- Email: [email protected]
Ionising radiation effect on the luminescence emission of inorganic and biogenic calcium carbonates
Nuclear Instruments and Methods in Physics Research B 401 (2017) 1–7
Contents lists available at ScienceDirect
Nuclear Instruments and Methods in Physics Research B journal homepage: www.elsevier.com/locate/nimb
Ionising radiation effect on the luminescence emission of inorganic and biogenic calcium carbonates C. Boronat a, V. Correcher a,⇑, M.D. Virgos a, J. Garcia-Guinea b a b
CIEMAT, Av. Complutense 40, Madrid 28040, Spain CSIC, Museo Nacional Ciencias Naturales, José Gutiérrez Abascal 2, Madrid 28006, Spain
a r t i c l e
i n f o
Article history: Received 19 August 2016 Received in revised form 14 March 2017 Accepted 10 April 2017
Keywords: Thermoluminescence Cathodoluminescence Dosimetry Calcite Aragonite
a b s t r a c t As known, the luminescence emission of mineral phases could be potentially employed for dosimetric purposes in the case of radiological terrorism or radiation accident where conventional monitoring is not available. In this sense, this paper reports on the thermo- (TL) and cathodoluminescence (CL) emission of both biogenic (common periwinkle – littorina littorera – shell made of calcite 90% and aragonite 10%) and inorganic (aragonite 100%) Ca-rich carbonates previously characterized by X-ray diffraction and Raman spectroscopy. Whereas the aragonite sample displays the main CL waveband peaked in the red region (linked to point defects), the more intense emission obtained from the common periwinkle shell appears at higher energies (mainly associated with structural defects). The UV-blue TL emission of the samples, regardless of the origin, displays (i) an acceptable ionizing radiation sensitivity, (ii) linear dose response in the range of interest (up to 8 Gy), (iii) reasonable stability of the TL signal after 700 h of storage with an initial decay of ca. 88% for the mineral sample and 60% for the biogenic sample and maintaining the stability from 150 h onwards. (iv) The tests of thermal stability of the TL emission performed in the range of 180–320 °C confirm a continuum in the trap system. Ó 2017 Elsevier B.V. All rights reserved.
1. Introduction Calcium-rich carbonates (mainly calcite, aragonite and dolomite) comprise about 2.5% of the whole volume of the Earth’s crust including not only limestones and marbles, but also produced through biogenic processes (main component of shells of marine organisms, snails, winkles, pearls or eggshells). These materials are employed for the production of cement, as a building material, for health applications (Ca supplement or to produce toothpaste), etc. Based on the luminescence emission, both calcite and aragonite could be used in the field of dating to determine past environmental and changes in the climatic conditions [1,2] or even for the detection of irradiated food [3]. However, according to Ziegelmann et al. [3] the radiation-sensitive samples usually contain calcite and in most cases, also aragonite, but the non-sensitive samples contained only aragonite in the range of 0.05–4 kGy. Such luminescence emission is associated with (i) the appearance of point defects, Frenkel defects, vacancies, planar defects, Schottky defects, dislocations, chemisorbed ions such as H+, OH , HCO3 , [Ca(OH)]+ and [Ca(HCO3)]+ together with frequent hydrocarbon hydrous bonds (C–OH) which could give rise to groups forming ⇑ Corresponding author. E-mail address: [email protected] (V. Correcher). http://dx.doi.org/10.1016/j.nimb.2017.04.035 0168-583X/Ó 2017 Elsevier B.V. All rights reserved.
Non-bridging Oxygen Hole Center (NBOHC) etc. distributed along the calcium carbonate lattice and (ii) defects linked to the structure of calcite (transparent or translucent and white crystals with a rhombohedral habit, prismatic and platy) that considerably differs from the aragonite that usually crystallizes as pseudohexagonal twinned intergrowths in the orthorhombic system. The ionizing radiation (natural or artificially induced) absorbed by the material at RT, gives rise to freed electrons that become trapped in the lattice defects of the material. During this process, the electrons will be trapped for non-defined periods whilst the material is stored at RT. This physical property can be potentially used for the radiation absorbed dose measurement in the fields of dating, retrospective dosimetry, detection of irradiated food or radiological terrorism, as well as for material characterization based on the thermoluminescence (TL) and cathodoluminescence (CL) emission of these phosphors [4,5]. Both luminescence techniques give us information about the trapped charge recombination sites related to metastable defects in the lattice depending on whether the detrapping process is due to heat (TL) or electron exposure (CL). Thus, TL is a method based on the photon emission from an insulator or semiconductor samples when it is heated after being irradiated by ionizing radiation [6] and one can obtain information about the depth of the traps involved during the TL readout. The calculation of the activation energy (to induce the
2
C. Boronat et al. / Nuclear Instruments and Methods in Physics Research B 401 (2017) 1–7
electron transition) is directly linked to the trapped charge recombination due to the metastable defects of the lattice and the subsequent detrapping process due to heat. Additionally, CL provides information about transient defects after irradiation of an energetic electron beam on the surface of the lattice. Thus, the CL emission is usually employed to identify the migration and diffusion of some luminescent centers depending on the range of the emission bands [7]. Factors such as lifetime, efficiency, emission spectra, etc. are involved in the luminescence process and depend directly, not only on the crystallinity grade, but also on small variations in the lattice structure due to the presence of surface defects, impurities, substituted ions, inclusions, etc. All of them induce changes in the intensity and wavelength position of the spectral emission. The main aim of this paper is to determine the suitability of these types of materials to be potentially employed for dose reconstruction in the case of radiological terrorism or radiation accident where conventional monitoring is not available. In this sense, we herein report on the ionizing radiation effect on the CL and TL properties of Ca-rich carbonates from both mineral (aragonite) and biogenic (common periwinkle – littorina littorera – shell) origins, previously characterized by means of X-ray diffraction (XRD) and Raman techniques. The dosimetric characterization were performed considering the (i) dose response in the retrospective dosimetry range (up to 8 Gy), (ii) stability of the TL signal with the elapsed time (up to 700 h) and (iii) trap system. 2. Materials and methods Mineral aragonites from Minglanilla (Cuenca, Spain) and biogenic common periwinkles from Vigo (Pontevedra, NW Spain) were studied by means of (i) XRD, (ii) Raman spectroscopy and (iii) TL and CL techniques. XRD characterization were performed using a Phillips PW1710/00 diffractometer with a CuKa (1.54 Å) radiation source, equipped with a graphite monochromator where the X-ray diffractograms were compared with the XRD PDF2 card files of the Joint Committee on Powder Diffraction Standards using the XPowder diffraction software. The structural characterization was performed by Raman spectroscopy at RT using a Thermo Fisher DRX Raman microscope (1 mm spatial resolution and 20 x objective and a laser source at 532 nm of 6 MW). The Raman spectra were collected in a range of 70–3500 cm 1 with a resolution of 1.92 cm 1. The CL spectral emission of the carbonate samples was measured using a Gatan MonoCL3 detector with a PA-3 photomultiplier tube attached to the ESEM model XLS30 covering a spectral range of 250–850 nm measured at 27 kV. The TL glow emission, observed through a blue filter (a FIB002 of the Melles-Griot Company) peaked at 320–480 nm was carried out using an automated Risø TL reader model TL DA-12 with an EMI 9635 QA photomultiplier [8]. The reader is provided with a 90Sr/90Y beta source with a dose rate of 0.011 Gys 1 calibrated against a 137Cs gamma source in a secondary standard laboratory [9]. The samples, which were carefully powdered under 90 mm with an agate pestle and mortar to avoid triboluminescence [10], were measured using a linear heating rate of 5 °Cs 1 from RT up to 500 °C in a N2 atmosphere. Aliquots of 5.0 ± 0.1 mg of the sample were used for TL measurements. 3. Results and discussion 3.1. Sample characterization: XRD and Raman spectroscopy The XRD patterns corresponding to aragonite and common periwinkle shell samples are displayed in Fig. 1. The analysis performed on the aragonite sample indicates 100% of this mineral that fairly agrees with the 76-0606 PDF2 card with the main maxima
Fig. 1. XRD obtained from the common periwinkle shell and aragonite samples measured at room temperature.
placed at 26.3°, 33.2° and 46° 2h. The periwinkle shell is composed by 90% of calcite with the main maximum peaked at 29.5° 2h and 10% of aragonite (the main maximum peaked at 26.3° 2h) according respectively to the 05-0586 and 05-1475 PDF2 cards. It could be expected a priori that common periwinkle shells is only composed by aragonite, however whether CaCO3 precipitates as calcite or aragonite will depend on the Mg/Ca ratio. According to Demicco et al., [11] ratios over 2 promote the formation of aragonite structure against calcite structure, so assuming such assertion, one can consider that the periwinkle samples here studied come from an ‘aragonite-rich sea’ [11–13]. Additionally, the experimental Raman spectrum recorded from a transparent mineral aragonite specimen (Fig. 2a) shows main peaks at 1080 (mode v1) and 703 (mode v3) together with less intensity Raman peaks at lower frequencies (140, 160, 189, 213, 270 and 282 cm 1) attributed to lattice oscillations. The Raman spectrum of aragonite was firstly studied in detail in 1960 in the Raman Research Institute (Bangalore, India) looking for new features of interest and the need for a reinterpretation of some of the observed spectral facts [14]. As described by Krishnamurti et al. [14], the experimental Raman pattern of aragonite displays the asymmetric unit of the unit cell (Z = 4) corresponding to the orthorhombic CaCO3 aragonite comprises 5 atoms that have 3NZ = 60 zone-center (k = 0) vibration degrees of freedom, described by the set of irreducible representation: C30 = 9A1g + 6B1g + 9B3g + 6B2g + 9B1u + 9B2u + 6B3u + 6A1u. Thus, the symmetry of vibrational modes (i) (9A1g + 6B1g + 9B3g + 6B2g) are Raman active, (ii) (8B1u + 8B2u + 5B3u) are IR-active, (iii) (B1u + B2u + B3u) are acoustic, and (iv) 6A1u is optically inactive (‘‘silent”) [15]. Raman spectra recorded from white areas of the periwinkle (Fig. 2b) exhibit main peaks at circa 155, 281, 712 and 1085 cm 1, which accurateness match to many other Raman patterns of calcite specimens measured under the same laboratory conditions and to those other observed in the RRUFF database of the Arizona University. Eckhardt et al. [16] delivered a pioneering work on the coherent Raman emission from single rhombohedral crystals of calcite because of their strong internal modes must produce a large effect due to the totally symmetric vibration modes of the (CO3)2 ion results producing an intense Raman line at 1985 cm 1 with linewidth 5.5 cm 1. Fig. 3b shows our experimental (Ag1 + Eg)-spectrum with symmetry attribution of their lines 155 (Eg), 281(Eg), 712(Eg) and 1085(Ag). The strongest Raman shifted line at 1086.5 cm 1, related to the stimulated Raman scattering promoting vibration transition of the calcite crystal belongs to the totally symmetric A1g breathing mode of the triangular (CO3)2 groups. The calcite Raman spectrum is explained
C. Boronat et al. / Nuclear Instruments and Methods in Physics Research B 401 (2017) 1–7
3
appeared at 1100–1130 cm 1 and 1500–1530 cm 1 regions are respectively attributed to ‘–C–C–’ and ‘–C@C–’ stretching vibrational modes that are main features of molecules possessing a central polyene chain, e.g., b-carotene, with different substitutions. According to Saito and Tasumi [18], these main peaks of the Raman spectrum are typically associated with all-trans-b-carotene where the fine structure above the peak at 1496 cm 1 seems specific to the b-carotene and the peak at 1294 cm 1 can be attributed to the C–C stretching mode with one carbon bonded to a methyl group. The peaks over 2000 cm 1 are overtones and combination tones of the strongest –C–C– and –C@C– main peaks. Taking into account our experimental main peak positions, i.e., at 1118 and 1496 cm 1 and the black color of the shell areas, one can matched the obtained data on the Table 1 of Hedegaard et al. [19] which includes 35 taxa with different shell colors and Raman wavenumbers of both main peaks. The common periwinkle sample herein analyzed shows some similarities with strombus, cymbula and nautilus shells. 3.2. CL characterization
Fig. 2. Raman spectrum of (a) aragonite (b) common periwinkle white zone and (c) common periwinkle brown zone.
by the primitive D63d-cell of calcite (CaCO3) with space group symmetry D6ed R3 c containing two formula units (Z = 2) that give rise to 3 N = 30 zone center (at k = 0) vibration degrees of freedom, described as: C30 = A1g + 4Eg + 4A2u + 6Eu + 2A1u + 3A2g. Here, the symmetry modes (A1g + 4Eg) are Raman active, (4A2u + 6Eu) are IR-active (among them three modes A2u and Eu are acoustic modes), and the rest (2A1u + 3A2g) are optically inactive (‘‘silent”) [17]. The Raman spectrum corresponding to the brownish part of the periwinkle shell recorded in the range of 500–4000 cm 1 is shown in Fig. 2c. As appreciated, the highest intensity peaks are observed in the spectral region of 800–1700 cm 1 where the maxima
As illustrated in Fig. 3, CL spectra of aragonite (Fig. 3a) and periwinkle shell (Fig. 3b) show a very complex emission in the UV–IR region (from 250 to 850 nm) with non-well-defined peaks. Such complex structures differ among them in the main glow emission since (i) the mineral sample exhibits the maximum in the red region (about 75% higher in terms of intensity values respect to the bioinorganic sample) and (ii) the periwinkle shell displays the more intense luminescence in the range of 300–500 nm (ca. 60% more than the aragonite in the same area). It means that, according to Correcher et al. [20], higher wavebands should be more associated with point defects due to impurities hosted in the lattice, and high-energy emissions with structural defects of the sort of Schottky or Frenkel defects, dislocations, planar defects, poor ordering in the crystal, radiation damage, shock damage etc. or vacancies; i.e. there is a predominance of point defects in aragonite crystals while the emission of the common periwinkle shell would mainly be governed by structural defects [21]. In fact, one can assume that the CL emission curves displaying similar broad wavebands in the UV-blue (peaked at 380 nm), green-yellow (500–600 nm) and red-infrared (600 nm onwards) regions could be due to the same origin in both calcium carbonate lattices (aragonite and common periwinkle shell -10– 90% aragonite-calcite-). Thus, the 330–480 nm emission could be linked to several and simultaneous processes involving (i) the presence of the Non-bridging Oxygen Hole Center (NBOHCs) defects produced by dehydration processes where the electron beam induces the formation of „C–Od + H+ that would be the responsible of the UV emission [22]; both oxygen deficient centers (ODC) and non-bridging oxygen hole centers (NBOHCs) are formed by two hydroxyl precursors linked to the main structure with a large concentration of defects at grain boundaries and cracks. (ii) C–O bonds stressed by hydroxyl groups that have been also observed in smithsonite (ZnCO3) and strontianite (SrCO3) specimens [23,24]; OH and H+ are chemisorbed in the bulk CaCO3 structure, since the OH filling of the vacant O sites are performed during cleavage on the Ca sites. (iii) Radiation-induced luminescence centers that are connected with electron-hole liberation followed by a transition towards the valence band and a subsequent recombination [25]; (iv) presence of carbonate anions that act as a precursor for the emission related to intrinsic structural defects [26] and/or (v) presence of fulvic or humic acids [27]. The broad greenyellow emission (500–600 nm), according to the Tanabe-Sugano diagram [28], is associated with the transitions between excited and ground states of divalent Mn ions (incorporated on the Ca sites) that have all of the 3 d electrons aligned with parallel spins.
4
C. Boronat et al. / Nuclear Instruments and Methods in Physics Research B 401 (2017) 1–7
Fig. 3. UV–IR CL spectral emission of (a) aragonite and (b) common periwinkle shell.
Thus, the yellow emission peaked at 580–590 nm emission should be linked to the transition from the 4G(4Eg, 4A1g) and the green one could be due to the transition from the 4G(4T2g) excited states to 5D (5Eg) ground state [27]. The red-infrared band should be induced by a redox reaction where Fe+3 impurities gives rise to Fe+2 due to the electron beam in two steps (i) a reduction process where ferric ions trap the electrons creating hole centers and (ii) holes are trapped at the aforementioned hole centers by oxidation of the Fe+2 ion. There is an intermediate step where the excited energy state of the Fe+3 is followed by a subsequent relaxation to the ground state that yields radiative emission in the red-infrared region of the spectrum (4T1(G) ? 6A1(S) transition) [26,29]. Similar CL emission, that has been also observed in smithsonite (ZnCO3) and strontianite (SrCO3) samples measured under the same conditions, indicate that parameters such as coordination cavity, concentration, temperature, distortions in the crystal lattice due to imperfections of the cation layer etc. do not scarcely affect to the waveband position in the UV-infrared spectral region [23,24]. Despite the similar CL emission behavior, one can appreciate how the aragonite curve (Fig. 3a) differs from that belonging to the periwinkle shell (Fig. 3b) respect to the sharp band peaked at 312 nm that would be related to a defect center shielded from the influence of the crystal field (i.e. REE or other ion with transitions in the inner levels) [30]; such emission, according to Gorobets and Rogojine [27], could be due to the presence of Gd3+ in aragonite lattice. 3.3. UV-blue TL emission Based on the CL results, the TL response has been measured considering the UV-blue spectral region since appears as the more intense signal in the, a priori, the more complex sample (i.e. periwinkle shell with 90% of calcite and 10% of aragonite). As appreciated in Fig. 4, the 400 nm natural TL (NTL) emission of both aragonite (Fig. 4a) and periwinkle shell (Fig. 4b) exhibits glow curves that differs considerably in shape and intensity. Natural TL (i.e. emission of the ‘as received’ samples) of the aragonite sample shows a well-defined structure with a main maximum at 280 °C and a lower one (at ca. 180 °C) with 85% less of intensity, meanwhile the blue emission from the common periwinkle shell has non-defined low intensity structure (never more than 300 ± 100 a.u. in the group of 5 aliquots analyzed) where was not possible to distinguish any group of components. Such low emission could be linked to the age of the sample that is of some decades for the common periwinkle that mainly absorbs dose from to U-238 and K-40 (naturally occurring in the ocean), Cs-137 (from the global nuclear weapons tests and Chernobyl fallout) and Sr-90
(from the Fukushima accident), in contrast to the mineral sample that is of 200–220 millions of years since belongs to the Iberian Keuper facies. Such NTL spectra exhibit a structure that cannot be studied considering the commonly accepted physical model to describe the trap structure. The curves were tried to analyze in terms of both first and second order kinetics, but the obtained results were unsatisfactory since the best fitting parameters were always over 4–5% considering the value of the factor of merit. Therefore, these TL emissions cannot be explained assuming the discrete trap distribution model since it was not possible to calculate some physical parameters such as trap-energies or preexponential factors. Alternatively, and due to the complexity of the glow curves, one can consider a structure of a continuous trap distribution, as described in other mineral phases involving general order kinetics [31]. In this sense, the stability of TL signal was studied for natural non-irradiated aliquots from aragonite sample using the Tstop preheating technique. It consists of linear heating of the samples up to a temperature (Tstop) followed by quenching at room temperature and final readout to record the whole remaining TL glow curve. The thermal preheating varies from 180 to 320 °C with the aim of getting aliquots with different grades of lattice modulation and, thus, determining the trap structure [6]. Fig. 4a displays how the increase of Tstop gives rise to (i) the maximum of the TL glow curve that shifts progressively to higher temperatures and (ii) a change in the shape and intensity of the TL emission that is linked to the thermal pre-treatment. This thermolabile wide band of the glow maximum shows TL curves that involve successive electron trapping–detrapping processes due to (i) consecutive breaking and linking of bonds of C–O, C@O, C–OH, OH–Ca–OH, (ii) redox reactions associated with a continuum in the trap distribution or (iii) the existence of a tunneling recombination process. Similar response has been observed in many different natural (e.g. microcline [32]; plagioclases rich polymineral phases [33]) and synthetic (amorphous silica [34]) materials studied in our laboratory under the same conditions. The periwinkle shell sample could not be analyzed using this protocol to explain the trap structure due to the low TL intensity values, but considering the similar chemical and mineralogical composition, one can speculate with a behavior associated with a continuum in the trap distribution. On this basis, it is possible to conclude that would be necessary to take into account a range of temperature of the TL glow curve in case this material could potentially be employed for environmental or retrospective dosimetry purposes. As appreciated in Fig. 5, the dose response of the samples (previously heated up to 500 °C to remove the NTL and irradiated in the range of 0.5–8 Gy) measured under the same conditions, shows a similar TL behavior regardless of the sample (–Fig. 5a– aragonite
C. Boronat et al. / Nuclear Instruments and Methods in Physics Research B 401 (2017) 1–7
5
Fig. 4. TL glow curves of non-irradiated (a) aragonite and (b) common periwinkle shell samples.
Fig. 5. Dose dependence in a range of 0.5–8 Gy of the Tl glow curve of (a) aragonite and (b) common periwinkle shell. Each inset shows the good linearity (r(a) = 0.999 and r(b) = 0.998) of the TL glow emissions considering the area under the curve in the range of 30–450 °C.
or –Fig. 5b– periwinkle shell). The thermal treatment allows us to determine specifically the effect of the artificial dose on the TL emission trying to study its use considering a potential radiological terrorism or NPP radiological accident that are usually up to 8 Gy. For that reason zero dose has not been considered in this case. One can observe (i) a low temperature maxima peaked at 70 °C associated with oxygen vacancies [6] and (ii) a lower intensity broad group of components at higher temperature with a non-welldefined structure (about 200 °C onwards) that could be attributed to consecutive breaking and linking of bonds of Ca–O, C–O and Ca– C, including redox reactions, involving the impurities [6] and, also, partial conversion of aragonite into calcite that, according to Davis and Adams [35] and Ponnusamy et al. [36], can be induced at temperatures above 400 °C at atmospheric pressure. Additionally, the shape of the TL glow curves (in each case) does not change while the dose increases, although it is possible to detect a slight shift of the main maximum at 70 °C with the increase of the dose that indicates that the classical first-order kinetic theory does not apply in these cases. Such effect could be associated with traps and recombination centers in a system of interacting clusters. The increase of the dose induces the growth of the size of the clusters, giving rise to an increase of the effective activation energy and, consequently, shifting the TL maximum towards higher temperatures [37]. This fact supposes that the ionizing radiation does not (i) give rise to modifications in the lattice structure and (ii) induce
the appearance of new defects that involve changes in the valence state of impurities atoms and, consequently, potential variations in the intensity or shape of the spectral emission. The dose dependence analysis were performed individually on four aliquots of aragonite and common periwinkle shell samples previously heated until 500 °C to remove any signal corresponding to traps that are not easily bleached by optical processes. Dose responses exhibit a highly linear correlation of the TL intensity is with the radiation exposure, being fitted by a straight line with r values over 0.998 in the studied range of doses (0.5–8 Gy) in both samples (insets in Fig. 6a and b). Additionally, the dosimetric characterization must be completed considering the potential fading effect of the TL emissions (Fig. 6a –aragonite- and Fig. 6b –common periwinkle shell) presented with a log time scale. For such purpose, all the aliquots were consecutively (i) preannealing up to 500 °C to remove its natural TL, (ii) 2 Gy beta irradiated and (iii) stored under red light at RT to prevent trapped electron releasing from semi-stable sites into hole centers, including luminescence centers. The TL measurements were carried out after increasing the storage periods of time (up to 700 h) and the relative intensity of each point was calibrated individually, referring the direct delayed measurement to 2 Gy-induced TL prompt glow curve (area under 30–500 °C). The temporal evolution of the TL emission from the 2 Gy-irradiated aragonite (Fig. 6a) follows a similar evolution to
6
C. Boronat et al. / Nuclear Instruments and Methods in Physics Research B 401 (2017) 1–7
Fig. 6. Stability of the blue TL emission obtained from (a) the aragonite samples, up to 700 h of storage at RT in darkness and (b) common periwinkle shell. The uncertainties (1r) correspond to the group of four aliquots each in a log-time scale graph.
that observed in several natural materials measured under the same conditions (silicates [31], oxides, [38] etc.) Such behavior consists on an initial rapid decay (ca 88%) maintaining the signal stability from 150 h onwards that decreases asymptotically by the X-axis that can be fitted to a first order decay mathematical statement and is directly linked to the probability of electron release from the shallower traps that takes place quickly at RT. It could be expected a non-exponential decay for first order kinetics due to the energy distribution of trapped charges [39], however the obtained results can be well-fitted considering a single exponential component, therefore, only the lowest energy traps are involved at RT. The stability of the TL signal coming from the periwinkle shell shows a fading effect too, but differs from the inorganic phase in (i) the behavior in the evolution of the relative intensity of the TL emission that could not be fitted to a first order decay equation due to the scattering of the results probably associated with the lattice disorder and (ii) the initial decay is slower compared to the evolution of the aragonite TL emission (up to 60%). However, similar to the aragonite sample, one can appreciate how the signal starts to be stable from 150–200 h onwards. 4. Conclusions The study performed on the CL and TL emission of aragonite and common periwinkle – littorina littorera – shell (composed by 10% of aragonite and 90% of calcite) samples, indicates that both natural materials could be potentially employed in the field of retrospective dosimetry in the case of radiological terrorism or radiation accident where conventional monitoring is not available. The samples, previously characterized by XRD and Raman spectroscopy, exhibit similar TL behavior regardless of the origin (mineral or biogenic), but differs from the CL emission where the main waveband of the mineral sample appears at lower energies (probably associated with point defects) and the more intense maximum obtained from the periwinkle shell is peaked in the UV-blue spectral region (linked to structural defects). The 400 nm-TL characterization shows for both Ca-rich carbonates (i) an acceptable radiation sensitivity, (ii) linear dose response in the range of interest (up to 8 Gy), (iii) The stability of the TL signal after 700 h of storage, shows an initial rapid decay (ca. 88%) for the aragonite sample and a slower initial decay for the periwinkle shell (ca. 60%) and maintaining (in both cases) the stability from 150 h onwards which indicates that the electron population decreases asymptotically. Additionally, (iv) the tests of thermal stability at different temperatures confirm a continuum in the trap system.
Acknowledgments Cecilia Boronat thanks to ‘‘Consejería de Educación, Juventud y Deporte de la Comunidad de Madrid, Spain” and ”Fondo Social Europeo, Belgium” (PEJ15/BIO/AI-0418) for the support provided under the ‘‘Operativo de Empleo Juvenil y la Iniciativa de Empleo Juvenil (YEI)” program (B.O.C.M. Núm.152. Orden 1880/2015, de 16 de junio del 2015).
References [1] R. Nagtegaal, C.A. Grove, S. Kasper, J. Zinke, W. Boer, G.A. Brummer, Chem. Geol. 318 (2012) 6–15. [2] C. Aydasß, B. Engin, S. Kapan, T. Komut, T. Aydin, U. Paksu, Appl. Radiat. Isot. 105 (2015) 72–79. [3] B. Ziegelmann, K.W. Bögl, G.A. Schreiber, Radiat. Phys. Chem. 54 (1999) 413– 423. [4] M. Marrale, A. Longo, A. Bartolotta, M.C. D’Oca, M. Brai, Nucl. Instrum. Meth. Phys. Res. B 297 (2013) 58–63. [5] A.N. Yazici, M. Bedir, H. Bozkurt, H. Bozkurt, Nucl. Instrum. Meth. Phys. Res. B 266 (2008) 613–620. [6] S.W.S. McKeever, New York, Cambridge University Press, 1985. [7] M.A.S. Kalceff, M.R. Phillips, Phys. Rev. 52 (1995) 3122–3134. [8] L. Bøtter-Jensen, G.A.T. Duller, Nucl. Tracks Radiat. Meas. 20 (1992) 549–553. [9] V. Correcher, A. Delgado, Radiat. Meas. 29 (1998) 411–414. [10] J. Garcia-Guinea, V. Correcher, Spectrosc. Lett. 33 (2000) 103–113. [11] R.V. Demicco, T.K. Lowenstein, L.A. Hardie, Geology 31 (2003) 793–796. [12] B.J. Broadaway, Master thesis, University of Massachusetts Boston, 2010. [13] C. Soliman, A.M. Massoud, M.A. Hussein, Nucl. Instrum. Meth. Phys. Res. B 222 (2004) 163–168. [14] D. Krishnamurti, Proc. Ind. Acad. Sci. 51 (1960) 285–295. [15] A.A. Kaminskii, H. Rhee, O. Lux, H.J. Eichler, V.V. Koltashev, R. Kleinschrodt, L. Bohaty, P. Becker, Laser Phys. Lett. 9 (1960) 259–284. [16] G. Eckhardt, D.P. Bortfeld, M. Geller, Appl. Phys. Lett. 3 (1963) 137–138. [17] V.N. Denisov, B.N. Mavrin, V.B. Podobedov, K.E. Sterin, Phys. Status. Solidi 110 (1982) 183–189. [18] S. Saito, M. Tasumi, J. Raman Spectrosc. 14 (1983) 310–321. [19] C. Hedegaard, J.F. Bardeau, D. Chateigner, J. Mollus. Stud. 72 (2006) 157–162. [20] V. Correcher, J. Garcia-Guinea, C. Martin-Fernandez, N. Can, Spectrosc. Lett. 44 (2011) 486–489. [21] D. Habermann, J.R. Niklas, J. Meijer, A. Stephan, T. Gotte, Nucl. Instrum. Meth. Phys. Res. B 181 (2001) 563–569. [22] K. Polikreti, C. Christofides, Phys. Chem. Miner. 36 (2009) 271–279. [23] J. Garcia-Guinea, E. Crespo-Feo, V. Correcher, J. Rubio, M.V. Roux, P.D. Townsend, Phys. Chem. Miner. 36 (2009) 431–438. [24] J. Garcia-Guinea, E. Crespo-Feo, V. Correcher, A. Cremades, J. Rubio, L. Tormo, P. D. Townsend, Radiat. Meas. 44 (2009) 338–343. [25] M. Gaft, L. Nagli, G. Panczer, G. Waychunas, N. Porat, Am. Mineral. 93 (2008) 158–167. [26] R. Chapoulie, F. Bechtel, D. Borschneck, M. Schvoerer, G. Remond, Scan. Microsc. Suppl. 9 (1995) 225–232. [27] B.S. Gorobets, A.A. Rogojine, Moscow All-Russia Institute for Mineral Resources (VIMS), 2002. [28] Y. Tanabe, S. Sugano, Phys. Soc. Jpn. 9 (1954) 766–779. [29] D. Habermann, R.D. Neuser, D.K. Richter, Sediment. Geol. 101 (1995) 1–7.
C. Boronat et al. / Nuclear Instruments and Methods in Physics Research B 401 (2017) 1–7 [30] E. Crespo-Feo, J. Garcia-Guinea, V. Correcher, A. Garralon, A.I.P. Conf, Proc. 1163 (2009) 121–127. [31] V. Correcher, J.M. Gomez-Ros, J. Garcia-Guinea, Radiat. Meas. 38 (2004) 689– 693. [32] V. Correcher, J. Garcia-Guinea, A. Delgado, L. Sanchez-Munoz, Radiat. Prot. Dosim. 84 (1999) 503–506. [33] V. Correcher, D. Molina, J. Garcia-Guinea, Rev. Mex. Fis. 49 (2003) 235–241. [34] M. Martini, G. Spinolo, A. Vedda, Solid State Commun. 91 (1994) 751–756.
7
[35] B.L. Davis, L.H. Adams, J. Geophys. Res. 70 (1965) 433–441. [36] V. Ponnusamy, V. Ramasamy, M. Dheenathayalu, J. Hemalatha, Nucl. Instrum. Meth. Phys. Res. B 217 (2004) 611–620. [37] A. Mandowski, Radiat. Meas. 43 (2008) 167–170. [38] V. Correcher, J. Garcia-Guinea, F.J. Valle-Fuentes, Geophys. Res. Lett. 30 (2003) 1949. [39] S.O. Souza, J.F.D. Chubaci, P.C. Selvin, M.D. Sastry, S. Watanabe, J. Phys. D Appl. Phys. 35 (2002) 1562–1565.
Contents lists available at ScienceDirect
Nuclear Instruments and Methods in Physics Research B journal homepage: www.elsevier.com/locate/nimb
Ionising radiation effect on the luminescence emission of inorganic and biogenic calcium carbonates C. Boronat a, V. Correcher a,⇑, M.D. Virgos a, J. Garcia-Guinea b a b
CIEMAT, Av. Complutense 40, Madrid 28040, Spain CSIC, Museo Nacional Ciencias Naturales, José Gutiérrez Abascal 2, Madrid 28006, Spain
a r t i c l e
i n f o
Article history: Received 19 August 2016 Received in revised form 14 March 2017 Accepted 10 April 2017
Keywords: Thermoluminescence Cathodoluminescence Dosimetry Calcite Aragonite
a b s t r a c t As known, the luminescence emission of mineral phases could be potentially employed for dosimetric purposes in the case of radiological terrorism or radiation accident where conventional monitoring is not available. In this sense, this paper reports on the thermo- (TL) and cathodoluminescence (CL) emission of both biogenic (common periwinkle – littorina littorera – shell made of calcite 90% and aragonite 10%) and inorganic (aragonite 100%) Ca-rich carbonates previously characterized by X-ray diffraction and Raman spectroscopy. Whereas the aragonite sample displays the main CL waveband peaked in the red region (linked to point defects), the more intense emission obtained from the common periwinkle shell appears at higher energies (mainly associated with structural defects). The UV-blue TL emission of the samples, regardless of the origin, displays (i) an acceptable ionizing radiation sensitivity, (ii) linear dose response in the range of interest (up to 8 Gy), (iii) reasonable stability of the TL signal after 700 h of storage with an initial decay of ca. 88% for the mineral sample and 60% for the biogenic sample and maintaining the stability from 150 h onwards. (iv) The tests of thermal stability of the TL emission performed in the range of 180–320 °C confirm a continuum in the trap system. Ó 2017 Elsevier B.V. All rights reserved.
1. Introduction Calcium-rich carbonates (mainly calcite, aragonite and dolomite) comprise about 2.5% of the whole volume of the Earth’s crust including not only limestones and marbles, but also produced through biogenic processes (main component of shells of marine organisms, snails, winkles, pearls or eggshells). These materials are employed for the production of cement, as a building material, for health applications (Ca supplement or to produce toothpaste), etc. Based on the luminescence emission, both calcite and aragonite could be used in the field of dating to determine past environmental and changes in the climatic conditions [1,2] or even for the detection of irradiated food [3]. However, according to Ziegelmann et al. [3] the radiation-sensitive samples usually contain calcite and in most cases, also aragonite, but the non-sensitive samples contained only aragonite in the range of 0.05–4 kGy. Such luminescence emission is associated with (i) the appearance of point defects, Frenkel defects, vacancies, planar defects, Schottky defects, dislocations, chemisorbed ions such as H+, OH , HCO3 , [Ca(OH)]+ and [Ca(HCO3)]+ together with frequent hydrocarbon hydrous bonds (C–OH) which could give rise to groups forming ⇑ Corresponding author. E-mail address: [email protected] (V. Correcher). http://dx.doi.org/10.1016/j.nimb.2017.04.035 0168-583X/Ó 2017 Elsevier B.V. All rights reserved.
Non-bridging Oxygen Hole Center (NBOHC) etc. distributed along the calcium carbonate lattice and (ii) defects linked to the structure of calcite (transparent or translucent and white crystals with a rhombohedral habit, prismatic and platy) that considerably differs from the aragonite that usually crystallizes as pseudohexagonal twinned intergrowths in the orthorhombic system. The ionizing radiation (natural or artificially induced) absorbed by the material at RT, gives rise to freed electrons that become trapped in the lattice defects of the material. During this process, the electrons will be trapped for non-defined periods whilst the material is stored at RT. This physical property can be potentially used for the radiation absorbed dose measurement in the fields of dating, retrospective dosimetry, detection of irradiated food or radiological terrorism, as well as for material characterization based on the thermoluminescence (TL) and cathodoluminescence (CL) emission of these phosphors [4,5]. Both luminescence techniques give us information about the trapped charge recombination sites related to metastable defects in the lattice depending on whether the detrapping process is due to heat (TL) or electron exposure (CL). Thus, TL is a method based on the photon emission from an insulator or semiconductor samples when it is heated after being irradiated by ionizing radiation [6] and one can obtain information about the depth of the traps involved during the TL readout. The calculation of the activation energy (to induce the
2
C. Boronat et al. / Nuclear Instruments and Methods in Physics Research B 401 (2017) 1–7
electron transition) is directly linked to the trapped charge recombination due to the metastable defects of the lattice and the subsequent detrapping process due to heat. Additionally, CL provides information about transient defects after irradiation of an energetic electron beam on the surface of the lattice. Thus, the CL emission is usually employed to identify the migration and diffusion of some luminescent centers depending on the range of the emission bands [7]. Factors such as lifetime, efficiency, emission spectra, etc. are involved in the luminescence process and depend directly, not only on the crystallinity grade, but also on small variations in the lattice structure due to the presence of surface defects, impurities, substituted ions, inclusions, etc. All of them induce changes in the intensity and wavelength position of the spectral emission. The main aim of this paper is to determine the suitability of these types of materials to be potentially employed for dose reconstruction in the case of radiological terrorism or radiation accident where conventional monitoring is not available. In this sense, we herein report on the ionizing radiation effect on the CL and TL properties of Ca-rich carbonates from both mineral (aragonite) and biogenic (common periwinkle – littorina littorera – shell) origins, previously characterized by means of X-ray diffraction (XRD) and Raman techniques. The dosimetric characterization were performed considering the (i) dose response in the retrospective dosimetry range (up to 8 Gy), (ii) stability of the TL signal with the elapsed time (up to 700 h) and (iii) trap system. 2. Materials and methods Mineral aragonites from Minglanilla (Cuenca, Spain) and biogenic common periwinkles from Vigo (Pontevedra, NW Spain) were studied by means of (i) XRD, (ii) Raman spectroscopy and (iii) TL and CL techniques. XRD characterization were performed using a Phillips PW1710/00 diffractometer with a CuKa (1.54 Å) radiation source, equipped with a graphite monochromator where the X-ray diffractograms were compared with the XRD PDF2 card files of the Joint Committee on Powder Diffraction Standards using the XPowder diffraction software. The structural characterization was performed by Raman spectroscopy at RT using a Thermo Fisher DRX Raman microscope (1 mm spatial resolution and 20 x objective and a laser source at 532 nm of 6 MW). The Raman spectra were collected in a range of 70–3500 cm 1 with a resolution of 1.92 cm 1. The CL spectral emission of the carbonate samples was measured using a Gatan MonoCL3 detector with a PA-3 photomultiplier tube attached to the ESEM model XLS30 covering a spectral range of 250–850 nm measured at 27 kV. The TL glow emission, observed through a blue filter (a FIB002 of the Melles-Griot Company) peaked at 320–480 nm was carried out using an automated Risø TL reader model TL DA-12 with an EMI 9635 QA photomultiplier [8]. The reader is provided with a 90Sr/90Y beta source with a dose rate of 0.011 Gys 1 calibrated against a 137Cs gamma source in a secondary standard laboratory [9]. The samples, which were carefully powdered under 90 mm with an agate pestle and mortar to avoid triboluminescence [10], were measured using a linear heating rate of 5 °Cs 1 from RT up to 500 °C in a N2 atmosphere. Aliquots of 5.0 ± 0.1 mg of the sample were used for TL measurements. 3. Results and discussion 3.1. Sample characterization: XRD and Raman spectroscopy The XRD patterns corresponding to aragonite and common periwinkle shell samples are displayed in Fig. 1. The analysis performed on the aragonite sample indicates 100% of this mineral that fairly agrees with the 76-0606 PDF2 card with the main maxima
Fig. 1. XRD obtained from the common periwinkle shell and aragonite samples measured at room temperature.
placed at 26.3°, 33.2° and 46° 2h. The periwinkle shell is composed by 90% of calcite with the main maximum peaked at 29.5° 2h and 10% of aragonite (the main maximum peaked at 26.3° 2h) according respectively to the 05-0586 and 05-1475 PDF2 cards. It could be expected a priori that common periwinkle shells is only composed by aragonite, however whether CaCO3 precipitates as calcite or aragonite will depend on the Mg/Ca ratio. According to Demicco et al., [11] ratios over 2 promote the formation of aragonite structure against calcite structure, so assuming such assertion, one can consider that the periwinkle samples here studied come from an ‘aragonite-rich sea’ [11–13]. Additionally, the experimental Raman spectrum recorded from a transparent mineral aragonite specimen (Fig. 2a) shows main peaks at 1080 (mode v1) and 703 (mode v3) together with less intensity Raman peaks at lower frequencies (140, 160, 189, 213, 270 and 282 cm 1) attributed to lattice oscillations. The Raman spectrum of aragonite was firstly studied in detail in 1960 in the Raman Research Institute (Bangalore, India) looking for new features of interest and the need for a reinterpretation of some of the observed spectral facts [14]. As described by Krishnamurti et al. [14], the experimental Raman pattern of aragonite displays the asymmetric unit of the unit cell (Z = 4) corresponding to the orthorhombic CaCO3 aragonite comprises 5 atoms that have 3NZ = 60 zone-center (k = 0) vibration degrees of freedom, described by the set of irreducible representation: C30 = 9A1g + 6B1g + 9B3g + 6B2g + 9B1u + 9B2u + 6B3u + 6A1u. Thus, the symmetry of vibrational modes (i) (9A1g + 6B1g + 9B3g + 6B2g) are Raman active, (ii) (8B1u + 8B2u + 5B3u) are IR-active, (iii) (B1u + B2u + B3u) are acoustic, and (iv) 6A1u is optically inactive (‘‘silent”) [15]. Raman spectra recorded from white areas of the periwinkle (Fig. 2b) exhibit main peaks at circa 155, 281, 712 and 1085 cm 1, which accurateness match to many other Raman patterns of calcite specimens measured under the same laboratory conditions and to those other observed in the RRUFF database of the Arizona University. Eckhardt et al. [16] delivered a pioneering work on the coherent Raman emission from single rhombohedral crystals of calcite because of their strong internal modes must produce a large effect due to the totally symmetric vibration modes of the (CO3)2 ion results producing an intense Raman line at 1985 cm 1 with linewidth 5.5 cm 1. Fig. 3b shows our experimental (Ag1 + Eg)-spectrum with symmetry attribution of their lines 155 (Eg), 281(Eg), 712(Eg) and 1085(Ag). The strongest Raman shifted line at 1086.5 cm 1, related to the stimulated Raman scattering promoting vibration transition of the calcite crystal belongs to the totally symmetric A1g breathing mode of the triangular (CO3)2 groups. The calcite Raman spectrum is explained
C. Boronat et al. / Nuclear Instruments and Methods in Physics Research B 401 (2017) 1–7
3
appeared at 1100–1130 cm 1 and 1500–1530 cm 1 regions are respectively attributed to ‘–C–C–’ and ‘–C@C–’ stretching vibrational modes that are main features of molecules possessing a central polyene chain, e.g., b-carotene, with different substitutions. According to Saito and Tasumi [18], these main peaks of the Raman spectrum are typically associated with all-trans-b-carotene where the fine structure above the peak at 1496 cm 1 seems specific to the b-carotene and the peak at 1294 cm 1 can be attributed to the C–C stretching mode with one carbon bonded to a methyl group. The peaks over 2000 cm 1 are overtones and combination tones of the strongest –C–C– and –C@C– main peaks. Taking into account our experimental main peak positions, i.e., at 1118 and 1496 cm 1 and the black color of the shell areas, one can matched the obtained data on the Table 1 of Hedegaard et al. [19] which includes 35 taxa with different shell colors and Raman wavenumbers of both main peaks. The common periwinkle sample herein analyzed shows some similarities with strombus, cymbula and nautilus shells. 3.2. CL characterization
Fig. 2. Raman spectrum of (a) aragonite (b) common periwinkle white zone and (c) common periwinkle brown zone.
by the primitive D63d-cell of calcite (CaCO3) with space group symmetry D6ed R3 c containing two formula units (Z = 2) that give rise to 3 N = 30 zone center (at k = 0) vibration degrees of freedom, described as: C30 = A1g + 4Eg + 4A2u + 6Eu + 2A1u + 3A2g. Here, the symmetry modes (A1g + 4Eg) are Raman active, (4A2u + 6Eu) are IR-active (among them three modes A2u and Eu are acoustic modes), and the rest (2A1u + 3A2g) are optically inactive (‘‘silent”) [17]. The Raman spectrum corresponding to the brownish part of the periwinkle shell recorded in the range of 500–4000 cm 1 is shown in Fig. 2c. As appreciated, the highest intensity peaks are observed in the spectral region of 800–1700 cm 1 where the maxima
As illustrated in Fig. 3, CL spectra of aragonite (Fig. 3a) and periwinkle shell (Fig. 3b) show a very complex emission in the UV–IR region (from 250 to 850 nm) with non-well-defined peaks. Such complex structures differ among them in the main glow emission since (i) the mineral sample exhibits the maximum in the red region (about 75% higher in terms of intensity values respect to the bioinorganic sample) and (ii) the periwinkle shell displays the more intense luminescence in the range of 300–500 nm (ca. 60% more than the aragonite in the same area). It means that, according to Correcher et al. [20], higher wavebands should be more associated with point defects due to impurities hosted in the lattice, and high-energy emissions with structural defects of the sort of Schottky or Frenkel defects, dislocations, planar defects, poor ordering in the crystal, radiation damage, shock damage etc. or vacancies; i.e. there is a predominance of point defects in aragonite crystals while the emission of the common periwinkle shell would mainly be governed by structural defects [21]. In fact, one can assume that the CL emission curves displaying similar broad wavebands in the UV-blue (peaked at 380 nm), green-yellow (500–600 nm) and red-infrared (600 nm onwards) regions could be due to the same origin in both calcium carbonate lattices (aragonite and common periwinkle shell -10– 90% aragonite-calcite-). Thus, the 330–480 nm emission could be linked to several and simultaneous processes involving (i) the presence of the Non-bridging Oxygen Hole Center (NBOHCs) defects produced by dehydration processes where the electron beam induces the formation of „C–Od + H+ that would be the responsible of the UV emission [22]; both oxygen deficient centers (ODC) and non-bridging oxygen hole centers (NBOHCs) are formed by two hydroxyl precursors linked to the main structure with a large concentration of defects at grain boundaries and cracks. (ii) C–O bonds stressed by hydroxyl groups that have been also observed in smithsonite (ZnCO3) and strontianite (SrCO3) specimens [23,24]; OH and H+ are chemisorbed in the bulk CaCO3 structure, since the OH filling of the vacant O sites are performed during cleavage on the Ca sites. (iii) Radiation-induced luminescence centers that are connected with electron-hole liberation followed by a transition towards the valence band and a subsequent recombination [25]; (iv) presence of carbonate anions that act as a precursor for the emission related to intrinsic structural defects [26] and/or (v) presence of fulvic or humic acids [27]. The broad greenyellow emission (500–600 nm), according to the Tanabe-Sugano diagram [28], is associated with the transitions between excited and ground states of divalent Mn ions (incorporated on the Ca sites) that have all of the 3 d electrons aligned with parallel spins.
4
C. Boronat et al. / Nuclear Instruments and Methods in Physics Research B 401 (2017) 1–7
Fig. 3. UV–IR CL spectral emission of (a) aragonite and (b) common periwinkle shell.
Thus, the yellow emission peaked at 580–590 nm emission should be linked to the transition from the 4G(4Eg, 4A1g) and the green one could be due to the transition from the 4G(4T2g) excited states to 5D (5Eg) ground state [27]. The red-infrared band should be induced by a redox reaction where Fe+3 impurities gives rise to Fe+2 due to the electron beam in two steps (i) a reduction process where ferric ions trap the electrons creating hole centers and (ii) holes are trapped at the aforementioned hole centers by oxidation of the Fe+2 ion. There is an intermediate step where the excited energy state of the Fe+3 is followed by a subsequent relaxation to the ground state that yields radiative emission in the red-infrared region of the spectrum (4T1(G) ? 6A1(S) transition) [26,29]. Similar CL emission, that has been also observed in smithsonite (ZnCO3) and strontianite (SrCO3) samples measured under the same conditions, indicate that parameters such as coordination cavity, concentration, temperature, distortions in the crystal lattice due to imperfections of the cation layer etc. do not scarcely affect to the waveband position in the UV-infrared spectral region [23,24]. Despite the similar CL emission behavior, one can appreciate how the aragonite curve (Fig. 3a) differs from that belonging to the periwinkle shell (Fig. 3b) respect to the sharp band peaked at 312 nm that would be related to a defect center shielded from the influence of the crystal field (i.e. REE or other ion with transitions in the inner levels) [30]; such emission, according to Gorobets and Rogojine [27], could be due to the presence of Gd3+ in aragonite lattice. 3.3. UV-blue TL emission Based on the CL results, the TL response has been measured considering the UV-blue spectral region since appears as the more intense signal in the, a priori, the more complex sample (i.e. periwinkle shell with 90% of calcite and 10% of aragonite). As appreciated in Fig. 4, the 400 nm natural TL (NTL) emission of both aragonite (Fig. 4a) and periwinkle shell (Fig. 4b) exhibits glow curves that differs considerably in shape and intensity. Natural TL (i.e. emission of the ‘as received’ samples) of the aragonite sample shows a well-defined structure with a main maximum at 280 °C and a lower one (at ca. 180 °C) with 85% less of intensity, meanwhile the blue emission from the common periwinkle shell has non-defined low intensity structure (never more than 300 ± 100 a.u. in the group of 5 aliquots analyzed) where was not possible to distinguish any group of components. Such low emission could be linked to the age of the sample that is of some decades for the common periwinkle that mainly absorbs dose from to U-238 and K-40 (naturally occurring in the ocean), Cs-137 (from the global nuclear weapons tests and Chernobyl fallout) and Sr-90
(from the Fukushima accident), in contrast to the mineral sample that is of 200–220 millions of years since belongs to the Iberian Keuper facies. Such NTL spectra exhibit a structure that cannot be studied considering the commonly accepted physical model to describe the trap structure. The curves were tried to analyze in terms of both first and second order kinetics, but the obtained results were unsatisfactory since the best fitting parameters were always over 4–5% considering the value of the factor of merit. Therefore, these TL emissions cannot be explained assuming the discrete trap distribution model since it was not possible to calculate some physical parameters such as trap-energies or preexponential factors. Alternatively, and due to the complexity of the glow curves, one can consider a structure of a continuous trap distribution, as described in other mineral phases involving general order kinetics [31]. In this sense, the stability of TL signal was studied for natural non-irradiated aliquots from aragonite sample using the Tstop preheating technique. It consists of linear heating of the samples up to a temperature (Tstop) followed by quenching at room temperature and final readout to record the whole remaining TL glow curve. The thermal preheating varies from 180 to 320 °C with the aim of getting aliquots with different grades of lattice modulation and, thus, determining the trap structure [6]. Fig. 4a displays how the increase of Tstop gives rise to (i) the maximum of the TL glow curve that shifts progressively to higher temperatures and (ii) a change in the shape and intensity of the TL emission that is linked to the thermal pre-treatment. This thermolabile wide band of the glow maximum shows TL curves that involve successive electron trapping–detrapping processes due to (i) consecutive breaking and linking of bonds of C–O, C@O, C–OH, OH–Ca–OH, (ii) redox reactions associated with a continuum in the trap distribution or (iii) the existence of a tunneling recombination process. Similar response has been observed in many different natural (e.g. microcline [32]; plagioclases rich polymineral phases [33]) and synthetic (amorphous silica [34]) materials studied in our laboratory under the same conditions. The periwinkle shell sample could not be analyzed using this protocol to explain the trap structure due to the low TL intensity values, but considering the similar chemical and mineralogical composition, one can speculate with a behavior associated with a continuum in the trap distribution. On this basis, it is possible to conclude that would be necessary to take into account a range of temperature of the TL glow curve in case this material could potentially be employed for environmental or retrospective dosimetry purposes. As appreciated in Fig. 5, the dose response of the samples (previously heated up to 500 °C to remove the NTL and irradiated in the range of 0.5–8 Gy) measured under the same conditions, shows a similar TL behavior regardless of the sample (–Fig. 5a– aragonite
C. Boronat et al. / Nuclear Instruments and Methods in Physics Research B 401 (2017) 1–7
5
Fig. 4. TL glow curves of non-irradiated (a) aragonite and (b) common periwinkle shell samples.
Fig. 5. Dose dependence in a range of 0.5–8 Gy of the Tl glow curve of (a) aragonite and (b) common periwinkle shell. Each inset shows the good linearity (r(a) = 0.999 and r(b) = 0.998) of the TL glow emissions considering the area under the curve in the range of 30–450 °C.
or –Fig. 5b– periwinkle shell). The thermal treatment allows us to determine specifically the effect of the artificial dose on the TL emission trying to study its use considering a potential radiological terrorism or NPP radiological accident that are usually up to 8 Gy. For that reason zero dose has not been considered in this case. One can observe (i) a low temperature maxima peaked at 70 °C associated with oxygen vacancies [6] and (ii) a lower intensity broad group of components at higher temperature with a non-welldefined structure (about 200 °C onwards) that could be attributed to consecutive breaking and linking of bonds of Ca–O, C–O and Ca– C, including redox reactions, involving the impurities [6] and, also, partial conversion of aragonite into calcite that, according to Davis and Adams [35] and Ponnusamy et al. [36], can be induced at temperatures above 400 °C at atmospheric pressure. Additionally, the shape of the TL glow curves (in each case) does not change while the dose increases, although it is possible to detect a slight shift of the main maximum at 70 °C with the increase of the dose that indicates that the classical first-order kinetic theory does not apply in these cases. Such effect could be associated with traps and recombination centers in a system of interacting clusters. The increase of the dose induces the growth of the size of the clusters, giving rise to an increase of the effective activation energy and, consequently, shifting the TL maximum towards higher temperatures [37]. This fact supposes that the ionizing radiation does not (i) give rise to modifications in the lattice structure and (ii) induce
the appearance of new defects that involve changes in the valence state of impurities atoms and, consequently, potential variations in the intensity or shape of the spectral emission. The dose dependence analysis were performed individually on four aliquots of aragonite and common periwinkle shell samples previously heated until 500 °C to remove any signal corresponding to traps that are not easily bleached by optical processes. Dose responses exhibit a highly linear correlation of the TL intensity is with the radiation exposure, being fitted by a straight line with r values over 0.998 in the studied range of doses (0.5–8 Gy) in both samples (insets in Fig. 6a and b). Additionally, the dosimetric characterization must be completed considering the potential fading effect of the TL emissions (Fig. 6a –aragonite- and Fig. 6b –common periwinkle shell) presented with a log time scale. For such purpose, all the aliquots were consecutively (i) preannealing up to 500 °C to remove its natural TL, (ii) 2 Gy beta irradiated and (iii) stored under red light at RT to prevent trapped electron releasing from semi-stable sites into hole centers, including luminescence centers. The TL measurements were carried out after increasing the storage periods of time (up to 700 h) and the relative intensity of each point was calibrated individually, referring the direct delayed measurement to 2 Gy-induced TL prompt glow curve (area under 30–500 °C). The temporal evolution of the TL emission from the 2 Gy-irradiated aragonite (Fig. 6a) follows a similar evolution to
6
C. Boronat et al. / Nuclear Instruments and Methods in Physics Research B 401 (2017) 1–7
Fig. 6. Stability of the blue TL emission obtained from (a) the aragonite samples, up to 700 h of storage at RT in darkness and (b) common periwinkle shell. The uncertainties (1r) correspond to the group of four aliquots each in a log-time scale graph.
that observed in several natural materials measured under the same conditions (silicates [31], oxides, [38] etc.) Such behavior consists on an initial rapid decay (ca 88%) maintaining the signal stability from 150 h onwards that decreases asymptotically by the X-axis that can be fitted to a first order decay mathematical statement and is directly linked to the probability of electron release from the shallower traps that takes place quickly at RT. It could be expected a non-exponential decay for first order kinetics due to the energy distribution of trapped charges [39], however the obtained results can be well-fitted considering a single exponential component, therefore, only the lowest energy traps are involved at RT. The stability of the TL signal coming from the periwinkle shell shows a fading effect too, but differs from the inorganic phase in (i) the behavior in the evolution of the relative intensity of the TL emission that could not be fitted to a first order decay equation due to the scattering of the results probably associated with the lattice disorder and (ii) the initial decay is slower compared to the evolution of the aragonite TL emission (up to 60%). However, similar to the aragonite sample, one can appreciate how the signal starts to be stable from 150–200 h onwards. 4. Conclusions The study performed on the CL and TL emission of aragonite and common periwinkle – littorina littorera – shell (composed by 10% of aragonite and 90% of calcite) samples, indicates that both natural materials could be potentially employed in the field of retrospective dosimetry in the case of radiological terrorism or radiation accident where conventional monitoring is not available. The samples, previously characterized by XRD and Raman spectroscopy, exhibit similar TL behavior regardless of the origin (mineral or biogenic), but differs from the CL emission where the main waveband of the mineral sample appears at lower energies (probably associated with point defects) and the more intense maximum obtained from the periwinkle shell is peaked in the UV-blue spectral region (linked to structural defects). The 400 nm-TL characterization shows for both Ca-rich carbonates (i) an acceptable radiation sensitivity, (ii) linear dose response in the range of interest (up to 8 Gy), (iii) The stability of the TL signal after 700 h of storage, shows an initial rapid decay (ca. 88%) for the aragonite sample and a slower initial decay for the periwinkle shell (ca. 60%) and maintaining (in both cases) the stability from 150 h onwards which indicates that the electron population decreases asymptotically. Additionally, (iv) the tests of thermal stability at different temperatures confirm a continuum in the trap system.
Acknowledgments Cecilia Boronat thanks to ‘‘Consejería de Educación, Juventud y Deporte de la Comunidad de Madrid, Spain” and ”Fondo Social Europeo, Belgium” (PEJ15/BIO/AI-0418) for the support provided under the ‘‘Operativo de Empleo Juvenil y la Iniciativa de Empleo Juvenil (YEI)” program (B.O.C.M. Núm.152. Orden 1880/2015, de 16 de junio del 2015).
References [1] R. Nagtegaal, C.A. Grove, S. Kasper, J. Zinke, W. Boer, G.A. Brummer, Chem. Geol. 318 (2012) 6–15. [2] C. Aydasß, B. Engin, S. Kapan, T. Komut, T. Aydin, U. Paksu, Appl. Radiat. Isot. 105 (2015) 72–79. [3] B. Ziegelmann, K.W. Bögl, G.A. Schreiber, Radiat. Phys. Chem. 54 (1999) 413– 423. [4] M. Marrale, A. Longo, A. Bartolotta, M.C. D’Oca, M. Brai, Nucl. Instrum. Meth. Phys. Res. B 297 (2013) 58–63. [5] A.N. Yazici, M. Bedir, H. Bozkurt, H. Bozkurt, Nucl. Instrum. Meth. Phys. Res. B 266 (2008) 613–620. [6] S.W.S. McKeever, New York, Cambridge University Press, 1985. [7] M.A.S. Kalceff, M.R. Phillips, Phys. Rev. 52 (1995) 3122–3134. [8] L. Bøtter-Jensen, G.A.T. Duller, Nucl. Tracks Radiat. Meas. 20 (1992) 549–553. [9] V. Correcher, A. Delgado, Radiat. Meas. 29 (1998) 411–414. [10] J. Garcia-Guinea, V. Correcher, Spectrosc. Lett. 33 (2000) 103–113. [11] R.V. Demicco, T.K. Lowenstein, L.A. Hardie, Geology 31 (2003) 793–796. [12] B.J. Broadaway, Master thesis, University of Massachusetts Boston, 2010. [13] C. Soliman, A.M. Massoud, M.A. Hussein, Nucl. Instrum. Meth. Phys. Res. B 222 (2004) 163–168. [14] D. Krishnamurti, Proc. Ind. Acad. Sci. 51 (1960) 285–295. [15] A.A. Kaminskii, H. Rhee, O. Lux, H.J. Eichler, V.V. Koltashev, R. Kleinschrodt, L. Bohaty, P. Becker, Laser Phys. Lett. 9 (1960) 259–284. [16] G. Eckhardt, D.P. Bortfeld, M. Geller, Appl. Phys. Lett. 3 (1963) 137–138. [17] V.N. Denisov, B.N. Mavrin, V.B. Podobedov, K.E. Sterin, Phys. Status. Solidi 110 (1982) 183–189. [18] S. Saito, M. Tasumi, J. Raman Spectrosc. 14 (1983) 310–321. [19] C. Hedegaard, J.F. Bardeau, D. Chateigner, J. Mollus. Stud. 72 (2006) 157–162. [20] V. Correcher, J. Garcia-Guinea, C. Martin-Fernandez, N. Can, Spectrosc. Lett. 44 (2011) 486–489. [21] D. Habermann, J.R. Niklas, J. Meijer, A. Stephan, T. Gotte, Nucl. Instrum. Meth. Phys. Res. B 181 (2001) 563–569. [22] K. Polikreti, C. Christofides, Phys. Chem. Miner. 36 (2009) 271–279. [23] J. Garcia-Guinea, E. Crespo-Feo, V. Correcher, J. Rubio, M.V. Roux, P.D. Townsend, Phys. Chem. Miner. 36 (2009) 431–438. [24] J. Garcia-Guinea, E. Crespo-Feo, V. Correcher, A. Cremades, J. Rubio, L. Tormo, P. D. Townsend, Radiat. Meas. 44 (2009) 338–343. [25] M. Gaft, L. Nagli, G. Panczer, G. Waychunas, N. Porat, Am. Mineral. 93 (2008) 158–167. [26] R. Chapoulie, F. Bechtel, D. Borschneck, M. Schvoerer, G. Remond, Scan. Microsc. Suppl. 9 (1995) 225–232. [27] B.S. Gorobets, A.A. Rogojine, Moscow All-Russia Institute for Mineral Resources (VIMS), 2002. [28] Y. Tanabe, S. Sugano, Phys. Soc. Jpn. 9 (1954) 766–779. [29] D. Habermann, R.D. Neuser, D.K. Richter, Sediment. Geol. 101 (1995) 1–7.
C. Boronat et al. / Nuclear Instruments and Methods in Physics Research B 401 (2017) 1–7 [30] E. Crespo-Feo, J. Garcia-Guinea, V. Correcher, A. Garralon, A.I.P. Conf, Proc. 1163 (2009) 121–127. [31] V. Correcher, J.M. Gomez-Ros, J. Garcia-Guinea, Radiat. Meas. 38 (2004) 689– 693. [32] V. Correcher, J. Garcia-Guinea, A. Delgado, L. Sanchez-Munoz, Radiat. Prot. Dosim. 84 (1999) 503–506. [33] V. Correcher, D. Molina, J. Garcia-Guinea, Rev. Mex. Fis. 49 (2003) 235–241. [34] M. Martini, G. Spinolo, A. Vedda, Solid State Commun. 91 (1994) 751–756.
7
[35] B.L. Davis, L.H. Adams, J. Geophys. Res. 70 (1965) 433–441. [36] V. Ponnusamy, V. Ramasamy, M. Dheenathayalu, J. Hemalatha, Nucl. Instrum. Meth. Phys. Res. B 217 (2004) 611–620. [37] A. Mandowski, Radiat. Meas. 43 (2008) 167–170. [38] V. Correcher, J. Garcia-Guinea, F.J. Valle-Fuentes, Geophys. Res. Lett. 30 (2003) 1949. [39] S.O. Souza, J.F.D. Chubaci, P.C. Selvin, M.D. Sastry, S. Watanabe, J. Phys. D Appl. Phys. 35 (2002) 1562–1565.