Passive Dosimeters Research Articles

Why diamond dimensions and electrode geometry are crucial for small photon beam dosimetry

Recent use of very small photon beams (down to 4 mm) in stereotactic radiotherapy requires new detectors to accurately determine the delivered dose. Diamond detectors have been presented in the literature as an attractive candidate for this application, due to their small detection volume and the diamond atomic number (Z = 6) which is close to water effective atomic number (Zeff ∼ 7.42). However, diamond exhibits a density 3.51 times greater than that of water and recent studies using Monte Carlo simulations have demonstrated the drawback of a high-density detector on small beam output factors. The current study focuses on geometrical parameters of diamond detector, namely, the diamond dimensions and the electrode geometry, in order to solve the dosimetric issues still observed in small photon beams with diamond detectors. To give better insights to these open questions, we have used both computational method and experimental analysis. This study highlighted that reducing diamond dimensions is crucial for small beam output factor measurements and to limit the influence of its high density. Furthermore, electrodes covering the whole diamond surface were essential for a dose rate independence of the diamond detector. The optimal dosimeter derived from this work presented small diamond dimensions of approximately 1 × 1 × 0.15 mm3, with diamond-like-carbon electrodes covering the whole diamond surface. A dose rate independence of this diamond detector (better than 0.5% over a wide range of dose rates available on a stereotactic dedicated facility) was obtained due to the electrode geometry. Concerning the output factor measurements, a good agreement (better than 1.1%) was observed between this carbon material detector and two types of passive dosimeters (LiF microcubes and EBT2 radiochromic films) for all beam sizes except the smallest field of 0.6 × 0.6 cm2 with a deviation of 2.6%. This new study showed the high performance of this diamond detector in small photon beams, in comparison with various commercially available passive and active dosimeters.

UNCERTAINTY EVALUATION FOR MULTIDETECTOR PASSIVE DOSEMETERS USING A TWO-STAGE MEASUREMENT MODEL AND THE MONTE CARLO METHOD.

This paper proposes a method for evaluating the standard uncertainty in the measurements with passive personal dosemeters using a numerical method (Monte Carlo). The paper builds on a previous paper where a two-stage measurement model for passive dosemeters was proposed. This model follows the course of events during the measurement, which also consists of two stages: (1) the exposure of the dosemeter in the workplace where a signal develops in the form of, e.g. electron/hole pairs in solid-state detectors and film or damages to a molecular structure in track films, the latent signal and (2) the evaluation at the service where the latent signal is 'developed' into an observable signal. In this paper, the study is extended to multielement dosemeters that have multiple outputs. The charm of the proposed method is that it needs no mathematical approximations and does inherently include any correlations that may exist between input quantities and, in the case of multiple outputs like Hp(10) and Hp(0.07), between these outputs.

Staff lens doses in interventional urology. A comparison with interventional radiology, cardiology and vascular surgery values

The purpose of this work is to evaluate radiation doses to the lens of urologists during interventional procedures and to compare them with values measured during interventional radiology, cardiology and vascular surgery. The measurements were carried out in a surgical theatre using a mobile C-arm system and electronic occupational dosimeters (worn over the lead apron). Patient and staff dose measurements were collected in a sample of 34 urology interventions (nephrolithotomies). The same dosimetry system was used in other medical specialties for comparison purposes. Median and 3rd quartile values for urology procedures were: patient doses 30 and 40 Gy cm2; personal dose equivalent Hp(10) over the apron (μSv/procedure): 393 and 848 (for urologists); 21 and 39 (for nurses). Median values of over apron dose per procedure for urologists resulted 18.7 times higher than those measured for radiologists and cardiologists working with proper protection (using ceiling suspended screens) in catheterisation laboratories, and 4.2 times higher than the values measured for vascular surgeons at the same hospital. Comparison with passive dosimeters worn near the eyes suggests that dosimeters worn over the apron could be a reasonable conservative estimate for ocular doses for interventional urology. Authors recommend that at least the main surgeon uses protective eyewear during interventional urology procedures.

Measurements of Radon Concentrations and Dose Assessments in Physics Department-Science College-Al-Mustansiriyah University, Baghdad, Iraq

Measurements of radon gas concentrations with their progeny and the annual effective dose indoor the building of Al-Mustansiriyah University College of Science-Physics Department have been carried out by using time-integrated passive radon dosimeters solid state nuclear track detector CR-39 technique. The detectors with 1cm x1cm have been distributed over 70 places and suspended for sitting (1m) and standing (1.75m) positions in each location under study. The dosimetric measurements are made over a period of 90 days from 30 January 2014 to 30 April 2014. The calibration process has been done using radium-226 source with known activity radiation. It has found that the indoor radon gas concentrations varing from 37.488±6.123Bg/m3 to 58.670±7.660Bg/m3 with an average value 51.398±7.156Bg/m3 at 1m , and varing from 35.964±5.997Bg/m3 to 56.994±7.549Bg/m3 with an average value 47.057±6.847Bg/m3 at 1.75m which are within the worldwide limits 148Bg/m3 (EPA, 2003) and 200-300Bg/m3 (ICRP, 2009). The annual effective dose of the inhalation exposure to radon gas has been estimated and this vary from 0.394mSv/y to 0.617mSv/y with an average value 0.540mSv/y at 1m, and varing from 0.378mSv/y to 0.599mSv/y with an average value 0.495mSv/y at 1.75m which are within the worldwide permissible limist 3-10mSv/y (ICRP, 1993). The potential alpha energy concentration found to vary from 4.053mWL to 6.343mWL with an average value 5.557mWL at 1m and vary from 3.888mWL to 6.162mWL with an average value 5.087mWL at 1.75m which are less than the recommended value 53.33mWL (UNSCEAR, 1993). The lung cancer cases per million person per year vary from 7.093 to 11.101 per million person per year with an average value 9.725 per million person per year at 1m and vary from 6.805 to 10.784 per million person per year with an average value 8.904 per million person per year which are less than the recommended range 170-230 per million person per year (ICRP, 1993). The number of decays per-minute using swabs measurements technique have been used for selected units within two swabs from building materials walls for each unite, with area of 100cm2 using Ludlum 3030, the average of three swabs measurements have been calculated. Hence, the effectiveness of emitted alpha particles from the walls has been calculated to be varied from 0.00000 to 0.02222Bq/cm2 with an average value 0.01169Bq/cm2 at 1m and 0.01015Bq/cm2 at 1.75m respectevily which are within the permissible limit 0.04Bq/cm2 (Danial, 2010).

Measurements of Radon Concentrations and Dose Assessments in Physics Department-Science College-Al-Mustansiriyah University, Baghdad, Iraq

Measurements of radon gas concentrations with their progeny and the annual effective dose indoor the building of Al-Mustansiriyah University College of Science-Physics Department have been carried out by using time-integrated passive radon dosimeters solid state nuclear track detector CR-39 technique. The detectors with 1cm x1cm have been distributed over 70 places and suspended for sitting (1m) and standing (1.75m) positions in each location under study. The dosimetric measurements are made over a period of 90 days from 30 January 2014 to 30 April 2014. The calibration process has been done using radium-226 source with known activity radiation. It has found that the indoor radon gas concentrations varing from 37.488±6.123Bg/m3 to 58.670±7.660Bg/m3 with an average value 51.398±7.156Bg/m3 at 1m , and varing from 35.964±5.997Bg/m3 to 56.994±7.549Bg/m3 with an average value 47.057±6.847Bg/m3 at 1.75m which are within the worldwide limits 148Bg/m3 (EPA, 2003) and 200-300Bg/m3 (ICRP, 2009). The annual effective dose of the inhalation exposure to radon gas has been estimated and this vary from 0.394mSv/y to 0.617mSv/y with an average value 0.540mSv/y at 1m, and varing from 0.378mSv/y to 0.599mSv/y with an average value 0.495mSv/y at 1.75m which are within the worldwide permissible limist 3-10mSv/y (ICRP, 1993). The potential alpha energy concentration found to vary from 4.053mWL to 6.343mWL with an average value 5.557mWL at 1m and vary from 3.888mWL to 6.162mWL with an average value 5.087mWL at 1.75m which are less than the recommended value 53.33mWL (UNSCEAR, 1993). The lung cancer cases per million person per year vary from 7.093 to 11.101 per million person per year with an average value 9.725 per million person per year at 1m and vary from 6.805 to 10.784 per million person per year with an average value 8.904 per million person per year which are less than the recommended range 170-230 per million person per year (ICRP, 1993). The number of decays per-minute using swabs measurements technique have been used for selected units within two swabs from building materials walls for each unite, with area of 100cm2 using Ludlum 3030, the average of three swabs measurements have been calculated. Hence, the effectiveness of emitted alpha particles from the walls has been calculated to be varied from 0.00000 to 0.02222Bq/cm2 with an average value 0.01169Bq/cm2 at 1m and 0.01015Bq/cm2 at 1.75m respectevily which are within the permissible limit 0.04Bq/cm2 (Danial, 2010).

영상의학과에서 사용되는 광자극 형광선량계와 전자식 개인선량계의 방향 의존성 비교

최근 개인선량계로 사용이 증가하고 있는 수동형 선량계인 OSLD와 능동형 선량계인 EPD의 상대 반응도(relative response), 측정 불확도(uncertainty of measurement)를 계산하여 방향의존성(angular dependence)을 비교, 분석하였다. OSLD는 수평, 수직방향의 <TEX>$0^{\circ}{\sim}{\pm}90^{\circ}$</TEX> 범위에서 평균 상대 반응도는 0.97, 0.95의 작은 변화를 보였고 방향의존성에 대한 불확도는 0.65, 0.62로 전체 불확도에 미치는 영향은 미미한 것으로 판단되었다. EPD는 <TEX>$0^{\circ}{\sim}{\pm}60^{\circ}$</TEX> 범위에서 수평, 수직방향 평균 상대 반응도는 0.94, 0.97로 확인되어 IEC 61526 규정을 만족하였다. 방향의존성에 대한 불확도는 수평, 수직방향에서 0.44, 0.40로 전체 불확도에 미치는 영향은 미미하였다. 그러나 수평방향에서 <TEX>$+90^{\circ}$</TEX>, <TEX>$-90^{\circ}$</TEX> 방향의 상대 반응도는 0.60, 0.37이고 수직방향에서 <TEX>$+90^{\circ}$</TEX> 방향의 반응도는 0.06으로 반응도의 큰 변화를 관찰할 수 있었다. OSLD의 방향 의존성은 <TEX>$0^{\circ}{\sim}{\pm}90^{\circ}$</TEX> 범위까지 EPD에 비해 우수하였으며 EPD의 경우 구조적 특징으로 반응도가 급변하는 특정방향이 존재하였다. 따라서 수동형선량계와 보조선량계의 병행사용이 개인피폭선량측정의 정확도를 기할 수 있을 것으로 판단된다. The angular dependence of active dosimeters, EPD, is analysed and compared with that of passive dosimeters, OSLD, after evaluating their relative response and uncertainty of measurement, where it is known that the personal use of them has been increased recently. There appeared a minor variation for average relative response of OSLD in the horizontal and vertical directions within the range <TEX>$0^{\circ}{\sim}{\pm}90^{\circ}$</TEX>, which are 0.97 and 0.95 respectively. The variations of angular dependence in the same situations with OSLD are 0.65 and 0.62, respectively, which also reveals a negligible effect on the overall uncertainty. EPDs within the interval <TEX>$0^{\circ}{\sim}{\pm}60^{\circ}$</TEX> for horizontal and vertical directions are 0.94 and 0.97, respectively. These satisfy the requirements of IEC 61526. Uncertainties about the dependence of direction from horizontal and vertical directions are 0.44, 0.40, respectively. The impact of these uncertainties on the overall uncertainty was negligible. However, we observed a significant change in reactivity: the relative reactivities for <TEX>$+90^{\circ}$</TEX> and <TEX>$-90^{\circ}$</TEX> from the horizontal direction are 0.60, 0.37, while that form vertical direction is 0.06. The direction dependence of OSLD was superior to EPD in the range of <TEX>$0^{\circ}{\sim}{\pm}90^{\circ}$</TEX>. There appeared a rapidly changing structural features in EPD response for a certain direction. Therefore, we conclude that concurrent use of passive dosimeters and auxiliary dosimeter provides accurate data for personal dose measurements.

Évaluation de l’exposition aux radiations du chirurgien lors d’un TLIF mini-invasif : comparaison entre fluoroscopie et navigation O-arm

IntroductionTransforaminal lumbar interbody fusion with a minimally invasive approach (MIS TLIF) has become a very popular technique in the treatment of degenerative diseases of the lumbar spine, as it allows a decrease in muscle iatrogenic. However, iterative radiological controls inherent to this technique are responsible for a significant increase in exposure to ionizing radiation for the surgeon. New techniques for radiological guidance (O-arm navigation-assisted) would overcome this drawback, but this remains unproven. ObjectivesTo analyze the exposure of the surgeon to intraoperative X-ray during a MIS TLIF under fluoroscopy and under O-arm navigation-assisted. Materials and methodsThis prospective study was conducted at the University Hospital of Lille from February to May 2013. Twelve patients underwent a MIS TLIF for the treatment of low-grade spondylolisthesis; six under standard fluoroscopy (group 1) and six under O-arm system (group 2). Passive dosimeters (rings and glasses) and active dosimeters for thorax were used to measure the radiation exposure of the surgeon. ResultsFor group 1, the average time of fluoroscopy was 3.718minutes (3.13–4.56) while no radioscopy was perform on group 2. For the first group, the average exposure dose was 12μSv (5–20μSv) on the thorax, 1168μSv (510–2790μSv) on the main hand and 179μSv (103–486μSv) on the lens. The exposure dose was measured zero on the second group. ConclusionThe maximum recommended doses can be reached, mainly for the lens. In addition to the radioprotection measures, O-arm navigation systems are safe alternatives to significantly reduce surgeon exposure.

Study of a new neutron dosimeter incorporating RPL detectors

We characterize a passive dosimeter incorporating RadioPhotoLuminescent (RPL) detectors capable of measuring both fast and thermal neutrons for personal dosimetry. These neutrons can be detected in a mixed n-γ field with appropriate converters. Monte Carlo simulations with MCNPX helped with the geometrical conception of the dosimeter and the choice of materials. The responses of the RPL dosimeter are linear in Hp(10) with detection limits of 1.83 mSv for fast neutrons and 0.19 mSv for thermal neutrons. The angular dependencies are satisfactory according to the ISO 21909 norm. A calibration factor of (9.5 ± 0.5) × 10−2 mSv cm2/RPL intensity was obtained for the fast neutrons of the IPHC's 241Am–Be calibrator. The factor was (9.7 ± 0.3) × 10−3 mSv cm2/RPL intensity for thermalized neutrons.

TU‐E‐201‐00: Eye Lens Dosimetry for Patients and Staff

TU‐E‐201‐00: Eye Lens Dosimetry for Patients and Staff

TU‐E‐201‐01: Methods for Eye Lens Dosimetry and Studies On Lens Opacities with Interventionists

TU‐E‐201‐01: Methods for Eye Lens Dosimetry and Studies On Lens Opacities with Interventionists

TU‐E‐201‐03: Eye Lens Dosimetry in Radiotherapy Using Contact Lens‐Shaped Applicator

TU‐E‐201‐03: Eye Lens Dosimetry in Radiotherapy Using Contact Lens‐Shaped Applicator

TU‐E‐201‐02: Eye Lens Dosimetry From CT Perfusion Studies

TU‐E‐201‐02: Eye Lens Dosimetry From CT Perfusion Studies

Characterization of neutron calibration fields at the TINT's 50 Ci americium-241/beryllium neutron irradiator

Reliable measurement of neutron radiation is important for monitoring and protection in workplace where neutrons are present. Although Thailand has been familiar with applications of neutron sources and neutron beams for many decades, there is no calibration facility dedicated to neutron measuring devices available in the country. Recently, Thailand Institute of Nuclear Technology (TINT) has set up a multi-purpose irradiation facility equipped with a 50 Ci americium-241/beryllium neutron irradiator. The facility is planned to be used for research, nuclear analytical techniques and, among other applications, calibration of neutron measuring devices. In this work, the neutron calibration fields were investigated in terms of neutron energy spectra and dose equivalent rates using Monte Carlo simulations, an in-house developed neutron spectrometer and commercial survey meters. The characterized neutron fields can generate neutron dose equivalent rates ranging from 156 μSv/h to 3.5 mSv/h with nearly 100% of dose contributed by neutrons of energies larger than 0.01 MeV. The gamma contamination was less than 4.2-7.5% depending on the irradiation configuration. It is possible to use the described neutron fields for calibration test and routine quality assurance of neutron dose rate meters and passive dosemeters commonly used in radiation protection dosimetry.

Space Radiation Dosimetry to Evaluate the Effect of Polyethylene Shielding in the Russian Segment of the International Space Station

As a part of the Alteino Long Term Cosmic Ray measurements on board the International Space Station (ALTCRISS) project, the shielding effect of polyethylene (PE) were evaluated in the Russian segment of the ISS, using active and passive dosimeter systems covered with or without PE shielding. For the passive dosimeter system, PADLES (Passive Dosimeter for Life-Science and Experiments in Space) was used in the project, which consists of a Thermo-Luminescent Dosimeters (TLD) and CR-39 Plastic Nuclear Track Detectors (PNTDs) attached to a radiator. Not only CR-39 PNTD itself but also a tissue equivalent material, NAN-JAERI, were employed as the radiator in order to investigate whether CR-39 PNTD can be used as a surrogate of tissue equivalent material in space dosimetry or not. The agreements between the doses measured by PADLES with CR-39 PNTD and NAN-JAERI radiators were quite satisfactorily, indicating the tissue-equivalent dose can be measured by conventional PADLES even though CR-39 PNTD is not perfect tissue-equivalent material. It was found that the shielding effect of PE varies with location inside the spacecraft: it became less significant with an increase of the mean thickness of the wall. This tendency was also verified by Monte Carlo simulation using the PHITS code. Throughout the flight experiments, in a series of four phases in the ALTCRISS project from December 2005 to October 2007, we assessed the ability of PE to decrease radiation doses in Low Earth Orbit(LEO).

Optically Stimulated Luminescence in Tm-Doped Calcium Fluoride Phosphor Crystal for Application to a Novel Passive Type Dosimeter

Optically Stimulated Luminescence in Tm-Doped Calcium Fluoride Phosphor Crystal for Application to a Novel Passive Type Dosimeter

Measurements of Radon Concentrations and Dose Assessments in Chemistry Department-Science College- Al-Mustansiriyah University, Baghdad, Iraq

Measurements of radon gas concentrations with their progeny and the annual effective dose indoor the building of Al-Mustansiriyah University College of Science-Physics Department have been carried out by using time-integrated passive radon dosimeters solid state nuclear track detector CR-39 technique. The detectors with 1cm x1cm have been distributed over 70 places and suspended for sitting (1m) and standing (1.75m) positions in each location under study. The dosimetric measurements are made over a period of 90 days from 30 January 2014 to 30 April 2014. The calibration process has been done using radium-226 source with known activity radiation. It has found that the indoor radon gas concentrations varing from 37.488±6.123Bg/m 3 to 58.670±7.660Bg/m 3 with an average value 51.398±7.156Bg/m 3 at 1m, and varing from 35.964±5.997Bg/m 3 to 56.994±7.549Bg/m 3 with an average value 47.057±6.847Bg/m 3 at 1.75m which are within the worldwide limits 148Bg/m 3 (EPA, 2003) and 200-300Bg/m 3 (ICRP, 2009). The annual effective dose of the inhalation exposure to radon gas has been estimated and this vary from 0.394mSv/y to 0.617mSv/y with an average value 0.540mSv/y at 1m, and varing from 0.378mSv/y to 0.599mSv/y with an average value 0.495mSv/y at 1.75m which are within the worldwide permissible limist 3-10mSv/y (ICRP, 1993). The potential alpha energy concentration found to vary from 4.053mWL to 6.343mWL with an average value 5.557mWL at 1m and vary from 3.888mWL to 6.162mWL with an average value 5.087mWL at 1.75m which are less than the recommended value 53.33mWL (UNSCEAR, 1993). The lung cancer cases per million person per year vary from 7.093 to 11.101 per million person per year with an average value 9.725 per million person per year at 1m and vary from 6.805 to 10.784 per million person per year with an average value 8.904 per million person per year which are less than the recommended range 170-230 per million person per year (ICRP, 1993). The number of decays per-minute using swabs measurements technique have been used for selected units within two swabs from building materials walls for each unite, with area of 100cm 2 using Ludlum 3030, the average of three swabs measurements have been calculated. Hence, the effectiveness of emitted alpha particles from the walls has been calculated to be varied from 0.00000 to 0.02222Bq/cm 2 with an average value 0.01169Bq/cm 2 at 1m and 0.01015Bq/cm 2 at 1.75m respectevily which are within the permissible limit 0.04Bq/cm 2 (Danial, 2010).

Radon Concentrations Measurement in Dwellings of Kufa Technical Institute, Iraq Using LR-115 Nuclear Track Detector

In this work, radon concentrations were measured in dwellings Kufa Technical institute, Iraq between November 2014 to February 2015 using time integrated passive radon dosimeters containing LR-115 Type II plastic track detectors. Also, we calculated the concentration of short-lived radon daughters, potential alpha energy, working level month, the annual effective dose rate, the annual equivalent dose rate and the excess lifetime cancer risk in all dwellings under study. The radon concentration in these dwelling ranges from (15.211 ± 2.745 to 32.445 ± 09.200) Bq/m3 with an average of (21.567 Bq/m3), which within the acceptable radon levels (50-150) Bq/m3 recommended by the International Commission on Radiological Protection (ICRP). The mean the excess lifetime cancer risk were found to be ranges from 35.458 to 75.633 with an average value of 50.297 per 106 persons. These values are within in the safe limits recommended by the international organizations.

Monitoring of indoor radon and assessment of lung cancer risk to population of Beit Ummar city, Palestine

Radon concentrations were measured using CR-39 passive dosimeters in Beit Ummar city. 150 dosimeters were distributed over the study area dwellings according to the fraction of the population. The exposure started from October 2014 and lasted for 90 days. The city was divided into five sectors with six categories for each; corridor, kitchen, living room, saloon, bedroom and store. The influence of floor number and building type was introduced. Obtained results have recorded relatively high radon concentration in 73% of the studied houses. This is explained due to several factors such as poor ventilation, construction materials, and continuous usage of heating during this period and age of the building. Different parameters were calculated based on the measurements of track density of the distributed dosimeters in order to estimate the risk of radiation exposure; those parameters are: radon concentration (CRn), exposure to radon progeny (EP), indoor annual effective dose (AED) and number of lung cancer cases per year per million persons (LCC). The results showed that the radon concentrations and the resulting doses in the monitored chambers exceed the safe limits recommended by the WHO and EPA in some aspects. Therefore, health risk due to radon is possible.

Fully-Depleted Silicon-on-Insulator Devices for Radiation Dosimetry in Cancer Therapy

The potential of using fully-depleted silicon-on-insulator (FDSOI) devices as dosimeters for radiation cancer therapy is investigated. The response of long-channel FDSOI MOSFETs to radiation from a linear accelerator under various clinical conditions has been measured. Linear response of the device threshold voltage, ${V_{\rm th}}$ , is observed for typical interventional energy X-rays up to absorbed doses as high as 160 Gy. The device response is observed to be strongly influenced by the application of a substrate bias, ${V_{\rm bg}}$ , with sensitivity improvements of up to $20 \times $ observed for ${V_{\rm bg}} =+ 5~\hbox{V}$ compared to ${V_{\rm bg}} = 0$ . The results have been used to calibrate numerical simulations that show the design space for using FDSOI variable capacitors (varactors) as passive wireless radiation dosimeters suitable for in vivo implantation. Simulation studies show that a design space exists to realize wireless sensors with both high quality factor ( $Q > 20$ at 1 GHz) and good sensitivity ( $\Delta f/f = 0.12\% /\hbox{Gy}$ ). These results indicate the promise of FDSOI to realize a new, convenient class of in vivo dosimeters for radiation therapy.

Cosmic radiation exposure of biological test systems during the EXPOSE-R mission

AbstractIn the frame of the EXPOSE-R mission outside the Russian Zvezda Module of the International Space Station (ISS) passive thermoluminescence dosimeters were applied to measure the radiation exposure of biological samples. The detectors were located beneath the sample carriers to determine the dose levels for maximum shielding. The dose measured beneath the sample carriers varied between 317 ± 10 and 230 ± 2 mGy, which amount to an average dose rate of 381 ± 12 and 276 ± 2 μGy d−1. These values are close to those assessed for the interior of the ISS and reflect the high shielding of the biological experiments within the EXPOSE-R facility. As a consequence of the high shielding (several g cm−2), the biological samples were predominantly exposed to galactic cosmic heavy ions and trapped protons in the Earth's radiation belts, whereas the trapped electrons did not reach the samples.