OSL Characteristics Research Articles

OSL Characteristics of Cu Activated NaLi2PO4 Phosphor

OSL Characteristics of Cu Activated NaLi2PO4 Phosphor

Luminescence dating of heated quartz extracted from burnt clay and pottery excavated from the Lingjiatan archaeological site, China

This study utilizes OSL-SAR, TL-SAR, and TL-MAAD methods to date heated quartz extracted from burnt clay and pottery samples from the Lingjiatan archaeological site, China. The OSL components of the heated quartz were determined by deconvoluting the CW-OSL curve, and the Fast Ratio value was used to distinguish whether the initial OSL signal was dominated by the fast component. The results show two types of quartz OSL characteristics in the initial signals: Type I is dominated by the fast component (Fast Ratio values > 10), while Type II is dominated by the medium and slow components (Fast Ratio values < 10). Type I samples show bright OSL signals, and a preheat plateau appears from a relatively low temperature. The recuperation is negligible, and reliable equivalent doses can be obtained using the conventional OSL-SAR measurement conditions. In contrast, the OSL signal of Type II samples is relatively dim, and the preheat plateau appears from a much higher temperature than in Type I samples. The recuperation of Type II samples increases significantly at higher preheat temperatures. Significant De underestimation of Type II samples was observed at lower preheat temperatures. It is noted that the thermal transfer effect can be attenuated by increasing the OSL stimulation temperature. Therefore, a modified OSL-SAR measurement condition, with higher preheat, cut-heat and stimulation temperatures, was used to date Type II samples. The OSL-SAR ages of most of these two types of samples agree well with the independent 14C ages, demonstrating that OSL-SAR can be used to date heated archaeological materials at high firing temperatures (∼900°C). The Lingjiatan archaeological site was determined to be approximately 5.4–5.8 ka BP 2022.

A combined OSL and 14C dating study of charcoal production in the sandy environment of Zoersel forest (N Belgium)

We investigate the potential of quartz-based OSL-dating for application to heated sandy sediments that are closely associated with the remains of charcoal production (charcoal kilns). This is particularly relevant for post-1650 CE features, where 14C-dating lacks resolution. We first document the general OSL characteristics using large aliquots of sand-sized quartz. Results from procedural tests indicate that the laboratory measurement procedure should allow reliable equivalent dose estimation. The scale of analysis is then reduced to smaller aliquots for all samples, each composed of 100–200 grains, as well as to single grains for eight heated samples. For one sample, both the small and single-grain ages are consistent with the 14C-ages obtained for charcoal fragments in the same sedimentary unit. Also for three other samples, single-grains yield ages consistent with 14C-dating; all other OSL-ages are older although, for three of these samples, single grains and small aliquots yield results that are not significantly different. We discuss potential sources of inaccuracy for the OSL-dates, such as dose rate determination and homogeneous incomplete resetting. The latter is the most difficult to assess and requires additional empirical data.

Quartz OSL dating of loess deposits since the late glacial in the Southeast of Caspian Sea

Here we present loess deposits since the late glacial dated by OSL technique in the southeast of the Caspian Sea, bordering continents of Asia and Europe. Chronology of Holocene loess deposits are rarely reported in Eastern Europe and Western Asia, especially for their spacious mid-latitude adjacent region, between Balkans to the west and Pamirs to the east. In this study, an OSL-based chronology was developed for loess deposits in northern Iranian Plateau, based on the YBD loess profile which locates close to center of hilly Iranian Loess Plateau in the southeast of the Caspian Sea and on the northern slope of the Alborz Mountains. The OSL characteristics and their reliability were investigated on coarse-grained quartz (63–90 μm) of the profile, a preheat plateau test and dose recovery test of which reveal that the lower preheat is suitable for loess equivalent dose determination in the area. In addition, the SAR-OSL is an appropriate methodology for dating loess deposited since the late glacial in situ. With preservation of a complete record of loess accumulation since the late glacial, YBD section contains a potentially valuable paleoclimatic record for Caspian region and hence the vast transitional region between Asia and Europe.

Investigation into the OSL and TT-OSL signal characteristics of ancient (>100 ka) Tasmanian aeolian quartz and its utility as a geochronometer for understanding long-term climate-driven landscape change

The luminescence characteristics and age estimates of nine samples of aeolian quartz are reported from the Southwood B section in the Arve Valley of southern Tasmania, Australia. New OSL and TT-OSL ages obtained from the deepest Tasmanian aeolian section found so far, the Southwood B section (>6 m deep), range from 20 ka (MIS 2) to 180 ka (MIS 6). Here we test two previously published TT-OSL protocols on our samples: the protocol of Brown and Forman (2012) and a protocol modified from Stevens et al. (2009). Congruencies between our TT-OSL chronology, OSL chronology and previously published TL ages suggest that the modified Stevens et al. (2009) protocol is the most robust for these samples. Furthermore, detailed comparisons of the laboratory data for TL, OSL, and TT-OSL samples provide information on their signal characteristics, their utility as chronometers, and give insight into the bleaching histories of the deposits. All OSL and TT-OSL ages obtained from the Southwood B section fall below the upper dating limits of these signals, which are reported to be as high as ∼280 ka and ∼570 ka, respectively. The TT-OSL signal saturates at doses that are two to three times those of the OSL signal, and may not only provide a chronology for sediments deposited during MIS 5, but also, according to the saturation limits, for any preserved sediments that accumulated during MIS 6 through to MIS 15. TT-OSL ages from older sediments in this region, combined with further stratigraphic studies have the potential to determine the climatic history of Tasmania over multiple glacial periods.

SOL-GEL α-Al2O3 detectors: TL and OSL response to beta radiation beams

The dosimetric properties of the SOL-GEL α-Al2O3 detectors with several different concentrations of impurities were studied in beta radiation beams. For the characterization of the detectors, the TL and OSL techniques were used. A TL spectrum was acquired. The detectors showed adequate OSL and TL dosimetric characteristics, such as good reproducibility, a glow curve with the peak at ~230 °C at 5 °C/s of heating rate, adequate OSL decay curve, good linearity of response and high phosphor sensitivity. A thermal treatment study was also performed. Moreover, the calibration factors and the lower detection limits were determined for beta radiation. These characteristics indicate the suitability of SOL-GEL α-Al2O3 detectors for the establishment of a transfer system or alternative/complementary method for beta radiation dosimetry.

Optically stimulated luminescence of α-Al2O3:C by the vertical gradient freezing (VGF) method

A highly sensitive α-Al2O3:C crystal was directly grown by the vertical gradient freezing (VGF) method, which combines the advantages of the crystal growth in the highly reducing atmosphere in the presence of graphite and the crystal directly grown by the using Al2O3 and graphite powder as raw materials. The main OSL characteristics of the detectors as grown were investigated. The OSL signal originates from the main TL peak, the responsible electron trap can be emptied basically by OSL readout. The mean OSL sensitivity per unit mass of the VGF α-Al2O3:C is 1.6 times higher than that of the TLD-500K. The OSL detection thresholds of the VGF α-Al2O3:C and the TLD-500K are 0.21 μGy and 0.51 μGy respectively. The OSL signals for the two kinds of detectors are reproducible within a coefficient of variation of less than 2.5% over ten re-use cycles without systematic decrease. The VGF α-Al2O3:C detectors shown an excellent linear response within the dose range from 1 μGy to 15 Gy. The dose can be independently re-analysed multiple times. The VGF α-Al2O3:C can be used to measure the very low dose in environmental monitoring and personnel dosimetry.

Temperature-dependent OSL properties of nano-phosphors LiAlO2:C and α-Al2O3:C

The present study focuses on the synthesis and characterization of carbon doped nano-phosphors, LiAlO2 and α-Al2O3 and their temperature-dependent optically stimulated luminescence (TA-OSL) characteristics in the temperature ranges of 25–350 °C. These nano-phosphors with the carbon concentration of 0.01 mol% exhibits high luminescent intensity for LiAlO2:C in the low dose range of 1 mGy-7 Gy and for α-Al2O3:C in the range of 100 mGy-1 kGy. Both these nano-phosphors are of polycrystalline in nature, having grain size 15–50 nm as confirmed by the X-ray diffraction (XRD) and Transmission Electron Microscopy (TEM), respectively. The maximum TA-OSL intensities are observed at 125 °C for LiAlO2:C and 200 °C for Al2O3:C, and reveal the presence of deep defect centres. The Arrhenius analysis shows the activation energies Ea = 0.06 ± 0.02 eV for LiAlO2:C and Ea = 0.04 ± 0.01 eV, & Eb = 0.48 ± 0.07 eV for Al2O3:C. The TA-OSL and OSL characteristics are discussed with special reference to the medical and high radiation dosimetry. These compounds, LiAlO2:C and α-Al2O3:C, are non-toxic, robust and are potential candidates for reusable dosimetry.

Radio-Optically- and Thermally Stimulated Luminescence of Zn(BO2)2:Tb3+ exposed to Ionizing Radiation

The optical absorption of zinc tetraborate at different concentrations of the terbium impurity (0, 0.5, 1, 2, 4, 8 mol%) was analyzed. The radioluminescence (RL) emission spectra was obtained after beta irradiation of a 90Sr/90Y source. The RL spectrum showed the characteristics bands of Tb3+ with two main emissions at 489 nm and 546 nm which corresponding to the5D4→7F6 and 5D4→7F5 transitions respectively in this ion. The OSL and TL characteristics have been analyzed. The stimulation blue light (497 nm) of a diode laser at 500 mA was used to bleach the thermoluminescent (TL) signals obtained with 5Gy of 60Co source. The two main glow peaks (79 and 161 °C) are sensitives under 497 nm stimulation, and they were shifted to higher temperature values and faded their TL intensities. Similar behavior of TL glow curves before and after OSL stimulation with blue light was observed when the samples were exposed to 30 Gy gamma dose of 137Cs irradiator. The OSL signal response was linear with the dose range of 1-10 Gy and increased their response up to 200 Gy gamma dose. The OSL shows a bleaching sensitive shallow traps and diminishing the intensity of the TL glow curves remaining a complex traps distribution. The RL, TL and OSL properties were investigated in Zn(BO2)2:Tb3+ phosphor.

Variations in luminescence properties of quartz and feldspar from modern fluvial sediments in three rivers

Abstract Studies of modern sediments, their sedimentology and depositional processes are important for understanding the behaviour of the luminescence characteristics of quartz and feldspar in fluvial settings. Previous studies have shown large variations in OSL characteristics of quartz from different fluvial systems, while the IRSL and pIRIR signals from K-feldspar have been understudied. We test the effects of fluvial setting on luminescence characteristics by collecting modern (

Optically stimulated luminescence of borate glasses containing magnesia, quicklime, lithium and potassium carbonates

The OSL characteristics of three different borate glass matrices containing magnesia (LMB), quicklime (LCB) or potassium carbonate (LKB) were examined. Five different formulations for each composition were produced using a melt-quenching method and analyzed in terms of both dose-response curves and OSL shape decay. The samples were irradiated using a 90Sr/90Y beta source with doses up to 30Gy. Dose-response curves were plotted using the initial OSL intensity as the chosen parameter. The OSL analysis showed that LKB glasses are the most sensitive to beta irradiation. For the most sensitive LKB composition, the irradiation process was also done using a 60Co gamma source in a dose range from 200 to 800Gy. In all cases, no saturation was observed. A fitting process using a three-term exponential function was performed for the most sensitive formulations of each composition, which suggested a similar behavior in the OSL decay.

Optically and Thermally Stimulated Luminescence in X-Ray Irradiated Sno-Doped Sro-B2O3 and ZnO-P2O3 Glasses for Passive-Type Dosimeter

Optically and thermally stimulated luminescence (OSL and TSL) phenomenon is based on the presence of electron and/or hole traps and luminescence centers in storage phosphor materials. During exposure to ionizing radiation such as x-ray, γ-ray and β-ray, the traps are occupied with charged carriers such as electrons and holes that are created by irradiation with ionizing radiation. De-trapping of these carriers requires energy. The energy is provided by stimulating of the phosphor materials with visible or infrared light (OSL) or by heating of the phosphor (TSL). During a de-trapping transition, free carriers created by the absorption of photons from the stimulating radiation field, recombine with the luminescence centers, whereby visible photons are emitted. Since the OSL or TSL intensity is in the most cases proportional to absorbed dose of ionizing radiation, the phosphor materials which exhibit the OSL and TSL phenomena adapt to two-dimensional imaging sensor for ionizing radiation. Although imaging plate (IP) using photostimulable phosphor materials such as BaFBr:Eu [1,2] and CsBr:Eu [3] can be now used as two-dimensional sensor for ionizing radiation, these phosphor materials with deliquescent property exhibit poor fading characteristics which is one problem on two dimensional radiation dose estimation using the IP. As a result of surveying many possible phosphor materials, we found that SnO-doped SrO-B2O3 and ZnO-P2O3 glass without deliquescent properties exhibit an efficient OSL and TSL, and good fading characteristics. Typical OSL stimulation and emission spectra of x-ray irradiated SnO-doped SrO-B2O3 glass are shown in Fig.1. In this work, the OSL and TSL characteristics in x-ray irradiated SrO-B2O3 and ZnO-P2O3glasses are in the first time reported and OSL and TSL characteristics are discussed for the passive type dosimeter. Ref. [1] K.Takahashi et al., J. Electrochemcal Soc., 32(1985) 1492.[2] M.Takebe and K.Abe, Nuclear Instruments and Methods, A345(1994) 606.[3]H.Nanto et al., Nuclear Instruments and Methods, A580 (2007)278. Figure 1

Ooptically and Thermally Stimulated Luminescence in x-Ray Irradiated Sn-Doped Sro-B2O3 and ZnO-P2O3 Glasses for Passive-Type Dosimeter

Optically and thermally stimulated luminescence (OSL and TSL) phenomenon is based on the presence of electron and/or hole traps and luminescence centers in storage phosphor materials. During exposure to ionizing radiation such as x-ray, γ-ray and β-ray, the traps are occupied with charged carriers such as electrons and holes that are created by irradiation with ionizing radiation. De-trapping of these carriers requires energy. The energy is provided by stimulating of the phosphor materials with visible or infrared light (OSL) or by heating of the phosphor (TSL). During a de-trapping transition, free carriers created by the absorption of photons from the stimulating radiation field, recombine with the luminescence centers, whereby visible photons are emitted. Since the OSL or TSL intensity is in the most cases proportional to absorbed dose of ionizing radiation, the phosphor materials which exhibit the OSL and TSL phenomena adapt to two-dimensional imaging sensor for ionizing radiation. Although imaging plate (IP) using photostimulable phosphor materials such as BaFBr:Eu [1,2] and CsBr:Eu [3] can be now used as two-dimensional sensor for ionizing radiation, these phosphor materials with deliquescent property exhibit poor fading characteristics which is one problem on two dimensional radiation dose estimation using the IP. As a result of surveying many possible phosphor materials, we found that SnO-doped SrO-B2O3 and ZnO-P2O3 glass without deliquescent properties exhibit an efficient OSL and TSL, and good fading characteristics. In this work, the OSL and TSL characteristics in x-ray irradiated SrO-B2O3 and ZnO-P2O3 glasses are in the first time reported. Ref. [1] K.Takahashi et al., J. Electrochemcal Soc., 32 (1985) 1492. [2] M.Takebe and K.Abe, Nuclear Instruments and Methods, A345 (1994) 606. [3]H.Nanto et al., Nuclear Instruments and Methods, A580 (2007)278.

A detailed post‐IR IRSL dating study of the Niuyangzigou loess site in northeastern China

In this study, we report standard quartz SAR OSL and post‐IR infrared (IR) stimulated luminescence (post‐IR IRSL; pIRIR290) measurements made on sand‐sized quartz and K‐feldspar extracts from the loess‐palaeosol sequence at Niuyangzigou in northeastern China. The quartz OSL characteristics are satisfactory. Extensive pIRIR50,290 dose recovery tests were performed by adding doses on top of the natural dose. We found that dose recovery ratios improve significantly when the test dose ranges between ~15 and ~80% of the total dose, and good dose recovery (within ±5% of unity) can be obtained up to ∼800 Gy. Otherwise, the dose recovery ratio deviates from unity. The De values also depend on the test dose size and so we conclude that the effect of test dose size should be routinely considered in pIRIR dating. First IR stimulation plateau pIRIR290 results are compared with multiple elevated temperature ‐pIRIR (MET‐pIRIR) data. It appears that the low temperature MET‐pIRIR data are strongly affected by poor dose recovery, but this is not the case for the pIRIR290 results. Natural signal measurements at the highest (first IR) stimulation temperature on a sample expected to be in field saturation suggest that ~10% signal loss occurs in pIRIR signals. Long‐term laboratory bleaching experiments (>80 days) show that a constant (or very difficult to bleach) residual pIRIR290 signal is reached after ~300 h, corresponding to a dose of 6.2±0.7 Gy. Quartz OSL and feldspar pIRIR50,290 ages are in good agreement at least back to c. 70 ka. Beyond this the quartz ages begin to underestimate but the feldspar ages are in agreement with the expected Last Interglacial age palaeosol.

High resolution OSL and post-IR IRSL dating of the last interglacial–glacial cycle at the Sanbahuo loess site (northeastern China)

Northeastern China is located in the East Asian monsoon region; it is sensitive to both high and low latitude global climate systems. Loess deposits in the region have considerable potential as sensitive archives of past climate changes. However, research into loess deposition and climate change in this region is restricted by the lack of independent age control. In this study, coarse-grained quartz SAR OSL and K-feldspar post-IR infrared (IR) stimulated luminescence (post-IR IRSL; pIRIR290) methods have been used to date the Sanbahuo loess site in northeastern China. The quartz OSL characteristics are satisfactory. The measured pIRIR290 De's do not vary significantly with IR stimulation temperatures between 50 °C and 260 °C; a first IR stimulation temperature of 200 °C was adopted. Dose recovery tests were performed by adding different laboratory doses to both laboratory bleached (300 h SOL2) samples and natural samples; the results are satisfactory up to ∼800 Gy. Resulting quartz OSL and feldspar pIRIR290 ages are in good agreement at least back to ∼44 ka; beyond this feldspar pIRIR290 ages are older. The feldspar ages are consistent with the expected age of the S1 palaeosol (MIS 5). There appears to have been a period of fast loess deposition at ∼62 ka, perhaps indicative of winter monsoon intensification with a very cold and dry climate that lead to a serious desertification of dunefields in northeastern China.

OSL and TL characteristics of fine grain quartz from Mongolian prehistoric pottery used for dating

Abstract The OSL, post-IR OSL and pulsed post-IR OSL applied to polymineral grains and calculated by fitting to the data the contributions from fast, medium and slow components revealed that the polymineral samples under study are dominated by the medium component. An increase in De’s with increasing integration intervals was observed, which is considered as an indication of increasing medium and decayed fast component; and the equivalent doses obtained using different components or minerals reflect also the shape of the dose distributions. The identified fast component in polymineral sample has photoionization cross section of 1.2±0.02 × 10−17 cm2. The present study shows the usefulness of the application of different luminescence techniques combined with fitting procedures as a check which should be adopted in dating protocols. Based on luminescence ages obtained on poly-mineral grains from prehistoric pottery samples from the Boroo settlement, Mongolia, which are in agreement with independent age control by 14C on charcoal material, it is argued that the manufacturing of Xiongnu — pottery at this site lasted until ca. 130±75 AD.

Luminescence dating of the PASADO core 5022-1D from Laguna Potrok Aike (Argentina) using IRSL signals from feldspar

We have measured and tested a luminescence chronology for the PASADO core 5022-1D from the maar lake of Laguna Potrok Aike. Because of unsuitable quartz OSL characteristics, sand-sized K-feldspar extracts were chosen as a dosimeter and the dose was measured using a post-IR IRSL (pIRIR290) measurement protocol. Using this approach we were able to access a stable signal and thus avoid the ubiquitous problem of feldspar signal instability. Extensive laboratory tests show that the chosen pIRIR290 protocol is applicable to these samples. We also developed a new criterion based on known relative bleaching rates of the conventional IRSL signal (IR50) and the pIRIR290 signal and the relationship between resulting equivalent doses; this is used to identify and reject poorly bleached samples. Eighteen samples out of 47 were rejected based on this criterion, without reference to absolute doses or stratigraphy; the resulting age–depth profile is self-consistent, increases smoothly with depth and is in agreement with independent age control based on volcanic ash layers (Reclús, Mt Burney and Hudson tephras) at the top and middle of the core. Our new luminescence chronology suggests that the 5022-1D core reaches back to ∼65 ka at ∼96 m below lake floor.

OSL and IRSL characteristics of quartz and feldspar from southern California, USA

Southern California comprises of a wide range of diverse landscapes and environments, from high mountains with glacial and periglacial sediments to deserts with large sand dunes, extensive alluvial fans and ephemeral playas. Highly active tectonic processes has exposed ancient (c. 2 Ga) plutonic and metamorphic basement from deep within the crust, while similar Palaeozoic, Mesozoic and Cenozoic rocks are also common. A rich array of volcanic lithologies extending into the late Quaternary complement many thick sedimentary sequences that formed in equally diverse ancient environments typical of an accreting active continental margin. In some locations, notably in the Coachella Valley close to Palm Springs and the Salton Sea, low OSL sensitivity and poor characteristics restrict the application of the quartz SAR protocol to date late Pleistocene and Holocene fluvial sediments. In other locations such as the Malibu coastline, high sensitivity of the quartz OSL signal is observed, despite local source rocks being dominated by volcanic lithologies. Problems of poor quartz characteristics, along with uncertainty in predicting quartz OSL behavior for future dating campaigns poses a significant problem for projects, in particular for neotectonic contexts. While K-feldspar has been used extensively to date eolian and fluvial sediments in southern California, little information regarding signal stability is available. We explore the characteristics of both quartz and feldspar sub-samples from eolian, fluvial, lacustrine environments, in order to help develop mineral selection criteria for optical dating applications and clarify these issues. The importance of radiation quenching in quartz grains recently eroded from bedrock and the role of fires in enhancing OSL sensitivity are considered. The relative bleachability of quartz and feldspar fractions, along with thermal stability considerations is discussed. A simple test for quartz OSL signal contamination based on thermal quenching and assistance, and the susceptibility of the OSL signal to IR bleaching is introduced. ► An overview of the characteristics of OSL/IRSL signals in quartz and feldspar from Southern California, USA. ► Problems associated OSL/IRSL dating in regions with neotectonics. ► A test for OSL/IRSL signal contamination of quartz and feldspar samples.

Optical dating of Romanian loess: A comparison between silt-sized and sand-sized quartz

The loess-palaeosol sequence near Mircea Vodă (Dobrogea, SE Romania) is thought to comprise at least five glacial/interglacial cycles. It is considered as one of the most significant records of Late Quaternary environmental and climatic change in the region. Age information for the sequence was previously obtained through time–depth modeling of magnetic susceptibility data and optically stimulated luminescence dating (OSL) of fine silt-sized (4–11 μm) quartz. This study documents the granulometric properties of the sequence, and compares the OSL characteristics and age of fine sand-sized (63–90 μm) quartz to those of silt-sized quartz. OSL signals from both sand and silt-sized quartz are dominated by a thermally-stable fast decaying component. A suite of laboratory test confirms that the single-aliquot regenerative dose (SAR) protocol is suitable for these samples. Each grain-size fraction yields a set of optical ages that is consistent with the stratigraphic position of the samples. The ages obtained using sand-sized grains, however, are up to 70% higher than those obtained using silt-sized quartz. The discrepancy in age results is not understood as, according to procedural tests, the OSL signal from both fractions should be suitable for dating the deposits. As such, it cannot be established whether the uppermost weakly-developed palaeosol was formed during MIS3 or MIS5 and if the rate of loess accumulation varied during the Last Glacial, only by using standard SAR-OSL techniques. Both sets of ages do confirm, however, that the first well-developed palaeosol (S1) is of Last Interglacial age.

RADIATION ACCIDENT DOSIMETRY ON ELECTRONIC COMPONENTS BY OSL

In the event of large-scale radiation accidents and considering a growing terrorism concern, non-invasive and sufficiently accurate retrospective dosimetry methods are necessary to carry out a fast population triage in order to determine which radiation-exposed individuals need medical treatment. Retrospective dosimetry using different electronic components such as resistors, capacitors, and integrated circuits present on mobile phone circuit boards have been considered. Their response has been investigated with luminescence techniques (OSL, IRSL, and TL). The majority of these electronic components exhibit radiation-induced luminescence signals, and the OSL technique seems the most promising for these materials. Results concerning three types of components that present the most interesting OSL characteristics (in terms of signal annealing and sensitivity) and that are the most often present on mobile phone circuit boards are presented. Preheating effects on OSL signal, sensitization, and dose-response curves from 0.7 to 27 Gy for resistors and from 0.7 to 160 Gy for capacitors and integrated circuits, dose recovery tests, and signal stability 10 h after irradiation have been studied and interests and limits of their use evaluated.