The dead layer near the front surface of aged or damaged Nal detectors produces both an energy dependent diminution in counting efficiency and a characteristic iodine K x-ray peak, which interferes with the registered radiation spectra. In this paper, the exploitation of this peak as an internal reference to assess the dead layer thickness and the relative loss of detector quality is proved by means of a comparison between experiments and Monte Carlo simulations. Investigations with different Nal-based equipments and photon transport simulations are carried out in order to assess the detector degradation in terms of peak interference, efficiency and resolution. Copyright (C) 2009 John Wiley & Sons, Ltd.

Accurate measurements (mostly within 5%) of L-alpha L-beta and L-gamma x-ray emission cross sections were carried out on thick foils of elements lying in 64 <= Z <= 73 interval, stimulated by 59.54 keV photons. They can be of help as an overall reference to compare the theoretical and semi-empirical approaches by which the atomic parameters included in the expressions of L emission cross sections are evaluated. An appropriate extension of the expression linking the cross section to the counting rate measured in reflection geometry on thick targets makes it possible to overcome the difficulties arising from the width in energy of the L-beta and L-gamma groups and from the jump present in the attenuation coefficients of the target elements within the energy interval of their L-gamma emission lines.

The anisotropy of L x-ray fluorescence induced by 59.54 keV unpolarized photons is investigated by means of an experimental procedure which allows the relative L x-ray production cross section to be evaluated without taking account of the angular set-up and the instrumental efficiency. Thick targets of Yb, Hf, Ta, W and Pb are considered, and the angular trend of the relative experimental ratios, ILα/ILβ, is calculated by simple evaluations of the peak area alone. Within the experimental uncertainties, which are found to be of the order of 1.6% in the worst cases, the results do not show any significant angular dependence of the Lα emission lines if the isotropy of the Lβ lines is assumed. This fact contrasts with the results of some groups, which report evidence of strong angular dependence at this level of photon energy.

An updating of photon transport modelling in tissues is carried out by including the effect of molecular interference in the coherent (Rayleigh) scattering. To this end, the present tabulations—which permit us to obtain the linear differential scattering coefficient of compounds from a simple weighted sum of the elemental components—are integrated by adding files for a limited set of molecular interference functions. This set originates from a four-component model which is found to be capable of reproducing human tissues in situations involving bony and soft tissues. The proposed procedure overcomes, in the computation, the hindrance that the dependence on molecular interference effects leads every tissue to have its own diffraction pattern, which is not easily obtained by means of measurements or calculations.

In order to include the molecular interference effect, a simple procedure is proposed and demonstrated to be able to update the usual cross section database for photon coherent scattering modelling in Monte Carlo codes. This effect was evaluated by measurement of coherent scattering distributions and by means of a model based on four basic materials composing biological tissues.

Changes to the general purpose EGS4 code were performed in order to include anomalous dispersion effects in the simulation of elastic scattering from atomic bound electrons. Moreover, experimental checks with 59.54 keV photons incident on Hf and Pb targets, at 90degrees and 120degrees scattering angles, were carried out.

We have developed a dedicated breast imager, which makes use of a pendulum geometry of the breast and of a combined imaging modality, namely CT and SPECT co-registration. The CT scanner is composed by a quasi-monochromatic source which produces a 28 keV-fan beam and a linear digital detection system. X-ray source and digital detector are assembled on a toroidal tomograph gantry with about 13 cm of circular field of view, The gantry also contains the SPECT acquisition system., composed by a detector made of CsI scintillating crystal matrices coupled to Hamamatsu position sensitive photomultipliers and lead collimators. The toroid rotates under computer control so as to acquire separated slices over an angle of 180 deg. Each X-ray and SPECT image is acquired and reconstructed by using a specifically developed software, that also allows the fusion of the morphological with the functional information. In this paper a description of the prototype and the preliminary results are presented. Images of various test phantoms have been acquired with both modalities and first images with the fusion technique are presented.

The suitability of introducing molecular interference effects into coherent scattering phenomenology is considered here in the case of X and gamma photon transport in biological tissues. In order to make its implementation practicable in most of the existing open user Monte Carlo codes, a self-consistent basic set of tabulations for the linear differential scattering coefficient was proposed. The tabulations were critically reviewed by testing their validity over the entire range of the momentum transfer variable from 0 to 10(10) nm(-1). Implementation in three different Monte Carlo codes was performed, and they proved to be reliable.

Accurate measurements, within 2%, of K radiation emission cross sections were carried out on thick foils of Gd-64, Dy-66, and Er-68 stimulated by 59.54-keV photons, i.e., an energy close to the K thresholds of the target atoms. The results obtained provide a good global reference test for the relativistic quantum-mechanic models used in the calculations of K fluorescence yields and K vacancy creation cross sections.

This paper explores the possibilities offered by basic photon scattering phenomenology in the study of a new collimator devised to enhance the collection of photons undergoing a single scattering in a volume of interest, In order to maximize the spatial resolution, a 90 degrees scattering geometry was considered. The collimator was composed of two parallel plates perpendicular to both the detector surface and the plane of first scattering defined by the trajectories of the incident and scattered photons, In this way, photons whose azimuthal angle ranges over a wide interval but with the same scattering angle could reach the detector, Experimental comparison between this collimation and the usual narrow one was performed at a photon energy of 59.54 keV under the same sample and irradiation geometry. The first results showed that an enhancement of about 10-fold could be reached with regard to the main Compton and coherent peaks. On the other hand, the multiple scattering fraction only rose to a maximum of 20% in the worst case, as compared with that observed in classical highly collimated geometry. The usual analytical capacity offered by the scattering techniques was demonstrated to be still valid in this situation, Copyright (C) 1999 John Wiley & Sons, Ltd.

This work exploits the possibilities offered by basic photon scattering phenomenology to study a new collimator devised to enhance the collection of photons which underwent a single scattering in a volume of interest. The collimator was composed of two parallel plates perpendicular to both the detector surface and the plane of first scattering defined by the trajectories of the incoming and scattered photons. In this way photons with a larger interval of azimuthal angle but with the same scattering angle could reach the detector. Comparison between this collimation and the usual narrow one was performed at a photon energy of 59.54 keV under the same sample and irradiation geometry. The first results showed that, depending on the object composition, enhancement of about ten times could be leached with regard to the main Compton and coherent peaks. On the other hand, in the worst case, the multiple scattering fraction rose only till two times compared to that observed in the classical high collimation situation.

Molecular differential cross sections for the coherent scattering of x-rays in polymethyl methacrylate (PMMA) and fat were determined from measured diffraction patterns in the interval chi = 0 to 6.4 nm-1 (chi = [sin theta/2)]/lambda; lambda being the incident wavelength having the units of nm and theta the scattering angle). All measurements were performed at a controlled temperature of 23 degrees C. The final results for PMMA show overall agreement when compared with the data existing in the literature. However, some discrepancies with the results reported by Kosanetzky et al in 1987 are found at the first three maxima. The data for filtered fat material are reported here for the first time. Finally, data sets of molecular form factors for fat and PMMA were compiled from the smoothed corrected experimental results by assuming these materials to be mono-molecular.

The feasibility of evaluating absolute differential cross-sections of coherently scattered X-rays by exploiting diffraction pattern measurements has been tested in the case of plastic and biological samples. The investigation takes into account three powder diffractometers with different irradiation facilities. The main relevant correction factors have been evaluated by means of Monte Carlo and computational algorithm approaches. A careful evaluation of the effect of non-monochromatic incident photon beams allows this procedure to be valid without resorting to sophisticated irradiation facilities. Moreover, in comparing the experimental data with the theory, it is shown that some assumptions usually made when calculating theoretical scattering cross-sections are not valid when a scattering angle ranging from forward to backscattering values is to be considered. These results, together with other usual instrumental corrections, permit us to evaluate the differential scattering cross-sections within acceptable uncertainties.

Mass attenuation coefficients of 59.54 keV photons were measured in elements with atomic number ranging from low to high, and including lanthanides whose K-shell binding energies were close to those of incident photons. Comparison with the most reliable data from tabulations in current use reveals some disagreement in the interval of binding energy values close to 59.54 keV. The significant disagreement reported by other authors for certain elements was not confirmed by the present investigation.

The interface effects arising in the measurement of absorbed dose by ionization chambers, owing to the inhomogeneity between the walls and the gas, have been evaluated by an analytical model. The geometrical situation considered here is appropriate for representing the behaviour of a plane-parallel ionization chamber exposed to a radiotherapeutic beam of protons. Two gases, dry air and tissue equivalent gas (methane based), as well as six materials commonly used in ionization chamber walls, i.e. graphite, A-150 tissue equivalent plastic, C-522 air equivalent plastic, nylon type 6, polymethyl methacrylate and polystyrene, have been examined. The analysis of the results shows that, within the limits of the detector dimensions and proton energies commonly used in the dosimetry of radiotherapeutic beams, these effects, if not taken into account in the measurement interpretation, can entail deviations of up to about 2% with respect to the correct absorbed dose in gas.

In this work we present the preliminary results of an investigation in to the bone burden of lead in occupationally exposed subjects. The assessment of bone lead levels normalised to the mineral content (mg/kg bone mineral) were carried out by means of an in vivo X ray fluorescence techniques (Pb-XRF). The measurements were performed on the second phalanx of the right index finger and the minimum detectable limits of the XRF techniques was estimated around 25-30 mg/kg. Although the blood lead level monitoring over long time seems to indicate working activities in environments with low sources of lead contamination, high Pb-XRF levels, and not well correlated with the exposure time, were found. These anomalous values could be explained in term of the dependence of zinc protoporphyrin assessment against the measurement time.

In the present paper, we described a technique which is based on the shape of the Compton scattered peak on the high energy side rather than its intensity using low resolution detector. A radioactive source of Am-241 emitting 59.54 keV gamma rays is used to analyse the sample in the backscattering geometry with NaI(TI) detector. Due to poor resolution of the detector, it is impossible to resolve the Compton scattered peak from the Rayleigh peak, but the composite peak is still Z-dependent. Other distinctive features of this technique are the compactness of the system, axially symmetric geometry which allow the sample analysis even with weak radioactive sources, short measuring time, low absorbed dose and less costly with the use of NaI(TI) detector. A comparison is made between the results obtained with NaI(TI) detector and solid state detector.

Coherent scattering cross sections of 59.54-keV photons on target foils of Gd-64, Dy-66, Er-68, Yb-70, Hf-72, and Ta-73 at 60 degrees, 90 degrees, and 120 degrees have been measured to provide information on the region of K anomalous elastic scattering. The results are compared with the values calculated by the second perturbative order S matrix and by two procedures based on the form-factor approximation corrected by the anomalous scattering factors. Agreement of the S matrix values is very satisfactory, on the whole, and that of the values given by the form-factor approximations is fairly good.

The exploitation of the information that can be obtained from the energy analysis of Compton-scattered photons is discussed. It is shown that the use of the high-energy wing part of this energy distribution adds a further tool for EDXRS analysis other than the evaluation of the total fluence area of the Compton (or incoherent) distribution and the total fluence area of the Rayleigh (or coherent) peak. Special attention is paid to those situations for which easy and unambiguous coherent peak evaluation is prevented.