Actinium decay products

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. 

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. 

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. 

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. 

Actinium-227 occurs in uranium ore and is a decay product of uranium-235. It is found in equilibrium with its decay products. It is prepared hy homhard-ing radium atoms with neutrons. Chemically, the metal is produced hy reducing actinium fluoride with lithium vapor at 1,100°C to 1,300°C. 

Francium occurs in decay products of actinium. It was discovered by... 

Francium-223 is produced from the decay of actinium-227. While the chief decay product is thorium-227 resulting from beta emission, actinium-227 also undergoes alpha emission to an extent of one percent giving francium-223 ... 

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. 

The actual discovery was made by Mile. Marguerite Perey at the Curie Institute in Paris. In 1939 she purified an actinium preparation by removing all the known decay products of this element. In her preparation she observed a rapid rise in beta activity which could not be due to any known substance. She was able to show that, while most of the actinium formed radioactinium, an isotope of thorium, by beta emission, 1.2 0.1 per cent of the disintegration of actinium occurred by alpha emission and gave rise to a new element, which she provisionally called actinium K, symbol AcK (35, 36). This decayed rapidly by beta emission to produce AcX, an isotope of radium, which was also formed by alpha emission from radioactinium. Thus AcK, with its short half-life, had been missed previously because its disintegration gave the same product as that from the more plentiful radioactinium. 

A tiny amount of a very unstable species (half-life, 21 minutes) has been detected among the decay products of actinium tracer experiments by Mile. M. Perey showed that this species has the same chemistry as that of cesium and is presumably the heaviest alkali metal. It is named francium after Mile. Perey s homeland. 

The study of even milligram amounts of actinium is difficult owing to the intense 7-radiation of its decay products that rapidly build up in the initially pure material. 

Since the chemistry of actinium is confined to the Ac + ion, it can readily be separated from thorium (and the lanthanides, for that matter) by processes like solvent extraction with thenoyltrifluoroacetone (TTFA) and by cation-exchange chromatography. The latter is an excellent means of purification, as the Ac + ion is much more strongly bound by the resin than its decay products. 

Actinium occurs naturally as a decay product of 235u ... 

After the discovery of uranium radioactivity by Henri Becquerel in 1896, uranium ores were used primarily as a source of radioactive decay products such as Ra. With the discovery of nuclear fission by Otto Hahn and Fritz Strassman in 1938, uranium became extremely important as a source of nuclear energy. Hahn and Strassman made the experimental discovery Lise Meitner and Otto Frisch provided the theoretical explanation. Enrichment of the spontaneous fissioning isotope U in uranium targets led to the development of the atomic bomb, and subsequently to the production of nuclear-generated electrical power. There are considerable amounts of uranium in nuclear waste throughout the world, see also Actinium Berkelium Einsteinium Fermium Lawrencium Mendelevium Neptunium Nobelium Plutonium Protactinium Rutherfordium Thorium. 

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. 

When an element has more than one radioisotope, determinations and data analysis are generally more complex because the isotopes may differ in half-life, especially when a series is involved, e.g., radium, thorium, polonium, radon, actinium, protactinium, and uranium. One possibility is to make measurements after the decay of the short-lived radionuclides, but this may require long waiting times. In favorable cases, it is more convenient to measure the activity of decay products (e.g., radon, thoron ( Rn), actinon ( Rn)), or correct the measurements of the short-lived radioisotopes after determination of the isotopic composition. 

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. 

Then what did Dehierne discover It was a complex mixture of radioactive substances including actinium. But the weak beta radiation of actinium was quite indistinguishable against the background of the alpha rays emitted by the products of actinium decay. It took several years to extract the real actinium from this mixture of radioactive products. 

The chemistry of actinium has not been extensively studied due to its scarcity, radioactivity and the difficult nature of its decay products. Its chemistry should be very similar to that of lanthanium and therefore its white-colored sesquioxide is expected to be hexagonal (A-type see table 25) (Weigel and Hauske 1977). 

Most important mineral Actinium is a decay product of and is found naturally i ores. 

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