The symbol Fm is a synthetic element.It is an actinide and the heaviest element that can be formed by bombarding lighter elements with neutrons.257Fm is the longest-lived with a half-life of 100.5 days.
The debris from the first hydrogen bomb explosion was named after one of the pioneers of nuclear physics.It’s chemistry is typical for the late actinides, with a majority of the +3 oxidation state but also an accessible +2 oxidation State.Due to the small amounts of produced fermium and all of its isotopes having relatively short half-lives, there are no uses for it outside of basic scientific research.
The ‘Ivy Mike’ nuclear test was the first successful test of a hydrogen bomb.A new type of plutonium, 24494 Pu, could only have been formed by the absorption of six neutrons and two decays, according to the initial examination of the debris from the explosion.At the time, the absorption of neutrons by a heavy nucleus was thought to be rare, but the identification of 24494 Pu raised the possibility that still more could have been absorbed by the uranium nuclei, leading to new elements.
The same sampling technique that led to the discovery of 24494 Pu was used to discover element 99.Albert Ghiorso and co-workers at the University of California at Berkeley identified it in December of 1952.They discovered the isotope 253Es, which was made by the capture of 15 neutrons and underwent seven successive decays.
The yield was expected to be at least an order of magnitude lower than that of element 99, and so contaminated coral from the Enewetak atoll was shipped to.Two months after the test, a new component was isolated emitting high-energy -particles with a half-life of about a day.It had to be an element of the new element 100 because of its short half-life, and it was quickly identified as 255Fm.
Cold War tensions caused the US military to keep the new elements and data secret until 1955.Nevertheless, the Berkeley team was able to prepare elements 99 and 100 by civilian means and published their work in 1954.The “Ivy Mike” studies were published in 1955.
The Berkeley team was worried that another group might discover lighter isotopes of element 100 through ion-bombardment techniques before they could publish their classified research, and this proved to be the case.A group at the Nobel Institute for Physics in Sweden discovered the element by bombarding a 23892U target with oxygen-16 ion and published their work in May 1954.The Berkeley team’s priority was generally recognized, and with it the right to name the new element after the developer of the first artificial self-sustained nuclear reactor.
257Fm is the longest-lived fermium with a half-life of 100.5 days.The half-life of 253Fm is 3 days, and it has a time of 2.6 hours.Half-lives range from 30 minutes to less than a second.The capture product of fermium- 257, 258Fm is unstable due to its half-life of just 14 microseconds.Unless carried out in a nuclear explosion, nuclides with a mass number greater than 257 cannot be created.The last element that can be prepared by a neutron-capture process is mendelevium, as 257Fm is an -emitter, decaying to 253Cf.Thefermium gap is caused by this impediment in forming heavier isotopes.
There is a bombardment of lighter actinides with neutrons in a nuclear reactor.The heaviest isotope that can only be produced in picogram quantities is Fermium- 257.The main source is the Oak Ridge National Laboratory in Tennessee, USA, which is dedicated to the production of transcurium.It is possible to find lower mass fermium in greater quantities.In a typical processing campaign at Oak Ridge, tens of grams of curium are irradiated to produce decigram quantities of californium.Specific experiments can be prepared for 20 grams of fermium.The amount of fermium produced in 20–200 kiloton thermonuclear explosions is believed to be of the order of milligrams, although it is mixed in with a huge quantity of debris.The Hutch experiment produced an estimated 257Fm.
The fermium needs to be separated from other products.This is usually achieved by ion-exchange chromatography with the standard process using a cation exchanger.Smaller cations are preferentially eluted from the column.A rapid fractional crystallization method has also been described.
The decay product of 257Fm can be easily isolated since it has a half-life of 100.5 days.
One goal of the long-term project was to study the efficiency of production of transuranium elements in high-power nuclear explosions.The purpose of these experiments was to find out if it is possible to synthesise elements from uranium.Nuclear explosions provide densities of the order 1023 neutrons/ cm2 within a microsecond and increase the probability of such events.There are about 1029 neutrons.The HFIR reactor has 51015 neutrons/( cm2s).A dedicated laboratory was set up at Enewetak atoll for preliminary analysis of debris, as some isotopes could have decayed by the time the debris samples reached the U.S.The laboratory was getting samples as soon as possible from the airplanes that flew over the atoll after the tests.New chemical elements heavier than fermium were not found after a series of megaton explosions at the atoll.[ 24]
The underground test data from the 1960s at the Nevada Test Site was used to supplement the atmospheric results, as it was hoped that powerful explosions in confined space would result in improved yields and heavier isotopes.Mixed plutonium-neptunium charges, as well as combinations of uranium with americium and thorium, have been tried.They were less successful in terms of yield due to the higher losses of heavy isotopes.It was found that the Isolation of the products was problematic, as the explosions were spreading debris through melting and vaporizing rocks under the great depth of 300– 600 meters, and drilling to such depth in order to extract the product was both slow and inefficient in terms of collected volumes.The 24th and 25th are the days
Between 1962 and 1969 there were nine underground tests, which included Anacostia, Kennebec, Par, Barbel, and Tweed.The yield showed a saw-toothed behavior with the lower values for odd isotopes due to their higher fission rates.The radioactive debris dispersed by the powerful blast was the major practical problem of the entire proposal.The fraction of the total amount that was increased by aircraft filters was only two orders of magnitude.60 days after the Hutch explosion, about 500 kilograms of underground rocks were removed.The amount of transuranium elements in this 500-kg batches was 30 times higher than in a rock picked up 7 days after the test.The amount of retrieved radioactive rock was shown to be dependent on the transuranium elements yield.In order to accelerate sample collection after explosion, shafts were drilled at the site not after but before the test, so that explosion would expel radioactive material from the epicenter, through the shafts, to collecting volumes near the surface.This method was tried in the Anacostia and Kennebec tests and instantly provided hundreds of kilograms of material, but with actinide concentration 3 times lower than in samples obtained after drilling, it could not improve.