Americium is a synthetic chemical element; it has symbol Am and atomic number 95. It is radioactive and a transuranic member of the actinide series in the periodic table, located under the lanthanide element europium and was thus named after the Americas by analogy.
The neutron is a subatomic particle, symbol
n
or
n0
, which has no electric charge, and a mass slightly greater than that of a proton. Protons and neutrons constitute the nuclei of atoms. Since protons and neutrons behave similarly within the nucleus, they are both referred to as nucleons. Nucleons have a mass of approximately one atomic mass unit, or dalton. Their properties and interactions are described by nuclear physics. Protons and neutrons are not elementary particles; each is composed of three quarks.
Neutronium is a hypothetical substance made purely of neutrons. The word was coined by scientist Andreas von Antropoff in 1926 for the hypothetical "element of atomic number zero" that he placed at the head of the periodic table. However, the meaning of the term has changed over time, and from the last half of the 20th century onward it has been also used to refer to extremely dense substances resembling the neutron-degenerate matter theorized to exist in the cores of neutron stars; hereinafter "degenerate neutronium" will refer to this.
Werner Karl Heisenberg was a German theoretical physicist, one of the main pioneers of the theory of quantum mechanics, and a principal scientist in the Nazi nuclear weapons program during World War II. He published his Umdeutung paper in 1925, a major reinterpretation of old quantum theory. In the subsequent series of papers with Max Born and Pascual Jordan, during the same year, his matrix formulation of quantum mechanics was substantially elaborated. He is known for the uncertainty principle, which he published in 1927. Heisenberg was awarded the 1932 Nobel Prize in Physics "for the creation of quantum mechanics".
Darmstadtium is a synthetic chemical element; it has symbol Ds and atomic number 110. It is extremely radioactive: the most stable known isotope, darmstadtium-281, has a half-life of approximately 14 seconds. Darmstadtium was first created in November 1994 by the GSI Helmholtz Centre for Heavy Ion Research in the city of Darmstadt, Germany, after which it was named.
Johannes Hans Daniel Jensen was a German nuclear physicist. During World War II, he worked on the German nuclear energy project, known as the Uranium Club, where he contributed to the separation of uranium isotopes. After the war, Jensen was a professor at the University of Heidelberg. He was a visiting professor at the University of Wisconsin–Madison, the Institute for Advanced Study, University of California, Berkeley, Indiana University, and the California Institute of Technology.
Tin (50Sn) is the element with the greatest number of stable isotopes. This is probably related to the fact that 50 is a "magic number" of protons. In addition, twenty-nine unstable tin isotopes are known, including tin-100 (100Sn) and tin-132 (132Sn), which are both "doubly magic". The longest-lived tin radioisotope is tin-126 (126Sn), with a half-life of 230,000 years. The other 28 radioisotopes have half-lives of less than a year.
Rutherfordium (104Rf) is a synthetic element and thus has no stable isotopes. A standard atomic weight cannot be given. The first isotope to be synthesized was either 259Rf in 1966 or 257Rf in 1969. There are 16 known radioisotopes from 253Rf to 270Rf and several isomers. The longest-lived isotope is 267Rf with a half-life of 48 minutes, and the longest-lived isomer is 263mRf with a half-life of 8 seconds.
Bohrium (107Bh) is an artificial element. Like all artificial elements, it has no stable isotopes, and a standard atomic weight cannot be given. The first isotope to be synthesized was 262Bh in 1981. There are 11 known isotopes ranging from 260Bh to 274Bh, and 1 isomer, 262mBh. The longest-lived isotope is 270Bh with a half-life of 2.4 minutes, although the unconfirmed 278Bh may have an even longer half-life of about 690 seconds.
Hassium (108Hs) is a synthetic element, and thus a standard atomic weight cannot be given. Like all synthetic elements, it has no stable isotopes. The first isotope to be synthesized was 265Hs in 1984. There are 13 known isotopes from 263Hs to 277Hs and up to six isomers. The most stable known isotope is 271Hs, with a half-life of about 46 seconds, though this assignment is not definite due to uncertainty arising from a low number of measurements. The isotopes 269Hs and 270Hs respectively have half-lives of about 12 seconds and 7.6 seconds. It is also possible that the isomer 277mHs is more stable than these, with a reported half-life 130±100 seconds, but only one event of decay of this isotope has been registered as of 2016.
Meitnerium (109Mt) is a synthetic element, and thus a standard atomic weight cannot be given. Like all synthetic elements, it has no stable isotopes. The first isotope to be synthesized was 266Mt in 1982, and this is also the only isotope directly synthesized; all other isotopes are only known as decay products of heavier elements. There are eight known isotopes, from 266Mt to 278Mt. There may also be two isomers. The longest-lived of the known isotopes is 278Mt with a half-life of 8 seconds. The unconfirmed heavier 282Mt appears to have an even longer half-life of 67 seconds.
Darmstadtium (110Ds) is a synthetic element, and thus a standard atomic weight cannot be given. Like all synthetic elements, it has no stable isotopes. The first isotope to be synthesized was 269Ds in 1994. There are 11 known radioisotopes from 267Ds to 281Ds and 2 or 3 known isomers. The longest-lived isotope is 281Ds with a half-life of 14 seconds. However, the unconfirmed 282Ds might have an even longer half-life of 67 seconds.
Bismuth-209 (209Bi) is an isotope of bismuth, with the longest known half-life of any radioisotope that undergoes α-decay. It has 83 protons and a magic number of 126 neutrons, and an atomic mass of 208.9803987 amu. Primordial bismuth consists entirely of this isotope.
Nuclear astrophysics studies the origin of the chemical elements and isotopes, and the role of nuclear energy generation, in cosmic sources such as stars, supernovae, novae, and violent binary-star interactions. It is an interdisciplinary part of both nuclear physics and astrophysics, involving close collaboration among researchers in various subfields of each of these fields. This includes, notably, nuclear reactions and their rates as they occur in cosmic environments, and modeling of astrophysical objects where these nuclear reactions may occur, but also considerations of cosmic evolution of isotopic and elemental composition (often called chemical evolution). Constraints from observations involve multiple messengers, all across the electromagnetic spectrum (nuclear gamma-rays, X-rays, optical, and radio/sub-mm astronomy), as well as isotopic measurements of solar-system materials such as meteorites and their stardust inclusions, cosmic rays, material deposits on Earth and Moon). Nuclear physics experiments address stability (i.e., lifetimes and masses) for atomic nuclei well beyond the regime of stable nuclides into the realm of radioactive/unstable nuclei, almost to the limits of bound nuclei (the drip lines), and under high density (up to neutron star matter) and high temperature (plasma temperatures up to 109 K). Theories and simulations are essential parts herein, as cosmic nuclear reaction environments cannot be realized, but at best partially approximated by experiments.
Cold fission or cold nuclear fission is defined as involving fission events for which fission fragments have such low excitation energy that no neutrons or gammas are emitted.
Hot spots in subatomic physics are regions of high energy density or temperature in hadronic or nuclear matter.
The NA49 experiment was a particle physics experiment that investigated the properties of quark–gluon plasma. The experiment's synonym was Ions/TPC-Hadrons. It took place in the North Area of the Super Proton Synchrotron (SPS) at CERN from 1991-2002.
Nuclear fission was discovered in December 1938 by chemists Otto Hahn and Fritz Strassmann and physicists Lise Meitner and Otto Robert Frisch. Fission is a nuclear reaction or radioactive decay process in which the nucleus of an atom splits into two or more smaller, lighter nuclei and often other particles. The fission process often produces gamma rays and releases a very large amount of energy, even by the energetic standards of radioactive decay. Scientists already knew about alpha decay and beta decay, but fission assumed great importance because the discovery that a nuclear chain reaction was possible led to the development of nuclear power and nuclear weapons. Hahn was awarded the 1944 Nobel Prize in Chemistry for the discovery of nuclear fission.
Reinhard Stock is a German experimental physicist, specializing in heavy-ion physics.
Michael C. F. Wiescher is a German-American experimental nuclear physicist and astrophysicist, known for his laboratory research in nuclear physics connected with various astrophysical phenomena such as stellar evolution and explosion environments.
