Thermoluminescence kinetic analysis of basaltic rocks using a generalized model for exponential distribution of activation energies

A new general order Thermoluminescence (TL) model for exponential distribution of activation energies has been presented. In the proposed model an effective kinetic-order has been introduced as an additional adjustable parameter. This makes it possible to take the re-trapping into account and would give a better estimate of the activation energy compared with the first order kinetics model. The proposed model has been applied to the basaltic rocks from central zone of Iran. The obtained results show that the proposed model gives a better fit to the experimental peaks compared to the first order model.     

Development of a non-destructive micro-analytical method for stable carbon isotope analysis of transmission electron microscope (TEM) samples

The biogenicity of ancient morphological microfossil-like objects can be established by linking morphological (e.g. cell remnants and extracellular polymeric matrix) and chemical (e.g. isotopes, biomarkers and biominerals) evidence indicative of microorganisms or microbial activity. We have developed a non-destructive micro-analytical ion beam system capable of measuring with high spatial resolution the stable carbon isotope ratios of thin samples used for transmission electron microscopy. The technique is based on elastic scattering of alpha particles with an energy of 2.751 MeV. At this energy the ¹³C cross section is enhanced relative to the pure Rutherford cross section for ¹³C, whereas the ¹²C cross section is reduced relative to its pure Rutherford cross section. Here we report the initial results of this experimental approach used to characterize ultramicrotomed sections of sulfur-embedded graphite and microbial cells.     

Phantom studies of Cd, Hg and Cl by prompt gamma neutron activation analysis using a Pu-Be neutron source

Prompt gamma neutron activation analysis is a means of non-invasive monitoring for occupational exposure to toxic heavy metals such as Cd and Hg. Preliminary kidney detection limits from previous phantom studies at McMaster were 13.6 ± 0.2 ppm for Cd (125 mL phantom) and 315 ± 24 ppm for Hg (125 mL phantom) using the ²³⁸Pu-Be neutron source and 0.88 ± 0.01 ppm for Cd (125 mL phantom) and 16.91 ± 0.05 ppm for Hg (30 mL phantom) using the thermal neutron beam port at the McMaster Nuclear Reactor. The detection limits vary greatly between the two methods due to differences in experimental set-up, neutron energy spectra and a difference in dose by more than a factor of 100. The Hg detection limit from preliminary data is much higher than expected for both neutron source types. In order to explain the apparent detection limit discrepancy, measurements of Hg and Cd phantoms were performed using the ²³⁸Pu-Be neutron source. The results were compared to phantom measurements of Cl, a well-known neutron activation element.     

CaF2:Tm (TLD-300) thermoluminescent response and glow curve induced by γ-rays and ions

The thermoluminescent response of CaF₂:Tm after exposure to ⁶⁰Co γ-rays at doses from 0.44 Gy to 8.75 kGy and to low fluences (10⁵ ∼ 10⁸ cm⁻²) of 25 and 40 MeV ¹H, 75 and 120 MeV ³He, 180, 300 and 480 MeV ¹²C, 400 MeV ¹⁶O and 800 MeV ²⁰Ne ion beams, spanning a LET interval up to about 500 keV/μm, has been investigated. A careful deconvolution analysis of the glow curve has been performed in order to obtain information for individual peaks. The region of linear response to gammas extends up to ≈1 Gy, while that for ions includes the complete dose interval covered in the study (up to ≈1.3 Gy). The ratio between the high- and low-temperature structures in the glow curve is correlated with radiation quality and dependence on ion identity, besides LET, is strongly suggested by the data. The thermoluminescent efficiency to ion exposure, with respect to irradiation with ⁶⁰Co γ-rays, shows a different dependence on LET for each of the peaks. In general terms, the efficiency reaches a maximum between 1.2 and 1.4 near 6 keV/μm and decreases for higher LET. Peak 3 displays a unique trend, its relative efficiency is always less than 1.0 and shows a strong monotonic inverse dependence with LET.     

Machinability of the high-strength corrosion-resistant high-ductility austenitic steel 06Kh22AG15N8M2F

The machinability of the high-nitrogen corrosion-resistant austenitic steel 06Kh22AG15N8M2F during turning is studied. The specific features of the structure of the surface layers in steel workpieces after turning are revealed. The cutting conditions that provide the lowest wear of VK8 alloy cutting tools upon turning are found: the cutting speed is 21–74 m/min, the feed is 0.15–0.60 mm/rev, and the cutting depth is 0.15–0.75 mm. The presence of a large amount of Cr₂N-type chromium nitrides in the structure of the steel annealed at 800°C for 2 h and a high nitrogen content in the austenite of the steel quenched from 1100°C increase the wear of the cutting tools. As to turning of the forged steel, the wear resistance of the cutting tools upon turning of the 06Kh22AG15N8M2F steel is higher than that upon turning of 08Kh18N10T steel, in which deformation martensite forms (in surface layers) during turning.     

Deconvolution problems and superresolution in Hilbert-transform spectroscopy based on a.c. Josephson effect

The analysis of the numerical aspects of Hilbert transform spectroscopy based on the a.c. Josephson effect is presented. The resolving power of Hilbert transform spectroscopy is determined by such factors as the linewidth of the Josephson oscillations (intrinsic or natural resolution limit) and the limitation of the measurement interval (extrinsic or technical resolution limit) like in any spectroscopic technique based on some integral transformations. The deconvolution problem in Hilbert transform spectroscopy is posed and its solution is considered using the approach of the 1st kind integral equation for the spectrum of the incident radiation constructed from the input data of the Hilbert transform spectroscopy—the ‘hilbertogram’. The program package RECOVERY based on the maximum likelihood method is used for this purpose. This method allows to attain the maximum possible resolution enhancement in output result for a given signal-to-noise ratio in the input experimental data. The samples of numerical simulations and the spectrum of frequency-modulated BWO radiation measured by means of the Josephson junction made from high-T_c superconductor are presented. It is shown also that the integral equation approach allows to recover the sought spectrum beyond the intrinsic resolution limit and to achieve the superresolution.     

Direct electron imaging in electron microscopy with monolithic active pixel sensors

A new imaging device for dynamic electron microscopy is in great demand. The detector should provide the experimenter with images having sufficient spatial resolution at high speed. Immunity to radiation damage, accumulated during exposures, is critical. Photographic film, a traditional medium, is not adequate for studies that require large volumes of data or rapid recording and charge coupled device (CCD) cameras have limited resolution, due to phosphor screen coupling. CCD chips are not suitable for direct recording due to their extreme sensitivity to radiation damage. This paper discusses characterization of monolithic active pixel sensors (MAPS) in a scanning electron microscope (SEM) as well as in a transmission electron microscope (TEM). The tested devices were two versions of the MIMOSA V (MV) chip. This 1M pixel device features pixel size of 17 x 17 microm(2) and was designed in a 0.6 microm CMOS process. The active layer for detection is a thin (less than 20 microm) epitaxial layer, limiting the broadening of the electron beam. The first version of the detector was a standard imager with electronics, passivation and interconnection layers on top of the active region; the second one was bottom-thinned, reaching the epitaxial layer from the bottom. The electron energies used range from a few keV to 30 keV for SEM and from 40 to 400 keV for TEM. Deterioration of the image resolution due to backscattering was quantified for different energies and both detector versions.     

An improved beam chopper setup at the Budapest PGAA facility

Modulating neutron beams with a beam chopper enables the investigation of time-dependent processes following neutron capture, such as emission of decay-gamma-radiation from short-lived nuclides. For this purpose, a redesigned beam chopper and controller electronics have been recently installed at the PGAA facility of the Budapest Research Reactor. The new electronics provides accurate timing and better control of routing of the signals. The upgraded instrumentation is capable of recording the events in the beam-on and beam-off phases in parallel. Simplified formulae were derived to relate the areas of prompt- and decay peaks to the partial γ-ray production cross-sections. Finally, preliminary results obtained with Ag- and Na-containing targets are presented.     

The pulsed beam facility at the Tandetron accelerator in Florence

An electrostatic chopper has been installed in the LABEC laboratory (Sesto Fiorentino) along one of the beamlines of the new Tandetron accelerator. The chopper allows us the creation of a pulsed beam, from a continuous one, with a variable and finely controllable number of particles in each pulse. The facility can be tuned to obtain an average of one ion per pulse. This feature allows us the study of the basic processes of particle-target interactions, useful when performing ion beam analysis. Increasing the beam current, bunches up to thousands of ions can be obtained with a total energy being always an integer multiple of the one of the single ion. This configuration can be employed e.g. in a detector energy calibration.     

Characterisation of a pre-cell hit detector to be used in single cell irradiation experiments at the Lund Nuclear Microprobe

This paper describes the characterisation of an ultra-thin silicon semiconductor ΔE detector to be used as a pre-cell ion hit detector in single ion experiments on individual, living cells. The characteristics of interest for this specific application are the hit detection efficiency, which has to be close to 100% to enable bombardment with either a single ion or a counted number of ions, the beam spreading, which should be as small as possible to maintain the targeting accuracy, and the vacuum tightness, since the detector is intended, if possible, to be used simultaneously as vacuum window. The hit detection efficiency was shown to be above 99% when detecting alpha particles or 2 MeV protons, the increase in beam size was about 1 μm and the vacuum tightness was comparable to that of the Si₃N₄ wafer which is normally used as vacuum window, thus the ΔE detector fulfils the main criteria to function properly as a single ion hit detector.