Irradiation sources

The neutrons in a research reactor can be used for many types of scientific studies, including basic physics, radiological effects, fundamental biology, analysis of trace elements, material damage, and treatment of disease. Neutrons can also be dedicated to the production of nuclear weapons materials such as plutonium-239 from uranium-238 and tritium, H, from lithium-6. Alternatively, neutrons can be used to produce radioisotopes for medical diagnosis and treatment, for gamma irradiation sources, or for heat energy sources in space. 

This section will deal briefly with some aspects of expls safety peculiar to neutron activation analysis expts. We are concerned here with a) the possible effect of the ionizing radiation dose on the energetic material which will cause it to be more sensitive or hazardous to normal handling as an expl, and b) the potential direct expl hazards involved in the physical and mechanical transportation of samples to and horn the irradiation source and in a nuclear counting system... 

A molecular absorption spectrophotometry method, using a sharp-line irradiation source, has been developed for the determination of sulfide (as hydrogen sulfide) in water and sludge samples. The method was tested with measurements of real waste-water samples. The limit of detection was 0.25 g (1-10 mL sample volume). 

Palladium acetate, [PdO —02CCH3)2l3, possesses a unique quality that makes it attractive for solid state decomposition studies as well as technological applications. It can be spin-coated from solution to form a homogeneous, apparently amorphous solid film. This provides large uniform areas over which we can study the effects of various irradiation sources on the chemical nature of the film. The bulky structure of palladium acetate, shown in Figure 1 (8), may offer a partial explanation of the molecule s ability to achieve an amorphous metastable phase upon rapid evaporation of solvent. 

The principal photochemical reactions of metal complexes include dissociation, ligand exchange and redox processes. Unlike organic photoreactions (which take place almost exclusively from the S3 or T3 states), the excited state formed on irradiation depends on the wavelength employed. Hence the quantum yield often depends on the wavelength of the irradiating source. The excited-state processes give rise to a reactive intermediate which may find application in the synthesis of new compounds. 

Similarly, fluorescent silver clusters could be prepared in so called molecular hydrogels, formed by polyglycerol-b/oc -poly(acrylic acid) (PG-b-PAA), using a ratio COOH Ag of 2 1 with UV irradiation (365 nm). The emission band centered at 590 nm reached a maximum after 200 min of irradiation. The authors claim improved photostability of the clusters since they are still luminescent even after 9 h of irradiation, but it has to be mentioned that the irradiation source was weak, only 0.5 mW/cm2. They claim that it is the number of arms in the star polymer rather than the length of the arms (thus the density of COOH) that plays a crucial role in the formation of silver clusters [30]. 

Photolytic. When a dilute aqueous solution (1-10 mg/L) of bromacil was exposed to sunlight for 4 months, the TV-dealkylated photoproduct, 5-bromo-6-methyluracil, formed in small quantities. This compound is less stable than bromacil and upon further irradiation, the de-brominated product, 6-methyluracil was formed (Moilanen and Crosby, 1974). Acher and Dunkelblum (1979) studied the dye-sensitized photolysis of aerated aqueous solutions of bromacil using sunlight as the irradiation source. After 1 h, a mixture of diastereoisomers of 3-5ec-butyl-5-acetyl-5-hydroxyhydantoin formed in an 83% yield. In a subsequent study, another minor intermediate was identified as a 5,5 -photoproduct of 3-5ec-butyl-6-methyluracil. In this study, the rate of photooxidation increased with pH. The most effective sensitizers were riboflavin (10 ppm) and methylene blue (2-5 ppm) (Acher and Saltzman, 1980). Direct photodegradation of bromacil is not significant (Acher and Dunkelblum, 1979 Ishihara, 1963). 

The photocycloaddition of a carbonyl compound to an alkene was discovered as early as 1909 by Paterno and Chiefifi [78] who employed sunlight as the irradiation source. In the 1950s the reaction was more intensively investigated by Biichi et al. [79] using artificial light sources. The Paterno-Biichi reaction has been studied mechanistically [80] and some important aspects are summarized in Scheme 37. Upon n r -excitation (1=280-350 nm), aldehydes... 

Mixed Salts Dose Rate (kGy hr Irradiation Source ... 

X-Ray Photoelectron Spectroscopy. During the 1960s, Kai Sieg-bahn and co-workers (12) developed a surface-sensitive, high-resolution photoelectron spectroscopy that used x-rays as the irradiation source. He designated it as Electron Spectroscopy for Chemical Analysis or ESCA. The generic denotation for x-ray photoelectron spectroscopy of XPS is more accurate than ESCA and is preferred for clarity and for indicating the relationship of UPS. 

Irradiation Source. One to two rad electron or x-ray pulses are required to produce 6 to 12 nAf e aq. We use 1 Msec, pulses of 16 m.e.v. tungsten x-rays generated with an ARCO electron accelerator. The pulse must, however, be introduced in a time short compared to the measured half-lives. Any similarly pulsed x-ray beam of 150 to 200 k.e.v. would serve equally well since there is no rigid requirement of uniform irradia-... 

For irradiation in vacuum, solutions were sealed in glass ampoules after thawing from the frozen state under 10 3mm. of Hg. Irradiation under 02 or N2 was performed in a vessel which permitted continuous bubbling of the gas. The irradiation source was a 4000-curie cobalt-60 unit with a dose rate of 1 Mrad/hr. 

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. 

APPI Atmospheric pressure photoionization (APPI) is an ionization source similar to APCI but the corona discharge needle is replaced with an irradiation source (e.g., krypton lamp). In comparison to ESI and APCI, APPI can be used to efficiently ionize broad classes of nonpolar compounds. In the bioanalytical tool box, APPI is an important complement to ESI and APCI (Hanold et al., 2004 Syage et al., 2004 Cai et al., 2005 Hsieh, 2005). 

Selection of the radiolysis conditions is of primary importance. If studies carried out with a pure extractant enable the intrinsic stability of the molecules to be verified, radiolysis in solution and especially in a basic medium are indispensable to guarantee the approaches good representativity, as much from the point of view of species formation as from that of their distribution (potential elimination of the shortest degradation products, the most polar to the aqueous phase). The characteristics of the irradiation source (nature, dose rate, integrated dose) and also the temperature are essential parameters. Thus, the nature of the irradiation depends on the composition of the fuel, and the dose rate is dependent on the bum-up and cooling time of the fuel, while the exposure time of a solvent depends on the implementation conditions of the proposed process (flowsheet and nature of the contactors). 

Nature of the Irradiation Source. The degradation of TBP-diluent in contact with an aqueous phase did not reveal any qualitative influence of the nature of the radiation (y, p, a, accelerator radiation). Moreover, the yield value of the decomposition products of TBP (8, 9,11, 26, 84), nitro and carbonyl products (RN02, RN03, RCOOH, and RCOR ) (16), alkanes (C5-C8), and butanol (8) were almost identical, whatever the nature of radiations. Nevertheless, after radiolysis of TBP in n-dodecane without aqueous solution, the yield of H2MBP was substantially lower under a-irradiation than under y-irradiation (Ga (H2MBP) = 0.158 and Gt(H2MBP) = 0.443) (5). 

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