Self-irradiation

Because of the multivalent nature of the actinide ions, understanding the radiation-induced change of the valence-state of the actinide in solutions under self-irradiation or external irradiation is a challenge in radiation chemistry. Some of the ions are strong a-emitters. It is also important from a practical viewpoint that the solution chemistry of actinide ions is closely related to the storage and the repository of the wastes. Much work combined with experiment and simulation has been conducted and reviews were summarized [136,140-144]. 

Further work is necessary to elucidate more completely both the solid state and solution chemistries of berkelium. Complete knowledge of its physicochemical behavior is important for more accurate extrapolations to the behavior of the still heavier elements, for which experimental studies are often precluded by intense self-irradiation and/or by lack of material. 

The nature of our concern is best illustrated by a specific example. Blank and Kidwell use a cocaine solution of 100,000 ng/mL for their contamination experiments, to which they add approximately 1 pCi of tritium-labeled cocaine, i.e., approximately one million counts per minute. Therefore, they have approximately a sensitivity of 10 cpm/ng of sample. Decontamination of hair means that residual drug concentration must drop below the endogenous cutoff level of 5 ng/10 mg of hair, i.e., to 50 cpm/10 mg hair. Now if the labeled cocaine has a radiochemical impurity of as little as 0.1%, this corresponds to 1000 cpm or to 100 ng of residual cocaine equivalents. Since self-irradiation of tritium-labeled material tends to form polymeric impurities, and since these are likely to preferentially bind to hair, one incurs a major risk of concluding erroneously that the residual radioactivity represents residual cocaine contamination rather than contamination by polymeric degradation products. 

Denaturation of proteins may result from low concentrations and elevated storage temperatures. These conditions must also be controlled for radioiodinated proteins that are also subject to internal self-irradiation damage, which is more pronounced in I-labeled proteins than I-la-beled proteins owing to the beta radiation emission of I. To minimize such problems, radioiodinated proteins are diluted in protective protein solutions that will not interfere in the subsequent studies to be made, such as 10% normal serum or BSA at 2 mg of protein per milliliter. Aliquots are kept frozen at -20° to -70° and thawed only as needed. 

The displacement of atoms just discussed is due to causes outside the affected crystal. But in the early days of radioactivity the destruction of radium salts by self-irradiation was recognised. Indeed the process occurs more or less in all minerals and compounds containing radioactive atoms. Recently D Eye (1957) calculated that 2 x 10 atoms in 1 mg of a polonium compound are knocked off their sites, mainly by recoil nuclei, in a day. As there are only about 10 atoms in this weight of the compound, every atom suffered, on the average, one displacement a day. By X-ray powder photography, with the special precautions necessitated by the polonium activity... 

The hydroxides of berklium(III), Bk(OH)3, and califomium(III), Cf(OH)s, behave in a similar fashion [3]. In their crystalline forms, Am(OH)s and Cm(OH)3 are anhydrous (as are hydroxides of light rare-earth elements), and are hexagonal, C 6h P s/m space group, a = 6.420 and 6.391 A, c = 3.745 and 3.712 A, for Am and Cm compounds, respectively. Due to self-irradiation, the unit-cell parameters increase with time, as does the sample amorphization. In the case of " Cm(OH)3, the stmcture decomposes within 1 day, but the same process for " Am(OH)3 takes up to 4-6 months [4]. The Mossbauer spectrum of Am(OH)3 [5] is characterized by 5 = 4.6 cm/c (relative to Am02). The nuclear magnetic resonance (NMR) studies indicate that, among the TUE(III) hydroxides, the Am compound has the most covalent chemical bonds. The TUE(III) hydroxides are readily soluble in different mineral acids under these conditions, the solutions of hydrated An ions are produced. 

Clinard FW Jr (1986) Review of self-irradiation effects in Pu-substituted zirconolite. Ceram Bull 65 1181-1187... 

Clinard FW, Rohr DL Jr., Roof RB (1984) Stmctural damage in a self-irradiated zirconolite-based ceramic. Nucl Instr Meth B 1 581-586... 

Foltyn EM, Clinard FW Jr, Rankin J, Peterson DE (1985) Self-irradiation effects in Pu-substituted zirconolite II. Effect of damage microstractrrre on recovery. J Nucl Mater 136 97-103 Frondel C (1958) Hydroxyl substitution in thorite and zircon. Am Mineral 38 1007-1018 Froude DO, Ireland TR, Kirmey PD, Williams IS, Compston W, Wilhams IR, Myers JS (1983) Ion microprobe identification of 4,100-4,200 Myr.-old terrestrial zircorts. Natrrre 304 616-618 Gibbons JG (1972) Ion implantation in semiconductors— Part II Damage production and armeahng. Proc IEEE 60 1062-1096... 

Kitahara (1987) studied the self-irradiation of a commercial CaS04 Tm (UD-200S) TLD. This is a high-sensitivity TLD. Ten samples, one of each of 10 hatches, were used for the measurements. The samples were kept in a lead brick enclosure located underground for 20 days. The average self-irradiation obtained was 2.6 0.36pRadh. This radiation was found to be due to the cap of the holder which served as a Sn-Pb alloy for energy compensation. Tokuyama et al. (1990) studied the self-dose and the cosmic ray dose of a UD-200 S TLD. The self-dose was measured in a tunnel where the cosmic rays are attenuated. A self-dose of 0.26 nC kg h was measured with and without the Sn-Pb filter of the TLD. The dose of the cosmic rays at sea level was 0.74 nC kg h . ... 

In recent years the field of studies has shifted towards complicated systems and phenomena in the case of polymers as well. Composites (Debowska et al. 2000), doped polymers (Huang et al. 2000), and membranes (Bi et al. 2000) were studied and self-irradiation effects caused by positrons (Balcaen et al. 2000) were observed. 

Radiation dose to the cell nucleus can come from either self-irradiation or cross fire (left) and will vary depending upon whether the site of decay was in the cell membrane, in the cytoplasm, or in the cell nucleus (right)... 

Cm-244 multi-g 18y a High radiation levels self-irradiation damage to solids operation in glove box limited to few mg... 

Es-253 multi ig 20.5 d a Severe self-irradiation damage to solids signifieant radiation field... 

The actinide with the highest atomic number that has been studied in a solid phase is Es the sesquioxide is its only known oxide phase. The scarcity of this element, and more importantly the intense self-irradiation from the Es-253 isotope which destroys rapidly the oxide matrix, may limit attaining higher oxygen stoichiometries. The structural identification of ES2O3 (Haire and Baybarz 1973) was only accomplished by using very small quantities (10-100 nanograms) and electron diffraction, which provided diffraction patterns in very short times as compared to conventional X-ray techniques. 

It has also been reported that self-irradiation transforms the C-form of the sesquioxide at room temperature to the A-form in about three years (Hurtgen and Fuger 1977). 

The Cm203 (white) displays three crystal modifications, namely the A-, B- and C-type lanthanide structures as shown in table 23 (Eller and Pennemann 1986). A small uptake of oxygen can cause the oxide to acquire a tan to light brown appearance. The C-type (bcc) structure is the low-temperature form, which converts to the B-type (monoclinic) structure above 800°C, which in turn changes to the A-type (hexagonal) structure above 1600°C (Baybarz and Haire 1976). It is the C-type structure that is readily oxidized to higher oxides the monoclinic form is very resistent to oxidation and the monoclinic to cubic transformation via temperature treatment is very diflicult ( irreversible transformation). The B to A and the A to B transformations occur more readily with temperature. Self-irradiation (especially noticeable with the more readily available, shorter-lived Cm-244 isotope) converts the C-form of the sesquioxide to the A-form (Wallmann 1964, Noe et al. 1970). 

The question of the actual O/M ratio in CmOj is an important one. Magnetic data (see later section) yield moments that are too high (1.5 to 3.0 /jB versus zero, as expected for an 5f electron core), which initially was interpreted to mean that the O/M ratio in the oxide was less than two. Several workers have tried different experiments to resolve this problem (Nave et al. 1983, Morss et al. 1989) and a theoretical evaluation of this problem has also been attempted (Goodman 1992). The simplest answer would be that the CmOj is nonstoichiometric (e.g., O/M < 2.00) but this is not a totally satisfactory explanation and is not supported by X-ray analyses of the oxides. Self-irradiation can lead to loss of oxygen in such oxides but the Cm-248 oxides should be relatively free of these effects over modest time periods. 

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