lawrencium

The nuclear chemists at the Lawrence Berkeley Laboratory worked with extremely smallsamples of lawrencium with short half-lives, which made it difficult to determine the newelement’s chemical and physical properties. Most of its isotopes spontaneously fission as theygive off alpha particles (helium nuclei). Lawrencium’s melting point is about 1,627°C, but itsboiling point and density are unknown.

There are a total of 14 isotopes of lawrencium. Lawrencium-252 has the shortesthalf-life of just 0.36 of a second, and lawrencium-262 has the longest half-life of fourhours. None are found in nature. All the isotopes of lawrencium are artificially manufacturedin particle accelerators or nuclear reactors.

Named for and in honor of Ernest O. Lawrence, who invented the cyclotron.

Because lawrencium does not exist in nature, it had to be produced artificially. This wasdone in 1961 by the team of scientists at Berkeley, using an ion accelerator to bombard threedifferent isotopes of the element californium with heavy ions of the elements ¹⁰boron and¹¹boron along with some neutrons that produced the isotope ₁₀₃Lr-258. The resulting productweighed only about two millionths of a gram and had a half-life of only 4.1 seconds, fissioningspontaneously.

Lawrencium is the last of the transuranic elements and the 15th in the actinide series (thereare 15 elements in the lanthanide series as well, assuming you start counting the series at theelements lanthanide and actinium, respectively.) It is assumed that lawrencium has somechemical and physical characteristics similar to lutetium, located just above it in the lanthanideseries. It is also located at the bottom of the group 17 (VIIA) elements, which makes itthe heaviest of the halides.

Lawrencium as the 5f transition elements (actinide series) was discovered in March 1961 by A. Ghiorso, T. Sikkeland, A. E. Larsh, and R. M. Latimer. A 3-μg californium target, consisting of a mixture of isotopes of mass number 249, 250, 251, and 252, was bombarded with either ¹⁰B or ¹¹B. The electrically charged transmutation nuclei recoiled with an atmosphere of helium and were collected on a thin copper conveyor tape which was then moved to place collected atoms in front of a series of solid-state detectors. The isotope of element 103 produced in this way decayed by emitting an 8.6-MeV alpha particle with a half-life of 8 s. In 1967, Flerov and associates of the Dubna Laboratory reported their inability to detect an alpha emitter with a half-life of 8 s which was assigned by the Berkeley group to 257103. This assignment has been changed to ²⁵⁸Lr or ²⁵⁹Lr. In 1965, the Dubna workers found a longer-lived lawrencium isotope, ²⁵⁶Lr, with a half-life of 35 s. In 1968, Ghiorso and associates at Berkeley were able to use a few atoms of this isotope to study the oxidation behavior of lawrencium. Using solvent extraction techniques and working very rapidly, they extracted lawrencium ions from a buffered aqueous solution into an organic solvent, completing each extraction in about 30 s. It was found that lawrencium behaves differently from dipositive nobelium and more like the tripositive elements earlier in the actinide series. Ten isotopes of lawrencium are now recognized.

There are no common uses. So little of it exists that it has no use outside of basic scientificresearch.

A radioactive transuranic element of the actinoid series, not found naturally on Earth. Several very short-lived isotopes have been synthesized by bombarding 252Cf with boron nuclei or 249Bk with 18O nuclei. Symbol: Lr; p.n. 103; most stable isotope 262Lr (half-life 261 minutes).

lawrencium: Symbol Lr. A radio radioactivemetallic transuranic element belonging to the actinoids; a.n. 103;mass number of the first discoveredisotope 257 (half-life 8 seconds). Anumber of very short-lived isotopes have now been synthesized. The elementwas identified by AlbertGhiorso and associates in 1961. It was named after E. O. Lawrence(1901–58).

Like the other short-lived radioactive isotopes, lawrencium is a radiation hazard. Also, aswith the others, the danger to individuals and the public is small since there is not much of itin existence. Also, the small amount that has been produced has a short half-life, so over shortperiods of time it ceases to exist.