Water Calorimetry Research Articles

2D range modulator for high-precision water calorimetry in scanned carbon-ion beams

Ionization chamber-based dosimetry for carbon-ion beams still shows a significantly higher standard uncertainty than high-energy photon dosimetry. This is mainly caused by the high standard uncertainty of the correction factor for beam quality . Due to a lack of experimental data, the given values for are based on theoretical calculations. To reduce this standard uncertainty, factors for different irradiation conditions and ionization chambers (ICs) can be determined experimentally by means of water calorimetry. To perform such measurements in a spread-out Bragg peak (SOBP) for a scanned carbon-ion beam, we describe the process of creating an almost cubic dose distribution of about 6 × 6 × 6 cm3 using a 2D range modulator. The aim is to achieve a field homogeneity with a standard deviation of measured dose values in the middle of the SOBP (over a lateral range and a depth of about 4 cm) below 2% within a scanning time of under 100 s, applying a dose larger than 1 Gy. This paper describes the optimization and characterization of the dose distribution in detail.

Monte Carlo and water calorimetric determination of kilovoltage beam radiotherapy ionization chamber correction factors

The in-phantom calibration method for radiotherapy kilovoltage x-ray beams requires ionization chamber correction factors. The overall ionization chamber correction factor accounts for changes in the chamber response due to the displacement of water by the chamber cavity and wall, the presence of the stem and the change in incident photon energy and angular distribution in the phantom to that in air. A waterproof sheath, if required, is accounted for in a sheath correction factor. The aim of this study is to determine chamber correction factors through Monte Carlo (MC) simulations and water calorimetry measurements. Correction factors are determined for the PTW TM30013, NE2571, IBA FC65-G, IBA FC65-P and Exradin A12 ionization chambers. They are compared to experimental values obtained at the German national metrology institute Physikalisch-Technische Bundesanstalt (PTB) with their water calorimetry-based absorbed dose to water primary standard and at other national metrological institutes. An uncertainty analysis considers the contributions to the uncertainty on the chamber correction factors from the field size, photon cross sections, photon fluence spectra and chamber wall and central electrode dimensions. The MC calculated chamber correction factors are within 2.2% of unity with a standard uncertainty of 0.3%. For the 50 kV and 100 - 140 kV radiation beam qualities, the calculated correction factors deviate from the measured correction factors (with a standard uncertainty of 1%) by up to 2.6%. The calculated chamber correction factors for the PTW TM30013 and Exradin A12 are consistent with those derived from the BIPM kilovoltage primary standard. The inconsistencies between the calculated and experimental chamber correction factors indicate the need to further investigate the accuracy of kilovoltage absorbed dose to water primary standards and the use of MC simulations to determine kilovoltage beam chamber correction factors.

High-resolution adiabatic calorimetry of supercooled water

Liquid water exhibits anomalous behavior in the supercooled region. A popular hypothesis to explain supercooled water’s anomalies is the existence of a metastable liquidliquid transition terminating at a critical point. The hypothesized phase transition is not directly accessible in a bulk experiment because it is expected to occur in “no-man’s” below the kinetic stability limit of the liquid phase at about 233 K, the temperature of homogeneous ice formation. Therefore, verifications of this hypothesis are usually based on extrapolations from the experimentally accessible region. In this work, we present the results of highresolution adiabatic calorimetry measurements of cold and supercooled liquid water in the range from 294 to 244 K, the lowest temperature of water’s supercooling achieved so far in a bulk adiabatic-calorimetry experiment. The resolution of the measurements is also record-high, with the average statistical (random) error of about 0.1%. The data are consistent with adiabatic-calorimetry measurements of supercooled water earlier reported by Tombari et al (1999 Chem. Phys. Lett. 300 749) but significantly deviate from differential-scanning calorimetry measurements in emulsified water reported by Angell et al (1982 J. Phys. Chem. 86 998) and by Archer and Carter (2000 J. Phys. Chem. 104 8563) Consequences of the new heat-capacity data in interpretation of the nature of water’s anomalies are discussed.

Effect of different doses of supervised exercise on food intake, metabolism, and non-exercise physical activity: The E-MECHANIC randomized controlled trial

Exercise is recommended for weight management, yet exercise produces less weight loss than expected, which is called weight compensation. The mechanisms for weight compensation are unclear. The aim of this study was to identify the mechanisms responsible for compensation. In a randomized controlled trial conducted at an academic research center, adults (n=198) with overweight or obesity were randomized for 24 wk to a no-exercise control group or 1 of 2 supervised exercise groups: 8 kcal/kg of body weight/wk (KKW) or 20 KKW. Outcome assessment occurred at weeks 0 and 24. Energy intake, activity, and resting metabolic rate (RMR) were measured with doubly labeled water (DLW; with and without adjustments for change in RMR), armband accelerometers, and indirect calorimetry, respectively. Appetite and compensatory health beliefs were measured by self-report. A per-protocol analysis included 171 participants (72.5% women; mean±SD baseline body mass index: 31.5±4.7 kg/m2). Significant (P<0.01) compensation occurred in the 8 KKW (mean: 1.5 kg; 95% CI: 0.9, 2.2 kg) and 20 KKW (mean: 2.7 kg; 95% CI: 2.0, 3.5 kg) groups, and compensation differed significantly between the exercise groups (P=0.01). Energy intake by adjusted DLW increased significantly (P<0.05) in the 8 KKW (mean: 90.7 kcal/d; 95% CI: 35.1, 146.4 kcal/d) and 20 KKW (mean: 123.6 kcal/d; 95% CI: 64.5, 182.7 kcal/d) groups compared with control (mean: -2.3 kcal/d; 95% CI: -58.0, 53.5 kcal/d). Results were similar without DLW adjustment. RMR and physical activity (excluding structured exercise) did not differentially change among the 3 groups. Participants with higher compared with lower compensation reported increased appetite ratings and beliefs that healthy behaviors can compensate for unhealthy behaviors. Furthermore, they increased craving for sweet foods, increased sleep disturbance, and had worsening bodily pain. Compensation resulted from increased energy intake and concomitant increases in appetite, which can be treated with dietary or pharmacological interventions. Compensation was not due to activity or metabolic changes. This trial was registered at clinicaltrials.gov as NCT01264406.

43 Reference dosimetry for high dose rate pulsed scanned proton beams

Introduction The newly installed ProteusONE (IBA PT, LLN, Belgium) relies on a super-conducting synchro-cyclotron which delivers a pulsed scanned proton beams from 100 MeV to 226 MeV with a dose rate between 2.65 μGy/pulse and 230 μGy/pulse respectively. Its beam structure of 1 kHz frequency and high dose rate per pulse makes it particular considering recombination effect in plane parallel ionization chambers. Methods The aim of this work is firstly to characterize the beam monitor ionization chambers response in a pulsed scanned proton beam with a high dose rate per pulse, and secondly to find a proper protocol for reference dosimetry with a plane parallel ionization chamber in this kind of proton beams. Following the TRS398 protocol [1] , temperature and pressure (kT,P), polarity effect (kpol), beam quality factor (kQ,Q0) and recombination effect (ks) correction factors were computed and applied to the considered ionization chamber. In particular, for a scanned pulsed proton beam the recombination effect in the ionization chamber is not negligible. Therefore, the recombination factor has been theoretically evaluated with Boag’s formulae [2] and measured in water for a plane parallel ionization chamber through saturation curves. The quality beam kQ,Q0 factor evaluation was based on Monte-Carlo Goma’s results [3] for PBS proton beams. The assumptions made for a high dose rate per pulse pulsed scanned proton beam based on TRS 398 for 3 energies were validated against water calorimetry [4] measurements for 3 energies. Results The recombination factor study shows that plane parallel ionization chamber should be used with −500 V voltage to limit the effect of recombination. In the same set-up conditions, water calorimetry and ionometry give less than 2% difference for the 3 mono-energetic beams. Conclusions The presented reference dosimetry protocol is validated for clinical high dose rate per pulse pulsed scanned proton beams.

OA028] On the potential of direct MV calibration of ionization chambers by secondary standards laboratories

Purpose The IAEA protocol (TRS-398) for absorbed dose to water measurements in therapeutic MV photon beams, recommends that ionization chambers be calibrated directly in MV accelerator photon beams rather than in cobalt-60 combined with generic beam quality correction factors ( k Q ) tabulated in the protocol. The purpose of this work was to study the feasibility for secondary standards laboratories to provide direct MV calibrations for hospitals and to evaluate the benefit of such calibrations versus conventional cobalt calibrations. Methods A laboratory with the potential to provide direct MV calibrations was established. It includes both a cobalt irradiator and a linear accelerator with the following MV beams: 4, 6, 10, 15, and 18 MV with flattening filter and 6 and 10 MV without flattening filter. Procedures were designed for accurate positioning of ionization chambers, beam output monitoring and relevant ionization chamber correction factors. Over a two-month period, k Q -factors were measured in all beams for seven nominally identical chambers (IBA FC65G) covering a wide range of serial numbers. Traceability to primary standards were established using transfer chambers. The results were compared with published k Q -factors from TRS-398. Results The monitoring of beam output using an external monitor chamber was found to be essential for calibration purposes: The raw accelerator output changed systematically by 0.4% over the measurement period. However, with an external monitor chamber, the output variability was reduced to less than 0.05% (1 sd). For each beam quality, the relative standard deviation for the measured k Q factors for the seven ionization chambers was about 0.07%. Conclusions The study demonstrates the feasibility of highly reproducible MV calibrations at the level of a secondary standards laboratory, and the closeness of agreement (sd k Q -factors may be adequate for the tested ionization chamber model. Ongoing work focuses on characterization of additional ionization chambers models (PTW30013, PTW31021, and NE2571) and on an improved estimation of the uncertainty related to establishing traceability to primary standards. The latter work includes direct use of water calorimetry in the specific accelerator beams of the laboratory.

Direct determination of kQ factors for cylindrical and plane-parallel ionization chambers in high-energy electron beams from 6 MeV to 20 MeV

For the ionometric determination of the absorbed dose to water, Dw, in high-energy electron beams from a clinical accelerator, beam quality dependent correction factors, kQ, are required. By using a water calorimeter, these factors can be determined experimentally and potentially with lower standard uncertainties than those of the calculated kQ factors, which are tabulated in various dosimetry protocols. However, one of the challenges of water calorimetry in electron beams is the small measurement depths in water, together with the steep dose gradients present especially at lower energies. In this investigation, water calorimetry was implemented in electron beams to determine kQ factors for different types of cylindrical and plane-parallel ionization chambers (NE2561, NE2571, FC65-G, TM34001) in 10 cm × 10 cm electron beams from 6 MeV to 20 MeV (corresponding beam quality index R50 ranging from 1.9 cm to 7.5 cm). The measurements were carried out using the linear accelerator facility of the Physikalisch-Technische Bundesanstalt. Relative standard uncertainties for the kQ factors between 0.50% for the 20 MeV beam and 0.75% for the 6 MeV beam were achieved. For electron energies above 8 MeV, general agreement was found between the relative electron energy dependencies of the kQ factors measured and those derived from the AAPM TG-51 protocol and recent Monte Carlo-based studies, as well as those from other experimental investigations. However, towards lower energies, discrepancies of up to 2.0% occurred for the kQ factors of the TM34001 and the NE2571 chamber.

Electron beam water calorimetry measurements to obtain beam quality conversion factors.

To provide results of water calorimetry and ion chamber measurements in high-energy electron beams carried out at the National Research Council Canada (NRC). There are three main aspects to this work: (a) investigation of the behavior of ionization chambers in electron beams of different energies with focus on long-term stability, (b) water calorimetry measurements to determine absorbed dose to water in high-energy beams for direct calibration of ion chambers, and (c) using measurements of chamber response relative to reference ion chambers, determination of beam quality conversion factors, kQ , for several ion chamber types. Measurements are made in electron beams with energies between 8MeV and 22MeV from the NRC Elekta Precise clinical linear accelerator. Ion chamber measurements are made as a function of depth for cylindrical and plane-parallel ion chambers over a period of five years to investigate the stability of ion chamber response and for indirect calibration. Water calorimetry measurements are made in 18MeV and 22MeV beams. An insulated enclosure with fine temperature control is used to maintain a constant temperature (drifts less than 0.1mK/min) of the calorimeter phantom at 4°C to minimize effects from convection. Two vessels of different designs are used with calibrated thermistor probes to measure radiation induced temperature rise. The vessels are filled with high-purity water and saturated with H2 or N2 gas to minimize the effect of radiochemical reactions on the measured temperature rise. A set of secondary standard ion chambers are calibrated directly against the calorimeter. Finally, several other ion chambers are calibrated in the NRC 60 Co reference field and then cross-calibrated against the secondary standard chambers in electron beams to realize kQ factors. The long-term stability of the cylindrical ion chambers in electron beams is better (always <0.15%) than plane-parallel chambers (0.2% to 0.4%). Calorimetry measurements made at 22MeV with two different vessel geometries are consistent within 0.2% after correction for the vessel perturbation. Measurements of absorbed dose calibration coefficients for the same secondary standard chamber separated in time by 10yr are within 0.2%. Drifts in linac output that would affect the transfer of the standard are mitigated to the 0.1% level by performing daily ion chamber normalization measurements. Calibration coefficients for secondary standard ion chambers can be achieved with uncertainties less than 0.4% (k=1) in high-energy electron beams. The additional uncertainty in deriving calibration coefficients for well-behaved chambers indirectly against the secondary standard reference chambers is negligible. The kQ factors measured here differ by up to 1.3% compared to those in TG-51, an important change for reference dosimetry measurements. The measurements made here of kQ factors for eight plane-parallel and six cylindrical ion chambers will impact future updates of reference dosimetry protocols by providing some of the highest quality measurements of this crucial dosimetric parameter.

An original piecewise model for computing energy expenditure from accelerometer and heart rate signals

Objective: Activity energy expenditure (EE) plays an important role in healthcare, therefore, accurate EE measures are required. Currently available reference EE acquisition methods, such as doubly labeled water and indirect calorimetry, are complex, expensive, uncomfortable, and/or difficult to apply on real time. To overcome these drawbacks, the goal of this paper is to propose a model for computing EE in real time (minute-by-minute) from heart rate and accelerometer signals. Approach: The proposed model, which consists of an original branched model, uses heart rate signals for computing EE on moderate to vigorous physical activities and a linear combination of heart rate and counts per minute for computing EE on light to moderate physical activities. Model parameters were estimated from a given data set composed of 53 subjects performing 25 different physical activities (light-, moderate- and vigorous-intensity), and validated using leave-one-subject-out. A different database (semi-controlled in-city circuit), was used in order to validate the versatility of the proposed model. Comparisons are done versus linear and nonlinear models, which are also used for computing EE from accelerometer and/or HR signals. Main results: The proposed piecewise model leads to more accurate EE estimations (, and J kg−1 min−1 and , , and J kg−1 min−1 on each validation database). Significance: This original approach, which is more conformable and less expensive than the reference methods, allows accurate EE estimations, in real time (minute-by-minute), during a large variety of physical activities. Therefore, this model may be used on applications such as computing the time that a given subject spent on light-intensity physical activities and on moderate to vigorous physical activities (binary classification accuracy of 0.8155).

Preparation of the ELISE test facility for long-pulse extraction of negative ion beams

The test facility ELISE (Extraction from a Large Ion Source Experiment) at IPP Garching, Germany, aims to demonstrate ITER-relevant negative ion beam parameters which are required for the NBI system of ITER. ELISE is equipped with a Radio Frequency driven source and an ITER‐like extraction system with half the ITER size. An H− or D− beam can be extracted for 10s every 3min from the continuously operating plasma source. The duration of the beam pulses is currently limited by the power supplies available at IPP. Although up to now record-setting 1h plasmas have been produced in H− as well as in D−, long plasma pulse operation with multiple beam blips showed a key issue: the co-extracted electron current during the extraction phase is strongly dynamic and temporally instable, particularly in D−. These instabilities are likely caused by back-streaming positive ions and Cs dynamics in the source. In order to investigate the source physics in long beam pulses, an upgrade of ELISE using a steady state high voltage power supply is envisaged. This upgrade requires a new steady state diagnostic calorimeter for which a few concepts are being investigated, which make use of several thermocouples, IR thermography and water calorimetry to measure beam intensity, divergence, profile and homogeneity. In addition the suitability of a tungsten wire calorimeter to characterize the steady state beam is being examined. Shielding of delicate components in the beam line, e.g. a large DN 1250mm gate valve, by means of suitable protection scrapers, is being considered. A selection of these technical solutions is presented and discussed in the paper.

OC-0339: Water calorimetry in a pulsed PBS proton beam

OC-0339: Water calorimetry in a pulsed PBS proton beam

PV-0422: Direct determination of kQ in a clinical carbon ion beam using water calorimetry

PV-0422: Direct determination of kQ in a clinical carbon ion beam using water calorimetry

Direct determination of kQ for Farmer-type ionization chambers in a clinical scanned carbon ion beam using water calorimetry

Until now, the dosimetry of carbon ions with ionization chambers has not reached the same level of accuracy as that of high-energy photons. This is mainly caused by the approximately threefold larger uncertainty of the kQ factor of ionization chambers, which, due to the lack of experimental data, is still derived by calculations. Measurements of absorbed dose to water, Dw, by means of water calorimetry have now been performed in the entrance channel of a scanned 6 cm × 6 cm radiation field of 429 MeV/u carbon ions, allowing the direct calibration of ionization chambers and thus the experimental determination of kQ. Within this work, values for kQ have been determined for the Farmer-type ionization chambers FC65-G and TM30013. A detailed investigation of the radiation field enabled the accurate determination of correction factors needed for both calorimetric and ionometric measurements. Finally, a relative standard measurement uncertainty of 0.8% (k = 1) could be achieved for the experimental kQ values.For both chambers, the experimental kQ factors were found to be about 1% larger than those tabulated in the German DIN 6801-1 protocol, whereas compared to the theoretical values stated in the TRS-398 protocol, the experimental kQ value agrees within 0.4% for the TM30013 chamber but is about 1% lower in the case of the FC65-G chamber.

Experimental determination of ionization chamber overall correction factor in medium-energy X-ray beams

Introduction According to the IAEA TRS 398, in kilovoltage X-ray beams the calibration factor in terms of absorbed dose to water ( N D , w , Q ) for an ionization chamber can be derived from its calibration factor in terms of air kerma ( N K , Q ) if the chamber overall correction factor, p Q , is known. However, literature p Q values are lacking, especially when referring to the reference depth of 2 g/cm 2 . Purpose To determine the p Q factor at 2 g/cm 2 depth using a new absorbed-dose-to-water ( D w ) primary standard based on an in-water-phantom graphite calorimeter recently established for medium-energy X-ray beams. Materials and methods N D , w , Q factors are directly determined against the D w primary standard. Using the same beam qualities, the N K , Q factors are also determined. Values of p Q are obtained by comparing the N D , w , Q factors with the analogous calibration factors derived by N K , Q using the IAEA TRS 398 formalism. Ratios of mean mass-energy absorption coefficients, water to air, are taken from literature. Results For a Farmer type ionization chamber, the p Q factor was respectively 1.002 and 1.012 for the 180 kV and the 250 kV medium-energy quality of the CCRI series, with a relative combined standard uncertainty of 2%. This figure is going to be reduced to around 1% with the ongoing improvements on the new D w primary standard. Conclusion The new D w primary standard based on graphite calorimetry, although affected by a larger uncertainty compared to primary standards based on water calorimetry, allows independent measurements of p Q factors for ionization chambers currently used in radiotherapy dosimetry.

Development and application of a water calorimeter for the absolute dosimetry of short-range particle beams

In this work, we describe a new design of water calorimeter built to measure absorbed dose in non-standard radiation fields with reference depths in the range of 6–20 mm, and its initial testing in clinical electron and proton beams. A functioning calorimeter prototype with a total water equivalent thickness of less than 30 mm was constructed in-house and used to obtain measurements in clinical accelerator-based 6 MeV and 8 MeV electron beams and cyclotron-based 60 MeV monoenergetic and modulated proton beams. Corrections for the conductive heat transfer due to dose gradients and non-water materials was also accounted for using a commercial finite element method software package. Absorbed dose to water was measured with an associated type A standard uncertainty of approximately 0.4% and 0.2% for the electron and proton beam experiments, respectively. In terms of thermal stability, drifts were on the order of a couple of hundred µK min−1, with a short-term variation of 5–10 µK. Heat transfer correction factors ranged between 1.021 and 1.049. The overall combined standard uncertainty on the absorbed dose to water was estimated to be 0.6% for the 6 MeV and 8 MeV electron beams, as well as for the 60 MeV monoenergetic protons, and 0.7% for the modulated 60 MeV proton beam. This study establishes the feasibility of developing an absorbed dose transfer standard for short-range clinical electrons and protons and forms the basis for a transportable dose standard for direct calibration of ionization chambers in the user’s beam. The largest contributions to the combined standard uncertainty were the positioning (⩽0.5%) and the correction due to conductive heat transfer (⩽0.4%). This is the first time that water calorimetry has been used in such a low energy proton beam.

Sci‐Sat AM: Radiation Dosimetry and Practical Therapy Solutions ‐ 09: Stability of a water calorimetry system as a primary standard for absorbed dose to water

Purpose:To investigate the stability of a water calorimetry system as a primary standard for absorbed dose to water using measurements performed in cobalt‐60 and high‐energy linac photon beams over a span of more than a decade.Methods:Calorimetry measures adsorbed dose directly by recording the amount of heat created when ionizing radiation passes through matter. The radiation‐induced temperature rise was measured using two thermistors calibrated against the NRC temperature primary standard, using an AC bridge with lock‐in amplifier for precise measurement. The calorimeter system was operated under thermal equilibrium at 4 °C (to eliminate convection) with drifts in water temperature less than 0.1 mK/min. Seven water vessels of various designs were used to make repeated measurements over the course of 17 years.Results:The standard uncertainty achieved for a set of ten calorimeter measurements (4 Gy delivered) was generally well below 0.15 % while the variation between multiple sets for a given vessel was consistent with this value. The long‐term stability of the system combined with inter‐vessel variations indicated that there was good control of the radiochemistry (chemical heat defect).Conclusions:The measurements performed over a period of several years showed that the combined water calorimeters showed stability at +/− 0.25 % level. Thus, rather than relying on a particular vessel as an artifact one can realize the Gray through the more generalized method of combining a glass vessel, high‐purity water and thermistor probes. This provides increased robustness in the dissemination of absorbed dose to Canadian users.

TH-CD-BRA-05: First Water Calorimetric Dw Measurement and Direct Measurement of Magnetic Field Correction Factors, KQ,B, in a 1.5 T B-Field of An MRI Linac

Purpose: Reference dosimetry in MR-guided radiotherapy is performed in the presence of a B-field. As a consequence the response of ionization chambers changes considerably and depends on parameters not considered in traditional reference dosimetry. Therefore future Codes of Practices need ionization chamber correction factors to correct for both the change in beam quality and the presence of a B-field. The objective was to study the feasibility of water calorimetric absorbed-dose measurements in a 1.5 T B-field of an MRLinac and the direct measurement of kQ,B calibration of ionization chambers. Methods: Calorimetric absorbed dose to water Dw was measured with a new water calorimeter in the bore of an MRLinac (TPR20,10 of 0.702). Two waterproof ionization chambers (PTW 30013, IBA FC-65G) were calibrated inside the calorimeter phantom (ND,w,Q,B). Both measurements were normalized to a monitor ionization chamber. Ionization chamber measurements were corrected for conventional influence parameter. Based on the chambers’ Co-60 calibrations (ND,w,Q0), measured directly against the calorimeter. In this study the correction factors kQ,B was determined as the ratio of the calibration coefficients in the MRLinac and in Co-60. Additionally, kB was determined based on kQ values obtained with the IAEA TRS-398 Code of Practice. Results: The kQ,B factors of the ionization chambers mentioned above were respectively 0.9488(8) and 0.9445(8) with resulting kB factors of 0.961(13) and 0.952(13) with standard uncertainties on the least significant digit(s) between brackets. Conclusion: Calorimetric Dw measurements and calibration of waterproof ionization chambers were successfully carried out in the 1.5 T B-field of an MRLinac with a standard uncertainty of 0.7%. Preliminary kQ,B and kB factors were determined with standard uncertainties of respectively 0.8% and 1.3%. The kQ,B agrees with an alternative method within 0.4%. The feasibility of water calorimetry in the presence of B-fields was demonstrated by the direct determination of Dw and kQ,B. This work was supported by EMRP grant HLT06. The EMRP is jointly funded by the EMRP participating countries within EURAMET and the European Union.

The effects of group and single housing and automated animal monitoring on urinary corticosterone levels in male C57BL/6 mice.

Mice are used extensively in physiological research. Automated home-cage systems have been developed to study single-housed animals. Increased stress by different housing conditions might affect greatly the results when investigating metabolic responses. Urinary corticosteroid concentration is considered as a stress marker. The aim of the study was to compare the effects of different housing conditions and an automated home-cage system with indirect calorimetry located in an environmental chamber on corticosterone levels in mice. Male mice were housed in different conditions and in automated home-cage system to evaluate the effects of housing and measuring conditions on urine corticosterone levels. Corticosterone levels in single-housed mice in the laboratory animal center were consistently lower compared with the group-housed mice. Single-housed mice in a separate, small animal unit showed a rise in their corticosterone levels a day after they were separated to their individual cages, which decreased during the following 2days. The corticosterone levels of group-housed mice in the same unit were increased during the first 7days and then decreased. On day 7, the corticosterone concentrations of group-housed mice were significantly higher compared with that of single-housed mice, including the metabolic measurement protocol. In conclusion, single housing caused less stress when compared with group-housed mice. In addition, the urine corticosterone levels were decreased in single-housed mice before the metabolic measurement started. Thus, stress does not affect the results when utilizing the automated system for measuring metabolic parameters like food and water intake and calorimetry.

High heat flux testing of divertor plasma facing materials and components using the HHF test facility at IPR

The High Heat Flux Test Facility (HHFTF) was designed and established recently at Institute for Plasma Research (IPR) in India for testing heat removal capability and operational life time of plasma facing materials and components of the ITER-like tokamak. The HHFTF is equipped with various diagnostics such as IR cameras and IR-pyrometers for surface temperature measurements, coolant water calorimetry for absorbed power measurements and thermocouples for bulk temperature measurements. The HHFTF is capable of simulating steady state heat load of several MW m−2 as well as short transient heat loads of MJ m−2. This paper presents the current status of the HHFTF at IPR and high heat flux tests performed on the curved tungsten monoblock type of test mock-ups as well as transient heat flux tests carried out on pure tungsten materials using the HHFTF. Curved tungsten monoblock type of test mock-ups were fabricated using hot radial pressing (HRP) technique. Two curved tungsten monoblock type test mock-ups successfully sustained absorbed heat flux up to 14 MW m−2 with thermal cycles of 30 s ON and 30 s OFF duration. Transient high heat flux tests or thermal shock tests were carried out on pure tungsten hot-rolled plate material (Make:PLANSEE) with incident power density of 0.49 GW m−2 for 20 milliseconds ON and 1000 milliseconds OFF time. A total of 6000 thermal shock cycles were completed on pure tungsten material. Experimental results were compared with mathematical simulations carried out using COMSOL Multiphysics for transient high heat flux tests.

Direct measurement of electron beam quality conversion factors using water calorimetry.

In this work, the authors describe an electron sealed water calorimeter (ESWcal) designed to directly measure absorbed dose to water in clinical electron beams and its use to derive electron beam quality conversion factors for two ionization chamber types. A functioning calorimeter prototype was constructed in-house and used to obtain reproducible measurements in clinical accelerator-based 6, 9, 12, 16, and 20 MeV electron beams. Corrections for the radiation field perturbation due to the presence of the glass calorimeter vessel were calculated using Monte Carlo (MC) simulations. The conductive heat transfer due to dose gradients and nonwater materials was also accounted for using a commercial finite element method software package. The relative combined standard uncertainty on the ESWcal dose was estimated to be 0.50% for the 9-20 MeV beams and 1.00% for the 6 MeV beam, demonstrating that the development of a water calorimeter-based standard for electron beams over such a wide range of clinically relevant energies is feasible. The largest contributor to the uncertainty was the positioning (Type A, 0.10%-0.40%) and its influence on the perturbation correction (Type B, 0.10%-0.60%). As a preliminary validation, measurements performed with the ESWcal in a 6 MV photon beam were directly compared to results derived from the National Research Council of Canada (NRC) photon beam standard water calorimeter. These two independent devices were shown to agree well within the 0.43% combined relative uncertainty of the ESWcal for this beam type and quality. Absorbed dose electron beam quality conversion factors were measured using the ESWcal for the Exradin A12 and PTW Roos ionization chambers. The photon-electron conversion factor, kecal, for the A12 was also experimentally determined. Nonstatistically significant differences of up to 0.7% were found when compared to the calculation-based factors listed in the AAPM's TG-51 protocol. General agreement between the relative electron energy dependence of the PTW Roos data measured in this work and a recent MC-based study are also shown. This is the first time that water calorimetry has been successfully used to measure electron beam quality conversion factors for energies as low as 6 MeV (R50=2.25 cm).