Mylar Foil Research Articles

Experimental study of fast electron generation from intense laser irradiated mylar foil with thin metal coating on front or rear surfaces

We report angular and spectral distribution of fast electrons in the interaction of a high intensity laser pulse (30 fs, I∼1019 W/cm2) with uncoated transparent mylar foil (thickness: 8 μm). The effect of thin Al coating (50 nm) on either the front or rear surface of the mylar foil on fast electron generation was also investigated. An electron flux enhancement of ∼1.8× (from ∼45 pC to ∼80 pC) and an increase in the maximum electron energy from ∼ 400 keV to ∼ 800 keV were observed in the case of front coated foil compared to the uncoated one. In the case of rear coated foil, an enhancement of ∼1.4× in the electron flux with no change in maximum electron energy was observed compared to the uncoated foil. The observations are understood in terms of possible different preplasma conditions for various target configurations used, which is also supported by 1D hydrodynamic simulation carried out for the present experimental conditions. The observed enhancement in electron flux and temperature is also supported by 2D Particle in Cell (PIC) simulation.

Fission fragment velocity distribution measurement using time of flight technique

Two large area position sensitive Multi Wire Proportional Counters (MWPCs) have been developed for the detection of Fission Fragments (FFs). The detectors were characterized using FFs from 252Cf source to obtain position information by employing delay-line read out method and the resolution is about 1 mm in both X and Y directions. Velocity distribution of the FFs produced from spontaneous fission of 252Cf has been measured employing a time-of-flight (TOF) technique, using a barium fluoride (BaF2) detector and a MWPC. The most probable velocities obtained for the heavy and light fragment groups are 1.035 ± 0.003 and 1.378 ± 0.004 cm/ns, respectively. The energy dependence of fragment velocity distribution was also studied after degrading the energy of the fragments by using Mylar foils. It is observed that the width of the distribution for the heavy fission fragments decreases with the reduction in the energies, but for light fragments it does not show any significant dependence on the energy.

Characterization of protons accelerated from a 3 TW table-top laser system

We report on benchmark tests of a 3 TW/50 fs, table-top laser system specifically developed for proton acceleration with an intrinsic pump rate up to 100 Hz. In two series of single-shot measurements differing in pulse energy and contrast the successful operation of the diode pumped laser is demonstrated. Protons have been accelerated up to 1.6 MeV in interactions of laser pulses focused on aluminium and mylar foils between 0.8 and 25 μm thickness. Their spectral distributions and maximum energies are consistent with former experiments under similar conditions. These results show the suitability of our system and provide a reference for studies of laser targets at high repetition rate and possible applications.

Nano and micro structured targets to modulate the spatial profile of laser driven proton beams

Nano and micro structured thin (μ m-scale) foils were designed, fabricated and irradiated with the high intensity laser system operating at LLC (Lund Laser Centre, Sweden) in order to systematically study and improve the main proton beam parameters. Nano-spheres deposited on the front (laser irradiated) surface of a flat Mylar foil enabled a small enhancement of the maximum energy and number of the accelerated protons. Nano-spheres on the rear side allowed to modify the proton beam spatial profile. In particular, with nanospheres deposited on the rear of the target, the proton beam spatial homogeneity was clearly enhanced. Silicon nitride thin foils having micro grating structures (with different step dimensions) on the rear surface were also used as targets to influence the divergence of the proton beam and drastically change its shape through a sort of stretching effect. The target fabrication process used for the different target types is described, and representative experimental results are shown and discussed along with supporting 3D particle-in-cell simulations.

X-ray microbeam stand-alone facility for cultured cells irradiation

The article describes an X-ray microbeam standalone facility dedicated for irradiation of living cultured cells. The article can serve as an advice for such facilities construction, as it begins from engineering details, through mathematical modeling and experimental procedures, ending up with preliminary experimental results and conclusions. The presented system consists of an open type X-ray tube with microfocusing down to about 2μm, an X-ray focusing system with optical elements arranged in the nested Kirckpatrick-Baez (or Montel) geometry, a sample stand and an optical microscope with a scientific digital CCD camera. For the beam visualisation an X-ray sensitive CCD camera and a spectral detector are used, as well as a scintillator screen combined with the microscope. A method of precise one by one irradiation of previously chosen cells is presented, as well as a fast method of uniform irradiation of a chosen sample area. Mathematical models of beam and cell with calculations of kerma and dose are presented. The experiments on dose-effect relationship, kinetics of DNA double strand breaks repair, as well as micronuclei observation were performed on PC-3 (Prostate Cancer) cultured cells. The cells were seeded and irradiated on Mylar foil, which covered a hole drilled in the Petri dish. DNA lesions were visualised with γ-H2AX marker combined with Alexa Fluor 488 fluorescent dye.

The impact of wrapping method and reflector type on the performance of rod plastic scintillators

Abstract This research paper revolves around, the effect of the reflector type and its applying method on the output of the rod shaped plastic scintillators. This effect is more considerable in the case of the rod plastic scintillators because of their larger dimensions compared to other types of scintillators. The experiments were repeated for 4 different reflectors, namely aluminum metallized Mylar, white paper, titanium dioxide and aluminum foil tape. The spectral responses of the scintillators for the mentioned reflectors were assessed in the presence of 60Co and 137Cs gamma sources.

Dosimetric response of radiochromic films to protons of low energies in the Bragg peak region

One of the major advantages of proton or ion beams, applied in cancer treatment, is their excellent depth-dose profile exhibiting a low dose in the entrance channel and a distinct dose maximum (Bragg peak) near the end of range in tissue. In the region of the Bragg peak, where the protons or ions are almost stopped, experimental studies with low-energy particle beams and thin biological samples may contribute valuable information on the biological effectiveness in the stopping region. Such experiments, however, require beam optimization and special dosimetry techniques for determining the absolute dose and dose homogeneity for very thin biological samples. At the National Centre of Accelerators in Seville, one of the beam lines at the 3 MV Tandem Accelerator was equipped with a scattering device, a special parallel-plate ionization chamber with very thin electrode foils and target holders for cell cultures. In this work, we present the calibration in absolute dose of EBT3 films [Gafchromic radiotherapy films, http://www.ashland.com/products/gafchromic-radiotherapy-films] for proton energies in the region of the Bragg peak, where the linear energy transfer increases and becomes more significant for radiobiology studies, as well as the response of the EBT3 films for different proton energy values. To irradiate the films in the Bragg peak region, the energy of the beam was degraded passively, by interposing Mylar foils of variable thickness to place the Bragg peak inside the active layer of the film. The results obtained for the beam degraded in Mylar foils are compared with the dose calculated by means of the measurement of the beam fluence with an ionization chamber and the energy loss predicted by srim2008 code.

Development of an extremely thin-wall straw tracker operational in vacuum – The COMET straw tracker system

The COMET experiment at J-PARC aims to search for a lepton-flavour violating process of muon to electron conversion in a muonic atom, μ-e conversion, with a branching-ratio sensitivity of better than 10−16, 4 orders of magnitude better than the present limit, in order to explore the parameter region predicted by most of well-motivated theoretical models beyond the Standard Model. The need for this sensitivity places several stringent requirements on the detector development. The experiment requires to detect the monochromatic electron of 105MeV, the momentum resolution is primarily limited by the multiple scattering effect for this momentum region. Thus we need the very light material detector in order to achieve an excellent momentum resolution, better than 2%, for 100MeV region. In order to fulfil such a requirement, the thin-wall straw-tube planar tracker has been developed by an extremely light material which is operational in vacuum. The COMET straw tracker consists of 9.8mm diameter straw tube, longer than 1m length, with 20-μm-thick Mylar foil and 70-nm-thick aluminium deposition. Currently even thinner and smaller, 12μm thick and 5mm diameter, straw is under development by the ultrasonic welding technique.

Real-time SAXS study of a strain gauge based on a self-assembled gold nanoparticle monolayer

A strain gauge based on a monolayer of colloidal gold nanoparticles deposited on a flexible Mylar foil by a modified Langmuir-Schaefer method was tested in situ under external uniaxial stress by the small-angle X-ray scattering (SAXS) technique. Simultaneously, the stress-strain curve of the foil was measured. A high-flux laboratory X-ray source allowed fast data collection with 10s temporal resolution. The monolayer exhibits a linear response in terms of the interparticle distances up to the 13% substrate strain while keeping its full integrity. This result indicates the dominant role of the pair potential function between the nanoparticle surfactant molecules and molecules of the substrate and compares well with previous quasi-static measurements of a similar strain gauge, suggesting none or negligible effect of the transient strain phenomena longer than the sampling interval on the gauge response. Keeping a constant strain on finishing the stretching, fast transient effects with characteristic times down to the limit imposed by the X-ray detector time resolution were not observed either during the SAXS pattern collection. A different stress behavior of the interparticle distance in the direction perpendicular to stretching comparing with a monolayer of colloidal iron-oxide nanoparticles studied previously reveals the surfactant effect on the gauge response controlled by the interparticle pair potential function. The results obtained suggest that the colloidal gold-nanoparticle monolayer on a flexible substrate is a prospective strain gauge with a very fast linear response in a broad strain range.

Preliminary study of the applicability of the thin gap method on alpha emitters

The thin gap method as an in-situ radiotracer technique is widely used. This study investigated the applicability of alpha emitters. PIPS and CsI alpha spectrometers were applied in a thin gap cell. A suitable 210Po source was prepared by spontaneous deposition, Mylar foil was used to simulate water. A maximum intensity decrement of 7% within 25μm was observed. Even though this method is suitable for the study of surface phenomena, further investigation is necessary e.g. into water and heat sensitivity.

A unique alpha dosimetry technique using Gafchromic EBT3(®) film and feasibility study for an activity calibrator for alpha-emitting radiopharmaceuticals.

To develop an alpha dosimetry technique for activity calibration of alpha-emitting radiopharmaceuticals using the Gafchromic(®) EBT3 (Gaf-EBT3) radiochromic film (International Speciality product, Wayne, NJ). The Gaf-EBT3 has a tissue equivalent radiosensitive layer (approximately 28 μm) sandwiched between two 100-μm thick polyester sheaths, thereby making it insensitive to alpha particles. We have split a Gaf-EBT3 sheet using a surgical scalpel to remove one of the polyester protective layers and covered the radiosensitive layer with thin Mylar(®) foil (Goodfellow Cambridge Limited, Huntingdon, UK) (2.5 μm). Small pieces of modified film were exposed at contact with a 560-Bq thin (241)Am source for 5, 10, 24 and 94 h. The optical density of the films was evaluated using an optical densitometer. The alpha energy spectra of the (241)Am source were recorded using a Si(Li) surface barrier detector. Time-integrated specific alpha surface activity (kBq cm(-2) h) was represented as a function of optical density. By removing one of the 100 μm thick polyester protective layers, the authors have modified the Gaf-EBT3 film to a sensitive alpha dosemeter. The calibration function relevant to a (241)Am reference source was evaluated from the optical densities of the dosemeter foils. Furthermore, calibration functions for important alpha emitters such as (223)Ra, (225)Ac or (210)Bi were parameterized from the (241)Am reference data. The authors have developed and tested the principle of a clinical alpha dosemeter using Gaf-EBT3 radiochromic films originally developed for photon dosimetry. This novel, user-friendly technique could be implemented in quality assurance and calibration procedures of important alpha-emitting radiopharmaceuticals prior to their clinical applications.

Morphological and Electrical Properties of Stretched Nanoparticle Layers

To examine perspectives of nanoparticle films in the role of active elements in strain sensors, morphological and electrical properties of self-assembled Au nanoparticle monolayer prepared by modified Langmuir-Schaefer technique onto supporting Mylar foil were studied under elongation. Along the probing of electrical response (characterized by the gauge factor of about 60), the small-angle x-ray scattering (SAXS) characterization assessed an average interparticle distance change, which was shown to vary proportionally to the substrate elongation. The approach allowed to unambiguously address the mechanism of the deformation-resistivity transduction.

A compact high-resolution elastic recoil detection system for lithium depth profiling

A compact high-resolution elastic recoil detection analysis (ERDA) system was developed for precise Li analysis. 200–400keV He+ ions were used as primary ions and the energy spectra of recoiled Li ions were measured using a magnetic spectrometer. Due to its dispersion the background originating from the scattered primary ions is reduced. The recoiled ions of the substrate other than Li, which may also contribute to the background, were rejected by a thin mylar foil placed in front of a focal plane detector. An electrostatic quadrupole lens was installed at the entrance of the magnetic spectrometer to improve the depth resolution by correcting the effect of the kinematic broadening. The performance of the developed high-resolution ERDA was examined by measuring several samples. A thin Li layer (1.5×1015cm−2) deposited on a graphite surface was clearly observed and the detection limit was estimated to be less than 0.01ML under typical measurement conditions. The depth resolution was estimated to be 0.5nm at the surface and was better than 3nm in the surface region within 5nm from the surface.

Measurements of proton induced γ-ray emission cross sections on MgF2 target in the energy range 1.95–3.05 MeV

In this work we present differential cross sections for γ-ray emission from the reactions 19F(p,p′γ)19F (Eγ=110, 197, 1236 and 1349+1357keV), 24Mg(p,p′γ)24Mg (Eγ=1369keV) and 25Mg(p,p′γ)25Mg (Eγ=390, 585 and 975keV). Differential cross sections were measured for proton energies from 1.95 to 3.05MeV with a 15keV step and beam energy resolution of 0.06%. Thin reference standard, 54.1μg/cm2 of MgF2 deposited on thin Mylar foil with additionally evaporated 4nm Au layer, was used as a target. The γ-rays were detected by a 20% relative efficiency HPGe detector placed at an angle of 135° with respect to the beam direction, while the backscattered protons were collected using silicon surface barrier detector placed at the scattering angle of 165°. Obtained cross sections were compared with the previously measured data available from the literature.

Transportation of Perishable and Refrigerated Foods in Mylar Foil Bags and Insulated Containers: A Time-Temperature Study

Data are lacking on the temperature changes of food during transport without the use of refrigerated trucks. The purpose of this study was to evaluate the ability of several insulated and noninsulated containers with or without frozen gel packs to keep perishable and refrigerated foods within the temperature safe zone in relationship to duration of transport. The study was designed to duplicate the practices exhibited by customers purchasing perishable food products from a cash-and-carry business. Approximately 40 perishable food items were evaluated. Four types of containers were tested: a mylar foil bag, a commercial insulated bag, a generic insulated bag, and a commercial insulated blanket. Mixed foods were placed into these containers with or without frozen gel packs, transported in unrefrigerated vehicles, and monitored for 4 h for temperature changes. Two environmental temperatures, room temperature of 21.1°C and a stress temperature of 37.8°C, were evaluated. The internal temperature and surface temperature of the food products in these containers increased slowly but remained well below the U.S. Food and Drug Administration Food Code requirements. The various containers were similar in their ability to retain coolness. The presence of frozen gel packs dramatically enhanced the cold-holding capacity of the containers. The temperature of foods increased more rapidly when stressed in a heated environment. The containers tested used with the frozen gel packs can keep the surface and internal temperatures of various perishable foods (starting at 4.4°C or less) within the Food Code recommendation of under 21.1°C for 4 h. Cash-and-carry businesses should strongly encourage their retail customers to utilize these containers with frozen gel packs to safely transport perishable foods.

Tilted foils polarization at REX-ISOLDE

The tilted-foils nuclear-spin polarization method has been evaluated using the REX-ISOLDE linear accelerator at the ISOLDE facility, CERN. A beam of 8Li delivered with an energy of 300keV/u traversed through one Mylar foil to degrade the beam energy to 200keV/u and consequently through 10 thin diamond-like carbon foils to polarize the nuclear spin. The attained nuclear spin polarization of 3.6±0.3% was measured with a β-NMR setup.

Analysis of a gold solidus of roman emperor Valentinian I

A gold solidus of Valentinian I, Emperor of Rome (A.D. 364-375) shown in Figure 1, and belonging to a private collection, was subjected to material and stylistic analysis, in order to ascertain about its authenticity. Due to the rarity of such a coin, only non-destructive analytical techniques were used, namely Scanning Electron Microscopy (SEM), Particle Induced X-ray Emission (PIXE), electrical resistivity and optical microscopy.Examination by SEM revealed that, in common with coins minted by this emperor, the solidus was die-struck as evidenced by the surface flow lines indicating metal movement under the dies (Figure 2). Wear traces presented an unorganized pattern. The coin was also examined for signs of stress-corrosion cracking but no evidence of this were found. The coin also shows traces of what appear to be soil residues; small quantities of these residues can also be seen in porosities in the coin face (arrow in Figure 3).Analysis by PIXE showed that the coin was made from an alloy of gold (97.9%), silver (2.0%) and copper (0.1%) (Figure 4). The high gold content is likely to be overestimated due to surface depletion of the silver and particularly the copper, which is caused by slight dissolution of these more reactive metals in the burial environment. Nevertheless, this effect is usually small and in agreement with other solidus from Valentiniano I. Also, the high gold content may lie behind the lack of stress-corrosion cracking.The presence of platinum group element (PGE) inclusions is, in some cases, indicative of alluvial gold provenience. Both, optical microscopy and PIXE, were used to detect them but it was not possible to identify their presence. Typically, the concentration of these elements is in the order of ppm, although for this specific period different values have been reported. Considering the experimental conditions used (2 MeV accelerated proton beam and a 50 μm Mylar foil in front of the X-ray detector) the limit of detection of the PIXE technique is close to the expected trace concentration. More energetic proton beam (>3MeV) or the use of specific filter for the X-ray signal in the low energy region, i.e. Zinc foil 75 μm thick, are the future experiments to be carried out in order to detect the presence of such characteristics PGE elements.In order to understand the presumable surface gold enrichment, electrical conductivity measurements were used. The values obtained (1.50-1.56)x1017 S/m show a lower conductivity as compared with the reference value for a 97% Au, 3% Ag alloy (3.54x1017 S/m), indicating that indeed the coin bulk has a lower gold content.As for the stylistic analysis, there is no sound agreement about the coin authenticity, but the tendency is to consider it a good one. The compositional and structural characterization of cultural heritage artefacts usually limit the number of available techniques to those considered as non-destructive and non-invasive, such the one presented in this work. This restriction also constricts and difficult the desired straight conclusions but, on the other hand, increase the multidisciplinary of the work, applying techniques usually dedicated to the material science characterization to cultural heritage.V. Corregidor acknowledges the funding support from the FCT-Ciência program. Financial support was also received through the PEST-OE/CTM-UI0084/2011 and PEST-OE/FIS/UI0275/2011 grants.

Experimental study on the effect of high humidity environments on the response of long-term exposed nuclear track detectors

Abstract In Spain, a recent modification in the regulations of protection against ionizing radiation obligates to determine radon levels in particular workplaces like spas, mines and caves. Most of these workplaces may present extreme measurement conditions like high aerosol content, temperature, and humidity that can affect the radon detector response. In our laboratory we use to determine mean radon activity concentration in air with the nuclear track detector Makrofol DE covered with an aluminized Mylar foil and placed within the FzK FN diffusion chamber with a glass fibre filter. We have compared detector response using different filter configurations in common laboratory ambient conditions. The configuration with a better response (polyethylene filter) and our reference configuration took part in a study of the effect of different temperature and humidity on our detector response carried out in the INTE radon chamber. Results obtained did not show a significant difference between detector responses with both filters. However, when we exposed them for long periods to real environmental conditions at underground sites we could observe Mylar deterioration. To look in detail into a possible effect of long-term high-humidity exposures we exposed nine sets of detectors with three different polyethylene bags, first five sets under controlled conditions in the INTE radon chamber and then four sets in long-term exposures at high humidity environments. We have seen that the Mylar foil can be damaged depending on the duration of exposure. In a radon chamber exposure time is normally limited to a few days for practical and financial reasons; therefore, results do not show if humidity affects the glass fibre filter and detectors response. To analyse it we exposed detectors in a real humid environment up to a month where we already observed Mylar deterioration due to humidity but the possible impact on track density is hidden by the scattering of the results found, so a clear conclusion cannot be stated.

Relative Biological Effectiveness of Single-Shot Irradiation With Laser-Driven Nanosecond Proton Bunches

Owing to their superior depth-dose curve, protons are a favorable choice in radiation therapy. High intensity table-top lasers are a proposed mechanism of reducing the cost and space consumed by conventional means of proton acceleration. However, before clinical application of laser-driven protons can be considered, cell experiments with laser-driven beams constitute an important preliminary step to demonstrate the increasing maturity of this technology. Here we present first biological results of single-shot irradiation with laser-driven nanosecond proton bunches. The ATLAS Ti-Sapphire laser delivered 400 mJ in a 30 fs pulse on a diamond-like Carbon target for proton acceleration. Two mini-quadrupole magnets focused the protons over a distance of 1.2 m and acted as an energy filter to produce a quasi-monoenergetic beam with an energy of 5.3 ± 0.15 MeV. The beam manifested as a line focus of ∼0.5 mm in width and 6 mm in length. This was used to irradiate human tumor cells over a dose range of 0.13 to 7 Gy, realized by single laser shots. Due to the inhomogeneous dose distribution across the line focus, full dose response curves for single, nanosecond proton bunches were obtained for each irradiated sample. For obtaining a reference dose-response curve cells were irradiated at the Munich tandem accelerator with the same proton energy using a delivery mode where the radiation was given within 100 ms. For all experiments, HeLa cells were seeded directly onto the cell holder window composed of 6 μm Mylar foil 48 hours prior to irradiation. Cells were fixed 30 minutes after irradiation and stained using Alexa 488 for 53bp1 and Cy3 for γ-H2AX foci. Dose was measured using radiochromic film (Gafchromic EBT2) placed immediately behind the back layer of the cell holder. Foci (γ-H2AX and 53bp1) were counted after irradiation with laser-driven protons and with protons from the conventional accelerator. An RBE of 1.3 ± 0.3 relative to 200 kV X-rays was determined for the induction of γ-H2AX foci and also for 53bp1 foci for laser-driven protons. These results indicate no substantial difference between laser-driven proton beams and those produced by conventional acceleration means. The RBE obtained in this study for laser-driven protons is in agreement with RBE values in conventional beams at comparable proton energies. This indicates that no new radiobiological effects are to be expected with nanosecond proton delivery, in line with previous studies in single, nanosecond proton bunches at conventional sources. This confirms that for future applications in radiation therapy, the same RBE as for conventional sources can be assumed.

32 MEASUREMENT OF PARASITIC NEUTRON FIELD IN THE TREATMENT ENVIRONMENT OF A VARIAN CLINAC 2100 MEDICAL LINAC USING SUPERHEATED BUBBLE DETECTORS

TLDs drops with increasing LET due the track structure of interacting densely ionising radiations. This phenomenon is known as quench effect (QE). Evidently the QF averts the application of tiny TLD chips in “in field” dosimetry relevant to hadron therapy. The light conversion efficiency (LCE) of Lithium Fluoride thermoluminescent dosimeters TLD-700 (LiF:Mg,Ti) decreases with the increasing linear energy transfer (LET) of the interacting radiation particles. On the contrary, the LCE of Beryllium-Oxide increases with increasing LET of the particles impinging on it. By utilizing these two phenomena we have developed a simple technique to estimate the “quench corrected” LET of interacting particles using a pair of thin TLD-700 and BeO chips. Furthermore, the self-attenuation characteristics of both types of TLD were estimated using a spectrophotometer. The TLDs were calibrated using alpha particles from a Am source attenuated using Mylar foils of different thicknesses for the LETTissue: 165, 178 and 195keV/m. The predicted LET estimation range was found to be 1-200 keV/m, encompassing a wide area of interest from Plateau-toBragg Peak region of a therapeutic proton beam to hadron-therapy, based on Carbon ions as well as fast neutrons of different energies.