A methodology for expanding the use of NaI(Tl) based spectrometry in environmental radioactivity measurements.

A methodology that extends the usability of low and medium resolution γ-ray detectors to a wide range of energies that appear in environmental radioactivity measurements is described. Results of the implementation of the methodology in the analysis of 20 granite samples measured with a (3″ × 3″) NaI(Tl) are presented. A comparison with the activity results obtained by a high-resolution detector (HPGe) for two samples was found in good agreement, within the uncertainties, validating the results of the proposed method.

(137)Cs vertical distribution at the deep basins of the North and Central Aegean Sea, Greece.

Large volume seawater samples were collected for the determination of (137)Cs concentration along with depth in the deep basins of North and Central Aegean Sea. The vertical (137)Cs distribution showed maximum concentration at the bottom of the basins, while the minimum values corresponded to the intermediate layer, where Levantine water exists. The surface (137)Cs activity is found to lie between the two limits and is originated from the Black Sea waters. The typical oceanographic advection-diffusion balance model is modified to a diffusion-settling-decay balance model to better understand the vertical distribution and variation of the (137)Cs concentration in the deep basins. In addition, the diffusivity of each basin, as well as the settling speed of particulate (137)Cs is also estimated. The results are compared with theoretical approach as well as with previous data.

Radioactivity measurements in the aquatic environment using in-situ and laboratory gamma-ray spectrometry.

The in-situ underwater gamma-ray spectrometry method is validated by inter-comparison with laboratory method. Deployments of the spectrometer KATERINA on a submarine spring and laboratory measurements of water samples with HPGe detector were performed. Efficiency calibrations, Monte Carlo simulations and the Minimum Detectable Activity (MDA) estimations were realized. MDAs varied from 0.19 to 10.4 (lab) and 0.05 to 0.35 (in-situ) Bq/L, while activity concentrations differed from 7% (for radon progenies) up to 10% (for (40)K), between the two methods.

Radioactivity levels of recent sediments in the Butrint Lagoon and the adjacent coast of Albania.

Sediment samples have been collected in the Butrint area, located in the south-west Albania to determine the radioactivity levels of (40)K, (137)Cs, (212)Bi, (212)Pb, (214)Bi, (214)Pb, (226)Ra and (228)Ac on the bed of the lagoon and adjacent sea, using direct counting gamma spectroscopy. The concentration of (137)Cs and (40)K varied from 2.8 to 37.5 Bq/kg and from 266 to 675 Bq/kg dry weight (dw), respectively (central values). The average concentrations of (238)U and (232)Th daughter products varied from 8 to 27 Bq/kg and from 13 to 40 Bq/kg dw, respectively. The measured (235)U activity ranged from 0.7 to 2.5 Bq/kg dw. Samples of different sedimentary properties, studied for the radioactivity concentration, revealed an inversely proportional relation between grain size and a linear combination of measured specific activities of (226)Ra, (232)Th ((228)Ac, (212)Bi and (212)Pb), (40)K and (137)Cs.

Conformational properties of DNA after exposure to gamma rays and neutrons.

DNA aqueous solutions were irradiated with 0-40 Gy of 60Co gamma rays and 0-1.5 Gy of (Pu-Be) neutrons. Thermal transition spectrophotometry (TTS) was used to trace the changes in the DNA conformation at the above doses. Previous results using the perturbed angular correlation (PAC) method were used to complement to the current analysis. The TTS and PAC methods are two different approaches to the study of the effects of radiation on DNA. Both showed that neutrons are more effective than gamma rays in inducing DNA damage. The TTS method showed that neutrons are 11 +/- 5 times more efficient than gamma rays, while the PAC method had shown this value to be 34 +/- 4. From the current study we deduced that the radiation damage to DNA is not a spontaneous effect but rather is an ensemble of damaging events that occur asynchronously. Any single method selected for the study of such damages can concentrate on only a part of the damage, leading to over- or underestimation of the relative effectiveness of the neutrons.

Changes in DNA flexibility after irradiation with gamma rays and neutrons studied with the perturbed angular correlation method.

Neutron and gamma irradiation of buffered solutions of calf thymus DNA resulted in changes in the dynamics of the macromolecule. In the low-dose region (0.8-10 cGy of 239Pu-Be neutrons and 0.34-3 Gy of 60Co gamma rays), the flexibility of DNA decreased as indicated by slower rotation of the molecules. Neutrons appeared to be approximately 35 times more effective than 60Co gamma rays. The rotational correlation time, tau C, was measured using the perturbed angular correlation (PAC) method. Its variation appears to follow a linear-exponential behavior. An attempt is made to formulate this behavior as a function of the energy deposited on the macromolecule (radiation dose), the average threshold energy (dose) required to form new lesions, and the available population of intact DNA sites.

Radiosensitivity of V79 cells after alpha particle radiation at low doses.

Low dose hyper-radiosensitivity (HRS) of V79 cells was demonstrated after irradiation with gamma rays and 4He2+ ions of various linear energy transfer (LET) values (58.9, 79.3 and 101.7 keV.micron-1). In parallel, the cytogenetic analysis showed an LET dependence of aberrations at a dose of 1 Gy, while the observed chromatid fragments appeared to vary with the number of 4He2+ ions traversing the cell nucleus. The results of both studies are correlated so as to achieve a better understanding of the so-called induced radioresistance. The cell mechanism of radioresistance appears to be induced after a certain amount of energy is deposited in the cell nucleus. This amount depends both on the radiation quality as well as the number of particles traversing the cell, inducing chromosome alterations and chromatid damage.

Coulomb energy differences in t = 1 mirror rotational bands in (50)Fe and (50)Cr.

Gamma rays from the N = Z-2 nucleus (50)Fe have been observed, establishing the rotational ground state band up to the state J(pi) = 11+ at 6.994 MeV excitation energy. The experimental Coulomb energy differences, obtained by comparison with the isobaric analog states in its mirror (50)Cr, confirm the qualitative interpretation of the backbending patterns in terms of successive alignments of proton and neutron pairs. A quantitative agreement with experiment has been achieved by exact shell model calculations, incorporating the differences in radii along the yrast bands, and properly renormalizing the Coulomb matrix elements in the pf model space.

Low-dose hypersensitivity of V79 cells under exposure to gamma-rays and 4He ions of different energies: survival and chromosome aberrations.

PURPOSE: To examine the low-dose sensitivity of V79 cells under exposure to gamma-rays and 4He ions of different energies. MATERIALS AND METHODS: Cell survival and cytogenetic analysis using the Giemsa technique were studied following irradiation to doses of 0-3 Gy at the INFN-LNL facilities. RESULTS: Low-dose hyper-radiosensitivity (HRS) of V79 was demonstrated after irradiation with gamma-rays and alpha-particles of various linear energy transfers (LET) (58.9, 79.3 and 101.7 keV microm(-1)). Cytogenetic analysis showed an LET dependence of aberrations at a dose of 1Gy; the frequency of chromatid fragments appeared to vary with the number of alpha-particles traversing the cell nucleus. The results of both studies fit together to give a better understanding of so-called 'induced radioresistance' phenomenon. CONCLUSIONS: The mechanism of induced cellular radioresistance appears to be initiated after a certain amount of energy is deposited in the cell nucleus. This amount depends on both radiation quality and the number of particles traversing the cell.

Probing irradiated DNA with the perturbed angular correlation method.

The technique of perturbed angular correlations of gamma rays has been used to study the effects of radiation on DNA molecules. The samples are buffered solutions of calf thymus DNA exposed to various doses (0-80 Gy) of gamma rays. Indium-111 is used as a probe. Rotational correlation times, tau(c), a parameter measuring the flexibility of a macromolecule, are obtained that show a dependence on radiation dose.

Low doses of alpha- and gamma-radiation enhance DNA thermal stability.

Isolated calf thymus DNA in buffered solutions has been exposed to 0-150 Gy of alpha- and gamma-radiation. The effects of alpha- and gamma-radiation on the thermal stability and electrophoretic mobility of the DNA molecules have been studied by UV spectroscopic 'melting' and Pulsed Field Gel Electrophoresis (PFGE), respectively. The observed thermal denaturation parameters were fitted to the energy propagation descriptive model. The experimental results for the samples exposed to relatively low (low) doses indicate an increased thermal stability and a reduced mobility over that of the controls. The expected overall degradation of the DNA molecules was confirmed for the samples exposed to high doses. Our results are in good agreement with the predictions of the energy propagation model, which now is also tested in the low dose region and for an additional type of ionising radiation (alpha-particles). Our findings are consistent with conformational changes at low doses resulting in a DNA form characterised by localised alterations, which affect the energy flow along the DNA molecule.

Perturbed gamma-gamma angular correlation studies of 111In bound to double and single stranded DNA.

Using 111In as a probe, the dynamics of double and single stranded DNA have been studied by performing time-differential gamma-gamma angular correlation measurements on the 173-247 keV transitions in 111Cd. Binding of indium to DNA was investigated by analysis of sedimentation profiles, thermal transition spectrophotometry and electrochromatography. Rotational correlation times tau c greater than or equal to 400 ns and tau c = 27 +/- 7 ns were obtained respectively for double stranded (native) and single stranded (denatured) DNA. The corresponding quadrupole interaction frequencies were omega 0 = 711 +/- 15 Mrad/s and omega 0 = 151 +/- 13 Mrad/s.