Mylar Foil Research Articles

Indirect determination of beryllium by X-ray fluorescence spectrometry via a complex with cobalt

An indirect method for determination of beryllium by X-ray fluorescence spectrometry (XRF) is described. The beryllium is precipitated as hexamminecobalt(III) carbonatoberyllate complex Co(NH3)6][Be2(OH)3(CO3)2(H2O)2]·3H2O from the analyzed solution, filtered and then dissolved and pipetted onto the Mylar foil. Due to stoichiometry of the complex, beryllium can be determined viaCo Kα measurement. Moreover, the ratio of Be to Co (1 : 3) allows one to obtain satisfactory sensitivity. The carried out method allows determination of the element, which is practically undeterminable directly by XRF due to its very long-wavelength radiation and extremely low fluorescent yield. The calibration samples are prepared by pipetting a standard solution of cobalt onto the Mylar foil. The very simple calibration (reference samples without toxic beryllium) and elimination of the self-absorption effects in the prepared thin samples are important advantages of the described method.

Polymer ERD standards and charge integration for low intensity He ion microbeams

Mylar and Kapton foils were used as elastic recoil detection (ERD) calibration standards for He ion microbeam currents of the order of 1pA. At these beam currents, electronic charge integration is inadequate. Therefore, the number of incident He ions Q was determined from RBS spectra taken concurrently with the ERD. In one method, a Ta mask was overlaid on the polymer, and the beam was scanned across the boundary. Q was determined using the RBS peak from the Ta surface. Another method used the RBS spectrum from the polymer surface directly, where Q was determined from the nuclear resonances of He scattered from C at 5.67MeV and He scattered from O at 3.039MeV.

Energy loss straggling measurements for helium ions in Mylar and polypropylene polymeric foils

In the present contribution, we report results on energy straggling of He ions penetrating Mylar and polypropylene thin polymeric foils. The measurements were performed in the 900–3000 keV incident particle energy range by using the indirect transmission technique developed previously. The experimental straggling data are corrected to consider the roughness effects due to target thickness inhomogeneity. As expected, the roughness contribution to straggling is more important for helium than for proton ions and decreases as the ion energy increases. At low velocities, (<500 keV/amu), the variation of the experimental energy straggling results differs strongly from predictions based on Bohr’s formalism, and with increasing energies, the experimental results approach gradually the Bohr values.

Energy loss straggling of Li, C and O ions in mylar and polycarbonate absorber foils

Measurements of energy loss straggling for Li, C and O ions in varying thicknesses of mylar (C10H8O4) and polycarbonate (C16H14O3) absorber foils in the energy range ∼3.0–6.0MeV/u have been carried out, utilizing the Pelletron accelerator facility at Nuclear Science Centre, New Delhi, India. These measured values have been compared with the calculated values in order to establish the validity of various energy loss straggling formulations viz. Bohr, Lindhard and Scharff and Bethe–Livingston. From the energy loss straggling measurements in these two polymers having same atomic constituents and almost same effective Z, the validity of Bragg’s rule has been checked.

Monte Carlo modeling of the response of NRC's Sr90∕Y90 primary beta standard.

The BEAMnrc/EGSnrc Monte Carlo code system is employed to develop a model of the National Research Council of Canada primary standard of absorbed dose to tissue in a beta radiation field, comprising an extrapolation chamber and Sr90∕Y90 beta source. We benchmark the model against the measured response of the chamber in terms of absorbed dose to air, for three different experimental setups when irradiated by the Sr90∕Y90 source. For the first setup, the chamber cavity depth is fixed at 0.2cm and the source-to-chamber distance varied between 11 and 60cm. In the other two cases, the source-to-chamber distance is fixed at 30cm. In one case the response for different chamber depths is studied, while in the other case the chamber depth is fixed at 0.2cm as different thicknesses of Mylar™ are added to the front surface of the extrapolation chamber. The agreement as a function of distance between the calculated and measured responses is within 0.37% for a variation in response of a factor of 29. In the case of dose versus chamber depth, the agreement is within 0.4% for the ISO-recommended nominal depths of 0.025-0.25cm. Agreement between calculated and measured responses is very good (between 0.02% and 0.2%) for added Mylar foils of thicknesses up to 10.8mgcm-2. For larger Mylar thicknesses, deviations of 0.6%-1.2% are observed, which are possibly due to the systematic uncertainties associated with the restricted collisional stopping powers of air or Mylar used in the calculations. We conclude that our simulation model represents the extrapolation chamber and Sr90∕Y90 source with adequate accuracy to calculate correction factors for accurate realization of dose rate to tissue at a depth of 7mgcm-2 in an ICRU tissue phantom, despite the fact that the uncertainties in the physical characteristics of the source leave some uncertainty in certain calculated quantities.

Effects of ambient versus reduced UV‐B radiation on high arctic Salix arctica assessed by measurements and calculations of chlorophyll a fluorescence parameters from fluorescence transients

A UV‐B exclusion‐experiment was conducted in the high Arctic Zackenberg, NE Greenland, in which Salix arctica leaves during most of the growing season were fixed perpendicular to the solar zenith angle, thereby receiving maximal solar radiation. Covered with Teflon and Mylar foil, the leaves received approximately 90 and 40% of the ambient UV‐B irradiance, respectively. The effects were examined through recordings of chlorophyll a fluorescence transients, determination of biomass and analysis of total carbon and nitrogen content and amount of soluble flavonoids in the leaves. The processing of light was analysed by means of the chlorophyll a fluorescence transient, using the so‐called JIP test, as evolved by Reto J. Strasser and his coworkers. Reduction of the UV‐B irradiance caused a rise in many of the fluorescence parameters during July, but not in August (late season). Thus increases in the efficiency that an absorbed photon will be trapped by the PSII reaction centre with the resultant reduction of QA to QA– (ET0/ABS = FV/FM) and the efficiency that an electron residing on QA– will enter the intersystem electron transport chain (ET0/TR0) were observed in reduced UV‐B. Moreover, estimated per cross‐section of leaf sample, the number of active PSII reaction centres (RC/CSM) and electron transport rate (ETM/CSM) and all performance indexes (PIABS, PICSo and PICSm) were increased in reduced UV‐B. The total soluble flavonoid content was highest in ambient UV‐B. The treatment effects on fluorescence parameters that were directly measured (e.g. F0 and FM) and those that were derived (e.g. quantum efficiencies, parameters per PSII reaction centres and per cross‐section of leaf sample) are discussed in relation to one another, in relation to daily and seasonal variation, and from the perspective of evaluating the relative importance of UV‐B of donor and acceptor side capacity in Photosystem II. In conclusion, the experimental set‐up and non‐invasive measurements proved to be a sensitive method to screen for effects of UV‐B stress.

Self- and Interdiffusion in Ternary Cu-Fe-Ni Alloys

Self- and Interdiffusion in Ternary Cu-Fe-Ni Alloys

Hydrogen depth profiling by p–p scattering in nominally anhydrous minerals

Hydrogen has been shown to occur as a trace element in many nominally anhydrous minerals. The presence of hydrogen in several of the major minerals in the Earth’s mantle has received attention, due to the possibility that these phases provide a significant hydrogen reservoir. Recently an experimental and analytical procedure for hydrogen measurements in thin mineral samples by proton–proton scattering has been developed at the Lund Nuclear Microprobe facility. An annular surface barrier detector, divided in two insulated halves, is used to detect the scattered proton and the recoiled proton in coincidence. The summed energy of each detected proton pair can be used to produce depth profiles if the individual scattering angles are known. The easiest case is when only a small difference in energy between each detected proton pair is allowed, i.e. scattering angles very close to 45°. This limitation criterion considerably reduces the statistics. For this reason the analytical method has been expanded to use the full detector area (35–55°) and to identify the scattering angles individually for each hydrogen event.Nominally anhydrous minerals, both synthesized and of natural occurrence, with hydrogen concentrations from 10 to 100ppm have been analysed. Hydrous minerals, as well as Mylar foils were used as standards. Depth profiles show that intrinsic hydrogen can be distinguished from surface contaminations, e.g. water adsorbed on the sample surfaces.

Angular distribution of sputtered particles and surface morphology: the case of beryllium under a krypton beam at various incidences

A beryllium target is bombarded with 5keV krypton ions at incidence angles of 0° and 70°. The sputtered material is collected on a Mylar cylindrical foil surrounding the target, the foil is cut into pieces and the deposit on them is measured by inductively coupled plasma optical emission spectroscopy (ICP-OES). Experiment is combined with simulations using the computer code OKSANA. The method supplies accurate angular distributions of sputtered particles. The surface morphology is observed by scanning electron micrography. Depending on the incidence angle, sputtering forms craters and rippled areas or deep grooves. The resulting differences between simulations and experiment are explained qualitatively.

Irradiation facility for radiobiology and molecular biophysics studies at the University of São Paulo Pelletron Accelerator laboratory

In this work, we describe the new facility for Radiobiology and Molecular Biophysics studies with charged particle beams, built at the University of São Paulo Pelletron Accelerator Laboratory. It consists of a dedicated beam line, sample holder and dose monitoring system. The beam line is designed in such a way that a 15 mm diameter and 2% uniformity external beam is delivered to the sample. In order to reach these beam features, the beam line is composed of one focusing system with tantalum slits and a Faraday cup, two scattering chambers with 1 mm tantalum collimators and 2 mg/cm 2 Au diffusing foils, and one 10 μm thick mylar foil serving as exit window. The sample holder has x, y and z movement with 10 μm precision and the dose monitoring system consists of one Si detector inside each scattering chamber, and one Si detector in air at the sample location. A multiwire position sensitive detector will be soon installed right before the exit window to monitor the beam shape and help in the beam uniformity measurements. The facility and tests of the beam uniformity and dose monitoring system are described. The dose tests are performed through the irradiation of LiF TLD-100 crystals and the comparison of their results with the calculated values based on the counting rate on the Si detectors.

Impact of ultraviolet-B radiation on the development of phytoplankton communities in the eastern Atlantic sector of the Southern Ocean—results from on-deck model ecosystem experiments

Abstract Two model ecosystem experiments to assess the effects of UVB radiation (UVBR, 280–320 nm) on phytoplankton communities were performed on-deck during the SWEDARP 97/98 expedition to the eastern Atlantic sector of the Southern Ocean in January 1998. The first experiment was run in the Spring Ice Edge, around 60°S, and the second at the Antarctic Polar Front, around 50°S. The duration of the experiments were 12 and 10 days, respectively. Ambient UVBR was modified to three levels (i.e. treatments): NoUVB—shielded from UVBR (mylar foil); AMB—ambient UVBR; UVB+—enhanced UVBR. The development of the phytoplankton communities was followed by measuring primary production and composition of pigments and diatom species. At the start of the first experiment UVB+ had lower primary production per volume, but not when normalised to chlorophyll a. At the end there were no differences between treatments in primary production per volume but there were differences when normalised to chlorophyll a. In addition, a significant increase in the stimulation of primary production for UVB+ when excluding UVBR and in chlorophyll a concentration was found. These changes, together with changes in species composition, are assumed to be the result of an adaptation to the enhanced UVBR. During the second experiment, the effects from changes in UVBR were generally smaller but resembled to some extent the first experiment. The chlorophyll a concentration increased significantly in the UVB+ treatment at the end of the experiment and there was a strong tendency towards a reduction in primary production per chlorophyll a, but not per volume. The results are important when estimating the effects of increased UVBR as they show variability in short-term sensitivity, and also the capacity of phytoplankton communities to adapt to UVBR and retain primary production even in enhanced UVBR.

A low-mass neutron flux monitor for the n _TOF facility at CERN

A small-mass system has been developed for monitoring the flux of neutrons with energy up to 1 MeV at the new time-of-flight facility at CERN, n_TOF. The monitor is based on a thin Mylar foil with a 6Li deposit, placed in the neutron beam, and an array of Silicon detectors, placed outside the beam, for detecting the products of the 6Li(n, alpha)³H reaction. The small amount of material on the beam ensures a minimal perturbation of the flux and minimizes the background related to scattered neutrons. Moreover, a further reduction of the gamma-ray background has been obtained by constructing the scattering chamber hosting the device in carbon fibre. A detailed description of the flux monitor is here presented, together with the characteristics of the device, in terms of efficiency, resolution and induced background. The use of the monitor in the measurement of neutron capture cross-sections at n_TOF is discussed

Laser-Produced Radioactive Isotopes

Tagging pharmaceuticals with short-lived positron-emitting isotopes makes it possible to use the imaging technique positron emission tomography (PET) to follow the fate of these compounds non-invasively; for instance, in measuring neurotransmitter receptor distributions in the brain. Although essential from a biosafety point of view, the short lifetimes of these radioactive isotopes present logistical limitations on the locations of the scanners—requiring them to be in proximity to an isotope-producing nuclear facility or synchrotron—which may not always be where the patients are. Using the powerful VULCAN laser, Ledingham et al. present a proof-of-principle demonstration in which radioactive isotopes of carbon and fluorine are produced in sufficient abundance during the interaction between petawatt laser pulses and a solid target such as gold, aluminum, or mylar foils. As high-power lasers continue to shrink in size, the prospects for radioactive isotopes being produced in-house will improve. — ISO

Measurement of very low bulk concentrations (below 1 ppm) of hydrogen using ERDA

The measurement of small quantities of hydrogen (a few ppm) present in the bulk of materials by elastic recoil detection analysis is very difficult as the sensitivity is limited by a high background, almost continuous in level, in the low energy region, i.e. bulk region of the spectrum. We have quantified and successfully assigned the different contributions to the background to three main effects in the measurement of hydrogen in the bulk of Cu, Ge, Ag and Au samples. (A) The contribution from recoil hydrogen from the sample holder or the walls of the scattering chamber due to impact of ions scattered from the entrance slit. It is reduced by the placement of an entrance collimator which reduces the background by approximately 40%. (B) The second contribution is due to recoil hydrogen from the foil in front of the detector. Our study shows that the replacement of a mylar stopping foil by an Al foil reduces the apparent content of bulk hydrogen by more than a factor of 10. (C) The contribution of recoil hydrogen from the sample surface reaching the detector due to double scattering. This effect has been investigated by reducing the amount of surface hydrogen by Ar sputtering and studying its effect on the apparent hydrogen concentration in the bulk. It is found that a reduction of the surface hydrogen by a factor of 10 by sputtering results in a similar 10-fold reduction of the apparent bulk concentration. It is further shown that by consequently removing these contributions, it is possible to measure bulk concentrations of hydrogen well below 1 at ppm in single crystalline samples. The bulk concentrations measured for the samples of Ag, Au, Ge and Cu are found to be 36.8, 2.5, 1.6 and 0.7 at ppm.

Hydrogen analysis by p–p scattering in geological material

It has been concluded by geologists that a significant amount of hydrogen is stored as point defects in nominally anhydrous minerals. Determination of the amount of hydrogen bound in these minerals is a step towards determining the total water content of the earth mantle as well as comprehending its internal water cycle. The possibility to measure hydrogen in thin geological samples by elastic p–p scattering has been investigated at the Lund Nuclear Microprobe. In this work the development of the experimental procedure and standardisation of data analysis is described. Special emphasis has been put into doing the data analysis as simple as possible and at the same time applicable to all sorts of thin samples, even those of unknown nature. A special annular surface barrier detector composed of two insulated detector halves, which are read out simultaneously, is used to detect the recoiled proton and the scattered proton in coincidence. Conditions on the difference in time and energy of the detected particles, enables us to distinguish true hydrogen events from false or random ones. Homogeneous Mylar foils with known hydrogen content are used as reference material and enables determination of the total amount of hydrogen in the bulk of the geological samples as well as depth profiling, in order to separate contaminations in the surface from the bulk concentrations. The method has been tested with a 2.8 MeV proton beam on thin samples of both Muscovite, which is known to have a natural hydrogen concentration of about 0.5 wt%, and Pyroxene, which is a nominally anhydrous mineral.

A low background neutron flux monitor for the n_TOF facility at CERN

A small-mass system has been developed for monitoring the flux of neutrons with energy up to 1 MeV at the new time-of-flight facility at CERN, n_TOF. The monitor is based on a thin Mylar foil with a 6Li deposit, placed in the neutron beam, and an array of silicon detectors, placed outside the beam, for detecting the products of the 6Li( n, α) 3H reaction. The small amount of material on the beam ensures a minimal perturbation of the flux and minimizes the background related to scattered neutrons. Moreover, a further reduction of the γ-ray background has been obtained by constructing the scattering chamber hosting the device in carbon fibre. A detailed description of the flux monitor is here presented, together with the characteristics of the device, in terms of efficiency, resolution and induced background. The use of the monitor in the measurement of neutron capture cross-sections at n_TOF is discussed.

Tritium digital autoradiography with a Medipix2 hybrid silicon pixel detector

We report on the first measurements of 3H beta autoradiography obtained using a room temperature hybrid pixel detector, consisting of the Medipix2 single particle counting read-out chip bump-bonded to a 300 μm thick silicon pixel detector. This system has 256×256 square pixels of 55 μm pitch for a total sensitive area of 14×14 mm 2. Each pixel contains a double threshold discriminator and a 13-bit counter. Using a detection threshold equivalent to less than 6 keV and a background count rate of 5×10 −3 counts mm −2 s −1, with exposures up to several hours, real-time images have been obtained of tritium-labeled solution drops spotted on a thin mylar foil placed in contact with the continuous top electrode of the silicon detector, in open air condition.

Triaxial tests on snow at low strain rate. Part I. Experimental device

AbstractA deformation-controlled triaxial apparatus has been developed in order to investigate the mechanical behaviour of alpine snow. Cylindrical specimens (58 mm in diameter, 126 mm in height) can be axially deformed by applying tensile or compressive strain rates between 2.4 × 10−7s−1and 2.4 × 10−2s−1. Compressed air is used to laterally load the snow specimens with pressures of up to 40 k Pa.The volumetric deformation is found by carefully encapsulating the snow samples in an airtight Mylar foil and measuring the expelled pore air during sample deformation. The multidimensional stress–strain behaviour can therefore be determined, and constitutive theories of snow advanced. The device is located in the cold rooms of the Weissfluhjoch research station of the Swiss Federal Institute for Snow and Avalanche Research. Some 180 tests have been performed over the last four winters. The density of the snow specimens varied between 190 and 435 kg m−3. Part I of this two-part paper discusses the development of the apparatus and the applied testing methodology. Qualitative results are provided. In Part II, a detailed analysis of the results is presented and the viscoelastic properties of snow quantified.

Upgrade of the time-of-flight diffractometer EPSILON

At beam line 7A of the pulsed reactor IBR-2 (JINR Dubna) the strain diffractometer EPSILON has been working for several years. Due to a flight path of 102 m a good resolution (Δd/d<3×10-3) was achieved. Nevertheless, further improvements of the instrument were required because of intended studies on geological samples. The modernisation of EPSILON is a renewal of the whole recording system, including collimators and detectors. The two previously used Soller collimators are replaced by nine radial collimators. Each collimator consists of 48 gadolinium oxide coated mylar foils with an angular distance of about 20’ of arc to each other and therefore covers a range of nearly 16° for 2Θ. In the other direction a range of about 18° is covered. Three collimators in each case are grouped into a unit covering 66° in the plane perpendicular to the incident beam. Single 3He counter tubes with a diameter of 10 mm and an active length of 120 mm are used. Each collimator/detector block is mounted on a ring carrier with its surface perpendicular to the incident neutron beam. All blocks have the possibility of adjustment in three directions. The transparency of the collimators is about 90–95%.

Enhanced values of the RBE and H ratio for cytogenetic effects induced by secondary electrons from an X-irradiated gold gurface.

The low-energy secondary electrons emerging from the entrance surface of an X-irradiated gold foil increase the dose to cells in contact with or at micrometer distances from this surface (Radiat. Res. 150, 92-100, 1998). We examined the effect of the spectrum of these low-energy electrons on the RBE for cytogenetic effects and showed that this RBE was increased. A monolayer of surface-attached human T lymphocytes was exposed to 60 kV X rays in the absence or presence of a gold foil positioned immediately behind the cell layer or separated from it by a Mylar foil 0.9 or 2 microm thick. The enhancement of dose in the cell nuclei caused by the photoelectrons and Auger electrons emerging from the entrance surface of the gold foil was measured by TSEE dosimetry. Dose enhancement factors of 55.7, 46.6 and 37.5 were obtained with 0, 0.9 and 2 microm of Mylar inserted between the gold surface and the cell layer. This large enhancement results from the photoelectric effect in the gold foil, as shown by the accompanying Monte Carlo calculations of the secondary electron spectra at the gold surface. Auger electrons from the gold foil generally were not able to penetrate into the cell nuclei except for that fraction of the cells that had a very thin (< 0.7 microm) layer of cytoplasm and membranes between gold surface and cell nucleus. The dose-yield curves for dicentric chromosomes plus centric rings and for acentric fragments obtained after exposures without or with the gold foil were linear-quadratic. The coefficient alpha, the slope of the linear yield component, was increased in the presence of the gold foil and showed RBE values ranging from 1.7 to 2.2 compared to exposures in absence of the gold foil. The ratio of the yield of interstitial deletions and dicentrics (H ratio) was significantly increased from about 0.17 in the absence of the gold foil to about 0.22 in the presence of the gold foil. The increases in the RBE and the H ratio are interpreted in microdosimetric terms: The preferred occurrence of electron track ends in the vicinity of the gold surface causes an increase in the dose-mean restricted linear energy transfer in cell nuclei exposed to the photoelectrons and Auger electrons.