A Brief History of Element Discovery, Synthesis, and Analysis - Glen W. Watson

The half-life of lawrencium (Lw) is about 8 seconds, and its mass number is thought to be 257, although further research is required to establish this conclusively.

Research on lawrencium is complicated. Its total α activity amounts to barely a few counts per hour. And, since scientists had the α-particle "footprints" only and not the beast itself, the complications increased. Therefore no direct chemical techniques could be used, and element 103 was the first to be discovered solely by nuclear methods.[A]

For many years the periodic system was considered closed at 92. It has now been extended by at least eleven places (Table I), and one of the extensions (plutonium) has been made in truckload lots. Its production and use affect the life of everyone in the United States and most of the world.

Surely the end is again in sight, at least for ordinary matter, although persistent scientists may shift their search to the other-world "anti" particles. These, too, will call for very special techniques for detection of their fleeting presence.

Early enthusiastic researchers complained that a man's life was not long enough to let him do all the work he would like on an element. The situation has now reached a state of equilibrium; neither man nor element lives long enough to permit all the desired work.

[A] In August 1964 Russian scientists claimed that they created element 104 with a half-life of about 0.3 seconds by bombarding plutomium with accelerated neon-22 ions.

Table I. THE TRANSURANIUM ELEMENTS

Element	Name (Symbol)	Mass Number	Year Discovered; by whom; where; how
93	Neptunium (Np)	238	1940; E. M. McMillan, P. H. Abelson; University of California at Berkeley; slow-neutron bombardment of U²³⁸ in the 60-inch cyclotron.
94	Plutonium (Pu)	238	1941; J. W. Kennedy, E. M.McMillan, G. T. Seaborg, and A. C. Wahl; University of California at Berkeley; 16-MeV deuteron bombardment of U²³⁸ in the 60-inch cyclotron.
	Plutonium (Pu)	239	Pu²³⁹; the fissionable isotope of plutonium, was also discovered in 1941 by J. W. Kennedy, G. T. Seaborg, E. Segrè and A. C. Wahl; University of California at Berkeley; slow-neutron bombardment of U²³⁸ in the 60-inch cyclotron.
95	Americium (Am)	241	1944-45; Berkeley scientists A. Ghiorso, R. A. James, L. O. Morgan, and G. T. Seaborg at the University of Chicago; intense neutron bombardment of plutonium in nuclear reactors.
96	Curium (Cm)	242	1945; Berkeley scientists A. Ghiorso, R. A. James, and G. T. Seaborg at the University of Chicago; bombardment of Pu²³⁹ by 32-MeV helium ions from the 60-inch cyclotron.
97	Berkelium (Bk)	243	1949; S. G. Thompson, A. Ghiorso, and G. T. Seaborg; University of California at Berkeley; 35-MeV helium-ion bombardment of Am²⁴¹.
98	Californium (Cf)	245	1950; S. G. Thompson, K. Street, A. Ghiorso, G. T. Seaborg; University of California at Berkeley; 35-MeV helium-ion bombardment of Cm²⁴².
99 100	Einsteinium (Es) Fermium (Fm)	253 255	1952-53; A. Ghiorso, S. G. Thompson, G. H. Higgins, G. T. Seaborg, M. H. Studier, P. R. Fields, S. M. Fried, H. Diamond, J. F. Mech, G. L. Pyle, J. R. Huizenga, A. Hirsch, W. M. Manning, C. I. Browne, H. L. Smith, R. W. Spence; "Mike" explosion in South Pacific; work done at University of California at Berkeley, Los Alamos Scientific Laboratory, and Argonne National Laboratory; both elements created by multiple capture of neutrons in uranium of first detonation of a thermonuclear device. The elements were chemically isolated from the debris of the explosion.
101	Mendelevium (Md)	256	1955; A. Ghiorso, B. G. Harvey, G. R. Choppin, S. G. Thompson, G. T. Seaborg; University of California at Berkeley; 41-MeV helium-ion bombardment of Es²⁵³ in 60-inch cyclotron.
102	Unnamed [B]	254	1958; A. Ghiorso, T. Sikkeland, A. E. Larsh, R. M. Latimer; University of California, Lawrence Radiation Laboratory, Berkeley; 68-MeV carbon-ion bombardment of Cm²⁴⁶ in heavy-ion linear accelerator (Hilac).
103	Lawrencium	257	1961; A. Ghiorso, T. Sikkeland, A. E. Larsh, R. M. Latimer; University of California, Lawrence Radiation Laboratory, Berkeley; 70-MeV boron-ion bombardment of Cf²⁵⁰, Cf²⁵¹, and Cf²⁵² in Hilac.