Lawrencium isotopes

In 1965, the Dubna workers found a longer-lived lawrencium isotope, 256Lr, with a half-life of 35 s. In 1968, Thiorso and associates at Berkeley used 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. 

Ah lawrencium isotopes of masses 255 to 260 have been synthesized by bombardment of transuranium elements with heavy ions. 

After nobehum had been discovered, only one actinide remained to be found, element number 103. A. E. Larsh and R. M. Latimer at Berkeley in 1961 and E. D. Donets, V. A. Schegolev and V. A. Ermakov at Dubna in 1965 bombarded californium isotopes with a mixture of boron-10 and boron-11 ions and were able to identify element 103. It was named lawrendum. Bombardment of americium with oxygen ions created another lawrencium isotope. 

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. 

Americium (pronounced,, am-8- ris(h)-e-8m) is a man-made, radioactive, actinide element with an atomic number of 95. It was discovered in 1945. Actinides are the 15 elements, all of whose isotopes are radioactive starting with actinium (atomic number 89), and extending to lawrencium (atomic number 103). When not combined with other elements, americium is a silvery metal. Americium has no naturally occurring or stable isotopes. There are two important isotopes of... 

The element was generated by bombardment of californium with boron in a linear accelerator. The priority is debated. Isotopes of the elements were observed both by the group of Glenn T. Seaborg and by that of G. N. Flerov in Dubna. IUPAC proposed that the priority be shared. The longest-lived isotope has a half-life of 200 minutes. Lawrencium ends the series of actinides, as the 5f level is fully occupied with 14 electrons. 

Figure 10.6 The modern extended periodic table, showing the older (Roman) and modern (numerical) labeling for the groups. Elements heavier than lawrencium (Z= 103) have been omitted, since they have no naturally occurring isotopes, and the s-, p- and -blocks have been separated for clarity. Further details of the elements can be found in Appendix VI.

Actinium is the last (bottom) member of group 3 (IIIB) of elements in the periodic table and the first of the actinide series of metallic elements that share similar chemical and physical characteristics. Actinium is also closely related in its characteristics to the element lanthanum, which is located just above it in group 3. The elements in this series range from atomic number 89 (actinium) through 103 (lawrencium). Actiniums most stable isotope is actinium-227, with a half-life of about 22 years. It decays into Fr-223 by alpha decay and Th-227 through beta decay, and both of these isotopes are decay products from uranium-235. 

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

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

Because lawrencium does not exist in nature, it had to be produced artificially. This was done in 1961 by the team of scientists at Berkeley, using an ion accelerator to bombard three different isotopes of the element californium with heavy ions of the elements boron and "boron along with some neutrons that produced the isotope jj,jLr-258. The resulting product weighed only about two millionths of a gram and had a half-life of only 4.1 seconds, fissioning spontaneously. 

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

Lawrencium has been synthesized only in very minute quantities. It was first synthesized by irradiating a mixture of californium isotopes with boron ions ... 

As noted in Section 9.2, the heaver actinides were made an atom at a time . The last one, lawrencium, was synthesized in 1961 by bombarding a target of californium isotopes... 

Named after Ernest 0. Lawrence, lawrencium was first synthesized in 1961 by the team of Albert Ghiorso, Torbjprn Sikkeland, Almon E. Larsh, and R. M. Latimer at the Rerkeley Laboratory of the University of California. They bombarded californium with boron ions. The longest lasting isotope of lawrencium has a half-life of 35 seconds, just long enough to test its oxidation rate and to confirm its status as an element. 

Lawrencium Lr 103 artificial isotopes only mass number range 253-262... 

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