Cyclotron irradiation

The discovery of the elements 43 and 75 was reported by Noddack et al. in 1925, just seventy years ago. Although the presence of the element 75, rhenium, was confirmed later, the element 43, masurium, as they named it, could not be extracted from naturally occurring minerals. However, in the cyclotron-irradiated molybdenum deflector, Perrier and Segre found radioactivity ascribed to the element 43. This discovery in 1937 was established firmly on the basis of its chemical properties which were expected from the position between manganese and rhenium in the periodic table. However, ten years later in 1937, the new element was named technetium as the first artificially made element. 

As indicated above, a combination of reactor and cyclotron irradiations is used to prepare most radionuclides. While many of these radionuclides are available commercially, some are not. In addition, nuclear structure, nuclear reactions, and heavy-element research require accelerator or reactor irradiations to produce short-lived nuclei or to study the dynamics of nuclear collisions, and so on. One of the frequent chores of radiochemists is the preparation of accelerator targets and samples for reactor irradiation. It is this chore that we address in this section. 

Plutonium (Z = 94) was discovered in 1940 by Seaborg and co-workers. It was also named in analogy to uranium, after the planet Pluto. The first isotope of Pu was produced by cyclotron irradiation of uranium with 16 MeV deuterons ... 

The third means of radionuclide production involves target irradiation by ions accelerated in a cyclotron. One example of this approach is provided by the production of Ge, which decays with a 280 day half-life to the positron emitter Ga. Proton irradiation of Ga produces Ge in a (p,2n) reaction. After dissolution of the target material a solution of the Ge product in concentrated HCl is prepared and adsorbed on an alumina column which has been pre-equilibrated with 0.005 M EDTA (ethylenediaminetetraacetate) solution. The Ga daughter may then be eluted using an EDTA solution in a system which provides the basis of a Ga generator. Cyclotron production of radionuclides is expensive compared with reactor irradiations, but higher specific activities are possible than with the neutron capture process. Also, radionuclides with particularly useful properties, and which cannot be obtained from a reactor, may be prepared by cyclotron irradiation. In one example, cyclotron produced Fe, a positron emitter, may be used for bone marrow imaging while reactor produced Fe, a /3-emitter, is unsuitable. " ... 

The cyclotron irradiation of a mixture of N j, CO and Cl j gave a yield of COCl j of 25%, but was of relatively low specific activity owing to the presence of carrier amounts of non-radioactive COClj [275]. 

The 90-keV resonance in Ru was first reported in 1963, by Kistner, Monaro, and Segnan [20]. The first excited level is populated by a complicated EC decay of 16-day Rh (see Fig. 16.7). The latter is prepared by a Ru(p, ) Rh cyclotron irradiation [20, 21], or by the alternative Ru(ruthenium metal can be irradiated and used directly, although a process for chemical separation of the Rh activity followed by re-incorporation into ruthenium metal has been described [23]. 

Detailed correlations on the scale of Fe will not be possible until more data are available, but clearly similar trends will be found. Unavoidable difficulties are the very weak resonance effects even at helium temperature and the short lifetime of the cyclotron-irradiated source. 

Even a chemically pure target may yield products of several elem ts, particularly in cyclotron irradiation, where many reaction paths are often possible. In the bombardment of magnesium with deuterons, the following reactions occur ... 

In view of the frequently expressed concern that the ti/2 of is too short for interesting biochemistry, it is significant to note that the incubation time in these experiments was of the order of seconds to minutes. After longer times the spectrum of N-labeled products became so complex that thin-layer chromatography had to be done following electrophoresis. The extent of incorporation of into metabolic products was sufficient to affow analytical chemistry of the products as late as 2 h after a cyclotron irradiation. In fact, the ti/2 of was nearly ideally suited to these interesting and significant biochemical experiments. 

Lawrence happened to be visiting New York. Fermi, Lawrence, Pe-gram and I met in Dean Pegram s office at Columbia University and developed plans for a cyclotron irradiation that could produce a sufficient amount of [element 94]. After Christmas Segrd returned to Berkeley. 

The source of 7 rays needed for the teehnique is typically an excited-state nucleus, which is itself formed by a nuclear decay process from another nueleus. The most widely used Fe (where denotes excited state) is formed in an electron-capture proeess from radioactive 27C0 (half-life 270 days). This in turn is readily obtained by cyclotron irradiation of iron. f Co decays to Fe with nuclear spin quantum number 7 = 5/2, for which two relaxation processes exist, one with a 15% probability that leads directly to the Fe ground state (by emission of a 7 photon of 136.32 keV), and another with an 85% probability that leads to a different excited-state nucleus with 7 = 3/2. This is what is actually used for the Mossbauer experiment. It has a transition to the ground state (7 = 1/2) with emission of a 7 photon of 14.41 keV (Figure 6.1). 

Planet pluto) Plutonium was the second transuranium element of the actinide series to be discovered. The isotope 238pu was produced in 1940 by Seaborg, McMillan, Kennedy, and Wahl by deuteron bombardment of uranium in the 60-inch cyclotron at Berkeley, California. Plutonium also exists in trace quantities in naturally occurring uranium ores. It is formed in much the same manner as neptunium, by irradiation of natural uranium with the neutrons which are present. 

The sources used in Ni Mossbauer work mainly contain Co as the parent nuclide of Ni in a few cases, Cu sources have also been used. Although the half-life of Co is relatively short (99 m), this nuclide is much superior to Cu because it decays via P emission directly to the 67.4 keV Mossbauer level (Fig. 7.2) whereas Cu ti/2 = 3.32 h) decays in a complex way with only about 2.4% populating the 67.4 keV level. There are a number of nuclear reactions leading to Co [4] the most popular ones are Ni(y, p) Co with the bremsstrahlung (about 100 MeV) from an electron accelerator, or Ni(p, a) Co via proton irradiation of Ni in a cyclotron. 

The ability to selectively excite a particular ion (or group of ions) by irradiating the cell with the appropriate radiofrequencies provides a level of flexibility unparalleled in any other mass spectrometer. The amplitude and duration of the applied RF pulse determine the ultimate radius of the ion trajectories. Thus, by simply turning on the appropriate radiofrequency, ions of a single m/z may be ejected from the cyclotron. In this way, a gas-phase separation of analyte from matrix is achieved. At a fixed radius of the ion trajectories the signal is proportional to the number of orbiting ions. Quantitation therefore requires precise RF control. 

There had been some confusion about the discovery of element number 43 until in 1937 Perrier and Segre succeeded in producing it by deuteron irradiation of molybdenum placed in a cyclotron. A Japanese chemist by the name of Ogawa believed that he had succeeded in discovering this element in 1908, but in vain. Afterwards, in 1925 the Noddack group claimed to have discovered this element, but their claim turned out to be false. 

The apparatus and techniques of ion cyclotron resonance spectroscopy have been described in detail elsewhere. Ions are formed, either by electron impact from a volatile precursor, or by laser evaporation and ionization of a solid metal target (14), and allowed to interact with neutral reactants. Freiser and co-workers have refined this experimental methodology with the use of elegant collision induced dissociation experiments for reactant preparation and the selective introduction of neutral reactants using pulsed gas valves (15). Irradiation of the ions with either lasers or conventional light sources during selected portions of the trapped ion cycle makes it possible to study ion photochemical processes... 

Imura and Suzuki36 have prepared labelled organotin compounds from artificial tin isotopes produced in a cyclotron. The carrier-free tin-113 radioisotope was produced by irradiating indium-115 oxide with 40-MeV protons (equation 33). 

Cooperation of the staff of RIKEN cyclotron in many irradiation runs for the production of Sb-119 is gratefully acknowledged. 

Technetium (Tc, [Kr]4 /65.vl), name and symbol after the Greek Tsxrmos (tech-nikos, artificial). Detected in Italy (1937) by Carlo Perrier and Emilio Segre in a sample of Mo which had been irradiated with deuterons at the E.O. Lawrence cyclotron in California. It was the first artificially produced element. 

All the separation methods mentioned in this article, and, in general, the. chemical treatment, can be equally well applied to targets which have been irradiated with other particles, for example in a linear accelerator or cyclotron. 

Hofstadler, S. A., Wahl, J. H., Bakhtiar, R., Anderson, G. A., Bruce, J. E., and Smith, R. D. (1994). Capillary electrophoresis/Eourier-transform ion-cyclotron-resonance mass spectrometry with sustained off-resonance irradiation for the characterization of protein and peptide mixtures. ]. Am. Soc. Mass Spectrom. 5, 894 —899. 

BGeingeld and Nibbering et al. have shown that the intermediacy of such adducts can be demonstrated through the use of a double-resonance type of technique in which the transient [AB ] is continuously irradiated at its cyclotron frequency throughout the entire reaction time, even though it is not detectable in the ordinary mass spectrum. An overall decrease in the intensity of the product ion was then... 

All isotopes of the element are synthesized in the nuclear reactor. The first isotope synthesized had the mass 241, produced by irradiation of milligram quantities of americium-241 with alpha particles of 35 MeV in a cyclotron ... 

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