Actinium isotopes

Most of the radioactive actinium isotopes that are produced in nuclear reactors are in milligram quantities. There are not many common compounds. 

The only additional element about which there had been considerable uncertainty until comparatively recent times is element 87, francium (Fr), which is the last of the alkali metals in Group I. This element was finally identified by Perey in 1937 as a product of the decay of the naturally occurring actinium isotope of mass 227 ... 

All isotopes of all elements beyond bismuth (Z 83) are radioactive. In particular, isotope 227 of actinium (Z = 89) decays mainly with the emission of particles, forming a0Th227 (Chap. 27). It has been shown, however, that about 1 percent of this actinium isotope decays in a differ-... 

The great variety of radionuclides present in thorium and uranium ores are listed in Tables 4.1, 4.2 and 4.3. Whereas thorium has only one isotope with a very long half-life (- Th), uranium has two and giving ri.se to one decay scries for Th and two for U. In order to distinguish the two decay series of U, they were named after long-lived members of practical importance the uranium-radium series and the actinium series. The uranium-radium series includes the most important radium isotope ( Ra) and the actinium scries the most important actinium isotope ( Ac),... 

Actinium, isotope of mass 226 Actinium, isotope of mass 228 Aluminum... 

The actinium decay series consists of a group of nuclides whose mass number divided by 4 leaves a remainder of 3 (the 4n + 3 series). This series begins with the uranium isotope which has a half-life of 7.04 X 10 y and a specific activity of 8 X 10 MBq/kg. The stable end product of the series is ° Pb, which is formed after 7 a- and 4 /3-decays. The actinium series includes the most important isotopes of the elements protactinium, actinium, ftancium, and astatine. Inasmuch as U is a conqx>nmt of natural uranium, these elem ts can be isolated in the processing of uranium minerals. The longest-lived protactinium isotope, Pa (ti 3.28 X 10 y) has been isolated on the 100 g scale, and is the main isotope for the study of protactinium chemistry. Ac (t 21.8 y) is the longest-lived actinium isotope. 

O. Hahn and F. Strassmann by co-precipitating with barium a solution of the product of the bombardment of uranium with neutrons, obtained what they thought were isotopes of radium, and after j8-ray decay, products of these were precipitated with lanthanum, and hence regarded as actinium isotopes. Mme. Joliot-Curie and P. Savitch found that the product concentrated with lanthanum rather than with actinium, but thought it should be separable from lanthanum. Hahn and Strassman, early in 1939, found that their supposed radium was barium, and that the chemical evidence showed that their actinium and thorium were lanthanum and cerium. Such results, they said, would contradict accepted views in nuclear physics. 

There is only one beta decay event per 5 000 alpha decays of polonium-218. Things are even sadder for polonium-216 (1 per 7 000) and polonium-215 (1 per 200 000). The situation speaks for itself. The amount of natural francium on Earth is larger. It is produced by the longest-lived actinium isotope Ac (a half-life of 21 years) and its content is, of course, much higher than that of the extremely rare polonium isotopes capable of producing astatine. 

Actinium was discovered by A. Debierne in 1899. Its name is derived from the Greek word for beam or ray, referring to its radioactivity. The natural occurrence of the longest lived actinium isotope Ac, with a half-life of 21.77 years, is entirely dependent on that of its primordial ancestor, U. The natural abundance of Ac is estimated to be 5.7 10 ppm. The most concentrated actinium sample ever prepared from a natural raw material consisted of about 7 fig of Ac in less than 0.1 mg of... 

Twenty isotopes are known. Radon-22, from radium, has a half-life of 3.823 days and is an alpha emitter Radon-220, emanating naturally from thorium and called thoron, has a half-life of 55.6 s and is also an alpha emitter. Radon-219 emanates from actinium and is called actinon. It has a half-life of 3.96 s and is also an alpha emitter. It is estimated that every square mile of soil to a depth of 6 inches contains about 1 g of radium, which releases radon in tiny amounts into the atmosphere. Radon is present in some spring waters, such as those at Hot Springs, Arkansas. 

Gr. aktis, aktinos, beam or ray). Discovered by Andre Debierne in 1899 and independently by F. Giesel in 1902. Occurs naturally in association with uranium minerals. Actinium-227, a decay product of uranium-235, is a beta emitter with a 21.6-year half-life. Its principal decay products are thorium-227 (18.5-day half-life), radium-223 (11.4-day half-life), and a number of short-lived products including radon, bismuth, polonium, and lead isotopes. In equilibrium with its decay products, it is a powerful source of alpha rays. Actinium metal has been prepared by the reduction of actinium fluoride with lithium vapor at about 1100 to 1300-degrees G. The chemical behavior of actinium is similar to that of the rare earths, particularly lanthanum. Purified actinium comes into equilibrium with its decay products at the end of 185 days, and then decays according to its 21.6-year half-life. It is about 150 times as active as radium, making it of value in the production of neutrons. 

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. 

Argon-40 [7440-37-1] is created by the decay of potassium-40. The various isotopes of radon, all having short half-Hves, are formed by the radioactive decay of radium, actinium, and thorium. Krypton and xenon are products of uranium and plutonium fission, and appreciable quantities of both are evolved during the reprocessing of spent fuel elements from nuclear reactors (qv) (see Radioactive tracers). 

The final member of the group, actinium, was identified in uranium minerals by A. Debieme in 1899, the year after P. and M. Curie had discovered polonium and radium in the same minerals. However, the naturally occurring isotope, Ac, is a emitter with a half-life of 21.77 y and the intense y activity of its decay products makes it difficult to study. 

The actinoid elements (or actinides An) constitute a series of 14 elements which are formed by the progressive filling of the 5/ electron shell and follow actinium in the periodic table (atomic numbers 90-103). All of the isotopes of the actinide elements are radioactive and only four of the primordial isotopes, Th, and " " Pu, have a sufficient long half-life for there to be any of these left in nature. 

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... 

Various radium isotopes are derived through a series of radioactive decay processes. For example, Ra-223 is derived from the decay of actinium. Ra-228 and Ra-224 are the result of the series of thorium decays, and Ra-226 is a result of the decay of the uranium series. 

ISOTOPES There are 41 isotopes of polonium. They range from Po-188 to Po-219. All of them are radioactive with half-lives ranging from a few milliseconds to 102 years, the latter for its most stable isotope Po-209. Polonium is involved with several radioactive decay series, including the actinium series, Po-211 and Po-215 the thorium series, Po-212 and Po-216 and the uranium decay series, Po-210, Po-214, and Po-218. 

ISOTOPES There are a total of 35 isotopes of actinium, none of which are stable. All are radioactive, and none exist in the Earth s crust in any large amounts, although a few can be extracted from large quantities of pitchblende and other minerals. All are extremely scarce. Those produced artificially in nuclear reactors, cyclotrons, or linear accelerators have relatively short half-lives, ranging from 69 nanoseconds to 21 years. 

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. 

There are no significant uses for actinium because of its scarcity and the expense of producing it. The only practical use for small amounts of actinium is as a tracer in medicine and industry. It is too difficult to produce in substantial quantities to make it useful. Actinium can be used as a source of neutrons to bombard other elements to produce isotopes of those elements, but other neutron sources are less expensive. 

Most of the radioactive isotopes of actinium pose an extreme radiation hazard. They are bone-seeking radioactive poisons. 

The chemistry of neptunium (jjNp) is somewhat similar to that of uranium (gjU) and plutonium (g4Pu), which immediately precede and follow it in the actinide series on the periodic table. The discovery of neptunium provided a solution to a puzzle as to the missing decay products of the thorium decay series, in which all the elements have mass numbers evenly divisible by four the elements in the uranium series have mass numbers divisible by four with a remainder of two. The actinium series elements have mass numbers divisible by four with a remainder of three. It was not until the neptunium series was discovered that a decay series with a mass number divisible by four and a remainder of one was found. The neptunium decay series proceeds as follows, starting with the isotope plutonium-241 Pu-24l—> Am-24l Np-237 Pa-233 U-233 Th-229 Ra-225 Ac-225 Fr-221 At-217 Bi-213 Ti-209 Pb-209 Bi-209. 

Although in a strict sense not a member of the actinide series, actinium is included here for completeness as lanthanum is frequently included in the lanthanide series. The longest lived isotope of actinium is with a half-life of 21.8 years. It occurs in nature from the decay... 

Actinium decays via a series of short-lived isotopes, eventually ending with stable lead. The presence of these radioactive daughters, particularly Th (which is a strong y-emitter), necessitates the use of lead-lined gloved boxes and remote control manipulators. Consequently, the metallurgy of actinium has been little studied and, due to the great expense and trouble involved, probably will not be studied extensively in the future. 

Percival DR, Martin DB. 1974. Sequential determination of radium-226, radium-228, actinium-227, and thorium isotopes in environmental and process waste samples. Anal Chem 46 1742-1749. 

X 10 yr) and ends with stable ° Pb, after emission of eight alpha (a) and six beta (jS) particles. The thorium decay series begins with Th (ti/2 = 1.41 X 10 °yr) and ends with stable ° Pb, after emission of six alpha and four beta particles. Two isotopes of radium and Th are important tracer isotopes in the thorium decay chain. The actinium decay series begins with (ti/2 = 7.04 X 10 yr) and ends with stable Pb after emission of seven alpha and four beta particles. The actinium decay series includes important isotopes of actinium and protactinium. These primordial radionuclides, as products of continental weathering, enter the ocean primarily by the discharge of rivers. However, as we shall see, there are notable exceptions to this generality. 

Pa, protactinium, was first identified in 1913 in the decay products of U-238 as the Pa-234 isotope (6.7 h) by Kasimir Fajans and Otto H. Gohring. In 1916, two groups, Otto Hahn and Lisa Meitner, and Frederick Soddy and John A. Cranston, found Pa-231 (10 years) as a decay product of U-235. This isotope is the parent of Ac-227 in the U-235 decay series, hence it was named protactinium (before actinium). Isolation from U extraction sludges yielded over 100 g in 1960. 

---