Half-life  255Fm(20.1hr) 256Lr(28s) 260Ha(1.5s) 263Sg(0.8s) 266Mt(3.4ms)
The transuranium elements have atomic numbers higher than uranium (#92).  Twenty of these elements have been discovered; all  are unstable with half-lives (time needed for half the sample to decay)  ranging millions of years to mere fractions of a second.  Two of the twenty have been found in nature (neptunium and plutonium) but only in trace amounts.  Transuranium elements are produced artificially by bombarding heavy atoms either with neutrons produced in nuclear reactors or with charged particles accelerated to high energy.
In 1940 the first transuranium element was produced when McMillan & Abelson at Berkeley exposed uranium oxide to neutrons from a cyclotron.  The resulting product was named neptunium (#93).  The discovery of the next transuranium element was  in 1940 by Seaborg, Kennedy & Wah and named plutonium (#94).  Seaborg predicted the following electron configurations:
 
104-112  add to [Rn] 5f14 113-121  add to [Rn] 5f14 6d10
104       7s2    6d2 113      7s2   7p1
105       7s2   6d3 114      7s2   7p2
106       7s2   6d4 115      7s2   7p3
107       7s2   6d5 116      7s2   7p4
108       7s2   6d6 117      7s2   7p5
109       7s2    6d7 118      7s2   7p6
110       7s2   6d8 119      7s2   7p1   8s1
111       7s2  6d9 120      7s2   7p1   8s2
112       7s2   6d10 121      7s2   7p1   8s2 7d1 
Only Np, Pu, and Am have uses (very small amounts of the others have been made).
Np:   Component in neutron detection instruments
Pu:   Nuclear weapons, nuclear power, pacemakers
Am:  Source for smoke detectors and portable source of gamma rays

Until 1997, the International Union of Pure and Applied Chemistry (IUPAC) recommended different names for elements 104-109 than those suggested by American Chemical Society (ACS).  IUPAC and ACS currently differ only for elements 105 & 107.
           Element #  IUPAC until 1997  Current IUPAC  ACS
              104   unnilquadrium  rutherfordium (Rf)  rutherfordium
              105  unnilpentium  dubium (Db)  hahnium (Ha)
                106  unnilhexium  seaborgium (Sg)  seaborgium
              107  unnilseptium  bohrium (Bh)  nielsbohrium (Ns)
              108  unniloctium  hassium (Hs)  hassium 
                109  unnilennium  meitnerium (Mt)  meitnerium
The transuranium elements were named after planets (neptunium & plutonium), places (America, Berkeley, California, Nuclear Institute at Dubna Russia, & Latin word "Hess" for German state), and scientists.  Some scientists are highly recognizable (Einstein #99) or mentioned in freshman chemistry (Bohr #107).  The remainder of this article describes the work of Fermi (#100), Lawrence (#103), Hahn (#105), Seaborg (#106), and Meitner (#109).

Enrico Fermi (1901-1954)
In 1934, while professor of physics at the University of Rome, Fermi bombarded a variety of elements with neutrons. He discovered that slow moving neutrons were especially effective in producing radioactive atoms. In 1938 Fermi was awarded the Nobel Prize in physics for identification of new radioactive elements produced by neutron bombardment and for his discovery of nuclear reaction effected by slow neutrons. He was given permission by the Fascist government of Mussolini to travel to Sweden to receive the award; Fermi and his wife left Italy never to return. Unknown to Fermi and the Nobel Prize Committee, the "new elements" Fermi characterized weren't new but a result of splitting uranium.
Enrico Fermi settled in the United States and devised the crucial experiment on December 2, 1942 that produced the chain reaction needed to make an atomic bomb. During World War II he became part of the team that developed the atomic bomb and later pioneered research using high energy particles.

Ernest Lawrence (1901-1958)
When Lawrence joined the physics faculty at Berkeley in 1928, the hottest topic in physics was bombarding the atom's nucleus to see what new particles it might produce.  Lawrence read about a theoretical linear accelerator that was too long to be practicle.   Lawrence knew that a magnetic field would deflect the charged particles into a curved path. By making the particles go in a spiral, he could boost the energy bit by bit each time they circled an electrode  The university gave Lawrence approval and in 1930 the cyclotron was born.  This new tool launched the modern era of high-energy physics.  In 1961, element 103 was and named in his honor.

Otto Hahn (1879-1968)
In 1938, Otto Hahn repeated Fermi's experiments of bombarding uranium with neutrons.  Hahn and co-worker Fritz Strassmann discovered three isotopes of barium had been produced.  This was incredible because the mass of barium is about half of uranium and no known reaction could explain such a huge change.  Hahn, a chemist, could not offer an explanation.  He wrote to Lise Meitner, his longtime collaborator, describing his findings and asking "Perhaps you can suggest some fantastic explanation," which she explained as nuclear fission. Nevertheless, despite the contributions of Strassmann and Meitner, it was Hahn who was awarded the 1945 Nobel Prize in chemistry for the discovery.  Unfortunately, Hahn was not at the awards ceremony to receive his prize. At the time he learned of the award, he was being held by the British who were seeking information from him about the failed German effort to develop an atomic bomb. As the chairman of the Nobel Committee for Chemistry reported "Professor Hahn has informed us that he is regrettably unable to attend this ceremony."

Glenn Seaborg (1912-1999)
After graduating from UCLA with a degree in chemistry in 1934, Seaborg did graduate work at Berkeley under Gilbert Lewis (acid-base theory) and completed his Ph.D. in 1937 under Ernest Lawrence (fast neutrons).  During World War II he headed the group which devised the chemical extraction processes used in the production of plutonium for the Manhattan Project.  Besides plutonium, Seaborg discovered americium, curium, berkelium, californium, einsteinium, fermium, mendelevium and nobelium.  In 1944 Seaborg formulated the actinide series placing elements 90-103 at the bottom of periodic table.  For  discoveries of the transuranium elements, Seaborg was awarded the 1951 Nobel Prize in chemistry.  Seaborgium, atomic number 106, represents the first time an element had been named after a living person.

Lise Meitner (1878-1968)
Meitner, first woman to receive doctorate in physics from the University of Vienna, began work in 1907 with Otto Hahn at the University of Berlin.  They studied radioactive substances for the next 30 years; she did the physics and he the chemistry. Together and independently they achieved important results in the new field of nuclear physics including techniques for purifying radioactive material, discovering the element protactinium (#91), and explaining how gamma rays eject orbital electrons.
Leaving Germany in 1938 because of her Jewish ancestry, Meitner obtained an appointment at the Physics Institute in Stockholm.  Otto Hahn, who was still in Germany, repeated some of Fermi's early experiments. He wrote Meitner reporting how bombarding uranium with neutrons produced radioactive barium.  Meitner, realizing that uranium had been split, made calculations showing the formation of barium, krypton, additional neutrons, and energy.  When Leo Szilard at Columbia University discovered that more neutrons were produced than used in the fission, he convinced Einstein to write President Franklin Roosevelt (see letter) to set up program for creating Atomic Bomb.  The first fission bomb resulted from bombarding 235U with a neutron to form 236U; 236U  immediately barium, krypton, 3 additional neutrons, and enormous amount of energy.  The 3 neutrons can strike three 235U nuclei and generate 9 neutrons, which can generate 27 neutrons, and so on (chain reaction).
       235U  + 0n ® 236U ® 141Ba  +  92Kr  +  3 1n  + energy

Meitner & Hahn named the process "nuclear fission" and reported the results in the journal Nature (1939).  In 1945 the Nobel Prize in Chemistry was awarded to Otto Hahn for the discovery of nuclear fission.  Probably due to Meitner's leaving Germany, the Nobel committee failed to understand her part in the work.  Lise Meitner was probably the most significant woman scientist of the 20th century.