Mendelevium isotopes

Einsteinium-99 was found in the debris from the first thermonudear explosion on November 1,1952, at Enewetok Atoll. The einsteinium isotope obtained has a half-life of 20.5 days Fermium-100 was found in the debris from the first thermonuclear explosion at Enewetok Atoll on November 1,1952. The fermium isotope obtained has a half-life of 20.1 hours Mendelevium-101 is obtained by bombardment of einsteinium with helium ions. The mendelevium isotope obtained has a half-life of 1.3 hours... 

The use of larger particles in the cyclotron, for example carbon, nitrogen or oxygen ions, enabled elements of several units of atomic number beyond uranium to be synthesised. Einsteinium and fermium were obtained by this method and separated by ion-exchange. and indeed first identified by the appearance of their concentration peaks on the elution graph at the places expected for atomic numbers 99 and 100. The concentrations available when this was done were measured not in gcm but in atoms cm. The same elements became available in greater quantity when the first hydrogen bomb was exploded, when they were found in the fission products. Element 101, mendelevium, was made by a-particle bombardment of einsteinium, and nobelium (102) by fusion of curium and the carbon-13 isotope. 

Dmitri Mendeleev) Mendelevium, the ninth transuranium element of the actinide series discovered, was first identified by Ghiorso, Harvey, Choppin, Thompson, and Seaborg in early in 1955 during the bombardment of the isotope 253Es with helium ions in the Berkeley 60-inch cyclotron. The isotope produced was 256Md, which has a half-life of 76 min. This first identification was notable in that 256Md was synthesized on a one-atom-at-a-time basis. 

Each of the elements has a number of isotopes (2,4), all radioactive and some of which can be obtained in isotopicaHy pure form. More than 200 in number and mosdy synthetic in origin, they are produced by neutron or charged-particle induced transmutations (2,4). The known radioactive isotopes are distributed among the 15 elements approximately as follows actinium and thorium, 25 each protactinium, 20 uranium, neptunium, plutonium, americium, curium, californium, einsteinium, and fermium, 15 each herkelium, mendelevium, nobehum, and lawrencium, 10 each. There is frequently a need for values to be assigned for the atomic weights of the actinide elements. Any precise experimental work would require a value for the isotope or isotopic mixture being used, but where there is a purely formal demand for atomic weights, mass numbers that are chosen on the basis of half-life and availabiUty have customarily been used. A Hst of these is provided in Table 1. 

The other actinides have been synthesized in the laboratory by nuclear reactions. Their stability decreases rapidly with increasing atomic number. The longest lived isotope of nobelium (102N0) has a half-life of about 3 minutes that is, in 3 minutes half of the sample decomposes. Nobelium and the preceding element, mendelevium (ioiMd), were identified in samples containing one to three atoms of No or Md. 

ISOTOPES There are a total of 19 isotopes of mendelevium. All of them are extremely radioactive and have half-lives ranging from 900 microseconds (for Md-245) to 51.5 days (for Md-258). They are produced in very small amounts. 

Mendeleviums chemical and physical properties are not well known because such small amounts with short half-lives have been produced. Many of its isotopes are produced just one atom at a time, making it difficult to weigh and measure samples. Its melting point is thought to be about 1,827°C, but its boiling point and density are unknown. 

Mendeleviums most stable isotope is Md-258, with a half-life of 51.5 days. It decays into einsteinium-254 through alpha (helium nuclei) decay, or it may decay through the process of spontaneous fission to form other isotopes. 

Albert Ghiorso and his team of chemists that included Glenn T. Seaborg, Stanley G. Thompson, Bernard G. Harvey, and Gregory R. Ghoppin bombarded atoms of einsteinium-253 with hehum ions in the cyclotron at the University of California at Berkeley. This resulted in a few atoms of mendelevium-256, which is one of the isotopes of mendelevium plus a free neutron. 

The element first was made by Ghiorso, Harvey, Choppin, Thompson, and Seaborg in 1955 in Berkeley, California. It was synthesized by bombardment of einsteinium-253 with alpha particles of 41 MeV energy in a 60-inch cyclotron. The element was named Mendelevium in honor of Russian chemist Dimitri Mendeleev. Mendelevium —258 isotope with a half-life of 60 days was discovered in 1967. The element has no commercial use except in research to synthesize isotopes of other transuranium elements. 

As these superheavy elements get heavier, they become less stable the nuclei sit around for progressively shorter times before undergoing radioactive decay. Plutonium-239 has a half-life of 24,000 years, which means that it takes this long for half the atoms in a sample of Pu to decay. Califomium-249 (element 98) has a half-life of350 years mendelevium-258 (lOl), fifty-one days seaborgium-266 (106) twenty-one seconds. Isotope 272 of element 111 has a fleeting existence with a half-life of 1.5 milliseconds, and that of isotope 277 of element 112, made in 1996, is less than a third of a millisecond. This is one reason why it becomes increasingly hard to make and see these superheavy elements. ... 

The elements beyond uranium are increasingly unstable. The half-life of the plutonium isotope Pu-2S9, for example, is 24,000 years the half-life of mendelevium is about half an hour. 

Mendelevium is so short-lived that half of any sample decays in about half an hour, becoming an isotope of fermium which in turn decays by spontaneous fission. 

Mendelevium Md 101 artificial isotopes only mass number range 247-260... 

Mendelevium was discovered in 1955 by Albert Ghiorso, Bernard G. Harvey, Gregory R. Choppin, Stanley G. Thompson, and Glenn T. Seaborg via the bombardments of a minute quantity of a rare, radioactive isotope of einsteinium ( Es) with a-particles in the 60-inch cyclotron of the University of California, Berkeley, which produced Md. Only 17 atoms were detected. Md is the first element to be produced and chemically identified on a one-atom-at-a-time basis. Mendelevium-256 decayed by electron capture (with a 1.3-hour half-life) to the known daughter nuclide fermium-256 ( Tm), which decayed primarily by spontaneous fission (with a half-life of... 

After the discovery of uranium radioactivity by Henri Becquerel in 1896, uranium ores were used primarily as a source of radioactive decay products such as Ra. With the discovery of nuclear fission by Otto Hahn and Fritz Strassman in 1938, uranium became extremely important as a source of nuclear energy. Hahn and Strassman made the experimental discovery Lise Meitner and Otto Frisch provided the theoretical explanation. Enrichment of the spontaneous fissioning isotope U in uranium targets led to the development of the atomic bomb, and subsequently to the production of nuclear-generated electrical power. There are considerable amounts of uranium in nuclear waste throughout the world, see also Actinium Berkelium Einsteinium Fermium Lawrencium Mendelevium Neptunium Nobelium Plutonium Protactinium Rutherfordium Thorium. 

Mendelevium — (Dmitri Mendeleev [1834-1907]), Md at. wt. (258) at. no. 101 m.p. 827°C valence +2, +3. Mendelevium, the ninth transuranium element of the actinide series to be discovered, was first identified by Ghiorso, Harvey, Choppin, Thompson, and Seaborg early in 1955 as a result of the bombardment of the isotope Es with helium ions in the Berkeley 60-inch cyclotron. The isotope produced was Md, which has a half-life of 78 min. This first identification was notable in that Md was synthesized on a one-atom-at-a-time basis. Nineteen isotopes and isomers are now recognized. Md has a half-life of 51.5 days. This isotope has been produced by the bombardment of an isotope of einsteinium with ions of helium. It now appears possible that eventually enough Md can be made so that some of its physical properties can be determined. Md has been used to elucidate some of the chemical properties of mendelevium in aqueous solution. Experiments seem to show that the element possesses a moderately stable dipositive (II) oxidation state in addition to the tripositive (III) oxidation state, which is characteristic of actinide elements. 

---