, Aage N Bohr, and Ben R. Mottelson modeled non-spherical nuclei
– Nuclear medicine Source: https://en.wikipedia.org/wiki/Atomic_nucleus
This article needs additional citations for verification. (October 2022) |
The atomic nucleus is the small, dense region consisting of protons and neutrons at the center of an atom, discovered in 1911 by Ernest Rutherford based on the 1909 Geiger–Marsden gold foil experiment. After the discovery of the neutron in 1932, models for a nucleus composed of protons and neutrons were quickly developed by Dmitri Ivanenko and Werner Heisenberg. An atom is composed of a positively charged nucleus, with a cloud of negatively charged electrons surrounding it, bound together by electrostatic force. Almost all of the mass of an atom is located in the nucleus, with a very small contribution from the electron cloud. Protons and neutrons are bound together to form a nucleus by the nuclear force.
The diameter of the nucleus is in the range of 1.70 fm (1.70×10−15 m) for hydrogen (the diameter of a single proton) to about 11.7 fm for uranium. These dimensions are much smaller than the diameter of the atom itself (nucleus + electron cloud), by a factor of about 26,634 (uranium atomic radius is about 156 pm (156×10−12 m)) to about 60,250 (hydrogen atomic radius is about 52.92 pm).
The branch of physics concerned with the study and understanding of the atomic nucleus, including its composition and the forces that bind it together, is called nuclear physics.
