C. Potiriadis

Environmental radioactivity measurements in Greece following the Fukushima Daichi nuclear accident

Since the double disaster of the 9.0 magnitude earthquake and tsunami that affected hundreds of thousands of people and seriously damaged the Fukushima Daichi power plant in Japan on 11 March 2011, traces of radioactive emissions from Fukushima have spread across the entire northern hemisphere. The radioactive isotope of iodine (131)I that was generated by the nuclear accident in Fukushima arrived in Greece on 24 March 2011. Radioactive iodine is present in the air either as gas or bound to particles (aerosols). The maximum (131)I concentrations were measured between 3 and 5 April 2011. In aerosols the maximum (131)I values measured in Southern Greece (Athens) and Northern Greece (Thessaloniki) were 585±70 and 408±61 μΒq m(-3), respectively. (131)I concentrations in gas were about 3.5 times higher than in aerosols. Since 29 April 2011, the (131)I concentration has been below detection limits. Traces of (137)Cs and (134)Cs were also measured in the air filters with an activity ratio of (137)Cs/(134)Cs equal to 1 and (131)I/(137)Cs activity ratio of about 3. Since 16 May 2011, the (137)Cs concentration in air has been determined to be about the same as before the Fukushima accident. Traces of (131)I were also measured in grass and milk. The maximum measured activity of (131)I in sheep milk was about 2 Bq l(-1) which is 5000 times less than that measured in Greece immediately after the Chernobyl accident. The measured activity concentrations of artificial radionuclides in Greece due to the Fukushima release, have been very low, with no impact on human health.

Sputtering rates and nanoscale cluster production in a hollow-cathode apparatus

Abstract By combining a hollow-cathode plasma sputter device with the gas aggregation technique, an intense source of nanoscale metal clusters has been developed. Net sputtering rates have been measured as a function of pressure, flow velocity, electric current and cathode geometry, and in most instances they were found to behave differently than their planar-electrode sputtering counterparts. Deposition rates on substrates located away from the hot plasma region have been also measured. Clusters of Cu, Ag, Au and Ta have been produced and their size has been determined via XRD and TEM. The size of Cun clusters is found to increase with the sputter source discharge current.

Gamma spectroscopic measurements using the PID350 pixelated CdTe radiation detector

Spectroscopic measurements are presented using the PID350 pixelated gamma radiation detectors. A high-speed data acquisition system has been developed in order to reduce the data loss during the data reading in case of a high flux of photons. A data analysis framework has been developed in order to improve the resolution of the acquired energy spectra, using specific calibration parameters for each PID350s pixel. Three PID350 detectors have been used to construct a stacked prototype system and spectroscopic measurements have been performed in order to test the ability of the prototype to localize radioactive sources.

Experimental and theoretical study of the ratio between the electron emission yield and the electronic stopping power for protons incident on thin carbon foils

Abstract It is often assumed that the kinetic electron emission yield γ is proportional to the electronic stopping power dE/dx for ions incident on solid targets. Though these two phenomena are based on the same physical process in which the incident ions lose their energy in the target in electron excitations, there is no reason why the ratio Λ=γ/(dE/dx) should be constant. We present in this paper a comparison between experimental and theoretical results for protons incident on thin carbon foils in a wide energy range (200 keV–9.2 MeV). The ratios ΛB=γB/(dE/dx) and ΛF=γF/(dE/dx) for both the backward (B) and forward (F) emission yields are studied as a function of the incident proton energy as well as the target thickness.

PIXE ANALYSIS OF ANCIENT GREEK COPPER COINS MINTED IN EPIRUS, ILLYRIA, MACEDONIA AND THESSALY

Abstract Ancient copper coins from Greek cities and confederacies such as Amphipolis, Veroia, Dion, Edessa, Magnetes, Stobi, Apollonia, Kerkyra, Pella, Philippoi, Phoenike, and the Macedonian and Thessalian Koina, were analyzed non-destructively by proton induced X-ray emission (PIXE) after removal of the patina. The copper coins were minted during Roman Imperial times (31 b.c. –268 a.d. ). Eleven elements were determined quantitatively. The correlation between the composition and the minting time is examined. The results are compared with those of a previous study for coins from the cities of Nikopolis in Epirus and Thessaloniki in Macedonia, in the same period.

3-D localization of gamma ray sources with coded apertures for medical applications

Several small gamma cameras for radioguided surgery using CdTe or CdZnTe have parallel or pinhole collimators. Coded aperture imaging is a well-known method for gamma ray source directional identification, applied in astrophysics mainly. The increase in efficiency due to the substitution of the collimators by the coded masks renders the method attractive for gamma probes used in radioguided surgery. We have constructed and operationally verified a setup consisting of two CdTe gamma cameras with Modified Uniform Redundant Array (MURA) coded aperture masks of rank 7 and 19 and a video camera. The 3-D position of point-like radioactive sources is estimated via triangulation using decoded images acquired by the gamma cameras. We have also developed code for both fast and detailed simulations and we have verified the agreement between experimental results and simulations. In this paper we present a simulation study for the spatial localization of two point sources using coded aperture masks with rank 7 and 19.

Assessment of the occupational exposure at a fertiliser industry in the northern part of Greece.

In the northern part of Greece, close to the city of Kavala, a phosphoric acid production industry has operated since 1965. The raw material used is the phosphate rock imported from the foreign countries. During industrial processes, naturally occurring radioactive materials (NORM) deposits exist in many facilities in the industry, causing increased levels of radiation exposure. Additionally, increased levels of NORM concentrations are also detected in the waste material of the production process, the phosphogypsum. According to the Greek Regulations for Radiation Protection (no. 216B, 5/3/2001), which is in accordance with the 96/29/EURATOM 31/5/1996, the action levels concerning the effective dose to workers at workplaces due to natural radiation sources are 1 mSv y(-1). Work activities where the corresponding doses exceed 6 mSv y(-1) are under the control of the Greek Atomic Energy Commission (GAEC). The mean yearly radon concentration action level at workplaces is 400 Bq m(-3), while the corresponding concentration limit is 3000 Bq m(-3), respectively. GAEC, according to its constitutional law, is the responsible organisation to enforce and to implement the law by means of in situ surveys and laboratory measurements. The first inspection of the area was performed in 2002 and the first measures were proposed. Periodic inspections were performed every 2 y in order to extend the operation licensing of the industry. In this work a dose assessment of the workers based on in situ and laboratory measurements is presented. In order to assess the doses to the workers the external and the internal doses are estimated.

Electronic sputtering by swift highly charged ions of nitrogen on amorphous carbon

Abstract Electronic sputtering with heavy ions as a function of both electronic energy loss d E /d x and projectile charge state q was studied at the French heavy ion accelerator GANIL. Amorphous carbon (untreated, and sputter-cleaned and subsequently exposed to nitrogen) was irradiated with swift highly charged ions ( Z =6–73, q =6–54, energy 6–13 MeV/u) in an ultrahigh vacuum scattering chamber. The fluence dependence of ion-induced electron yields allows to deduce a desorption cross-section σ which varies approximately as σ ∼(d E /d x ) 1.65 or σ ∼ q 3.3 for sputter-cleaned amorphous carbon exposed to nitrogen. This q dependence is close to the cubic charge dependence observed for the emission of H + secondary ions which are believed to be emitted from the very surface. However, the power law σ ∼(d E /d x ) 1.65 , related to the electronic energy loss gives the best empirical description. The dependence on d E /d x is close to a quadratic one thus rather pointing towards a thermal evaporation-like effect.

Decommissioning a phosphoric acid production plant: a radiological protection case study

During a preliminary survey at the area of an abandoned fertilizer plant, increased levels of radioactivity were measured at places, buildings, constructions and materials. The extent of the contamination was determined and the affected areas were characterized as controlled areas. After the quantitative and qualitative determination of the contaminated materials, the decontamination was planned and performed step by step: the contaminated materials were categorized according to their physical characteristics (scrap metals, plastic pipes, scales and residues, building materials, etc) and according to their level of radioactivity. Depending on the material type, different decontamination and disposal options were proposed; the most appropriate technique was chosen taking into account apart from technical issues, the legal framework, radiation protection issues, the opinion of the local authorities involved as well as the owners wish. After taking away the biggest amount of the contaminated materials, an iterative process consisting of surveys and decontamination actions was performed in order to remove the residual traces of contamination from the area. During the final survey, no residual surface contamination was detected; some sparsely distributed low level contaminated materials deeply immersed into the soil were found and removed.

Simulation studies and spectroscopic measurements of a position sensitive detector based on pixelated CdTe crystals

Simulation studies and spectroscopic measurements are presented regarding the development of a pixel multilayer CdTe detector under development in the context of the COCAE project. The instrument will be used for the localization and identification of radioactive sources and radioactively contaminated spots. For the localization task the Compton effect is exploited. The detector response under different radiation fields as well as the overall efficiency of the detector has been evaluated. Spectroscopic measurements have been performed to evaluate the energy resolution of the detector. The efficiency of the event reconstruction has been studied in a wide range of initial photon energies by exploiting the detectors angular resolution measure distribution. Furthermore, the ability of the COCAE detector to localize radioactive sources has been investigated.