E. Okuno

How safe is ERCP to the endoscopist

AbstractBackground: Interventional techniques in endoscopy such as endoscopic retrograde cholangiopancreatography (ERCP) have greatly increased since laparoscopic cholecystectomy has become widespread; mainly these techniques deal with common bile duct stones. Fluoroscopy is usually employed, and chronic exposure to X-ray, in spite of the relative low dose, can lead to potentially unhealthy conditions such as malignancies like bone marrow and other solid cancers. A median of 18 years of life is lost per fatal cancer, including the time of latency since exposure. Nor should one forget benign condition such as cataracts that can lead to partial or complete blindness and which surely impair lifes quality. Methods: Simulated examinations were carried at the University Hospital (São Paulo, Brazil) using an anthropomorphic phantom in place of the physician. Four sets of dosimeters were placed in the forehead, neck, torso, and lower abdomen (with and without a lead apron) and standard ERCP fluoroscopic techniques were employed. Results: The dose equivalents were calculated and compared to the recommended exposure doses of national and international boards of radiation protection. Conclusions: Based on the results found and compared to standards, working safely means: (1) A lead (0.5 mm thickness) apron is fundamental. Without it less than one ERCP\/month should be performed. (2) With an apron, 23 examinations/month are allowed. (3) No thyroid protection grants only 19 exams/month. (4) Performing ERCP without lead glasses is hazardous to the eye, allowing only seven ERCPs monthly.

X-ray transmission through nanostructured and microstructured CuO materials.

This study presents a comparison of the X-ray transmission through microsized and nanosized materials. For this purpose CuO nanoparticles, with 13.4 nm average grain size, and CuO microparticles, with a mean particle size of 56 μm, were incorporated separately to beeswax in a concentration of 5%. Results show that the transmission through the above material plates with microsized and nanosized CuO was almost the same for X-ray beams generated at 60 and 102 kV tube voltages. However, for the radiation beams generated at 26 and 30 kV tube voltages the X-rays are more attenuated by the nanostructured CuO plates by a factor of at least 14%. Results suggest that the difference in the low energy range may be due to the higher number of particles/gram in the plates designed with CuO nanoparticles and due to the grain size effect on the X-ray transmission.

Effects of the particle sizes and concentrations on the X-ray absorption by CuO compounds

This work presents a study on the effects of the particle size, material concentration and radiation energy on the X-ray absorption. CuO nanoparticles and microparticles were incorporated separately into a polymeric resin in concentrations of 5%, 10% and 30% relative to the resin mass. X-ray absorption by these materials was analyzed with a CdTe detector. The X-ray absorption is higher for the nanostructured material compared to the microstructured one for low energy X-ray beams for all CuO concentrations.

Supralinearity and sensitization of thermoluminescence. I. A theoretical treatment based on an interactive trap system

A theoretical treatment is presented for the supralinearity of thermoluminescence glow peaks. The model assumes part of the thermoluminescence trap population as interactive with the thermally disconnected deep traps. These traps produce supralinear growth of the thermoluminescence response. The initial linear part of the response curve is assumed to be produced by the non-interactive part of the thermoluminescence trap population. The treatment enables determination of the relative concentration of deep traps. Resolution of the observed response curve into linear and supralinear parts allows determination of the relative trap populations responsible for producing the linear and supralinear parts of the response. We have also shown the procedure for determining the trap filling constant using the growth profile of the thermoluminescence glow peak of pre-dose sensitized samples. Apart from interpreting the linear and supralinear behaviour of the thermoluminescence response, the treatment provides a quantitative explanation for the pre-dose sensitization effect.

Supralinearity and sensitization factors in thermoluminescence

Abstract Supralinearity and pre-dose sensitization are two characteristics of thermoluminescence (TL) glow peaks which are seen together in many of the TL phosphors. In this paper, theoretical expressions are derived for the supralinearity and pre-dose sensitization factors, based on the interactive trap system model. A new term called sensitization factor ( S n F ) is introduced, which differs from the pre-dose sensitization factor ( PDSF ) but is related directly to the supralinearity factor ( SF ). The factors SF and S n F coincide in the low and medium dose range. At high doses the latter departs considerably from the former. The case of LiF TLD-100 is used to demonstrate the application of the theory to actual experimental results.

Supralinearity and sensitization of thermoluminescence. II. Interactive trap system model applied to LiF:Mg,Ti

For Part I see ibid., vol.27, pp.852-60 (1994). A theoretical treatment based on a partly interactive trap system (PITS) described in Part I is applied to peak 5 of LiF:Mg,Ti. The model assumes two types of thermoluminescence traps for the given glow peak: (i) those which produce a linear response with dose and (ii) those which produce a supralinear response. The former are spatially associated with the luminescent recombination centres. The latter are randomly distributed and the carriers released from them during readout heating may be recaptured by the thermally disconnected deeper traps non-radiatively in addition to undergoing recombination to produce luminescence. The trap filling constant, defined as the fraction of traps filled per unit dose, is determined using the intensity growth profile of the related optical absorption band and that of the thermoluminescence of pre-dose sensitized sample. The value of this constant is 1.16*10-3 Gy-1 for peak 5. For peak 12 it is an order of magnitude lower. Fractions of the thermoluminescence trap population responsible for linear and supralinear parts of the response are determined using pre-dose sensitization. The ratio of these two populations is calculated to be 1:13. A method is suggested to determine the relative concentration of the deep traps with respect to the shallower thermoluminescence traps. This estimation is carried out by separating the supralinear part of the response curve and calculating its under response factor at low doses. The relative concentration of deep traps is seen to be dependent on the relative coefficients for trapping and recombination. The calculated parameters are backfitted into the theoretical expression and the response profile so obtained is compared with the experimental response curve. The two are found to be in good agreement.

Some effects of γ-irradiation in soda-lime silicate glasses

Abstract Nanosized metallic silver particles have been formed in multicomponent commercial soda-lime silicate glasses partly substituted with ionic silver and irradiated at room temperature by γ-rays from a 60Co-source (1.33 MeV). To characterize the obtained composites, combined measurements of thermally stimulated depolarization current and optical absorption, accompanied by microspectrophotometric analysis and electron microscopy observations have been used. It has been shown that γ-irradiation might be an effective means to modify and control the concentration, size and spatial distribution of the dopant within the near-surface layer of the glass-matrix. This procedure also allows the conversion of some glassy areas in this region into a partially crystalline material with improved mechanical characteristics.

Radioactivity teaching: Environmental consequences of the radiological accident in Goiânia (Brazil)

Ionizing radiation and its effects on human beings, radiation protection, and radiological accident prevention are topics usually not included in the physics courses at the Brazilian universities. As a consequence, high school teachers are not able to enlighten their students when radiological or nuclear accidents occur. This paper presents a teaching program on ionizing radiation physics, to be applied to undergraduate physics students and to physics high school teachers. It is based on the environmental consequences of the 1987 radiological accident in Goiânia. This program was applied to two undergraduate physics students, in 1999, at the Universidade Federal Fluminense, Brazil. Results of the gamma ray spectrometry measurements of samples collected in Goiânia by the students are presented.

FORMATION OF SILVER COLLOIDS ON ION EXCHANGED SODA LIME SILICATE GLASSES BY IRRADIATION

Abstract The effect of ionizing radiation (gamma rays, X-rays and electrons) on soda lime silicate glasses, in which part of the Na+ was substituted by Ag+ by means of an ionic exchange process, was studied. The techniques of thermally stimulated depolarization current (TSDC) and transmission electron microscopy (TEM) were employed to follow the formation of silver colloids by irradiation. Also the thermoluminescence (TL) of the samples was measured and three peaks between room temperature and 450°C were observed. The TEM and TSDC results agree that, as expected, ionizing radiation promotes the formation of silver colloids on the ion exchanged surface of soda lime glasses. Soft X-rays are much more efficient in the process than gamma rays and electrons. The correlation with thermoluminescence glow curves indicates that the intensity of a TL peak at 230°C can provide a rapid means of evaluating the presence of silver colloids. TL sensitivities, measured as area under the glow curve per unit mass and unit dose, are very similar for ion exchanged and not exchanged samples submitted to X-ray irradiation, although the peak temperatures differ in about 40°C in the two cases. For both electron and gamma irradiated samples, the TL sensitivity drops about an order of magnitude when compared to the X-ray irradiated ones.

Paramagnetic radiation-induced defects in gamma-irradiated natural topazes

Abstract Gamma-radiation-induced defects in natural topazes were investigated using EPR spectroscopy in the X-band frequency (9.72 GHz). The most intense EPR lines were identified as due to paramagnetic impurities Fe3+, Ti3+ and complexes (PO4)0 and (AlO4)0. The growth of the EPR lines with 60 Co gamma-ray doses up to 5 kGy and the thermal stability of these lines in the range between 100–600 °C were studied. The results suggest that the hole center (AlO4)0 and the electron centers Ti3+ and (PO4)0 are involved in the recombination process which occurs around 200 °C and is responsible for the destruction of the brown color and for the thermoluminescent emission in this temperature region. The (AlO4)0 most probably acts as a recombination center, while the Ti3+ and (PO4)0 centers act as traps.