Physikalisch-Technische Bundesanstalt Research Articles

Experimental determination of the sulfur K-shell fundamental parameters employing the holistic approach

Abstract Sulfur and its compounds are both very abundant in the environment and very important for technological applications such as batteries. X-ray spectroscopic characterizations of sulfur compounds for a quantitative determination of the present amount of sulfur often requires a good knowledge on the atomic fundamental parameters involved. These quantitatively describe the processes of photoionization and X-ray fluorescence emission, making them crucial for X-ray spectroscopy-based quantifications. 
By employing the recently demonstrated holistic approach, the atomic fundamental parameters of the sulfur K-shell were experimentally determined using the radiometrically calibrated instrumentation of the Physikalisch-Technische Bundesanstalt (PTB). The transition probabilities of the main K-shell fluorescence lines, the K-shell fluorescence yield, the K-shell Auger yield, the subshell photoionization cross section and fluorescence production cross section were determined by means of photon energy dependent X-ray fluorescence and transmission measurements on a thin InS coated silicon nitride membrane. The results are also downloadable from Zenodo as plain text.

Study of the Accuracy and Reliability of Dosimetric Measurements for X-ray Beams with Radiation Qualities N-40, N-100, N-200

Radiation dosimetry is a critical aspect of medical, industrial, and scientific applications involving ionizing radiation. Accurate measurements of radiation doses ensure the safety and effectiveness of radiological practices, which is essential for protecting patients in medical procedures, maintaining safety in industrial applications, and ensuring accuracy in scientific research. Leading international organizations conduct research aimed at improving measurement accuracy and the dissemination of measurement units. One of the methods contributing to this effort is various international projects. The National Scientific Centre “Institute of Metrology” has participated in one such international project. This international project, involving several National Metrology Institutes (NMIs), aimed to improve the accuracy and consistency of radiation dosimetry across Europe. By standardizing measurement and calibration procedures, the project seeks to create a unified system for measuring radiation doses, thereby improving the reliability of ionizing radiation dosimetry. This project is particularly significant given the continuous increase in radiation-based technologies across various fields. For example, precise measurements of ionizing quantities are crucial in the medical field, especially for radiotherapy, to ensure that patients receive the necessary dose with minimal exposure to surrounding healthy tissues. Similarly, in industrial radiography, accurate dosimetry is essential for meeting safety standards and preventing excessive radiation exposure to workers. The international project, with the Physikalisch-Technische Bundesanstalt (PTB) and the Central Office of Measures (GUM) as leading organizations, aims to improve key factors in ionizing radiation dosimetry. These include developing reliable calibration protocols for various types of radiation, establishing traceability chains to ensure measurement accuracy, and sharing best dosimetry practices among project participants. Preliminary comparisons were performed between NMIs, with two control participants serving as references while other NMIs participated anonymously (knowing only their number and the numbers of the reference participants). Each participant had the opportunity to compare their obtained values with the reference values and make adjustments for future measurements. The collaborative nature of such cooperation also promotes knowledge and experience exchange, fostering innovation and improvement in dosimetry techniques. The NSC “Institute of Metrology”, a leading organization in the field of the ionizing radiation metrology, has actively participated in this project as a representative from Ukraine. The paper presents the results of international comparisons for X-ray beams with the radiation qualities N-40, N-100, N-200.

Verification of the results of the calibration of needle hydrophones on the measurement standard NDETU AUV-02-2018

The results of the verification of the calibration of needle hydrophones using the national primary measurement standard of the unit of ultrasonic pressure in the aquatic environment (NDETU AUV-02-2018) are presented. The main objective of the study was to confirm the accuracy of the calibration of needle hydrophones No. 2538 and No. 2515 by comparison with the calibration results obtained on the measurement standard at the Physikalisch-Technische Bundesanstalt (PTB), Germany. The paper describes the calibration methods used by laboratories to determine the sensitivity of hydrophones, including the two-transducer reciprocity method and the comparison method. The results of the calibration of needle hydrophones in the frequency range from 1 to 10 MHz obtained by the National Metrology Institute of Germany (PTB) and Ukraine (SE Research Institute “Systema”) were evaluated. Furthermore, the level of uncertainty of the calibration results was compared. The results of the study demonstrated a high degree of consistency in the measurement results. Added to this, the results confirmed the reliability of the results of the calibration of needle hydrophones using the NDETU AUV-02-2018 measurement standard by the calibration method selected and with the measurement equipment used. The conclusions confirmed the effectiveness of using the national measurement standard NDETU AUV-02-2018 and its conformity with international measurement standards, thus increasing the confidence in the results at the international level. Additionally, the study provides the ground for future international comparisons with measurement standards of other countries.

Shortened and simplified traceability chain for dimensional metrology based on self-traceable standards

Abstract Nanoscale measurement is an essential task of nanomanufacturing, and measurement traceability is a fundamental aspect of nanoscale measurement. High-precision nanoscale measurement instruments (e.g. atomic force microscopes (AFM) and scanning electron microscopes (SEM)) need to be calibrated by traceable standards to ensure their accuracy and reliability. However, due to the suboptimal accuracy, uniformity, and consistency of existing standards, they need to be calibrated by metrological instruments traceable to primary length standards (e.g. physical wavelength standards) before use. This results in a long traceability chain that leads to error accumulation and significantly reduces calibration efficiency. This paper proposes a novel shortened and simplified traceability chain, where the physical wavelength standard corresponding to the 7S3 → 7P4° transition frequency of chromium atoms is materialized into self-traceable gratings using the atom lithography technology. The self-traceable gratings can then be directly applied for calibrating measurement instruments. To verify this approach, the self-traceable gratings are calibrated using a metrological AFM of the Physikalisch-Technische Bundesanstalt. Measurement results confirmed the feasibility of the approach. Particularly, our results show that the self-traceable gratings have excellent uniformity over different measurement areas and consistency over different samples, both at 0.001 nm level. Finally, the application of the self-traceable gratings for the calibrations of a commercial AFM and SEM is demonstrated. The new traceability chain significantly simplifies the calibration process, providing a more reliable and higher efficient calibration approach for advanced nanomanufacturing than that of the state-of-the-art.

An emf-temperature reference function for Pt–20%Rh versus Pt thermocouples in the temperature range of 0 °C to 1100 °C

Abstract An electromotive force-temperature reference function for thermocouples made of platinum-20%rhodium versus platinum (Pt-20%Rh/Pt) was determined for the temperature range from 0 °C to 1100 °C. Three Pt-20%Rh/Pt thermocouples were constructed at the Physikalisch-Technische Bundesanstalt (PTB) and were compared with standard platinum resistance thermometers (SPRTs), an Au/Pt thermocouple and a Pt/Pd thermocouple, which were all calibrated at fixed points of the International Temperature Scale of 1990 (ITS-90). The comparison measurements were performed in stirred liquid baths in the range from 0 °C to 545 °C, in a sodium heat pipe from 560 °C to 980 °C, and in a five-zone furnace at temperatures between 1000 °C and 1100 °C. Furthermore, the Pt-20%Rh/Pt thermocouples were calibrated at fixed points of the ITS-90. The PTB reference function based on two of the three Pt-20%Rh/Pt thermocouples has an expanded measurement uncertainty of 0.25 K in the temperature range from 0 °C to 1100 °C.

An interpretable ensemble trees method with joint analysis of static and dynamic features for myocardial infarction detection

Objective. In recent years, artificial intelligence-based electrocardiogram (ECG) methods have been massively applied to myocardial infarction (MI). However, the joint analysis of static and dynamic features to achieve accurate and interpretable MI detection has not been comprehensively addressed. Approach. This paper proposes a simplified ensemble tree method with a joint analysis of static and dynamic features to solve this issue for MI detection. Initially, the dynamic features are extracted by modeling the intrinsic dynamics of ECG via dynamic learning in addition to extracting classical static features. Secondly, a two-stage feature selection strategy is designed to identify a few significant features, which substitute the original variables that are employed in constructing the ensemble tree. This approach enhances the discriminative ability by selecting significant static and dynamic features. Subsequently, this paper presents an interpretable classification method named StackTree by introducing a stacked ensemble scheme to modify the ensemble tree simplification algorithm. The representative rules of the raw ensemble trees are selected as the intermediate training data that is used to retrain a decision tree with performance close to that of the source ensemble model. Using this scheme, the significant precision and interpretability of MI detection are thus comprehensively addressed. Main results. The effectiveness of our method in detecting MI is evaluated using the Physikalisch-Technische Bundesanstalt (PTB) and clinical database. The findings suggest that our algorithm outperforms the traditional methods based on a single type of feature. Additionally, it is comparable to the conventional random forest, achieving 97.1% accuracy under the inter-patient framework on the PTB database. Furthermore, feature subsets trained on PTB are validated using the clinical database, resulting in an accuracy of 84.5%. The chosen important features demonstrate that both static and dynamic information have crucial roles in MI detection. Crucially, the proposed method provides clear internal workings in an easy-to-understand visual manner.

Towards a precise measurement of 157Tb nuclear decay data: Sample purification using resonance ionization mass spectrometry

In nuclear physics, 157Tb emerges as a prime candidate for experiments aimed at elucidating neutrino mass constraints and at searching for sterile neutrinos. Despite its importance, 157Tb exhibits highly uncertain values for its nuclear decay properties. A significant challenge in many efforts to measure such data lies in the simultaneous undesired presence of 158Tb in the samples, which hinders precise activity determination. Mass separation emerges as a crucial method for obtaining pure 157Tb specimens. This work outlines the production of an isotopically-pure 157Tb sample through mass separation and ion implantation, using the RISIKO facility at the University of Mainz. The initial material was obtained from proton-irradiated Ta samples through radiochemical separation at the Paul Scherrer Institute. In total, a sample containing 8.7(9) · 1012 atoms of 157Tb was obtained. The efficiency of the mass separation and ion implantation was 13(2) %. The purified material served as the basis for new research endeavors at the Physikalisch Technische Bundesanstalt Braunschweig aiming at the determination of nuclear data for 157Tb with significantly improved precision.

Calibrating the global network of gravitational wave observatories via laser power calibration at NIST and PTB

Current gravitational wave (GW) observatories rely on photon calibrators that use laser radiation pressure to generate displacement fiducials used to calibrate detector output signals. Reducing calibration uncertainty enables optimal extraction of astrophysical information such as source distance and sky position from detected signals. For the ongoing O4 observing run that started on 24 May 2023, the global GW detector network is employing a new calibration scheme with transfer standards calibrated at both the National Institute of Standards and Technology (NIST) and the Physikalisch-Technische Bundesanstalt (PTB). These transfer standards will circulate between the observatories and the metrology institutes to provide laser power calibration traceable to the International System of Units (SI) and enable assessment and reduction of relative calibration errors for the observatory network. The Laser Interferometer Gravitational-Wave Observatory (LIGO) project and the Virgo project are currently participating in the new calibration scheme. The Large-scale Cryogenic Gravitational-wave Telescope project (KAGRA) is expected to join in 2024, with the LIGO Aundha Observatory in India joining later. Before implementing this new scheme, a NIST-PTB bilateral comparison was conducted. It validated the scale representation by both laboratories, with a degree of equivalence of −0.2% and an associated expanded uncertainty of 0.32% (k = 2) which is significantly lower than previous studies. We describe the transfer of power sensor calibration, including detailed uncertainty estimates, from the transfer standards calibrated by NIST and PTB to the sensors operating continuously at the interferometer end stations. Finally, we discuss the ongoing calibration of Pcal-induced displacement fiducials for the O4 observing run. Achieved combined standard uncertainty levels as low as 0.3% facilitate calibrating the interferometer output signals with sub-percent accuracy.

Accurate characterisation of optical diffuse transmission—primary facility and extension to translucent samples

To perform accurate, high-quality and traceable measurement of optical diffuse transmission, which is quantified using the bidirectional transmittance distribution function (BTDF), a new primary facility has been developed at the Physikalisch–Technische Bundesanstalt (PTB), the German metrology institute. This newly developed reference facility will complement the available calibration services and research facilities at PTB for regular reflectance and transmittance and diffuse reflectance. The performance of the new BTDF setup has been investigated in an internal comparison, where consistency of the results was achieved. A thorough uncertainty analysis results in a minimum combined standard (k = 1) uncertainty of about 0.8 %. Research on the accurate characterisation of the BTDF of samples with non-negligible lateral scattering is being carried out on this new setup. Some first results have shown that the measured BTDF value depends on the applied irradiation area size. An empirical model has been found to describe the diffuse transmission of such translucent samples with different scattering parameters.

Experimental uncertainty evaluation by measuring a micro gear standard using focus variation

Abstract Micro gears play an increasingly important role in various industrial applications, and the minimization of their deviations is challenging for metrology and manufacturing. A promising method is the focus variation technology, which enables areal measurements of micro gears. Practice-related standards are used to determine measurement uncertainties by comparison with calibration values. In this work, the external micro gear standard of the Physikalisch-Technische Bundesanstalt (PTB) is used to evaluate experimental measurement uncertainties of a focus variation coordinate measurement system for the first time. The traceable standard with modules between 0.1 and 1 mm is calibrated using micro tactile coordinate measurements. Optical and tactile measurements are then compared. As a result, small expanded measurement uncertainties of less than 4 µm are achieved.

Time Transfer Link fusion algorithm based on wavelet multi-resolution analysis

To raise the precision and stability of time transfer links, a wavelet-based multi-resolution data fusion technique is offered. This approach fixes the “Day-Boundary discontinuities” in global positioning system (GPS) precise point positioning (PPP) link and lessens the diurnal in Two-way satellite time and frequency transfer (TWSTFT) link by integrating the model-based dynamic system analysis method with the statistically based multi-scale signal transformation method. It can also handle data from GPS PPP links and TWSTFT links at different sampling rates. More specifically, after applying wavelet transformation to the raw data and Kalman filtering estimation on various scales, this method uses the Mallat fast reconstruction algorithm of wavelet transform to achieve the fused results. The National Time Service Center (NTSC) and the Physikalisch-Technische Bundesanstalt (PTB) handle time transfer results using this method. Experiments show that this strategy greatly improves the link's short-term stability and can manage atypical interruptions while also boosting the link's robustness and reliability, which has a wide range of possible applications.

Study of a 2 kN·m Torque Transducer Tested at GUM and PTB, Including Creep Behaviour

Abstract This article presents a study carried out on a 2 kN·m torque transducer at the Central Office of Measures (GUM) and the Physikalisch-Technische Bundesanstalt (PTB). The weighted least squares method was used to generate the linear regression equations for this torque transducer. The Monte Carlo method and the law of uncertainty propagation were used to calculate the expanded uncertainty. In addition, a creep study was carried out at eight measurement points ranging from 200 N·m to 2000 N·m. The investigations showed that the highest readings of the torque transducer, expressed in electrical units as mV/V, occur within the initial few seconds of the test after the removal of the maximum reference torque.

A Micromegas-based gaseous detector for neutron-induced charged-particle reaction studies in nuclear astrophysics

The quasistellar neutron spectrum produced via 7Li (p, n)7Be reaction at a proton energy of 1.912 MeV has been extensively studied and employed reaction for neutron-induced reaction studies. We are working towards using this reaction at various proton energies from 1.9 MeV to 3.6 MeV to produce a neutron field at a temperature range of ∼ 1.5–3.5 GK to conduct measurements of neutron-induced charge particle reaction cross sections on various unstable nuclei at explosive stellar temperatures. In this paper, we are reporting our design and simulation study with regards to experimental set-up and a gaseous detector with a segmented Micromegas detector for conducting neutron-induced charge particle reactions studies for nuclei of astrophysics importance, for example, 26Al(p, n)26Mg, 26Al(n, α)23Na and 40K(p, n)40Ar, 40K(n, α)37Cl reactions. We plan to perform our experiments with a 10-μA proton beam at the Physikalisch Technische Bundesanstalt facility (PTB, Germany), with a Micromegas-based gaseous detector under construction as discussed in the paper.

Experimental determination of the hafnium L-subshell fundamental parameters using the holistic approach

By employing the recently demonstrated new holistic approach, the atomic fundamental parameters (FPs) of the three Hf-L subshells were experimentally determined using the radiometrically calibrated instrumentation of the Physikalisch-Technische Bundesanstalt. The Coster–Kronig factors, the L-subshell fluorescence yields, the L-subshell Auger yields, the subshell-photoionization cross sections, and the subshell fluorescence production cross sections were determined by means of photon energy dependent x-ray fluorescence and transmission measurements. The recently demonstrated new holistic evaluation approach allows to determine the FPs with significantly lower uncertainties as compared to the former data evaluation scheme, where only a limited regime of incident photon energies is being probed and the data evaluation scheme is performed in a sequential manner.

Multi-kilowatt cw laser power measurement comparison between national standards

We present here the first comparison between National Metrology Institutes of high accuracy continuous wave optical power measurements in the kilowatt regime. The National Institute of Standards and Technology (NIST) performed measurements with a power meter relying on photon momentum. The Physikalisch-Technische Bundesanstalt (PTB) performed measurements with a modified off-the-shelf thermal power meter. The non-absorbing photon momentum measurement approach permits the two power meters to measure the same laser beam optical path simultaneously, resulting in a direct comparison of the meters supported by an optical system to accommodate differences in instrument settling times. The results show agreement within the expanded uncertainties for each instrument. NIST and PTB illustrate a degree of equivalence of 0.49% with an expanded uncertainty of 1.37% (k = 2) for an average result across all power levels.

Key comparison BIPM.RI(I)-K8 of high dose-rate 192Ir brachytherapy standards for reference air kerma rate of the PTB and the BIPM

Main textAn indirect comparison of the standards for reference air kerma rate for 192Ir high dose rate (HDR) brachytherapy sources of the Physikalisch-Technische Bundesanstalt (PTB), Germany, and of the Bureau International des Poids et Mesures (BIPM) was carried out at the PTB in May 2023. The comparison result, based on the calibration coefficients for a transfer standard and expressed as a ratio of the PTB and the BIPM standards for reference air kerma rate, is 1.0022 with a combined standard uncertainty of 0.0101.To reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database https://www.bipm.org/kcdb/.The final report has been peer-reviewed and approved for publication by the CCRI, according to the provisions of the CIPM Mutual Recognition Arrangement (CIPM MRA).

Galileo E3 Total Time Delay Calibration in NTSC Time and Frequency Comparison

In order to improve the reliability of the time transfer link, Bureau International des Poids et Mesures (BIPM) has offcially taken the Galileo time comparison as the backup link for UTC calculation since 2020. Therefore, Galileo calibration of receiver is a necessary work for all timekeeping labs around the world to participate in the UTC link. Taking the GPS link calibrated by Physikalisch-Technische Bundesanstalt (PTB) and the National Time Service Center (NTSC) as reference, this paper sets PT09 as reference station to calibrate and verify the Galileo E3 (E1&E5a) total delay of NT02 and NT05 receivers from NTSC. The results show that the Galileo E3 total delay of NT02 and NT05 are 74.6 ns and 46.5 ns, respectively, the calibration uncertainty is 3.5 ns, and the calibration delay is relatively stable. After calibration, GPS P3 and Galileo E3 Common View results between NT02/NT05 and calibrated receivers of other timekeeping labs are basically consistent. Taking the GPS P3 links comparison results as reference between NTP3 and receivers from other labs, the average deviation is less than 1.5 ns, which is within the calibration uncertainty range.

MULTI-LAYERED ARCHITECTURE CONVOLUTION NEURAL NETWORKS FOR DIAGNOSING AND PREDICTING HEART DISEASES ON MULTI-MODAL

Recently, heart diseases are increasing daily with the current lifestyle. Different types of cardiac diseases need to be diagnosed accurately for faster treatment to avoid death rates. Heart diseases are susceptible to attack a person speedily and cause sudden deaths. Medical experts are confused while diagnosing a person who comes in a medical emergency. In-time diagnosis, accurate prediction, and the proper treatment can save patients from heart diseases. Heart-related diseases cannot be predicted only by ECG data related to other medical information of a patient. This paper aims to develop an advanced artificial intelligence algorithm for analyzing and detecting heart diseases on multi-modal data. One of the advanced machine learning algorithms, Convolution Neural Network, is implemented with different architectural configurations for analyzing Body Mass Index (BMI), Electrocardiogram (ECG), and Physikalisch-Technische Bundesanstalt (PTB). Multiple CNN models are used for analyzing the multi-modal patient data to predict the presence of heart diseases. The CNN models are created by 80% of the training data and validated by 20% of the testing data. Different hyperparameters of the CNN models are tuned well to extract more data features to improve the prediction accuracy. The CNN models are developed in Python for processing and categorizing the feature variables as to whether heart disease is present or not. Medical data analytics require this model to get 98% of prediction accuracy.

The contribution of the air and room scattered neutrons in the PTB calibration facility

Neutron detectors and dosimeters used for radiation protection purposes are commonly calibrated with radioisotope-based neutron sources in dedicated calibration facilities. Due to interactions of the neutrons emitted by the sources with components of the calibration room, the neutron fluence at the measuring point is a sum of several components. As the results of calibration procedures should ideally be independent of the environment in which the measurements are performed, the effects caused by neutrons which are not directly reaching the device under test need to be considered, i.e. the influence of scattered neutrons needs to be determined and corrections have to be made. The contribution of the neutrons scattered from the air and the room to the fluence and dose must be taken into consideration, especially in the case of small and medium sized calibration rooms. The scattered neutron component can be evaluated numerically provided a detailed model of the calibration facility is available. In this work, a realistic MCNP6 model of the calibration room at the Physikalisch-Technische Bundesanstalt (PTB) has been developed in order to evaluate carefully the contribution of scattered neutrons from the air, wall, and equipment in the irradiation room for 252Cf, 241Am–Be and D2O moderated 252Cf (with and without Cd-shielding) neutron sources at different reference points and with and without shadow objects. The calculation also considers new fission spectral data for the neutron reference field and recent cross section data libraries. The results show that the contribution of air out-scattered neutrons depends on the detector position and on the neutron source spectrum. This effect is particularly significant for the moderated 252Cf source. More than a third of the total scored neutrons come from the walls and ceiling and the total contributions of the scattered neutrons to the total fluence at the reference position 170 cm away from the source are 50.6 %, 46.6 %, 55.0 % and 52.5 % for 252Cf, 241Am–Be, D2O-252Cf–Cd and D2O-252Cf sources respectively.

Absolute calibration of the spectral sensitivity of an x-ray streak camera over the 0.1-10keV spectral range equipped with CsI photocathode.

In this paper, we report the absolute measurement of the spectral sensitivity of a bilamellar tube x-ray streak camera (XRSC) over the 0.1-10keV range equipped with a CsI photocathode for Laser MégaJoule (LMJ) fusion experiments. This calibration of the XRSC is performed in static mode by using two multi-anode x-ray generators. Two silicon drift detectors (SDDs) previously calibrated at the Physikalisch-Technische-Bundesanstalt radiometric laboratory are used as secondary standards. Both x-ray generators work with a specific monochromator for radiometric measurements. In the sub-keV region, a 1 m-grazing incidence Rowland geometry monochromator specifically developed to handle LMJ's x-ray camera is used, whereas for higher energies (>2keV), a double-crystal monochromator is employed. The absolute spectral sensitivity of the XRSC is obtained by comparing the CCD counts of the XRSC output with the output counts in x-ray lines recorded by the SDD. The results obtained below 1.2keV are, to our knowledge, the first measurements of the spectral sensitivity of an XRSC in the soft x-ray range with a CsI photocathode. Comparison with a model describing the spectral dependence of the sensitivity of the XRSC revealed that measurements obtained in the sub-keV region are greater than expected, whereas they agree with the model above 4.5keV. There may be several contributors to this behavior, including the grain morphology of the CsI layer and exposure to air.