The atomic nucleus is a small, dense region consisting of protons and neutrons in the center of atoms, discovered in 1911 by Ernest Rutherford based on the 1909 Geiger-Marsden gold foil experiment. After the discovery of neutrons in 1932, models for nuclei consisting of protons and neutrons were rapidly developed by Dmitri Ivanenko and Werner Heisenberg. An atom consists of a positively charged nucleus, with a cloud of negatively charged electrons surrounding it, bound together by the electrostatic force. Nearly all atomic masses are located in the nucleus, with very small contributions from the electron cloud. Protons and neutrons are bonded together to form nuclei by nuclear force.
The diameter of the nucleus is in the range 1.7566Ã, fm â € << span> ( 1,7566 ÃÆ' - 10 -15 m ) for hydrogen (single proton diameter) to about 11.7142Ã, fm for the heaviest uranium atoms. This dimension is much smaller than the diameter of the atom itself (cloud electron nucleus), with a factor of about 26,634 (the radius of a uranium atom is about 156 °, Â ° ( 156 ÃÆ'â € " 10 -12 m )) to about 60,250 (radius of hydrogen atom is about 52,92 pm ).
Branches of physics pertaining to research and understanding of atomic nuclei, including their composition and strength that bind them together, are called nuclear physics.
Video Atomic nucleus
Introduction
History
The nucleus was discovered in 1911, as a result of Ernest Rutherford's attempt to test Thomson's "pudding plum" of atoms. Electrons have been discovered previously by J.J. Thomson himself. Knowing that the atom is electrically neutral, Thomson postulates that there must be a positive charge as well. In his plum pudding model, Thomson suggests that the atom consists of negative electrons that are scattered randomly within the scope of positive charges. Ernest Rutherford then designed the experiments with his research partner, Hans Geiger and with the help of Ernest Marsden, which involved deflection of alpha particles (helium nuclei) directed to thin sheets of metal sheets. He reasoned that if the Thomson model is true, the positively charged alpha particle will easily pass through the foil with very little deviation in its path, since the foil must act as electrically neutral if the negative and positive charge are mixed very precisely to make it appear neutral. Surprisingly, many particles are deflected at very large angles. Since the mass of alpha particles is about 8000 times that of the electrons, it becomes clear that a very strong force must be present if it can deflect large, fast moving alpha particles. He realized that the plum pudding model could not be accurate and that the deflection of alpha particles could only be explained if the positive and negative charges were separated from each other and that the atomic mass was the concentrated point of positive charge. This justifies the idea of ​​a nuclear atom with a load center and a dense positive mass.
Etymology
The term nucleus is from the Latin nucleus , which is small from nux ("bean"), meaning kernel (ie "small bean") in aqueous fruit (like peaches). In 1844, Michael Faraday used the term to refer to the "atomic central point". The significance of modern atoms was proposed by Ernest Rutherford in 1912. The adoption of the term "nucleus" into atomic theory, however, is indirect. In 1916, for example, Gilbert N. Lewis stated, in his famous article Atom and Molecule, that "atoms are composed of kernel and external atoms or shell "
Nuclear makeup
The atomic nucleus consists of neutrons and protons, which in turn are manifestations of more elementary particles, called quarks, held by powerful nuclear forces in certain stable combinations of hadrons, called baryons. Strong nuclear forces extend far enough from every baryon to bind neutrons and protons together against the disgusting electrical forces between positively charged protons. The strong nuclear force has a very short range, and basically drops to zero just beyond the edge of the core. The collective action of a positively charged nucleus is to hold electrons with negatively charged electricity in its orbit about the nucleus. The collection of negatively charged electrons orbiting the nucleus indicates an affinity for a particular configuration and the number of electrons that make its orbit stable. The chemical element representing the atom is determined by the number of protons in the nucleus; neutral atoms will have the same number of electrons that orbit the nucleus. Individual chemical elements can create more stable electron configurations by combining to share their electrons. This is the division of electrons to create a stable electronic orbit about the nucleus that appears to us as our macro-chemical world.
Proton defines the entire charge of the nucleus, and hence its chemical identity. Neutrons are electrically neutrons, but contribute to the core mass to almost the same as the protons. Neutrons can explain the phenomenon of isotopes (the same atomic number as different atomic masses.) The main role of neutrons is to reduce electrostatic repulsion within the nucleus.
Maps Atomic nucleus
Composition and form
Protons and neutrons are fermions, with different values ​​from strong isospin quantum numbers, so two protons and two neutrons can share the same wave space functions as they are not identical quantum entities. They are sometimes viewed as two different quantum states of the same particles, nucleons . Two fermions, like two protons, or two neutrons, or proton neutrons (deuterons) can exhibit bosonic behavior when both are bonded in pairs, which have an integral spin.
In the rare case of hypernucleus, a third baryon called a hyperon, containing one or more peculiar quarks and/or unusual quarks, can also share wavefunctions. However, this type of nucleus is highly unstable and not found on Earth except in high energy physics experiments.
Neutrons have a positively charged radius nucleus? 0.3 fm is surrounded by a negative charge of compensation between 0.3 fm and 2 fm. The proton has a positive charge distribution that exponentially deteriorates with an average square radius of about 0.8 fm.
The nucleus may be round, rugby ball-shaped (deformation prolate), disc-shaped (oblate deformation), triaxial (combination of oblate and prolate deformation) or pear-shaped.
Troop
Nuclei are bonded together by the remaining strong forces (nuclear force). The strong force remaining is a small residue of the powerful interactions that bind the quark together to form protons and neutrons. This force is much weaker between neutrons and protons because it is largely neutralized in it, in the same way as electromagnetic forces between neutral atoms (such as van der Waals forces acting) between two atoms of inert gas) is much weaker than the electromagnetic force that holds the parts of the atom internally (for example, the force holding the electrons in an inert gas atom attached to its nucleus).
The nuclear force is very attractive at the typical separation distance of the nucleus, and this controls the repulsion between protons because of the electromagnetic force, allowing the nuclei to exist. However, the remaining strong force has a finite range because it decays rapidly with distance (see potential of Yukawa); thus only nuclei smaller than a certain size that can be completely stable. The absolutely largest stable nuclei (ie stable decay into alpha, beta, and gamma) are lead-208 containing a total of 208 nucleons (126 neutrons and 82 protons). The larger than maximum nuclei are unstable and tend to be shorter in size with larger numbers of nucleons. However, bismuth-209 is also stable for beta decay and has the longest half-life for alpha decay of any known isotope, estimated to be one billion times longer than the age of the universe.
The remaining strong force is effective over a very short range (usually only a few femtometres (fm), roughly one or two diameter nucleons) and causes a pull between a pair of nucleons. For example, between protons and neutrons to form deuterons [NP], and also between protons and protons, and neutrons and neutrons.
Hello nucleus and strong power range limit
The effective absolute limit of the strong force range is represented by the halo nuclei such as lithium-11 or boron-14, where dineutron, or other neutron collections, orbits at a distance of approximately 10 fm (nearly equal to the radius of 8Ã, fm of the uranium-238 nucleus). This nucleus is not solid to the fullest. The Halo nucleus forms at the extreme edge of the nuclide graph - neutron drip lines and proton drops - and all of them are unstable with short half-lives, measured in milliseconds; for example, lithium-11 has a half-life of 8.8Ã, ms .
Halos in effect is an excited state with nucleons in the outer quantum skin that have an unfilled energy level "below" it (both in terms of radius and energy). Hello can be made of neutron [NN, NNN] or proton [PP, PPP]. The nucleus that has a single halo neutron includes 11 Be and 19 C. Hello two-neutrons exhibited by 6 Dia, 11 Li, 17 B, 19 B and 22 C. The two-neutron halo nuclei breaks into three fragments, never two, and is called < i> Borromean nuclei because of this behavior (referring to a system of three interlocked rings in which violating any ring frees both of them). 8 Dia and 14 Be both showing a four-neutron halo. The nucleus that has a proton halo includes 8 B and 26 P. A two-proton halo is shown by 17 Ne and 27 S. Proton halos are expected to be more rare and unstable than the neutron example, due to the disgusting electromagnetic force of the excess proton (s).
Nuclear model
Although the standard model of physics is widely believed to fully describe the composition and behavior of the nucleus, generating predictions from the theory is much more difficult than most other fields of particle physics. This is for two reasons:
- In principle, physics within the nucleus can be derived entirely from quantum chromodynamics (QCD). But in practice, the current computational and mathematical approaches to solving QCD in low energy systems such as nuclei are very limited. This is due to the phase transitions that occur between the high energy quark material and the low energy isronic material, which makes perturbative techniques unusable, making it difficult to construct an accurate QCD model of the power between the nucleons. The current approach is limited to phenomenological models such as Argonne v18 potential or chiral effective field theory.
- Even if the nuclear force is well constrained, a large amount of computing power is required to accurately compute core properties of ab initio . Developments in many-body theory have enabled this for many low-mass nuclei and are relatively stable, but further improvements in both computing and mathematical approaches are required before heavy nuclei or highly unstable cores can be overcome.
Historically, experiments have been compared with relatively coarse models that are certainly imperfect. None of these models can fully explain experimental data about nuclear structures.
The nuclear radius ( R ) is considered to be one of the basic amounts to be predicted by any model. For stable nuclei (not the halo nucleus or other unstable distorted nucleus) the nuclear radius is roughly proportional to the cube root of the mass number ( A ) of the nucleus, and especially in nuclei containing many nucleons, as they set more rounded configuration:
Be able to make sure to keep in touch with hunger stomach dan oleh karena itu jari-jari nuklir R dapat didekati dengan rumus berikut,
where A = The atomic mass number (the number of protons Z , plus the number of neutrons N ) and r 0 Ã, = Ã, 1.25Ã, fmÃ, = 1,25Ã,ÃÆ' â € "10 -15 m. In this equation, the "constant" r 0 varies by 0.2 fm, depending on the core in question, but this is less than 20% change of the constants.
In other words, packing protons and neutrons in the nucleus gives approximately the same total size result as packing hard balls of constant size (such as marbles) into round or nearly spherical balls (some inadequately stable nuclei are not enough round, but known as prolate).
The nuclear structure model includes:
Liquid drop model
The initial model of the nucleus sees the nucleus as a rotating fluid drop. In this model, the trade-off of long-range electromagnetic forces and near-nuclear force, together causes a behavior that resembles the surface tension force in liquid drops of different sizes. This formula manages to explain many important phenomena of nuclei, such as changes in the amount of binding energy as changes in their size and composition (see semi-empirical mass formula), but this does not explain the special stability that occurs when the nucleus has a special. magic number "of protons or neutrons.
The terms in the semi-empirical mass formula, which can be used to estimate the binding energy of many nuclei, are considered as the sum of the five types of energy (see below). Then the image of the nucleus as a drop of a crude compressed fluid contributes to the observed variation of the binding energy of the nucleus:
Energy volume . When a collection of nuclei of the same size is packed together into the smallest volume, each interior nucleus has a number of other nucleons in contact with it. So, this nuclear energy is proportional to its volume.
Surface energy . The nucleons on the core surface interact with fewer nucleons than the nucleus at the nucleus and therefore their binding energy is reduced. The term surface energy takes this into account and is therefore negative and proportional to the surface area.
Coulomb Energy . Electrical expulsion between each pairs of protons in the nucleus contributes to the decrease in its binding energy.
Energy asymmetry (also called Pauli Energy). Energy associated with Pauli exclusion principle. If it were not for Coulomb's energy, the most stable form of nuclear material would have the same number of neutrons as protons, since the number of neutrons and unequal protons implies charging a higher energy level for one particle type, while leaving the lower energy level vacant for other types.
Pair energy . The energy that is a correction term arising from the tendency of the proton pairs and the neutron pairs to occur. Even the number of particles is more stable than the odd number.
Shell models and other quantum models
A number of models for the nucleus have also been proposed in which the nucleus occupies the orbitals, such as atomic orbitals in atomic physics theory. These wave models envision nucleons being particles of winged points in potential wells, or other probability waves as in "optical models", without friction orbiting at high speeds in potential wells.
In the above model, the nucleons may occupy pairs of orbital, due to being fermions, allowing the explanation of the famous and odd effects of Z and N from the experiments. The exact nature and capacity of the nuclear shell differs from electrons in atomic orbitals, mainly because of the good potentials in which nucleons move (especially in larger nuclei) are very different from the central electromagnetic potentials that bind electrons in atoms. Some similarities to the model of atomic orbitals can be seen in small atomic nuclei such as helium-4, where two protons and two neutrons separately occupy the 1s orbitals analogous to the 1s orbital for two electrons in the helium atom, and reach unusual. stability for the same reason. The nuclei with 5 nucleons are all very unstable and short-lived; however, helium-3, with 3 nucleons, is very stable even with a deficiency of the closed 1s shell orbital. Another nucleus with 3 nucleons, hydrogen-3 triton is unstable and will decay into helium-3 when isolated. Weak nuclear stability with 2 nucleons {NP} in 1s orbitals is found in hydrogen-2 deuterons, with only one nucleon in each potential well of protons and neutrons. While each nucleon is a fermion, {NP} deuterons are bosons and thus do not follow Pauli Exceptions for close packs in the shell. Lithium-6 with 6 nucleons is highly stable without a second closed shell orbital 1p. For a light nucleus with a total number of nucleons 1 through 6 only having 5 shows no evidence of stability. The observation of beta-stability of the light nuclei outside the closed shell indicates that nuclear stability is much more complex than the simple closing of shell orbital with the number of protons and magic neutrons.
For larger nuclei, the shells occupied by the nucleons start to differ significantly from the electron shells, however, the current nuclear theory predicts the magical quantity of the nuclear shell filled for protons and neutrons. A stable shell cover predicts a very stable configuration, analogous to the noble group of gas that is almost silent in chemistry. An example is the stability of a sealed shell of 50 protons, which allows the tin to have 10 stable isotopes, more than any other element. Similarly, the distance from the shell-closure describes the remarkable instability of isotopes far from the stable number of these particles, such as radioactive elements 43 (technetium) and 61 (promethium), each preceded and followed by 17 or more elements stable.
However there is a problem with the shell model when attempts are made to account for nuclear properties away from closed shells. This causes the complex post hoc distortion of the potential form well to match the experimental data, but the question remains whether this mathematical manipulation really corresponds to the spatial deformation in the real core. Problems with the shell model have led some to propose a two-body nuclear force effect and three objects involving nucleon groups and then build nuclei on this basis. The three cluster models are the 1936 Resonation Group Structure model from John Wheeler, the Spheron Close-Packed Model from Linus Pauling and the 2D Ising Model from MacGregor.
Consistency between models
Like the superfluid helium fluid, the atomic nucleus is an example of a state in which both (1) the physical rules of "ordinary" particles for volume and (2) the rule of non-intuitive quantum mechanics for wave-like properties apply. In helium superfluid, helium atoms have volumes, and essentially "touch" each other, yet at the same time exhibit strange bulk properties, consistent with Bose-Einstein condensation. Nucleons in atomic nuclei also exhibit wave-like properties and deficiencies in standard fluid properties, such as friction. For cores made from the fermion hadron, Bose-Einstein condensation does not occur; however, many nuclear properties can only be explained similarly to the combination of particle properties with volume, in addition to the friction motion characteristics of waves such as the behavior of objects trapped in quantum orbitals Erwin SchrÃÆ'Â ¶dinger.
See also
Note
References
External links
- The Nucleus - a chapter of an online textbook
- LIVEChart of Nuclides - IAEA in Java or HTML
- The article on "nuclear shell model", provides a nuclear shell for various elements. Retrieved 16 September 2009.
- Chronology: Subatomic Concepts, Nuclear Science & amp; Technology.
Source of the article : Wikipedia
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