Anomalous fading of the IRSL signal of polymineral grains in Chinese loess

Laboratory storage and preheating experiments were carried out to study anomalous fading of infrared stimulated luminescence (IRSL) signals derived from polymineral grains extracted from Chinese loess. Results of laboratory storage at 150 ^°C and higher temperature preheating experiments showed that such thermal treatments could lessen the effect of fading and indicated the presence of both thermal and non-thermal fading. In addition, the behavior of natural fading over the past 9–170 ka was investigated. By comparing with independent ages (obtained from fine-grain quartz using the optically stimulated luminescence (OSL) signal for the past 130 ka and the thermally transferred OSL (TT-OSL) signal in the age range of 130–170 ka) for the same samples, equivalent doses obtained from the IRSL signals were found to be underestimated by different amounts since the penultimate glacial; there was a linear dependence when the age underestimation was plotted against geological time.     

Optically stimulated luminescence from BeO ceramics: An LM-OSL study

Optically Stimulated Luminescence (OSL) signals of BeO ceramics were investigated using continuous wave (CW) OSL and Linearly Modulated (LM) OSL. It was found that both curves can be approximated using a linear combination of two first-order components. Experiments on the measurement temperature dependence have shown that these two components have nearly the same thermal quenching energies around 0.57 eV. Dependences of the OSL signal on preheat temperature and radiation dose were also examined. Thermal annealing experiments have shown that OSL signals originate from traps which are unstable near 340 °C, thus proving the suitability of the signals for dosimetric purposes. Dose response was found to be linear and a minimum detectable dose of ～10 μGy was found.     

The TL and room temperature OSL properties of the glow peak at 110 °C in natural milky quartz: A case study

The LM–OSL signal of quartz, while measured at room temperature, is dominated by an intermediate, broad and intense OSL component, so that its contribution and general characteristics are derived very accurately. Through a series of dose–response, bleaching and thermal decay at room temperature experiments, in conjunction with curve fitting studies, a component resolved analysis is carried out studying the correlation between this specific component, termed as LM–OSL component C₂ and the 110 °C TL glow peak in quartz. The dose–response of these two luminescence components behaves exactly similar being linear at low doses and saturating at almost 100 Gy. Both signals decay exponentially under illumination, providing identical optical detrapping cross-section values. Residual of both luminescence signals after thermal decay at room temperature follows an exponential law, yielding similar mean half-lives. All previous luminescence features provide strong evidence for the electron trap being the same for both the 110 °C TL trap and the LM–OSL component C₂. The results of the present work are very promising and clearly support the possibility of extrapolating the TL pre-dose methodology to the OSL pre-dose effect using only the LM–OSL component C₂.     

Luminescence property of volcanic quartz and the use of red isothermal TL for dating tephras

An optically stimulated luminescence (OSL) age obtained from a Japanese tephra using quartz phenocrysts severely underestimated the known age. The characteristics of the OSL signals were investigated in order to understand the cause of the underestimation; the main OSL component of volcanic quartz has a thermodynamic lifetime of about 1700 years at room temperature, and it also seems to fade anomalously (i.e. athermally). Measurement of conventional red thermoluminescence (RTL) using a Ga–As photomultiplier tube was difficult due to the presence of a strong thermal background, although RTL gave an age consistent with the independent age. Furthermore, red isothermal TL (RITL) at 380 °C allowed the RTL signal to be separated from to the thermal background, and RITL ages of three volcanic quartz samples show good agreement with independent ages.     

Retrospective dosimetry using Japanese brick quartz: A way forward despite an unstable fast decaying OSL signal

Quartz extracted from heated bricks has been previously suggested for use in dose estimation in accident dosimetry, but this technique has never been applied before to Japanese quartz which often has unusual OSL characteristics. In this study the optically stimulated luminescence (OSL) characteristics of quartz extracted from a Japanese commercial red brick produced by Mishima – Renga – Seizoujyo Co. are studied. These companies are based in the Aichi Prefecture (capital Nagoya), which accounts for about half of the red brick production in Japan. A comparison of TL (thermoluminescence) and OSL signals has been carried out towards identification of common source traps. It is observed that OSL from Japanese brick quartz shows unusual luminescence characteristics; in particular, the initial fast decaying OSL signal contains a dominant (>90%) thermally unstable component related to the 85 °C TL peak, which necessitates a prior heat treatment. A single-aliquot regenerative-dose (SAR) protocol is developed and tested using thermal treatments intended to isolate a stable dosimetric signal. A minimum detection limit of ～65 mGy is then estimated using this protocol. Following irradiation using ⁶⁰Co and ¹³⁷Cs, dose–depth profiles were measured on two different commercial brick types (Mishima – Renga – Seizoujyo Co. and Hase – Renga Co.) with 5 Gy and 10 Gy surface doses. The profiles derived from the two sources were readily distinguishable. It is concluded that the OSL signals from the two types of Japanese brick quartz examined here can be used to derive precise estimates of accident dose, and, possibly to distinguish between sources of gamma radiation in a nuclear accident.To our knowledge, this is the first report on the existence of an unstable fast decaying OSL signal in quartz derived from bricks, and demonstrates a way forward with such samples in retrospective dosimetry.     

Radiation dose response correlation between thermoluminescence and optically stimulated luminescence in quartz

The fast, linearly modulated optically stimulated luminescence (LM-OSL) component in quartz is the main dosimetric signal used for the dating applications of this material. Since the blue light stimulation (470 nm, 40 mW cm ${}^{?2}$) time needed to obtain the fast LM-OSL component is less than 50 s the electron trapping levels responsible for it are still highly populated. In this way an active radiation history is created which could play an important role in the dosimetric characteristics of the fast OSL signal. In the present work the dose response behavior of the fast OSL signal is investigated in quartz samples with an annealed radiation history and quartz samples possessing an artificial radiation history. A computerized curve de-convolution analysis of the LM-OSL curves for 50 s stimulation time showed that it consists of three individual OSL components. The faster component C₁ with peak maximum time around 5 s has a linear dose response in virgin samples, which turns to a slight superlinearity as a function of the artificial radiation history. On the other hand the component C₂ with peak maximum time at 12 s is slightly superlinear which turns into strong superlinearity as a function of artificial radiation history. Finally, component C₃ with peak maximum time at about 45 s is strongly superlinear for both virgin samples and as a function of artificial radiation history. The implications to practical application are discussed.     

Optically stimulated phosphorescence in orthoclase feldspar over the millisecond to second time scale

In the past, time-resolved IR stimulated luminescence (TR-IRSL) curves from feldspar have mainly been measured over a few hundred μs with the purpose of estimating the lifetimes of the components. In this study, we present the decay form of time-resolved IRSL and IR stimulated phosphorescence (IRSP) from orthoclase feldspar covering over 8 orders of magnitude (50 ns to ～7 s). A detailed characterisation of the slowly decaying signals (ms to s time scales) from feldspar is undertaken to obtain further insight into the role of re-trapping in both the IR stimulated luminescence (IRSL) and the relatively more stable post-IR IRSL signals. The decay form of the different signals examined here shows a weak dependence on preheat temperature and a strong dependence on stimulation temperature. Interestingly, the IRSP curves show a conspicuous kink of which the position is linearly dependent on the on-time duration.The data on thermal dependence of these signals might suggest that the decay behaviour of the time-resolved IRSL and phosphorescence signals mainly reflect the occupancy of electrons in the band tail states with a significant contribution from the shallow traps. This interpretation is supported by thermoluminescence (TL) curves showing the photo-transfer effect during short IR and post-IR IR stimulations.     

Mechanoluminescence characterisation of γ-irradiated (KNa)Br:Ce3+ phosphor

The mechanoluminescence (ML) of γ-irradiated coloured powder of (KNa)Br:Ce(0.1–10 mol%) phosphor is reported in this paper. The samples are prepared by wet chemical method. The ML intensities are found to be dependent on concentrations of Ce³⁺ ion and γ-rays radiation dose. The variation of peak ML intensity of (KNa)Br:Ce(0.5 mol%) with different γ-rays dose is found as linear up to 2.5 kGy high dose from 0.08 kGy, whereas for the KBr:Ce(0.5 mol%) and NaBr:Ce(0.5 mol%) samples the ML intensities increases sublinearly. The prepared sample shows minimum fading in ML intensity. The ML characterisation shows the good linearity, less fading and simple ML glow curve structure, thus the prepared material may be useful for radiation dosimetry.     

High LO-to-RF isolation 94 GHz coplanar monolithic down-converter for FMCW radar sensor applications

This paper presents a 94 GHz monolithic down-converter with low conversion loss and high local oscillator (LO)-to-RF isolation using the 0.1 μm T-gate metamorphic high electron-mobility transistor (MHEMT) technology. The down-converter consists of a one-stage amplifier and a single-balanced mixer based on the high-directivity tandem coupler structure using the air-bridge crossovers, thereby amplifying the RF signals and maximizing the LO-to-RF isolation by using an inherent S₁₂ isolation characteristic of the amplifier and good phase balance of the tandem coupler. The fabricated one-stage amplifier using a 30 μm × 2 MHEMT shows a small signal gain of 7 dB at 94 GHz. The single-balanced mixer comprising two 20 μm × 2 MHEMT Schottky diodes and the tandem coupler with an additional λ/4-length line exhibits the conversion loss less than 7.8 dB and the LO-to-RF isolation higher than 30 dB in a RF frequency range of 91–96 GHz. Two circuits designed both for a 50 Ω impedance system are integrated into the down-converter of a 2.6 × 2.5 mm² chip size, and it shows a low conversion loss of ∼1 dB at 94 GHz and excellent LO-to-RF isolation above 40 dB in a frequency range of 90–100 GHz. This is the best isolation among the W-band monolithic down-converters reported to date.     

Third-order photonic-crystal distributed-feedback quantum cascade lasers

We demonstrate room-temperature operation of broad-area edge-emitting photonic-crystal distributed-feedback quantum cascade lasers at λ ～ 4.6 μm. The lasers use a weak-index perturbed third-order photonic-crystal lattice to control the optical mode in the wafer plane. Utilizing this coupling mechanism, the near-diffraction-limited beam quality with a far-field profile normal to the facet can be obtained. Single-mode operation with a signal-to-noise ratio of about 20 dB is achieved in the temperature range of 85–290 K. The single-facet output power is above 1 W for a 55 μm × 2.5 mm laser bar at 85 K in pulsed mode.     

11-mJ pulse energy wideband Yb-doped fiber laser

We report a wide bandwidth (Δλ=8 nm) optical pulsed MOPA (master oscillator power amplifier) source emitting 11.23 mJ pulses (1.25 MW peak power) in the wavelength centered at (λ=1064 nm). Pulse duration and repetition rate were 9 ns and from 10 Hz to 100 Hz, respectively. In order to suppress amplified spontaneous emission (ASE), multi-stage pulse pump technology is applied. And the large core diameter (90 μm) and wide bandwidth ensures the high peak power and energy output.     

Using optically stimulated electrons from quartz for the estimation of natural doses

A flow-through Geiger-Müller pancake electron detector attachment has been fitted to a standard Risø TL/OSL reader enabling optically stimulated electrons (OSE) to be measured simultaneously with optically stimulated luminescence (OSL). Using this detector, OSE and OSL measurements from natural quartz samples are studied to examine the possible use of OSE as a chronometer. First the relative variability in OSE and OSL growth curve shapes and the effect of preheat on these are presented, and from these curves, conclusions are drawn concerning the charge movement in natural quartz. Secondly, a dose recovery test shows that OSE can successfully recover a laboratory dose of 300 Gy given before any laboratory thermal treatment, for preheating temperatures between 160 and 260 °C. Furthermore, for the first time natural OSE decay curves are detected and these signals are used to estimate a burial dose using the single-aliquot regenerative-dose (SAR) procedure. Finally, a comparative study of the equivalent doses estimated using both OSE and OSL from 10 quartz samples are presented, and it is shown that OSE has a significant potential in retrospective dosimetry.     

Investigations of the post-IR IRSL protocol applied to single K-feldspar grains from fluvial sediment samples

The post-IR IRSL protocol with single K-feldspar grains was applied to three samples taken from a fluvial sedimentary sequence at the archaeological site of the Dali Man, Shaanxi Province, China. K-feldspar coarse grains were extracted for measurement. Approximately 30–40% of the grains were sufficiently bright to measure, and after application of rejection criteria based on signal strength, recuperation, recycling ratio and saturation dose, ～10–15% of the grains were used for D_e calculation. The relationship of signal decay rate and form of D_e(t) with the recovery dose were investigated. The dose recovery ratios of the samples after initial bleaching with the four different light sources were within uncertainties of unity. No anomalous fading was observed. The over-dispersion of the recovered dose and D_e values were similar, suggesting neither incomplete resetting of the post-IR IRSL signals nor spatially heterogeneous dose rates significantly affected the natural dose estimates. The values of D_e obtained with the single K-feldspar grain post-IR IRSL protocol were in the range ～400–490 Gy. Combining all of the measured single-grain signals for each of the individual samples (into a ‘synthetic single aliquot’) increased the D_e estimates to the range ～700–900 Gy, suggesting that the grains screened-out by the rejection criteria may have the potential to cause palaeodose over-estimation, although this finding requires a more extensive investigation. Thermally transferred signals were found in the single K-feldspar grains post-IR IRSL protocol, and the proportion of thermally transferred signal to test-dose OSL signal (stimulation at 290 °C) from the natural dose was higher than from regenerative doses, and the proportion was grain- and dose-dependent. As such, TT-post-IR IRSL signals at 290 °C have the potential to cause dose underestimation, although this may be reduced by using larger test-dose irradiations. Our study demonstrates considerable potential in the post-IR IRSL method in providing chronological control in studies relevant to human evolution in the later-Pleistocene.     

Improving the accuracy and precision of equivalent doses determined using the optically stimulated luminescence signal from single grains of quartz

Optically stimulated luminescence (OSL) measurements of quartz are widely used to measure equivalent dose (D_e). At radiation doses above ～100 Gy, saturation of traps results in a decrease in the rate of growth of the OSL signal, and this makes calculation of D_e increasingly difficult. A series of dose recovery experiments was undertaken using single grains of quartz from Kalambo Falls, Zambia to explore saturation of single grains. When the OSL signal from many grains is averaged, the characteristic dose (D₀) is 47 Gy, typical of published values for quartz. However, D₀ for individual grains varies from ～10 to 100 Gy. Doses up to two times the average D₀ could be accurately recovered, but above this dose the D_e became increasingly underestimated. Overdispersion for this type of experiment should be zero, but was observed in all data sets; furthermore the value of overdispersion increased with D_e. An additional acceptance criterion, the Fast Ratio, is suggested for single grain OSL analysis. This criterion assesses the relative contribution of the fast component of the OSL signal. Including this as an additional acceptance criterion leads to an improved precision, with overdispersion reduced to zero, and improved accuracy in dose recovery at high doses.     

Bactericidal effects of negative and positive ions generated in nitrogen on Escherichia coli

The bactericidal effect of both negative and positive ions generated by a dc electrical corona in nitrogen were investigated. Tryptic soy broth agar plates inoculated with Escherichia coli (E. coli) (strain DH5-α) were placed into a custom-built multi-point-to-plane ion generator situated within a glass chamber. Under a nitrogen atmosphere the plates were exposed to either negative or positive ions for various time periods. The plates were then removed and incubated at 37°C for 15 h and the colonies counted. Exposure to either negative or positive ions produced significant reductions (p<0.05) in colony number. Bacterial plates exposed to a constant 200 μA negative current for 30 min demonstrated a 65% reduction in colony number compared to unexposed plates. Increasing the exposure current to 400 μA, further increased the level of disinfection at 30 min to 91%. Exposure to 200 μA current of positive ions produced a 72% reduction after 10 min and virtual sterilisation after 30 min with a 98% reduction in colony number. These results indicate that exposure to negative and particularly positive ions has a lethal effect on E. coli cells. Cell death could be due to a physiological change in the outer membrane as a result of ionic interactions.     

Low-intensity pulsed ultrasound enhances cell killing induced by X-irradiation

To determine the effect of pulsed ultrasound (US) on radiation-induced cell killing, U937 and Molt-4 cell lines were exposed to 1.0 MHz US with 50% of duty factor at 0.3 W/cm² and pulsed at 1 Hz immediately after exposure to X-rays at 0, 0.5, 2.5 and 5 Gy. The cells were assayed 24 h after the treatments. The result showed significant enhancement of cell killing in the combined treatments. However, the ratio of apoptotic cells induced either by X-rays or US alone did not significantly change. These findings suggest that pulsed US can enhance the anticancer effect of X-irradiation due to US streaming under non-inertial cavitational condition. This combined treatment can potentially enhance the therapeutic effect of radiation therapy.     

Ultrasmall optical logic gates based on silicon periodic dielectric waveguides

An ultrasmall silicon periodic dielectric waveguides-based multimode interference all-optical logic gate has been proposed. The device consists of three 205 nm wide single-mode input waveguides, a 1.1 μm wide and 5.5 μm long multimode interference waveguide, and three 205 nm wide single-mode output waveguides. The total length and width of the device are 13.7 μm and 3.2 μm, respectively. By changing the states of the input optical signals and/or control signals launched into the device, multifunctional logic functions including OR, NAND, NOR, and NOT gates are performed, and each logic function can be realized at a specific output waveguide in accordance with the launched control signals. The ultrasmall multifunctional logic device has potential applications in high density photonic integrated circuits.     

Development of an efficient coherent optical source at 6.04 μm

Efficiency as high as 26% is obtained for generation of mid-infrared radiation at 6.04 μm by frequency doubling of ammonia laser emission at 12.08 μm in a 15 mm long type-I cut AgGaSe₂ crystal. The NH₃ laser used for this work is optically pumped by a commercial TEA CO₂ laser operating on 9.22 μm and produces pulsed output of ∼210 mJ with a duration of ∼200 ns at 12.08 μm. The generated radiation at 6.04 μm is separated out from the residual radiation at 12.08 μm by exploiting the principle of polarization dependent diffraction of reflection grating.     

Compact WDM demultiplexer for seven channels in photonic crystal

We demonstrate a new device concept for wavelength division demultiplexing based on planar photonic crystal waveguides. The filtering of wavelength channels is realized by shifting the cutoff frequency of the fundamental photonic bandgap mode in consecutive sections of the waveguide. The shift is realized by modifying the size of the border holes.The proposed demultiplexer has an area equal to (16.5 μm × 6.5 μm) and thus it is verified that this structure is very small and can be integrated easily into optical integrated circuits with nanophotonic technologies. The output wavelengths of designed structure can be tuned for communication applications, around 1550 nm. The wavelengths of demultiplexer channels are λ₁ = 1.590 μm, λ₂ = 1.566 μm, λ₃ = 1.525 μm, λ₄ = 1.510 μm, λ₅ = 1.484 μm, λ₆ = 1.450 μm, λ₇ = 1.400 μm respectively. Designs offering improvement of number of the separate wavelengths (seven), miniaturization of the structure (107.25 μm²) is our aim in this work.In our structure, we consider that the 2D triangular lattice photonic crystal is composed of air holes surrounded by dielectric. Its parameters are: radius of holes (r = 0.130 μm), lattice constant (a = 0.380 μm), and index of membrane (n = 3.181:InP). The numerical model used to simulate the structure of the demultiplexer is based on the finite difference time domain (FDTD).     

Thickness dependence of Ic and Jc of LTG-SmBCO coated-conductor on IBAD-MgO tapes

We have reported SmBa₂Cu₃O_y (SmBCO) films on single crystalline substrates prepared by low-temperature growth (LTG) technique. The LTG-SmBCO films showed high critical current densities in magnetic fields compared with conventional SmBCO films prepared by pulsed laser deposition (PLD) method. In this study, to enhance critical current (I_c) in magnetic field, we fabricated thick LTG-SmBCO films on metal substrates with ion-beam assisted deposition (IBAD)-MgO buffer and estimated the I_c and J_c in magnetic fields.All the SmBCO films showed c-axis orientation and cube-on-cube in-plane texture. T_c of the LTG-SmBCO films were 93.1–93.4 K. J_c and I_c of a 0.5 μm-thick SmBCO film were 3.0 MA/cm² and 150 A/cm-width at 77 K in self-field, respectively. Those of a 2.0 μm-thick film were 1.6 MA/cm² and 284 A/cm-width respectively. Although I_c increased with the film thickness increasing up to 2 μm, the I_c tended to be saturated in 300 A/cm-width. From a cross sectional TEM image of the SmBCO film, we recognized a-axis oriented grains and 45° grains and Cu–O precipitates. Because these undesired grains form dead layers, I_c saturated above a certain thickness. We achieved that I_c in magnetic fields of the LTG-SmBCO films with a thickness of 2.0 μm were 88 A/cm-width at 1 T and 28 A/cm-width at 3 T.