The synthesis of compounds containing polyhedral boron cages and porphyrin or phthalocyanine units connected covalently in one molecule is reviewed. The importance of these compounds arises, on the one hand, from the use of polyhedral boron derivatives in neutron capture therapy for cancer; on the other hand, porphyrins and phthalocyanines are known as photosensitizers in photodynamic tumor therapy. Current interest in the binding of polyhedral boron compounds to porphyrins and phthalocyanines is due to the observation that porphyrins and phthalocyanines show improved uptake and good persistence in tissues. Medical applications of compounds containing polyhedral boron cages and porphyrin or phthalocyanine units in one molecule are briefly discussed.

Polyhedral boron derivatives of porphyrins and phthalocyanines

Under severe accident conditions, the chemistry of reactor coolant could be significantly different from that under normal operating conditions. Injection of standby liquid control (SBLC) solution, release of fission product cesium (Cs) from damaged fuel rods, and addition of NaOH and Na2S2O3 in spray water will certainly enhance the alkalinity of water. In addition, oxidation of fuel cladding (zircaloy) by hightemperature water and steam would produce a significant amount of hydrogen, and hydrogen in water could effectively suppress water radiolysis and make the water more reducing. It is believed that the chemistry and transport behavior of iodine released from damaged fuel rods are strongly dependent on the chemistry of reactor water under accident conditions, and it is expected that the released iodine will most likely remain in nonvolatile forms in water. The chemistry of reactor coolant and the activities of iodine released from a damaged core are reviewed in detail in this paper.

https://www.tandfonline.com/doi/pdf/10.1080/18811248.2009.9711612

Reassessment of Reactor Coolant and Iodine Chemistry under Accident Conditions

The thermal neutron diffusion cooling coefficient is a macroscopic material parameter which is needed for a description of the decay of the thermal neutron pulse in a medium and gives information on the diffusion cooling of the thermal neutron spectrum in a bounded volume. Experimental results from various measurements for Plexiglas (a hydrogenous substance) are overviewed in the paper. A method for a theoretical calculation of the parameter is presented. The formula used utilizes other thermal neutron parameters and a cooling function which describes the deviation of the neutron spectrum in a bounded system from the distribution in an infinite one. The energy dependence of the function is obtained numerically from relations which result from the eigenvalue problem of the scattering operator when both the decay constant and the spectrum of the thermal neutron flux are developed in powers of the geometrical buckling. The calculation utilizes Granada's synthetic scattering function. The obtained value of the diffusion cooling coefficient for Plexiglas is at the temperature of C. The uncertainty is estimated to be within the physical model of the scattering kernel used. Results obtained using the same type of kernel in other theoretical methods are also included.

The diffusion cooling coefficient for thermal neutrons in Plexiglas

The effects of four common organic species (methanol, phenoxide, acetone, and methane) on the partitioning of iodine were studied over a range of concentrations, pHs, and radiation dose rates at --20/sup 0/C. The primary goal of the study was to identify conditions leading to the production of significant quantities of volatile organic iodides. For all of the conditions studied, only the case of irradiated methane-iodine-air-water systems yielded sufficient volatile organic iodides to bring about decreases in the iodine partition coefficient.

The effects of organic impurities on the partitioning of iodine

This article deals with multiple scattering effects that are important for the method of small-angle neutron scattering (SANS). It considers three channels for the coherent elastic, the incoherent elastic and the incoherent inelastic scattering processes. The first channel contains the desired information on the experiment. Its multiple scattering effects can be desmeared, as shown in the later sections of the article. The other two channels display a nearly constant background as a function of the scattering angle. The incoherent elastic scattering is treated by the theory of Chandrasekhar, allowing for multiple scattering even at large scattering angles. The transfer to a single representative thermalized wavelength by the inelastic scattering – as a simplification – is assumed to happen by a single scattering event. Once the transition to this altered wavelength has happened, further incoherent multiple scattering is considered. The first part of the paper deals with the multiple scattering effects of light water. In the later part of the article, deconvolution algorithms for multiple scattering and instrumental resolution of the elastic coherent signal as implemented in the program MuScatt are described. All of these considerations are interesting for both reactor-based instruments with velocity selectors and time-of-flight SANS instruments and may improve the reliability of the data treatment.

/pdf/multiple-scattering-and-resolution-effects-in-small-angle-3w3svatq7a.pdf

Multiple scattering and resolution effects in small-angle neutron scattering experiments calculated and corrected by the software package MuScatt

Short-term values of the iodine partition coefficient (IPC) were evaluated experimentally by an air/water system over the following ranges of conditions: temperature = 25 to 70/sup 0/C, pH = 5 to 9, and iodine concentration = 10/sup -9/ to 10/sup -2/ kg iodine/m/sup 3/ H/sub 2/O. The experimental IPC values are relatively independent of temperature over the indicated range, but show a significant dependence on pH and iodine concentration. In basic solutions the short-term values are several orders of magnitude less than the true equilibrium values; in acid solutions, the differences are much less. These results are useful for predicting the disposition of iodine shortly (i.e., 1 to 10 h) after iodine has been released into an air/water environment.

Experimental Investigation of the Iodine Partition Coefficient

In this paper a variety of scattering model approximations are devised and evaluated. One such scattering model, designated the balanced single collision thermalization (BSCT) approximation, has proven to be very effective. It assumes that neutrons attain a thermalized distribution with only a single collision within the moderating material, independent of incident energy. This approximation leads to separability of the incident and outscattering energies and to significant simplification of the neutron scattering kernel for thermalization problems. The BSCT approximation is particularly useful in thermalization problems involving cold neutron sources, for which it yields flux predictions to within a few percent of exact solutions of theoretical problems. The BSCT approximation also predicts cold neutron fractions to within 10% of measured values for a cold neutron thermalization experiment done at Argonne National Laboratory.

Scattering model approximations for neutron thermalization problems

Many investigators are experimenting with new BNCT compounds in an attempt to introduce more boron in cancer cells. Accurate determination of boron levels in tissues and blood is rather tedious, requiring specialized equipment to perform prompt γ-ray analysis, inductively coupled plasma atomic emission spectroscopy or boron MRI1. Although these methods are sensitive with detection levels near or below 1 ppm boron, none of the facilities required for those techniques are available at the University of Virginia and similarly, at many other universities. Under such circumstances, alternative methods of analysis would be useful.

Robert U. Mulder

Papers

Experimental Investigation of the Iodine Partition Coefficient

Scattering model approximations for neutron thermalization problems

Determination of Mn-BOPP Concentrations Using Neutron Activation Analysis and MRI