Science report Essay
Francium (pronounced FRAN-see-em;formerly known as eka- caesium and actinitium K) is a chemical element that has the symbol Fr and atomic number 87. It is the second rarest naturally occurring elements after astatine. Francium is a highly radioactive metal that decays into astatine, radium and radon. As an alkali metal, it has one valence electron.
Francium was discovered by Marguerite Perey in France (from which the element takes its name) in 1939. It was the last element discovered in nature, rather than being man made. Outside the laboratory, francium is very rare, with trace amounts found in uranium and thorium ores, where the isotope francium-223 continually forms and decays. As little as 20-30g exist at any given time throughout the Earth’s crust; the other isotopes are synthetic. The largest amount ever collected of any isotope was a cluster of about 10,000 atoms (of francium-210) created as an extremely cold gas at Stony Brook in 1997. Francium can be made artificially by bombarding thorium with protons. In a given sample of uranium, there is estimated to be only one francium atom for every 1×1018 uranium atoms. Francium has not yet, as of 2009[update], been synthesized in amounts large enough to weigh.
As early as 1870, chemists thought that should be an alkali metal after caesium,with an atomic number of 87. It was then referred to by the provisional name eka-caesium. Research teams attempted to locate and isolate this missing element, and at least four false claims were made that the element had been found before an authentic discovery was made. Soviet chemist D.K.Dobroserdov was the first scientist to claim to have found eka-caesium,or francium. In 1925, he observed weak radioactivity in a sample of potassium, another alkali metal and concluded that eka-caesium was contaminating the sample.
He then published a thesis on his thoughts of the properties of eka-caesium, in which he named the element russium after his home country. Shortly thereafter, Dobroserdov began to focus on his teaching career at the Polytechnic Institute of Odessa, and he did not pursue the element further. The other three scientist who thought that the discovered the element were Gerald J.Fdruce (England), Fred Allison (U.S.A) and Horia Hulubei (Romania). The sole discoverer was Marguerite Perey of the Curie Institute in Paris, France. She discovered the element when she purified a sample of actinium-227.
Francium in Water
When you add a small amount of francium to water a huge explosion will happen. This is because it is a very weak radioactive element. The picture below shows the reaction.
Francium-223 is the result of the alpha decay of actinium-227 and can be found in trace amounts in uranium and thorium minerals.
Neutral francium atoms can be trapped in the MOT using a magnetic field and laser beams. Francium can be synthesized in the nuclear reaction:
197Au + 18O → 210Fr + 5 n
This process, developed by Stony Brook Physics, yields francium atoms with masses of 209, 210, and 211, which are then isolated by the magnetic-optical trap (MOT). The production rate of a particular isotope depends on the energy of the oxygen beam. An 18O beam from the Stony Brook creates 210Fr in the gold target with the nuclear reaction 197Au + 18O = 210Fr + 5n. The production required some time to develop and understand. It was critical to operate the gold target very close to its melting point and to make sure that its surface was very clean. The nuclear reaction puts the francium atoms deep in the gold target, and they must be removed efficiently. The atoms diffuse fast to the surface of the gold target and are released as atoms. The francium ions are guided by electrostatic glass until they land into a surface of hot yttrium and become neutral again. The francium is then injected into a glass bulb. A magnetic field and laser beams cool and confine the atoms. Although the atoms remain in the trap for
only about 20 seconds before escaping (or decaying), a steady stream of fresh atoms replaces those lost, keeping the number of trapped atoms roughly constant for minutes or longer. Initially, about 1000 francium atoms were trapped in the experiment. This was gradually improved and is capable of trapping over 300,000 neutral atoms of francium a time. Although these are neutral “metallic” atoms (“francium metal”), they are in a gaseous unconsolidated state. Enough francium is trapped that a video camera can capture the light given off by the atoms as they fluoresce. The atoms appear as a glowing sphere about 1 millimeter in diameter. This was the very first time that anyone had ever seen francium. The researchers can now make extremely sensitive measurements of the light emitted and absorbed by the trapped atoms, providing the first experimental results on various transitions between atomic energy levels in francium. Initial measurements show very good agreement between experimental values and calculations based on quantum theory. Other synthesis methods include bombarding radium with neutrons, and bombarding thorium with protons, deuterons, or helium ions. Isotopes
There are 34 known isotopes of francium ranging in atomic mass from 199 to 232. Francium has seven metastable nuclear isomers. Francium-223 and francium-221 are the only isotopes that occur in nature, though the former is far more common. Francium-223 is the most stable isotope with a half-life of 21.8 minutes, and it is highly unlikely that an isotope of francium with a longer half-life will ever be discovered or synthesized. Francium-223 is the fifth product of the actinium decay series as the daughter isotope of actinium-227. Francium-223 then decays into radium-223 by beta decay (1149 keV decay energy), with a minor (0.006%) alpha decay path to astatine-219 (5.4 MeV decay energy).
Francium-221 has a half-life of 4.8 minutes. It is the ninth product of the neptunium decay series as a daughter isotope of actinium-225. Francium-221 then decays into astatine-217 by alpha decay (6.457 MeV decay energy).
The least stable ground state isotope is francium-215, with a half-life of 0.12 μs. (9.54 MeV alpha decay to astatine-211): Its metastable isomer,
francium-215m, is less stable still, with a half-life of only 3.5 ns.
Brief description: francium occurs as a result of α disintegration of actinium. Francium is found in uranium minerals. It is the most unstable of the first 101 elements. The longest lived isotope, 223Fr, a daughter of 227Ac, has a half-life of 22 minutes. Since its properties should track those of caesium rather closely, he called it eka-caesium. Marguerite Perey noticed an α decay product from actinium, now recognized as 22387Fr. This is the longest-lived isotope of actinium with a half life of about 22 minutes. She called the new element Francium after her country.
This picture shows a huge reaction of Francium in water.
This sample of uraninite contains about 100,000 atoms (3.3 × 10−20 g) of francium-223 at any given time.
This image shows how thorium gets bombarded with protons to make Francium.
This sample of uraninite contains some francium because of a steady-state decay chain. An estimate suggests there is about 10-20 grams of francium (about 1 atom!) at any one time. Uses of Francium
Francium has no known uses yet, so it is being tested in laboratories across the globe.