Cobalt irradiation experiments

The °Co y-ray irradiation experiments were performed at the Cobalt 60 Irradiation Facilities of the Takasaki Advanced Radiation Research Institute, under the Shared Use Program of Japan Atomic Energy Agency (IAEA) Facilities. This work was partially supported by the Kurata Memorial Hitachi Science and Technology Foundation. 

Irradiation equipment won acceptance much more easily in medical circles, where CPD already sold most of its products. In the early 1950s, people in the nuclear field were excited about the possibilities of their technology and preoccupied with the notion that almost anything could be improved through irradiation. Irradiation experiments had to be conducted within shielded containers to prevent radiation leakage. Sometimes the researchers at Tunney s Pasture used a beam therapy-unit head loaded with a cobalt-60 source at other times they used the cases designed to transfer cobalt-60 sources. As they adapted these pieces of equipment for experiments, it occurred to them that there would probably be a market for a device constructed specifically for the purpose. Best of all, equipment of this sort would provide another outlet for CPD s cobaIt-60. Discussions with possible customers at universities, research laboratories, and hospitals confirmed that they could use such a device either to experiment with irradiations or to irradiate small amounts of material on a routine basis. 

There have been several reviews of mechanisms of photosubstitution in rhodium(III) complexes. Bond indexes for ground and excited states have been discussed in relation to D2h species. " The observation of stereospecificity has been discussed in relation to lifetimes for triplet singlet deactivation and geometric rearrangements. Direct evidence has been presented to support the intermediacy of, and role of rearrangement in, five-coordinate intermediates in ligand field irradiation experiments. Rhodium(III) has been discussed in relation to cobalt(III) and iridium(III), and to ruthenium(II) and ruthenium(III) as well. ... 

On photolyzing CoziCOg in the matrix (20), a number of photoproducts could be observed. The results of these experiments are summarized in Scheme 4, which illustrates the various species formed. Of particular interest is the formation of Co2(CO)7 on irradiation of Co2(CO)g in CO (254 nm), as this species had not been characterized in the metal-atom study of Hanlan et al. (129). Passage of Co2(CO)g over an active, cobalt-metal surface before matrix isolation causes complete decomposition. On using a less active catalyst, the IR spectrum of Co(CO)4 could be observed. An absorption due to a second decomposition product, possibly Co2(CO)g, was also noted. 

The hypothesis that the cobalt carbonyl radicals are the carriers of catalytic activity was disproved by a high pressure photochemistry experiment /32/, in which the Co(CO), radical was prepared under hydroformylation conditions by photolysis of dicobalt octacarbonyl in hydrocarbon solvents. The catalytic reaction was not enhanced by the irradiation, as would be expected if the radicals were the active catalyst. On the contrary, the Co(C0)4 radicals were found to inhibit the hydroformylation. They initiate the decomposition of the real active catalyst, HCo(C0)4, in a radical chain process /32, 33/. 

In these procedures 1 litre of seawater was shaken with 60 mg charcoal for 15 min. Complexing agents were added in amounts of 1 mg, dissolved in 1 ml of acetone. The pH was 5.5, or it was adjusted to 8.5 by addition of 0.1 M ammonia. The charcoal was filtered off and irradiated. Results of three sets of experiments with charcoal alone, charcoal in the presence of dithizone, and charcoal in the presence of sodium diethyldithiocarbamate are compared. The following elements are adsorbed to an extent from 75 to 100% silver, gold, cerium, cadmium, cobalt, chromium, europium, iron, mercury, lanthanum, scandium, uranium, and zinc. The amount of sodium is reduced to about 10 6, bromine to about 10 5, and calcium to about 10 2. 

Irradiations are carried out in Kimax glass ampoules. These ampoules are filled with 5 cc. of the solution, irradiated, using the apparatus previously described (7), and flame-sealed with a Perfe Keum Model HS-1 ampoule sealer. The irradiation source used for these experiments is a 1.3 X 106 curie cobalt-60 source consisting of two parallel plaques 56 inches wide by 48 inches high, spaced 16 inches apart. For most irradiations, the ampoules are placed in the center of a Masonite phantom which completely fills a No. 10 can (6 inches in diameter by 7 inches high). The can is placed in a fixed position in an aluminum carrier and transported into the irradiation cell to a predetermined position (5). The source is then elevated from the bottom of a 25-foot, water-filled pool into the irradiation position. After the desired exposure, the source is lowered to the bottom of the pool. 

Irradiation of the samples was performed at the Institut Armand-Frappier (IAF). Four irradiators with different dose rates were used. In all instances, Cobalt-60 ( Co, half-life 5.26 years, 1.25 MeV yray photon) was used as the gamma ray source. The GammaCell I, n, HI and the Calibrator emit y rays at 107,350,700 and 3000 krad/h respectively. At the end of the experimental runs, the 107 and 350 krad/h dose rates of the GammaCell I and n were down to 85 and 265 krad/h respectively, due to the Co half-life. The calibrator was kept constant at 3000 krad/h. The exact value of the various dose rates was constantly monitored during the experiments. 

In the radiation grafting work, experiments were performed in spent fuel element and cobalt-60 facilities of the Australian Atomic Energy Commission, dose rates being determined by ferrous sulfate dosimetry (G(Fe)= 15.6). For the specific irradiations, which were carried out in quadruplicate, small strips (5 x 4cm) of cellulose (Whatman No. 41, W.R. Balston Pty. Ltd., double acid-washed chromatography grade) were equilibrated at 65% relative humidity for 24 h at 23 °C, folded into test tubes (16 x 1.2 cm), monomer solution (6ml) added to the tubes which were then lightly stoppered. After irradiation, the strips... 

The sample used for the experiments is Aciplex-SF-1004 (10x10x0.117 mm3). The sample was irradiated at room temperature and atmospheric pressure with 1.17 and 1.33 MeV gamma-ray from a cobalt-60 source in the Takasaki Research Establishment of Japan Atomic Energy Research Institute (JAERI). The absorption doses of the sample by gamma-ray were from 1 to 173 kGy. 

Some of the techniques used in this study have been described previously (13). Solutions were saturated with Ar (99.99% pure, supplied by Linde), using a modification of the technique described by Swinnerton et al. (17). The normal dose rate of approximately 6 X 1016 e.v. gram-1 min. 1 was delivered by a Gammacell-220 (AECL) cobalt-60 irradiation unit. Lower dose rates by a factor of nine were achieved by enclosing the irradiation vessels inside a lead container. Temperatures of irradiated samples were controlled to 1°C. in experiments where the effects of temperature were studied but in other experiments were 24 2°C. Care was taken to minimize the effects of volume contraction and expansion at low temperatures in order to exclude air from Ar saturated solutions. 

New designs of irradiation devices for the production of radioactive isotopes, in particular cobalt-60, were tested in the steel blanket. The key innovation in these designs was the absence of the absorber elements. In the course of the experiments, power bursts up to 50% were revealed on the core boundary. Since the considerable decrease of power is observed in the core periphery, these bursts are unlikely to cause the parameters of power reactor standard fuel subassemblies to go over permissible operating limits. However, the final conclusion on this issue can be drawn only after the comprehensive analysis of S/A performance taking into account the obtained experimental data. 

Many experiments have been carried out with the objective of reducing the drastic reaction conditions which are necessary for carbonylation of olefins. Tetteroo [474] succeeded in stoichiometric hydrocarboxylation of olefins at 55-60 °C and atmospheric pressure with UV irradiation. In the presence of cobalt catalysts the reaction is accelerated remarkably by addition of 5-10 % of hydrogen to carbon monoxide (about factor 3). Obviously the acceleration is caused by favoring the formation of hydrocarbonyl from Co2(CO)g and hydrogen. 

The production of plutonium was a prime justification for building NRU and took precedence over other uses. Some would be used for reactor experiments in Canada, but it was expected that most would be exported to the United States for atomic bombs. Isotope production came next on the list of priorities, so CPD would have fair access to the reactor. NRU started up on November 3, 1957. After a shakedown period, irradiations began. In May 1958, a fuel rod broke as it was being withdrawn from the reactor, causing a radioactive spill that delayed cobalt-60 production to late 1959. 

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