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Biomedical subjects

Z B Alfassi

Publications and source records attributed to Z B Alfassi.

At least 19 recordsLinked to original sources
PubMed2006

HPGe virtual point detector for radioactive disk sources.

Validity of the model of a virtual point detector (implying existence of a point where all interactions virtually occur) was confirmed for measurements of radioactive disk sources with HPGe detectors. The existing correlation of the count rates with the distance between the virtual plain detector and the detector face makes it possible to inter- and extrapolate calibration curves for disk radioactive sources for use at different source-detector face distances. The dependence of the distance between the virtual plane detector and the detector face on the photon energy was studied for sources of various radii.

Journal Article↗
PubMed2006

On neutron-gamma mixed field dosimetry with LiF:Mg,Ti at radiation protection dose levels.

The possibility of using the specific responses of the high temperature Peaks 6 and 7 and Peaks 4 and 5 to different LET radiations was mentioned in the past mainly for very high doses. The applicability of the two regions method for thermal neutrons--gamma ray mixed field dosimetry was investigated by analysing the response of LiF:Mg,Ti dosemeters irradiated to different ratios of thermal neutrons and gamma rays at radiation protection dose levels encountered in routine work conditions, up to approximately 50 mSv. The Region of Interest method was used to define the areas of the Peaks 4 + 5 and 6 + 7. We found that a simple algorithm can be used to determine with good accuracy the separate contributions of neutron and gamma doses.

Computer Simulation↗
PubMed2005

Optimisation study of alpha-cyclotron production of At-211/Po-211g for high-LET metabolic radiotherapy purposes.

The production of no-carrier-added (NCA) alpha-emitter (211)At/(211g)Po radionuclides for high-LET targeted radiotherapy and immunoradiotherapy, through the (209)Bi(alpha,2n) reaction, together with the required wet radiochemistry and radioanalytical quality controls carried out at LASA is described, through dedicated irradiation experiments at the MC-40 cyclotron of JRC-Ispra. The amount of both the gamma-emitter (210)At and its long half-lived alpha-emitting daughter (210)Po is optimised and minimised by appropriate choice of energy and energy loss of alpha particle beam. The measured excitation functions for production of the main radioisotopic impurity (210)At-->(210)Po are compared with theoretical predictions from model calculations performed at ENEA.

Astatine↗
PubMed2005

The dependence of the counting efficiency of Marinelli beakers for environmental samples on the density of the samples.

The effect of the density of the radioactive material packed in a Marinelli beaker on the counting efficiency was studied. It was found that for all densities (0.4-1.7 g/cm(3)) studied the counting efficiency (epsilon) fits the linear log-log dependence on the photon energy (E) above 200 keV, i.e. obeying the equation epsilon=alphaE(beta) (alpha, beta-parameters). It was found that for each photon energy the counting efficiency is linearly dependent on the density (rho) of the matrix. epsilon=a-brho (a, b-parameters). The parameters of the linear dependence are energy dependent (linear log-log dependence), leading to a final equation for the counting efficiency of Marinelli beaker involving both density of the matrix and the photon energy: epsilon=alpha(1) x Ebeta1 - alpha2Ebeta2rho.

Environmental Monitoring↗
PubMed2005

On the high-resolution gamma-ray spectrometric measurement of 40K in natural and synthetic materials.

Many regulatory agencies require that all building materials and industrial waste be tested for their naturally occurring radioactive material (NORM) concentrations before they can be used or thrown away. Usually the NORM concentrations of 40K, 232Th and 238U are measured by gamma-ray spectrometry using high-purity germanium or NaI(Tl) detectors. 40K is measured through its 1460.8 keV gamma line, which is mixed with 1459.2 keV line of 228Ac from the chain of 232Th. This fact ignored till now, requires a correction in the computation of 40K concentration. Although in many cases the error is <1%, there are cases where there have been higher errors. It should be emphasised that even if the correction in 40K concentration is large, the correction of the external dose index is negligible owing to the weighing factor being higher for 232Th than for 40K (by at least a factor of 10).

Gamma Rays↗
PubMed2004

Development and application of Marinelli beaker standards for monitoring radioactivity in Dairy-Products by gamma-ray spectrometry.

Marinelli (reentrant) beakers are recommended for measurement of low-activity radioactive environmental samples, in both liquid and solid phase. The preparation of Marinelli beaker standards of milk powder containing 232ThO2 at secular equilibrium with its daughter radionuclides was studied. Standards were prepared by mixing of known amounts of solid ThO2 and milk powder. The densities of the standards were 0.5-0.7 kg dm(-3). Measurements of calibrated Marinelli beaker standards with HPGe detector showed that the energy dependence of the efficiency is similar to that of a point source, i.e. an almost linear dependence of log-efficiency vs. log-energy in the 200-2000 keV range, however the parabolic correlation fits better. The validity of these standards was checked by comparison with certified standard reference material IAEA-152-Milk powder containing radiocesium and radiopotassium. The results obtained were found to be in a good agreement with the published certified data. The limit of detection for the determination of radiocesium by gamma ray spectrometry under the prevailing experimental conditions is 0.03 Bq (i.e. 0.8 pCi), for samples of dairy products having lower densities of 0.7 kg dm(-1).

Dairy Products↗
PubMed2004

On fading corrections for LiF:Mg,Ti irradiated by thermal neutrons.

The phenomena of preirradiation and postirradiation fading of LiF:Mg,Ti phosphors are considered a significant practical problem in routine dosimetry because of the uncertainties introduced, especially for mixed neutron-gamma dosimetry, as different fading corrections may be necessary for the gamma and neutron contributions. We have investigated if the region of interest (ROI) method is applicable to minimizing the fading effect for thermal neutron irradiation as it is for gamma irradiation. By employing the ROI method, which consists of integration between channel 31 below the glow curve maximum and channel 16 above the glow curve maximum, a constant dose value was obtained for the period of 90 d. Thus, by employing the ROI method, a fading independent evaluation of the thermal neutron dose can be made.

Algorithms↗
PubMed2004

Improved neutron detection by gamma-ray spectroscopy.

Most high-efficiency interactions for neutron detection are with thermal neutrons, and the detection of the prompt gamma radiation emitted as a result of thermal neutron absorption in specific materials was sometimes used. These materials are named converters, the most widespread being 10B, 113Cd or 73Ge (the last two materials are detector materials themselves for CdZnTe and HPGe detectors). However, for these materials, the main gamma-ray energies are relatively low (in the region 473-600 keV), and there are interferences from other gamma rays present in background. Different combinations of moderator-converter-detector systems were employed to optimise the system efficiency and signal-to-background ratio, using B, Cd, Gd and Cl converters and HPGe, NaI(Tl) and BGO detectors. When using a Cl converter, the 1164.7 keV peak seems to be a good choice when a HPGe spectrometer is used. A very practical material containing chlorine is PVC.

Environmental Exposure↗
PubMed2003

Electrospray ionization mass spectrometry of ionic liquids and determination of their solubility in water.

Electrospray ionization mass spectrometry is used to detect both the cations (C+) and the anions (A-) of ionic liquids (CA). In this study, the ionic liquids are diluted with aqueous methanol before injection. In addition to the main peaks of the parent ions, fragmentation products are observed upon increasing the cone voltage, whereas aggregates of the parent ion with one or more ionic liquid molecules (e.g., C(CA)(n)(+), A(CA)(n)(-)) are observed upon decreasing the cone voltage. The ions of several ionic liquids in a mixture are also detected and the ratios of their concentrations estimated. A method is developed to determine quantitatively the concentration of an ionic liquid in solution by using the cation and anion of another ionic liquid as internal standards. By using this method, the solubilities in water at room temperature (22+/-1 degrees C) of three typical hydrophobic ionic liquids have been determined: 0.70+/-0.08 g L(-1) for methyltributylammonium bis(trifluoromethylsulfonyl)imide (MeBu(3)NNTf(2)), 6.0+/-0.5 g L(-1) for butylmethylpyrrolidinium bis(trifluoromethylsulfonyl)imide (BuMePyrNTf(2)), and 18.6+/-0.7 g L(-1) for 1-butyl-3-methylimidazolium hexafluorophosphate (BMIPF(6)).

Journal Article↗
PubMed2003

On the determination of the post-irradiation time from the glow curve of TLD-100.

The ratio of peak 3 to the sum of peaks 4 + 5 in TLD-100 was measured for various pre-irradiation and post-irradiation time periods, under conditions characteristic of routine personal dosimetry. It was confirmed that the value of this ratio depends only on the elapsed time between the prior readout and the present one, independent of the moment when the irradiation took place during the total time interval (storage time). This effect indicates that fading of peak 3 seems to be due mainly to changes in the unoccupied traps, and not to decay of trapped charges, being almost independent of the presence of electrons or holes in the traps. This observation leads to the conclusion that the suggestions in the past to use the decay of peak 3 in TLD-100 for the measurement of the elapsed time between irradiation and readout may have been wrong. On the other hand, the decay of peak 2 can be used to measure the elapsed time from irradiation, since the rate of decay is different when related to pre-irradiation and post-irradiation times, indicating a much higher decay rate of the trapped charges (Randall-Wilkins decay). However, because of the fast decay rate of peak 2, its use for determination of the elapsed time since irradiation is of little practical significance.

Equipment Failure Analysis↗
PubMed2001

Platinum concentrations in Danish air samples determined by instrumental neutron activation analysis.

Platinum, gold and calcium concentrations of 20 samples of airborne dust collected at two sampling sites between 1995 and 1997 in the city of Copenhagen, which suffers from heavy traffic, were determined by instrumental neutron activation analysis (INAA). INAA of platinum using the 199Au daughter of 199Pt was performed. Two interferences on the INAA of platinum were removed by calculations. The spectral interference on 199Au from the 47Sc daughter of 47Ca was removed by separating the 157-161 keV doublet peak into its components by calculating the counts due to 47Sc from the counts of the parent 47Ca. The contribution of 197Au to 199Au by two neutron absorption was corrected for using the ratio 198Au/199Au in a pure Au standard. From the INAA results, high platinum concentrations are present in air in the range 0.25-2.74 ng m-3 and gold concentrations in the range 0.10-1.96 ng m-3.

Air Pollution↗
PubMed1994

Determination of aluminium by instrumental neutron activation analysis in biological samples with special reference to NBS SRM 1577 bovine liver.

It was found that a well thermalized heavy water-moderated research reactor can be used to determine the Al content of biological samples without separation of P, Na and Cl. The contribution of the 31P(n,alpha)28Al reaction was corrected from the known concentration of P and the measured effective value. It was found that the contribution is only about 10%. A method is suggested for the determination of Al using instrumental neutron activation analysis.

Aluminum↗
PubMed1991

Long range electron transfer between tyrosine and tryptophan in hen egg-white lysozyme.

The azide, dibromide and dichloride radicals oxidize one or more tryptophan side chains in hen egg-white lysozyme. The indolyl radical produced in this second-order 1-electron oxidation subsequently oxidizes a tyrosine side chain to the phenoxy radical in an intramolecular reaction with a rate constant of 130 +/- 10 s-1 at pH 7, 25 degrees C. The final indolyl and phenoxy equilibrium mixture then decays with a t1/2 approximately 2 s. The faster intramolecular reaction exhibits a pH dependence; on decreasing the pH from 9 the first-order rate constant increases to a maximum near pH 5.4 and then declines as the pH is lowered further. In contrast, the first-order rate constant for the intramolecular electron transfer between the tyrosine and tryptophan of the peptide trpH-pro-tyrOH remains unchanged between approx. pH 11 and 6.5 and then increases as the pH is lowered further. This difference in the observed pH dependence suggests that changes in structure or ionization state influence the protein electron transfer rate. We also discuss the radiation inactivation of lysozyme in light of these observations.

Animals↗
PubMed1990

Determination of trace amounts of cadmium, cobalt, chromium, iron, molybdenum, nickel, selenium, titanium, vanadium and zinc in blood and milk by neutron activation analysis.

The concentrations of Cd, Co, Cr, Fe, Mo, Ni, Se, Ti, V and Zn in biological fluids, human blood serum and market milk were determined by neutron activation analysis, with enrichment by coprecipitation. The pre-concentration of these trace elements was accomplished by converting the dissolved trace metal ions into their pyrrolidinedithiocarbamate (1-pyrrolidinecarbodithioate) chelates, followed by coprecipitation with a metal carrier such as Ni, Pb or Bi. The coprecipitation was carried out prior to irradiation for the short-lived nuclides (V, Ti and Se) and after irradiation for the other elements. The validity of the method was checked using certified biological reference materials; the concentrations of trace elements found by the proposed method agreed well with the published certified data. The limits of detection for Cd, Co, Cr, Fe, Mo, Ni, Se (obtained through the long-lived isotope 75Se) and Zn under the present experimental conditions were found to be 5, 5, 10, 520, 5, 70, 10 and 150 ng, respectively, for 5 ml of biological liquor. The limits of detection for Ti and V obtained (through their short-lived radionuclides 51Ti and 52V, respectively) were found to be 180 and 1.4 ng, respectively, for 50 ml of market milk, or 70 and 0.7 ng for 1 ml of blood serum.

Animals↗