A new irradiated quartz for beta source calibration

For luminescence dating to be an accurate absolute dating technique it is very important that we are able to deliver absolutely known radiation doses in the laboratory. This is normally done using a radiation source (alpha, beta, X-ray) calibrated against an absolutely known reference source. Many laboratories have used the various different batches of Risø calibration quartz for the calibration of beta and X-ray sources, but these have been largely undescribed. Here we describe in detail the preparation and luminescence characteristics of a new quartz standard, based on a North Sea beach sand collected from south-western Denmark (Rømø). Two grain sizes (4–11 μm and 180–250 μm) have been examined in detail. These were pre-treated (annealed, dosed and annealed again) to sensitise and stabilise the luminescence signals before being given an absolutely known gamma dose from a point ¹³⁷Cs source in scatter-free geometry. The luminescence characteristics are described; the very intense blue-light stimulated signal is dominated by the fast OSL component and the IR-stimulated signal is negligible. The material is shown to be suitable for measurement using SAR, and the dose recovery ratio is indistinguishable from unity with a standard deviation of <2% for multi-grain aliquots. The material is also shown to be suitable for single-grain calibration, with >80% of the grains giving a useful signal. Although there is an unexplained dispersion in our calibration data of ∼3% (which we cannot attribute to instrument variability), we nevertheless conclude that this material is very suitable for transferring absolute known doses from a standardised gamma source to in-built irradiation sources.     

Absorbed dose evaluations in retrospective dosimetry: methodological developments using quartz

Dose evaluation procedures based on luminescence techniques were applied to 50 quartz samples extracted from bricks that had been obtained from populated or partly populated settlements in Russia and Ukraine downwind of the Chernobyl NPP. Determinations of accrued dose in the range 30–300 mGy were obtained using TL (210°C TL and pre-dose) and OSL (single and multiple aliquot) procedures. Overall, good inter-laboratory concordance of dose evaluations was achieved, with a variance (1σ) of ±10 mGy for the samples examined.     

Infrared (IR) stimulated luminescence from modern bricks in retrospective dosimetry applications

It has frequently been observed that certain roof tiles and bricks, especially from relatively modern European buildings, do not contain enough quartz grains in a suitable grain size range to permit dose reconstruction using thermoluminescence (TL) or optically stimulated luminescence (OSL) methods. In this paper the feasibility of using infrared-stimulated luminescence (IRSL) on the feldspar fraction of such bricks and tiles has been investigated. Appropriate preheating treatments were employed in order to select the most stable signals, and procedures were developed to enhance the signal to noise ratio. The possible effect of anomalous fading under application of these procedures was tested. In the dose range above 100 mGy, it has been demonstrated that using IRSL on the feldspar fraction of such material provides a feasible alternative to the use of green-light-stimulated luminescence (GLSL) on the quartz fraction, for the purposes of retrospective dosimetry. Furthermore, since the use of IRSL as described in this paper involves the measurement of polymineral fine grain fractions of bricks, a technique for the calibration of the built-in β source against the γ source in Secondary Standard Dosimetry facilities for routine use of the technique is described.     

Dating bricks of the last two millennia from Newcastle upon Tyne: a preliminary study

Bricks from a group of four independently dated late medieval buildings in Newcastle upon Tyne have been tested to establish their suitability for luminescence dating as part of a wider study of the dating of post-Roman and medieval brick buildings. The luminescence characteristics of quartz extracted from the bricks were determined using TL (210°C peak) and OSL measurement procedures. Both TL and OSL measurement procedures based on SAR and SARA protocols were applied to determine the palaeodose. The luminescence dates for three sampled locations are in good agreement with the assigned architectural dates; the fourth appears to be older raising doubts concerning the architectural assessment of the sampled phase.     

Luminescence sensitivity changes in quartz as a result of annealing

Retrospective dosimetry using optically stimulated luminescence (OSL) on quartz extracted from (for example) bricks needs to account for strong OSL sensitivity changes that are known to occur depending on the previous thermal treatment of the sample. Non-heated quartz exhibits OSL orders of magnitude less per unit radiation than that for heated material. The reason these temperature-induced sensitivity changes occur in quartz is presently not well understood. This phenomenon is also seen in the related area of luminescence dating in which sedimentary quartz and quartz from heated archaeological samples show very different OSL sensitivities. In this paper we report on studies of the effects of high temperature annealing on the OSL and phototransferred TL (PTTL) signals from sedimentary and synthetic quartz. A dramatic enhancement of both OSL and PTTL sensitivity was found especially in the temperature range 500–800°C. Computer simulations of the possible effects are shown to produce data that agree in all essential details with the experimental observations. It is further demonstrated that the enhanced OSL sensitivity as a function of annealing temperature is not a pre-dose effect.     

Aggregation of gold nanoparticles followed by methotrexate release enables Raman imaging of drug delivery into cancer cells

A certified reference material, ERM-FD100, for quality assurance and validation of various nanoparticle sizing methods, was developed by the Institute for Reference Materials and Measurements. The material was prepared from an industrially sourced colloidal silica containing nanoparticles with a nominal equivalent spherical diameter of 20?nm. The homogeneity and stability of the candidate reference material was assessed by means of dynamic light scattering and centrifugal liquid sedimentation. Certification of the candidate reference material was based on a global interlaboratory comparison in which 34 laboratories participated with various analytical methods (DLS, CLS, EM, SAXS, ELS). After scrutinising the interlaboratory comparison data, 4 different certified particle size values, specific for the corresponding analytical method, could be assigned. The good comparability of results allowed the certification of the colloidal silica material for nanoparticle size analysis.     

Characteristics of time-resolved luminescence in quartz

Time-resolved luminescence measurements were performed with samples of synthetic quartz (Sawyer Premium Q) and granular quartz extracted from ceramics and sediment samples under pulsed (5 ns) laser stimulation (OPO). The luminescence was detected in the UV region using colour glass filters (FWHM 280–380 nm). The time-resolved spectrum is dominated by a single exponential decay that remains substantially unaltered when the stimulation wavelength is changed from 600 to 450 nm indicating that the same recombination process is being observed. The lifetime measured at room temperature was 40±0.6 μs for the synthetic quartz; at elevated temperatures the measured lifetime is reduced in a manner that is consistent with a competitive non-radiative recombination process (thermal quenching). An average lifetime of 33±0.3 μs was obtained for seven samples of granular quartz, indicating a common recombination process in these natural samples that differs from the value for synthetic quartz.     

Temperature dependence of luminescence time-resolved spectra from quartz

Pulsed optical stimulation of luminescence has been used to study the thermal dependence of luminescence lifetimes in quartz over the temperature range 20–200°C. Time-resolved spectra for lifetime analysis were recorded from samples of quartz over a dynamic range of 64 μs following stimulation of luminescence by pulsed 525 nm green light emitting diodes (LEDs) using an 11 μs pulse and 12% duty cycle. It has been demonstrated that an increase in measurement temperature generally leads to a decrease in lifetimes from about 30 μs at 20°C to about 7 μs at 200°C. The form of the decrease is influenced by the initial optical or thermal pre-treatment of samples.     

Study of the 110°C TL peak sensitivity in optical dating of quartz

As the 110°C TL emission in quartz uses the same luminescence centers as the OSL emission, the 110°C TL signal from a test dose may be used to monitor the OSL sensitivity change. It is thus important to study the relationship between the 110°C TL peak and the OSL sensitivity in studies related to optical dating from quartz. We have conducted a series of experiments using sedimentary quartz, where the annealing temperatures were varied between 260 and 1000°C before the measurement of OSL and 110°C TL sensitivities. Another series of experiments on two sedimentary quartz samples investigated the 110°C TL peak and OSL dose-dependent sensitivity change after different annealing temperatures. In these experiments, the 110°C TL and OSL signals from the test dose are shown to have similar sensitization characteristics: the 110°C TL sensitivity change is proportional to the OSL sensitivity change if the annealing temperature is lower than 500°C. It is concluded that the 110°C TL signal can be used to correct the OSL sensitivity change in the single-aliquot additive-dose protocol.     

Time-resolved luminescence from annealed synthetic quartz under 525 nm pulsed green light stimulation

The influence of annealing on lifetimes has been studied in synthetic quartz annealed at temperatures up to 800°C using time-resolved optical stimulation in the range 20–200°C. Luminescence was stimulated using pulsed 525 nm light-emitting-diodes. There is an increase with annealing temperature in the lifetime measured at 20°C for samples annealed beyond 500°C. Further, lifetimes decrease with measurement temperature in a manner consistent with the thermal quenching of luminescence.     

Interlaboratory comparison for the measurement of particle size and zeta potential of silica nanoparticles in an aqueous suspension

The Institute for Reference Materials and Measurements has organised an interlaboratory comparison (ILC) to allow the participating laboratories to demonstrate their proficiency in particle size and zeta potential measurements on monomodal aqueous suspensions of silica nanoparticles in the 10–100 nm size range. The main goal of this ILC was to identify competent collaborators for the production of certified nanoparticle reference materials. 38 laboratories from four different continents participated in the ILC with different methods for particle sizing and determination of zeta potential. Most of the laboratories submitted particle size results obtained with centrifugal liquid sedimentation (CLS), dynamic light scattering (DLS) or electron microscopy (EM), or zeta potential values obtained via electrophoretic light scattering (ELS). The results of the laboratories were evaluated using method-specific z scores, calculated on the basis of consensus values from the ILC. For CLS (13 results) and EM (13 results), all reported values were within the ±2 |z| interval. For DLS, 25 of the 27 results reported were within the ±2 |z| interval, the two other results were within the ±3 |z| interval. The standard deviations of the corresponding laboratory mean values varied between 3.7 and 6.5%, which demonstrates satisfactory interlaboratory comparability of CLS, DLS and EM particle size values. From the received test reports, a large discrepancy was observed in terms of the laboratory’s quality assurance systems, which are equally important for the selection of collaborators in reference material certification projects. Only a minority of the participating laboratories is aware of all the items that are mandatory in test reports compliant to ISO/IEC 17025 (ISO General requirements for the competence of testing and calibration laboratories. International Organisation for Standardization, Geneva, 2005b). The absence of measurement uncertainty values in the reports, for example, hindered the calculation of zeta scores.     

Interlaboratory evaluation of hydrophone sensitivity calibration from 0.1 to 2 MHz via time delay spectrometry

Knowing the low-frequency response of hydrophones, down to 100 kHz at least, is important for accurate biomedical ultrasound measurements. However, current international standards do not extend below 500 kHz. Furthermore, commercial hydrophone sources typically do not supply sensitivity data below 1-2 MHz. Therefore, to help identify and validate practical calibration methods below 2 MHz, the authors have extended their previous individual efforts in an interlaboratory evaluation of sensitivity calibration using the swept-frequency technique, time delay spectrometry (TDS). Calibrations were performed for needle and membrane PVDF hydrophones using each laboratory's TDS system. Each site employed the same purpose-built broadband source transducers, comprising both plano-concave and biconcave 1-3 piezocomposite elements 4 cm in diameter, with maximum and minimum thicknesses of approximately 1.5 and 0.1 cm. Agreement between laboratories was within the estimated measurement precision of +/-0.6 dB. The results demonstrated that a TDS system employing such transducers constitutes a viable method for hydrophone calibrations in this frequency range.     

Limits to depletion of blue-green light stimulated luminescence in feldspars: implications for quartz dating

Feldspar contaminants in quartz aliquots, either as micro-inclusions or as remnant grains (due to inadequate etching) can affect the accuracy and precision of paleodose estimates based on blue-green light stimulated luminescence (BGSL). Such contamination could also alter the shape of the BGSL stimulation curve of otherwise pure quartz. In this study, the functional relationship between the infra-red stimulated luminescence (IRSL) and BGSL of feldspars, (1) at different preheats, and (2) with IR bleaching at different stimulation temperatures and durations, is examined. The results suggest two trap populations participate in the feldspar BGSL process. These are: (1) Type (A) trap populations that can be stimulated by both the infra-red and the blue-green light at 125°C and, (2) Type (B) trap populations that respond only to blue-green-light stimulation at 125°C. However, infra-red stimulation at elevated temperature (220°C) (ETIR) permits depletions of charges in Type (A) and Type (B) to the extent that the feldspar BGSL can be reduced by up to 97% in 5 min.

These results offer prospects for (1) improved precision in paleodose estimates based on quartz; (2) BGSL dating of quartz in a polyminerallic fine grain samples; (3) age estimates based on both quartz and feldspars from the same aliquots, and (4) dating based on feldspar micro-inclusions.     

Comparison of luminescence lifetimes in quartz following alpha and beta irradiation

The change in optically stimulated luminescence sensitivity of quartz associated with annealing is accompanied by a change in luminescence lifetime, whereas, in contrast, the change in sensitivity associated with irradiation by alpha particles rather than by beta particles is not accompanied by any change in luminescence lifetime. This is compatible with the usual ‘saturation’ explanation for the significantly lower luminescence sensitivity of quartz to alpha irradiation compared to the luminescence sensitivity to beta irradiation.     

Reproducibility experiments on measuring acoustical properties of rigid-frame porous media (round-robin tests)

This paper reports the results of reproducibility experiments on the interlaboratory characterization of the acoustical properties of three types of consolidated porous media: granulated porous rubber, reticulated foam, and fiberglass. The measurements are conducted in several independent laboratories in Europe and North America. The studied acoustical characteristics are the surface complex acoustic impedance at normal incidence and plane wave absorption coefficient which are determined using the standard impedance tube method. The paper provides detailed procedures related to sample preparation and installation and it discusses the dispersion in the acoustical material property observed between individual material samples and laboratories. The importance of the boundary conditions, homogeneity of the porous material structure, and stability of the adopted signal processing method are highlighted.     

Non-contact subsurface temperature measurements following mid-infrared laser irradiation

A difficult challenge in laser processing at nanosecond time scales is monitoring substrate temperature in the laser focal volume, particularly for mid-infrared laser irradiation where the absorption depth is relatively large and the attained temperatures are often relatively low. Here, we describe time-dependent measurements of the subsurface temperature of a target material following absorption of pulsed mid-infrared (MIR) laser irradiation, by detecting the luminescence from micron-size ceramic phosphor particles (Gd-doped YAG:Ce) embedded in the target material at a concentration of up to 10 %. Temperature calibrations were obtained by measuring the luminescence decay of the probe particles in an oil-bath heater. A silica-nanoparticle film was irradiated by an Er:YAG laser operating in a free-running mode over a fluence range up to but below the ablation threshold, while the third harmonic of the Nd:YAG laser excited the luminescence of the probe particles. From the temperature calibrations, it was possible to infer the thermal history of the target as a function of time delay between the Er:YAG and Nd:YAG laser pulses.     

Reliability of single aliquot regenerative protocol (SAR) for dose estimation in quartz at different burial temperatures: A simulation study

The single aliquot regenerative protocol (SAR) is a well-established technique for estimating naturally acquired radiation doses in quartz. This simulation work examines the reliability of SAR protocol for samples which experienced different ambient temperatures in nature in the range of −10 to 40 °C. The contribution of various experimental variables used in SAR protocols to the accuracy and precision of the method is simulated for different ambient temperatures. Specifically the effects of paleo-dose, test dose, pre-heating temperature and cut-heat temperature on the accuracy of equivalent dose (ED) estimation are simulated by using random combinations of the concentrations of traps and centers using a previously published comprehensive quartz model. The findings suggest that the ambient temperature has a significant bearing on the reliability of natural dose estimation using SAR protocol, especially for ambient temperatures above 0 °C. The main source of these inaccuracies seems to be thermal sensitization of the quartz samples caused by the well-known thermal transfer of holes between luminescence centers in quartz. The simulations suggest that most of this inaccuracy in the dose estimation can be removed by delivering the laboratory doses in pulses (pulsed irradiation procedures).     

Validation and traceability of XRF and SEM‐EDS elemental analysis results for solder in high‐reliability applications

A procedure and calibration samples were developed for X‐ray fluorescence spectrometry and scanning electron microscopy (SEM) with energy dispersive spectrometry (EDS) analysis methods for Sn and Pb amounts in solder and coatings. Test methods are needed by laboratories that perform destructive physical analysis of high‐reliability electronics for MIL‐STD‐1580B. Calibrants are prepared by evaporative deposition of multiple, alternating quantities of pure Sn and pure Pb having mass per unit area proportional to mass fractions of Sn and Pb in a solder being mimicked. Validation reference materials are prepared by evaporative deposition of thin films of SRM 1729 Tin Alloy (97Sn–3Pb). Films are created on high‐purity Ni foil to mimic some actual electronics structures and prevent charging during SEM‐EDS measurements. Maximum thickness of films prepared this way must be kept below approximately 1 µm to ensure that the entire thickness is probed by the primary X‐ray or electron beam and that measured X‐rays come from the entire thickness of all films. Detailed procedures are presented, and method performance was characterized. The primary purpose is to create calibrations for Sn and Pb that are simple to implement and establish traceability to the international system of units. The secondary purpose is to validate calibrations using a certified reference material to prove that, for simpler structures of thin solder coatings on metal, both X‐ray fluorescence and SEM‐EDS provide accurate results. Keeping films thin may be unrealistic in comparison with some, if not many, electronic structures, but this approach enables a laboratory to demonstrate competence in a controlled manner. Copyright © 2014 John Wiley & Sons, Ltd.     

Study of sensitivity change of OSL signals from quartz and feldspars as a function of preheat temperature

Optically stimulated luminescence (OSL) signals from feldspar and quartz samples were studied using infrared (860 nm) and green light (420–575 nm) stimulation. A serious problem connected with the regeneration technique used for dating is associated with a change of OSL sensitivity to radiation in the course of the measurement process. A typical effect seen is a large increase of the apparent strength of our beta source when calibrated against a gamma source. If the regeneration procedure is used, it is shown that the sensitivity increases up to 50% during the measurement process and as a result, the equivalent dose (ED) would be underestimated. A study of sensitivity changes in feldspars and quartz was carried out with emphasis on the effect of preheat and annealing on the OSL signal. Measurement results obtained are presented, and possible elimination of errors in dating caused by sensitivity changes is discussed.     

Relative response of TL and component-resolved OSL to alpha and beta radiations in annealed sedimentary quartz

Knowledge of the relative luminescence response to alpha and beta radiation is very important in TL and OSL dating. In the present study the relative alpha to beta response is studied in a sedimentary quartz sample, previously fired at 900 °C for 1 h, in the dose region between 1 and 128 Gy, for both thermoluminescence (TL) and linearly modulated optically stimulated luminescence (LM – OSL). The LM – OSL measurements were performed at room temperature and at 125 °C. All OSL signals were deconvolved into their individual components. Comparison of OSL curves after alpha and beta irradiation strongly supports that quartz OSL components follow first order kinetics in both cases. In the case of TL, the relative alpha to beta response is found to be very different for each TL glow-peak, but it does not depend strongly on irradiation dose. In the case of LM – OSL measurements, it is found that the relative behaviour of the alpha to beta response is different for three distinct regions, namely the fast OSL component, the region of medium OSL component originating from the TL glow-peak at 110 °C when stimulation takes place at room temperature and finally the region of slow OSL component. Following stimulation at ambient temperature, the relative alpha to beta response of all components was not observed to depend significantly on dose, with the value of ratio being 0.03 and a tendency to decrease with increasing dose. However, in the case of measurements performed at 125 °C, the relative response of the fast components is much enhanced, and for the remaining components it increases with increasing dose. Special care must be taken to examine the relative alpha to beta response of the fast component at 125 °C which contrasts the relative response of the TL peak at ca. 325 °C. The implications for the dating of annealed quartz are also briefly discussed.