SciCombinator

Discover the most talked about and latest scientific content & concepts.

Concept: Scintillation counter

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The determination of gross alpha, gross beta and (226)Ra activity in natural waters is useful in a wide range of environmental studies. Furthermore, gross alpha and gross beta parameters are included in international legislation on the quality of drinking water [Council Directive 98/83/EC].(1) In this work, a low-background liquid scintillation counter (Wallac, Quantulus 1220) was used to simultaneously determine gross alpha, gross beta and (226)Ra activity in natural water samples. Sample preparation involved evaporation to remove (222)Rn and its short-lived decay daughters. The evaporation process concentrated the sample ten-fold. Afterwards, a sample aliquot of 8 mL was mixed with 12 mL of Ultima Gold AB scintillation cocktail in low-diffusion vials. In this study, a theoretical mathematical model based on secular equilibrium conditions between (226)Ra and its short-lived decay daughters is presented. The proposed model makes it possible to determine (226)Ra activity from two measurements. These measurements also allow determining gross alpha and gross beta simultaneously. To validate the proposed model, spiked samples with different activity levels for each parameter were analysed. Additionally, to evaluate the model’s applicability in natural water, eight natural water samples from different parts of Spain were analysed. The eight natural water samples were also characterised by alpha spectrometry for the naturally occurring isotopes of uranium ((234)U, (235)U and (238)U), radium ((224)Ra and (226)Ra), (210)Po and (232)Th. The results for gross alpha and (226)Ra activity were compared with alpha spectrometry characterization, and an acceptable concordance was obtained.

Concepts: Ionizing radiation, Mathematics, Water, Uranium, Evaporation, Scintillator, Scintillation counter, Liquid scintillation counting

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Abstract Objective: This study compared three model decontaminant solutions (distilled water, 10% distilled water and soap and methanol) for their ability to remove salicylic acid and aminophylline from an in vitro skin model. Materials and methods: Human abdominal skin was dosed with 20 µL of either [(14)C]-aminophylline or [(14)C]-salicylic acid on 1 cm(2) per skin. After each exposure time (5, 30 and 60 min post-dosing, respectively), surface skin was washed three times with each solution and tape stripped 10 times. Wash solutions, tape strips, receptor fluid and remaining skin were then analyzed with liquid scintillation counting to quantify the amount of salicylic acid and aminophylline. Results: Total mass balance recovery for each chemical at three time exposure points was between 73.6 and 101.5%, except at 60 min where aminophylline was only 42.5%. Majority of salicylic acid and aminophylline were recovered from washing solution when compared to stratum corneum, epidermis, dermis, surrounding skin and receptor fluid. Conclusion: The three tested decontaminates possessed similar effectiveness in removing lipophilic and hydrophilic chemicals from the skin. Due to diminishing decontamination efficacy with time, it is suggested that skin should be washed as soon as possible following contamination to minimize percutaneous penetration and the deleterious effects associated with skin reservoir content.

Concepts: Chemistry, Skin, Liquid, Epidermis, Shutter speed, Scintillation counter, Washing, WASH

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Organic-inorganic halide perovskites (OIHPs) bring an unprecedented opportunity for radiation detection with their defect-tolerance nature, large mobility-lifetime product, and simple crystal growth from solution. Here we report a dopant compensation in alloyed OIHP single crystals to overcome limitations of device noise and charge collection, enabling γ-ray spectrum collection at room temperature. CH3NH3PbBr3 and CH3NH3PbCl3 are found to be p-type and n-type doped, respectively, whereas dopant-compensated CH3NH3PbBr2.94Cl0.06 alloy has over tenfold improved bulk resistivity of 3.6 × 10(9) Ω cm. Alloying also increases the hole mobility to 560 cm(2) V(-1) s(-1), yielding a high mobility-lifetime product of 1.8 × 10(-2) cm(2) V(-1). The use of a guard ring electrode in the detector reduces the crystal surface leakage current and device dark current. A distinguishable (137)Cs energy spectrum with comparable or better resolution than standard scintillator detectors is collected under a small electric field of 1.8 V mm(-1) at room temperature.

Concepts: Electric charge, Photon, Fundamental physics concepts, Density, Solid, Materials science, Scintillation counter, Gamma spectroscopy

2

Synchrotron microbeam radiation therapy is a novel external beam therapy under investigation, that uses highly brilliant synchrotron x-rays in microbeams 50 μm width, with separation of 400 μm, as implemented here. Due to the fine spatial fractionation dosimetry of these beams is a challenging and complicated problem. In this proof-of-concept work, we present a fibre optic dosimeter that uses plastic scintillator as the radiation conversion material. We claim an ideal one-dimensional resolution of 50 μm. Using plastic scintillator and fibre optic makes this dosimeter water-equivalent, a very desirable dosimetric property. The dosimeter was tested at the Australian Synchrotron, on the Imaging and Medical Beam-Line. The individual microbeams were able to be resolved and the peak-to-valley dose ratio and the full width at half maximum of the microbeams was measured. These results are compared to a semiconductor strip detector of the same spatial resolution. A percent depth dose was measured and compared to data acquired by an ionisation chamber. The results presented demonstrate significant steps towards the development of an optical dosimeter with the potential to be applied in quality assurance of microbeam radiation therapy, which is vital if clinical trials are to be performed on human patients.

Concepts: Electron, Medicine, Ionizing radiation, Diffraction, X-ray, Optics, Radiobiology, Scintillation counter

2

Current technologies for X-ray detection rely on scintillation from expensive inorganic crystals grown at high-temperature, which so far has hindered the development of large-area scintillator arrays. Thanks to the presence of heavy atoms, solution-grown hybrid lead halide perovskite single crystals exhibit short X-ray absorption length and excellent detection efficiency. Here we compare X-ray scintillator characteristics of three-dimensional (3D) MAPbI3 and MAPbBr3 and two-dimensional (2D) (EDBE)PbCl4 hybrid perovskite crystals. X-ray excited thermoluminescence measurements indicate the absence of deep traps and a very small density of shallow trap states, which lessens after-glow effects. All perovskite single crystals exhibit high X-ray excited luminescence yields of >120,000 photons/MeV at low temperature. Although thermal quenching is significant at room temperature, the large exciton binding energy of 2D (EDBE)PbCl4 significantly reduces thermal effects compared to 3D perovskites, and moderate light yield of 9,000 photons/MeV can be achieved even at room temperature. This highlights the potential of 2D metal halide perovskites for large-area and low-cost scintillator devices for medical, security and scientific applications.

Concepts: Electron, X-ray, Light, Atom, Temperature, Uranium, Solid, Scintillation counter

1

Pile Grade A graphite was used as a moderator and reflector material in the first generation of UK Magnox nuclear power reactors. As all of these reactors are now shut down there is a need to examine the concentration and distribution of long lived radioisotopes, such as 14C, to aid in understanding their behaviour in a geological disposal facility. A selection of irradiated graphite samples from Oldbury reactor one were examined where it was observed that Raman spectroscopy can distinguish between underlying graphite and a surface deposit found on exposed channel wall surfaces. The concentration of 14C in this deposit was examined by sequentially oxidising the graphite samples in air at low temperatures (450°C and 600°C) to remove the deposit and then the underlying graphite. The gases produced were captured in a series of bubbler solutions that were analysed using liquid scintillation counting. It was observed that the surface deposit was relatively enriched with 14C, with samples originating lower in the reactor exhibiting a higher concentration of 14C. Oxidation at 600°C showed that the remaining graphite material consisted of two fractions of 14C, a surface associated fraction and a graphite lattice associated fraction. The results presented correlate well with previous studies on irradiated graphite that suggest there are up to three fractions of 14C; a readily releasable fraction (corresponding to that removed by oxidation at 450°C in this study), a slowly releasable fraction (removed early at 600°C in this study), and an unreleasable fraction (removed later at 600°C in this study).

Concepts: Spectroscopy, Carbon, Raman spectroscopy, Scintillation counter, Liquid scintillation counting

0

A flexible γ detector using a liquid scintillation light guide (LSLG) was developed. The analyzed pulse height (PHA) spectrum depended on the diameter, length and scintillator concentration of the LSLG, and the distance of a γ ray irradiation point from the head of photomultiplier tube (PMT). From the analysis of PHA spectrum, it was found that the count ratio of two divided channel regions linearly decreases as the distance from the PMT head increases. It was further found that the radiation dose rate can be estimated by setting the flexible LSLG tube to a circular shape since the count rate is proportional to the dose rate measured by a conventional NaI (Tl) scintillation detector. Therefore, a flexible and long LSLG detector using a single PMT is useful for determination of the dose rate and has a potential to detect local contaminations in a certain narrow space.

Concepts: Photomultiplier, Height, Length, Absorbed dose, Scintillator, Scintillation counter, Gamma spectroscopy, Particle detectors

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In response to the increasing application of68Ge/68Ga and68Ga in nuclear medicine, an international comparison of activity measurement of68Ge in equilibrium with68Ga was organised. ANSTO standardised the comparison solution by the 4π(LS)β+-γ coincidence extrapolation and TDCR efficiency calculation methods, with excellent agreement between the two results. The primary standard was transferred to the ANSTO Secondary Standard Ionisation Chamber. Internationally traceable Australian Certified Reference Materials (ACRMs) of68Ge/68Ga can now be prepared in various measurement geometries applied in nuclear medicine.

Concepts: Nuclear medicine, Standard, Calibration, Certified reference materials, Standards, Gamma ray, Scintillation counter, Liquid scintillation counting

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In this work, a68(Ge+Ga) solution has been standardized at the National Institute of Ionizing Radiation Metrology (LNMRI), in Brazil, in the frame of an international key comparison CCRI(II)-K2.Ge-68 piloted by National Institute of Standards and Technology (NIST/USA). The 4πβ(LS)-γ(NaI(Tl)) anticoincidence method with live-time and extended dead-time was used and its result was validated by 4πβ(LS)-γ(NaI(Tl)) coincidence counting and liquid scintillation counting using the Triple to Double Coincidence Ratio (TDCR) method. The deviations of the activity concentration values of coincidence and TDCR measurements from the anticoincidence result were 1.7% and 0.63%, respectively, which were within experimental evaluated uncertainties at ~95% level of confidence (coverage factor k = 2). The combined relative standard uncertainties were 0.65%, 0.70% and 0.53% for anticoincidence, coincidence and TDCR methods, respectively. These values are consistent with the results reported by Cessna at the ICRM2017 conference.

Concepts: Ionizing radiation, Metrology, Test method, Standardization, Standard, Gamma ray, Scintillation counter, Liquid scintillation counting

0

To assess if apertures shall be mounted upstream or downstream of a range shifting block if these field-shaping devices are combined with the pencil-beam scanning delivery technique (PBS). The lateral dose fall-off served as a benchmark parameter. Both options realizing PBS-with-apertures were compared to the uniform scanning mode. We also evaluated the difference regarding the out-of-field dose caused by interactions of protons in beam-shaping devices. Methods: The potential benefit of the downstream configuration over the upstream configuration was estimated analytically. Guided by this theoretical evaluation a mechanical adapter was developed which transforms the upstream configuration provided by the proton machine vendor to a downstream configuration. Transversal dose profiles were calculated with the Monte-Carlo based dose engine of the commercial treatment planning system RayStation 6. Two-dimensional dose planes were measured with an ionization chamber array and a scintillation detector at different depths and compared to the calculation. Additionally, a clinical example for the irradiation of the orbit was compared for both PBS options and a uniform scanning treatment plan. Results: Assuming the same air gap the lateral dose fall-off at the field edge at a few centimeter depth is 20% smaller for the aperture-downstream configuration than for the upstream one. For both options of PBS-with-apertures the dose fall- off is larger than in uniform scanning delivery mode if the minimum accelerator energy is 100 MeV. The RayStation treatment planning system calculated the width of the lateral dose fall-off with an accuracy of typically 0.1 mm-0.3 mm.

Concepts: Electron, Particle physics, Proton, Aperture, Scintillation counter