A.L. Hanson

Interaction of keV photons with matter and new applications

Abstract The fundamental interactions of keV photons with matter, i.e. photoelectric effect and coherent and incoherent scattering are treated from a non-traditional point of view. Section 1 is designed to lay a foundation of the basic science. Section 2 deals with non-imaging analytical techniques that have been developed over the past 20 or so years. These techniques include energy-dispersive X-ray fluorescence, Compton profile measurements, and general scattering techniques. In section 3, imaging techniques are described. These imaging techniques ultilize the details of section 1, and some expand on techniques described in section 2. This section finishes with discussions of “traditional” computerized tomography (CT) techniques followed by newer developments such as differential tomography, Compton tomography, coherent scatter tomography, and fluorescent X-ray tomography.

THE CALCULATION OF SCATTERING CROSS SECTIONS FOR POLARIZED X-RAYS *

The scattering of low energy X-rays by atoms is dominated by coherent (Rayleigh) and incoherent (many times known as “atomic Compton”) scattering. As electron synchrotron storage rings become more widely used as sources of intense, polarized X-rays, it is important to be able to properly calculate the scattering cross sections since the polarization of the X-rays can be utilized to reduce the X-ray scattering. This paper reviews the methods of calculating the Rayleigh and atomic Compton scattering cross sections of polarized X-rays and presents analytical integrations of the cross sections over solid angles of circular detectors from point sources into 90°. Special attention is paid to the effects the scattering has on the background of spectra collected with energy dispersive detectors. It is shown that the ratio of scattering to fluorescence does not approach zero for small values of rR (r = detector radius, R = distance to detector).

Trace element measurements using white synchrotron radiation

Abstract Synchrotron radiation, when used for X-ray fluorescence (XRF) has several advantages over conventional X-ray sources. Our group at Brookhaven National Laboratory is developing the equipment and expertise to make XRF measurements with synchrotron radiation. The apparatus is briefly described, along with the alignment techniques. Some minimum detectable limits for trace elements in thin biological standards measured with white light irradiations are presented.

Application of synchrotron radiation to elemental analysis

Abstract The use of a synchrotron storage ring as a high brightness source for production of monoenergetic variable energy, and highly polarized X-ray beams promises to revolutionize the field of elemental analysis. The results of exploratory work using the Cornell synchrotron facility, CHESS, will be described. Design considerations and features of the new X-ray microprobe facility now under construction at the Brookhaven National Synchrotron Light Source will be presented. This facility will be used for bulk analysis and for microanalysis with an initial spatial resolution of the order of 30 μm.

Response of the rat spinal cord to X-ray microbeams

BACKGROUND AND PURPOSE To quantify the late dose-related responses of the rat cervical spinal cord to X-ray irradiations by an array of microbeams or by a single millimeter beam. MATERIALS AND METHODS Necks of anesthetized rats were irradiated transversely by an 11 mm wide array of 52 parallel, 35 μm wide, vertical X-ray microbeams, separated by 210 μm intervals between centers. Comparison was made with rats irradiated with a 1.35 mm wide single beam of similar X-rays. Rats were killed when paresis developed, or up to 383 days post irradiation (dpi). RESULTS Microbeam peak/valley doses of ≈357/12.7 Gy to 715/25.4 Gy to an 11 mm long segment of the spinal cord, or single beam doses of ≈146-454 Gy to a 1.35 mm long segment caused foreleg paresis and histopathologically verified spinal cord damage; rats exposed to peak/valley doses up to 253/9 Gy were paresis-free at 383 dpi. CONCLUSIONS Whereas microbeam radiation therapy [MRT] for malignant gliomas implanted in rat brains can be safe, palliative or curative, the high tolerance of normal rat spinal cords to similar microbeam exposures justifies testing MRT for autochthonous malignancies in the central nervous system of larger animals with a view to subsequent clinical applications.

Application of SRIXE and XANES to the determination of the oxidation state of iron in prostate tissue sections

Normal prostate and cancerous prostate tissue sections were analyzed using synchrotron radiation-induced X-ray emission and X-ray absorption near-edge structure (XANES) at the X-26A microprobe beam line located at the National Synchrotron Light Source, Brookhaven National Laboratory, USA. In both measurements, a monochromatic beam of size of 16×14 μm2 was applied. Two-dimensional scans of selected areas of non-cancerous and cancerous tissue sections were performed in order to obtain the distributions of various trace element concentrations. The XANES spectra were recorded for selected points containing high concentrations of iron. These measurements were performed with the aim of determining the oxidation state of iron. It was found that the iron concentration was much higher in the cancerous sections of the analyzed tissues than in the non-cancerous sections. From the results of XANES spectra analysis, iron in cancerous prostate tissue sections mostly occurs in the +3 oxidation state.

Preliminary study on the distribution of selected elements in cancerous and non-cancerous kidney tissues

In this study special interest was given to trace elements recognized as to be carcinogenic to humans. The kidney tissue sections were analyzed in order to determine the concentrations of elements present in the sample. The Synchrotron Radiation Induced X-ray Emission (SRIXE) technique was applied using a white photon microbeam. The results from cancerous parts of the kidney tissues were compared to non-cancerous parts and to the control group. In addition the iron concentration level was determined in the serum of those patients. Two-dimensional scans are presented to illustrate the differences between perfused and not-perfused tissues. According to this study there is no significant difference in the Mn concentration between cancerous and non-cancerous parts of the kidney, but the concentrations of Cd, Cr, Ti, V, Cu, Se, and Zn are at a lower concentration level in the cancerous parts than in the non-cancerous parts. A converse observation has been made for Fe. This may be associated with different metabolism and dynamics of the cancer process and both higher vascularization and need of higher blood supply in the cancerous tissue. The two-dimensional scanning of thin kidney sections showed differences in the trace element distributions depending on the analyzed samples: perfused and non-perfused. Perfusion removed blood mostly from the peritubular capillaries while in the glomerulus some capillaries had a relatively high Fe content. A low Fe concentration was observed in nephron tubules while a converse observation has been made for Cd. This may indicate that Cd is localized in the cells but not in the blood.

X-RAY FLUORESCENCE WITH SYNCHROTRON RADIATION

The use of synchrotron radiation for X-ray fluorescence has several advantages over the use of other conventional X-ray sources. The principles of synchrotron radiation and methods for applying synchrotron radiation to the X-ray fluorescence measurements of trace elements are discussed. The Brookhaven National Laboratory X-ray microprobe, facilities dedicated to X-ray fluorescence, and related analytical techniques are discussed. Some examples of trace element analyses in biological materials with synchrotron radiation are presented.

Activation of natural Hf and Ta in relation to the production of 177Lu.

The isotope (177)Lu is used in nuclear medicine and biology for in vivo applications as a radioactive label of various targeting agents. To extend the availability of no-carrier added (177)Lu, we investigated the feasibility of its production in a proton accelerator. Tantalum and Hf targets were irradiated and chemically processed to determine the radioisotope yield and cross-sections. The largest cross-sections (approximately 20 mb) were found for the Hf target at 195 MeV; however, the presence of co-produced Lu isotopes may limit the product applications. The results are in good agreement with theoretical data calculated using computer codes MCNPX and ORIGEN2S. Production of relevant medical isotopes such as (167)Tm and (169)Yb from the above targets is discussed as well.

Total cross sections for the production of 22Na and 24Na in proton-induced reactions on 27Al from 0.40 to 22.4 GeV

Total cross sections for production of 22 Na and 24 Na from the irradiation of 27 Al by protons with incident energies between 0.40 and 22.4 GeV have been measured. The overall uncertainties for these measurements were less than 3%. The measured values compare well with previous measurements and evaluations. � 2003 Elsevier B.V. All rights reserved.