Various types of scattering experiments suggest that nuclei are roughly spherical and appear to have essentially the same density. The data are summarized in the expression called the Fermi model:
where r is the radius of the nucleus of mass number A. The assumption of constant density leads to a nuclear density |
The most definitive information about nuclear sizes comes from electron scattering. The comparison of calculated and experimental radii for nuclei are very sensitive to the exact onset of the overlap between the probe particle and the nuclear matter. These comparisons have made it clear that there is a 'tail' where the density of nuclear matter decreases toward zero. The nucleus is not a hard sphere. Krane comments that the evidence points to a mass radius and a charge radius which agree with each other within about 0.1 fermi. Since heavy nuclei have about 50% more neutrons than protons, one might expect a mass radius larger than the charge radius. One can visualize the protons being pushed toward the outside by the proton repulsion and the neutrons being pulled inward by the neutron-proton attraction, so the observed result agrees with what one might expect with this kind of model.
- This was in a gold atom known to be 10 −10 metres or so in radius—a very surprising finding, as it implied a strong central charge less than 1/3000th of the diameter of the atom. The Rutherford model served to concentrate a great deal of the atom's charge and mass to a very small core, but didn't attribute any structure to the remaining.
- Gold is the most malleable of all metals and soft enough to be cut with a knife. Stone age peoples hammered gold into plates for ornamental purposes. Really quite large amounts were gathered together. Though King Tutankhamun was a minor Pharaoh and died aged 18, his coffin alone contained 112 kg of gold.
| Scale model of nucleus | Implications about the strong force |
Category: Physics Published: May 2, 2014
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Gold Atomic Number
Yes, gold can be created from other elements. But the process requires nuclear reactions, and is so expensive that you currently cannot make money by selling the gold that you create from other elements.
All regular matter is made out of atoms. All atoms are made out of a small nucleus containing protons and neutrons bound together, and a large cloud of electrons bound to the nucleus. Since most of an atom's physical and chemical properties are determined by the number and shapes of its electrons, and since the number and shapes of its electrons are determined by the number of protons in the nucleus, the nature of an atom is largely determined by the number of protons in its nucleus. All atoms with the same number of protons in their nucleus behave almost identically. For this reason, we call a group of atoms with the same number of protons a 'chemical element', and we associate various properties with particular elements.
Gold Atomic Mass
Gold is the chemical element with 79 protons in each atomic nucleus. Every atom containing 79 protons is a gold atom, and all gold atoms behave the same chemically. In principle, we can therefore create gold by simply assembling 79 protons (and enough neutrons to make the nucleus stable). Or even better, we can remove one proton from mercury (which has 80) or add one proton to platinum (which has 78) in order to make gold. The process is simple in principle but hard to do in practice. Adding or removing protons from a nucleus are types of nuclear reactions. As such, no series of chemical reactions can ever create gold. Chemical reactions change the number and shape of the electrons in an atom but leave the nucleus of the atom unchanged. The ancient alchemist dream of creating gold by simply reacting chemicals is therefore impossible. You have to use nuclear reactions to create gold. The difficulty is that nuclear reactions require a lot of energy.
The nucleus of a stable atom is very tightly bound together, so it is hard to get anything permanently into or out of the nucleus. To induce a nuclear reaction, we have to shoot high-energy particles at a nucleus. We can get such particles either from radioactive decay, from nuclear reactions in a reactor, from the acceleration of slow particles, or from a mix of these techniques. For example, Sherr, Bainbridge, and Anderson created gold in 1941 by shooting neutrons at mercury. The neutrons were generated by a series of nuclear reactions that were kick-started by the Harvard cyclotron particle accelerator.
Usually gold is created from platinum, which has one less proton than gold, or from mercury, which has one more proton than gold. Bombarding a platinum or mercury nucleus with neutrons can knock off an neutron or add on a neutron, which through natural radioactive decay can lead to gold. As should be obvious by this production process, much of the gold created from other elements is radioactive. Radioactive gold is hazardous to humans and cannot be sold commercially. Furthermore, when radioactive gold undergoes radioactive decay after a few days, it is no longer gold. Therefore, in order to create non-radioactive gold that you can sell to consumers you have to:
Gold Atom Model
- Build a nuclear reactor to act as your source of neutrons.
- Place mercury in the reactor. After a large amount of work, only a tiny portion of gold is created.
- Decontaminate the resulting gold. This is harder than it sounds because you can't separate out non-radioactive gold from radioactive gold using purely chemical methods.
Gold Atomic Number
It should be obvious from this process that it currently costs much more money to create non-radioactive gold than you could ever earn by selling the gold. Creating gold from other elements is currently an expensive laboratory experiment and not a viable commercial activity. Perhaps technology will improve enough in the future to make creation of gold in nuclear reactors a profitable economic enterprise.