Californium isotopes

Studier, P. R. Fields and J. R. Huizenga Berkelium and Californium Isotopes Produced in Neutron Irradiation of Plutonium. Phys. Rev. 96, 1576 (1954). 

K. Street jr. and G. T. Seaborg Californium isotopes from bombard-... 

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

All isotopes of medelevium have been synthesized by other nuclear reactions since its discovery. They are prepared by bombarding uranium, einsteinium, and californium isotopes with heavy ions, such as boron-11, carbon-12 and carbon-13. 

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... 

Interferences to Americium, Curium, and Californium Measurement. Table III lists the americium, curium, and californium isotopes... 

Samples adsorbed on a solid probe surface are not only desorbed by a chemical ionization plasma but also by charged particles originating from an atom nucleus decay as well. This has been shown for the Californium isotope 252 - Samples... 

Seaborg and his coworkers synthesized element 98 very soon after berklium. In January-February 1950 they carried out the calculated nuclear reaction Cm(a, n) 98 and named the new element californium in honour of the state of California and the University of California moreover, element 98 was an analogue of the rare-earth element dysprosium (difficult to reach) and in the last century to reach California was as difficult as to extract dysprosium from a mixture of rare earths. Forteen californium isotopes are currently known. The longest-lived one is californium-251 synthesized in 1954 (a half-life of 900 years). Californium was obtained in weighable quantities in 1958 and metallic californium was produced in 1971. 

The first identification of an isotope of element 103 was by the Berkeley group in 1961 (Ghiorso et al. 1961). The californium isotopes, 249,250,25i,252q bombarded with boron beams ... 

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. 

Berkelium-97 is obtained by bombardment of americium with helium ions. The isotope obtained has a half-life of 4.5 hours Californium-98 is synthesized from curium-96 by bombardment with helium ions. The californium isotope obtained has a half-life of 45 min... 

Californium isotopes with a higher neutron content are usually prepared by irradiation in nuclear reactors having a high neutron flux ( 10 n cm s ). These isotopes are also generated in nuclear explosions, where for short periods of time the neutron flux is much higher ( > 10 ° n cm s " ). In the latter case it would be expected that higher-Z elements and heavier isotopes would be favored. 

Preparation and nuclear properties Table 11.1 Nuclear properties of californium isotopes. 

For basic studies on weighable quantities of californium, the Cf isotope is used. Its alpha half-life of 351 4 years [2,3] makes it suitable for chemical/physical experiments, where weighable quantities of californium are required. The Cf isotope is available as an isotopically pure material from the decay of Bk (beta emitter, half-life of 320 days), the latter being the major berkelium isotope obtained from reactors ( Bk is also formed, but it has a 3.5 h half-life). To obtain Cf free of other californium isotopes, it is first necessary to separate berkelium chemically from the californium produced in a reactor, and then permit the Bk to decay to Cf, which can subsequently be chemically separated from the berkelium. Currently, up to 60 mg per year of Bk are produced in the HFIR at ORNL, which is sufBdent to provide multi-milligram amounts of Cf [4]. The only other known production of Bk, and hence isotopically pure Cf (excluding the use of a mass separator), is in the USSR. The quantity of these materials available in the USSR is believed to be less than that produced by the HFIR. 

The separation procedure most suitable for californium isotopes generated in accelerators may not be the same as that used for californium produced in reactor targets. In some accelerator experiments the desired californium isotopes may be physically separated via recoil mechanisms, which simplifies the rapid separations required for short-lived isotopes. The need for nuclear or radioactive purity, as opposed to chemical purity, will also affect the particular separative processes to be used. A considerable amount of information on californium chemistry was determined using tracer levels of californium. The major purification schemes for californium at the tracer level involved ion-exchange techniques to separate californium from other transcurium elements. 

Californium-252 attracted early attention as a possible therapeutic agent in cancer treatment. The general impression formed from early work was that neutron therapy was inferior to x-ray therapy. More recent studies, however, indicate that neutron irradiation may have advantages over x-rays or y-rays in certain situations. In the period 1976-82, several hundred cancer cases were treated by neutron irradiation supplied by Cf [94]. Although not a cure, Cf neutron therapy appears to have promise in the treatment of pelvic cancer and in brachytherapy (short exposure therapy). Neutrons appear to have particular utility in tumors whose oxygen supply is impaired, and which, as a consequence, are relatively insensitive to x-rays or y-rays. While the applications of neutrons in the treatment of cancer are still experimental, there is a possibility that further clinical studies may well find a use for the neutron-emitting californium isotopes in therapy. 

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