National Physical Laboratory Research Articles

Key comparison BIPM.RI(I)-K1 of the air-kerma standards of the NPL, United Kingdom and the BIPM in 60Co gamma radiation

A key comparison of the standards for air kerma of the National Physical Laboratory (NPL), United Kingdom and of the Bureau International des Poids et Mesures (BIPM) was carried out in the 60Co radiation beam of the BIPM in November 2017. The comparison result, based on the calibration coefficients for two transfer chambers and expressed as a ratio of the NPL and the BIPM standards for air kerma, is 0.9996 with a combined standard uncertainty of 3.0×10-3. The results are analysed and presented in terms of degrees of equivalence, suitable for entry in the BIPM key comparison database.KEY WORDS FOR SEARCHRadiation dosimetry, air kerma, key comparison, Co-60 gamma radiationMain textTo 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 kcdb.bipm.org/.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).

Comparison of the standards for absorbed dose to water of the NPL, United Kingdom and the BIPM for 60Co γ rays

A key comparison of the standards for absorbed dose to water of the National Physical Laboratory (NPL), United Kingdom and of the Bureau International des Poids et Mesures (BIPM) was carried out in the 60Co radiation beam of the BIPM in November 2017. The comparison result, based on the calibration coefficients for two transfer standards and expressed as a ratio of the NPL and the BIPM standards for absorbed dose to water, is 1.0013 with a combined standard uncertainty of 7.1×10-3. The results are analysed and presented in terms of degrees of equivalence, suitable for entry in the BIPM key comparison database.KEY WORDS FOR SEARCHRadiation dosimetry, key comparison, absorbed dose to water, 60CoMain textTo 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 kcdb.bipm.org/.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).

Absolute cross section measurements of 238U(n,f) and 237Np(n,f) in the neutron energy range 1-2.4 MeV

New standard (n,f) cross sections other than 235U are important to study the relevant cross sections for Generation-IV power plants. A specific need for such standards is for performing new experiments with quasimonoenergetic neutron beams, such as those produced by Van de Graaf accelerators. Neutrons down-scattered to low energies in the experimental environment, so called room-return, become relevant for this type of measurements. Hence, a standard (n,f) cross section with a fission threshold is of great interest, in order to suppress the contribution from room-return background. For this reason we have performed two experiments at the VDG of the National Physical Laboratory to measure absolutely the (n,f) cross sections of 235U, 238U and 237Np in the fast neutron energy region. Our preliminary results are in agreement with the most up-to-date evaluations.

Final report: key comparison EURAMET.AUV.A-K5

This is the final (Draft B) report for key comparison EURAMET.AUV.A-K5 on the pressure calibration of laboratory standard microphones in the frequency range from 2 Hz to 10 kHz. Twelve national metrology institutes took part in the key comparison and the National Physical Laboratory piloted the project. Two travelling standard microphones were circulated to the participants and results in the form of regular calibration certificates were collected throughout the project. The analysis used the results for one of the microphones only and values for both sensitivity level and sensitivity phase and have been linked to the CCAUV.A K5 key comparison reference value (KCRV) via two linking laboratories (NPL and INRIM).KEY WORDS FOR SEARCHacoustics, microphones, metrology, key comparison, pressure calibrationMain textTo 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 kcdb.bipm.org/.The final report has been peer-reviewed and approved for publication by the CCAUV, according to the provisions of the CIPM Mutual Recognition Arrangement (CIPM MRA).

The potential radio-immunotherapeutic α-emitter 227Th – part I: Standardisation via primary liquid scintillation techniques and decay progeny ingrowth measurements

Thorium-227 is a potential therapeutic radionuclide for applications in targeted α-radioimmunotherapy for the treatment of various types of cancer. To provide nuclear medicine departments involved in Phase I clinical trials traceability to the SI unit of radioactivity (Bq), a standardisation of a radiochemically pure 227Th aqueous solution has been performed at the National Physical Laboratory. This was achieved via two primary liquid scintillation (LS) techniques −4π(LS)-γ digital coincidence counting (DCC) and 4π LS counting. These absolute techniques were supported by the indirect determination of the 227Th activity via the measurement of the ingrowth and decay rate of the decay progeny by both ionisations chambers and high purity germanium (HPGe) gamma-ray spectrometry. The results of the primary techniques were found to be consistent, both with each other (zeta score = 1.1) and to the decay progeny ingrowth measurements. An activity per unit mass of 20.726 (51) kBq g−1 was determined for the solution. A procedure has been developed that provided an effective separation of the 227Th from its decay progeny, which was shown by the effective time zero of the 227Th-223Ra nuclear chronometer measured by HPGe gamma-ray spectrometry.

Accurate Fiber Length Measurements Using Time-Of-Flight Technique

Fiber artifacts of very well measured lengths are required for the calibration of optical time-domain reflectometers (OTDR). In this paper, accurate length measurement of different fiber lengths using the time-of-flight technique is performed. A setup is proposed to measure accurately lengths from 1 km to 40 km at 1550 nm and 1310 nm using a high speed electro-optic modulator, a photodetector and a time interval counter (TIC). This setup offers traceability to the SI unit of time, the second, (and hence to the meter by definition) by locking the time interval counter to the GPS-disciplined quartz oscillator. Additionally, the length of a recirculating loop artifact is measured and compared with the measurement made for the same fiber by the National physical laboratory of United Kingdom (NPL). Finally, a method is proposed to relatively correct the fiber refractive index to allow accurate fiber length measurement.

University physicists and the origins of the National Physical Laboratory, 1830-1900.

Traditionally, historians have taken it for granted that Britain's National Physical Laboratory (NPL) was created as the result of demands from a "professional" body of university-based physicists for a state-funded scientific institution. Yet paying detailed attention to the history of the NPL's originating institution, Kew Observatory, shows that the story is not so clear-cut. Starting in the 1850s, Kew Observatory was partly a center for testing meteorological instruments and other scientific equipment in return for fees. Long after the 1850s, the observatory was run by self-funded devotees of science. Paid university physicists only assumed a dominant role on its governing committee in the last two decades of the nineteenth century, by which time instrument-testing was already the observatory's main role. This paper argues that the rise of the university physicists - together with the desire of some of these physicists for a national institution that tested electrical standards - can only partially explain the origins of the NPL, and that Kew was in some ways a national physical laboratory before there were many physics teaching posts in British universities. This paper is a case study that illustrates a need to reassess the importance of university physicists in shaping British science at the end of the nineteenth century.

Validation of ammonia diffusive and pumped samplers in a controlled atmosphere test facility using traceable Primary Standard Gas Mixtures

We report the determination of ammonia (NH3) diffusive sampling rates for six different designs of commercial diffusive samplers (CEH ALPHA sampler, Gradko diffusion tube, Gradko DIFRAM-400, Passam ammonia sampler, and ICS Maugeri Radiello radial sampler (blue and white turbulence barriers)), together with the validation test results for a pumped sampler (CEH DELTA denuder). The devices were all exposed in the UK's National Physical Laboratory's (NPL) controlled atmosphere test facility (CATFAC). For each of the seven diffusive sampler exposure tests there were traceable concentrations of ammonia (in the range 3–25 μg m−3) generated under well-defined conditions of temperature, relative humidity and wind speed, which are applicable to a variety of ambient monitoring environments. The sampler exposure time at each concentration was 28 days, except for the radial devices, which were exposed for 14 days. The work relied on the dilution of newly developed stable Primary Standard Gas Mixtures (PSMs) prepared by gravimetry in passivated gas cylinders as a method of improving the metrological traceability of ammonia measurements. The exposed diffusive samplers were sent blind to the participants for analysis and the reported NH3 concentrations were then compared against the known reference concentration. From the results for each sampler type a diffusive sampling rate was calculated and compared against the rate used routinely by the participants. Some measurement results were in good agreement with the known traceable reference concentration (particularly for one diffusive sampler design (ALPHA)), while other devices exhibited over-reading and under-reading (each with a clear bias). The new diffusive sampling rates determined in the laboratory study were then applied to measurements in a field comparison campaign, and this was found to deliver an improvement in agreement between the different devices deployed.

Combining UK and German emissions monitoring proficiency testing data based on stack simulator facilities to determine whether increasingly stringent EU emission limits are enforceable

We report an examination of the capability of the existing measurement infrastructure in the industrial emissions sector for successfully enforcing emission limits across three generations of legislation: the Waste Incineration Directive and Large Combustion Plant Directive (WID and LCPD); the Industrial Emissions Directive (IED) which superseded the aforementioned directives in 2013; the Waste Incineration and Large Combustion Plant Best Available Technique Reference documents (BREFs) where the former is currently at the draft stage (WI BREF and LCP BREF). The significant volume of proficiency testing data based on semi-tech stack simulator facilities operated by the National Physical Laboratory in the UK and the Hessian Agency for Nature Conservation, Environment and Geology in Germany were combined into a unique database. The emission species considered and their associated standard reference methods (SRMs) were: CO EN 15058; NOx (NO + NO2) EN 14792; total organic carbon EN 12619; total dust EN 13284-1. Collectively analysing participant distributions from 2002 to 2015, it was found that emission limits: under the WID and LCPD could be enforced (the directives for which the SRMs were originally designed); under the IED could in principle be enforced; under the WI BREF and LCP BREF would struggle to be enforced. This evidenced the need for improvements in the existing measurement infrastructure, without which test laboratories would struggle to provide the data quality needed by process plant operators for reporting into national emission inventories, and for national regulators who are legally responsible for enforcing emission limits aimed at improving European health and environmental impact.

Photochemistry of ozone over urban area: a case study for Delhi City

Ozone (O3), oxides of nitrogen (NOx), and carbon monoxide (CO) were monitored at CSIR National Physical Laboratory, New Delhi, during May and October, 2014. One-hour O3 concentrations exceeding more than 120 ppb were observed for 9 days in May and 16 days in October months with concurrent high NOx and CO values. The higher ozone episodes in October 2014 as compared to May 2014 may be due to contribution of biomass burning. The nitrogen oxide (NO), nitrogen dioxide (NO2), O3, and the photolysis rate of NO2 (i.e., JNO2) values of May and October, 2014, were used to evaluate the photo-stationary state ratio (or Leighton ratio, ϕ) for clear sky conditions. Leighton ratio ranged from 0.4 to 2.6 (average values 0.89 ± 0.4) for May 2014 and from 0.3 to 3.6 (average value 1.01 ± 0.52) for October 2014. The observed NOy values in October 2014 indicated the production of O3 through hydrocarbon-sensitive O3 chemistry. The sum of reactive nitrogen species’ (i.e., NOy) mixing ratios recorded during October 2014 varied from 259.4 to 10.4 ppb with an average value of 80.5 ± 39 ppb. The averaged diurnal ratio of NOx–NOy of > 0.3 indicated the presence of freshly emitted pollutants.

Cs Fountain Clocks for Commercial Realizations-An Improved and Robust Design.

We report on the design, assembly, testing, and delivery of a series of new cesium fountain primary frequency standards built through commercial and scientific collaboration with international users. The new design, based on proven National Physical Laboratory solutions, improves reliability, simplicity of operation, and transportability. The complete system consists of a novel physics package, a specially developed optical package, and dedicated electronics for system control. We present results showing that despite their simplified and more compact design, the new fountains have state-of-the-art performance in terms of signal-to-noise ratio and robust long-term operation. With a sufficiently low-noise local oscillator, they are capable of reaching a short-term stability below 3×10-14 (1 s) and have potential accuracy in the low 10-16 range, similar to the best cesium fountains currently in operation. This cost-effective solution could be used to increase the availability of accurate frequency references and timescales and provide redundancy in critical locations.

METHODOLOGY FOR DIRECT REFLECTANCE MEASUREMENT FROM A DRONE: SYSTEM DESCRIPTION, RADIOMETRIC CALIBRATION AND LATEST RESULTS

Abstract. We study and analyse performance of a system for direct reflectance measurements from a drone. Key instruments of the system are upwards looking irradiance sensor and downwards looking imaging spectrometer. Requirement for both instruments is that they are radiometrically calibrated, the irradiance sensor has to be horizontally stabilized, and the sensors needs to be accurately synchronized. In our system, irradiance measurements are done with FGI Aerial Image Reference System (FGI AIRS), which uses novel optical levelling methodology and can compensate sensor tilting up to 15°. We performed SI-traceable spectral and radiance calibration of FPI hyperspectral camera at the National Physical Laboratory NPL (Teddington, UK). After the calibration, the radiance accuracy of different channels was between ±4 % when evaluated with independent test data. Sensors response to radiance proved to be highly linear and was on average 0.9994 for all channels. The spectral response calibration showed side peaks on several channels that were due to the multiple orders of interference of the FPI and highlighted the importance of accurate calibration. The drone-based direct reflectance measurement system showed promising results with imagery collected over Jokioinen agricultural grass test site, Finland. AIRS-based image- and band wise image adjustment provided homogenous and seamless image mosaics even under varying illumination conditions and under clouds.

Uncertainty Estimation in PM10 Mass Measurements

Mass measurements of particles in the atmosphere are important for regulatory and scientific purposes. In nearly all of the countries, particulates ≤ 10 µm in aerodynamic size (PM10) are one of the most significant parameters of National Ambient Air Quality Standards (NAAQS). In India, as given in NAAQS, the PM10 regulatory limit is 60 µg m−3 which is based on the annual mean weight of samples (minimum 104) annually at a specific site taken for two/three days in a week for 24 h. In this paper, the components of uncertainty involved in the filter-based sampling of PM10 along with the gravimetric determination of mass have been calculated. As per the EPA guidelines, PM10 mass was monitored for a year at NPL (National Physical Laboratory), New Delhi from January 2014 to January 2015. The 24-h time-weighted mean mass concentration (n = 104) for one-year measurement varied from 32.5 to 480.2 µg m−3.During the study, high mass loading was observed in the month of December to February. In general, the flow rate of the sampling has been reported to be major uncertainty component in size-segregated PM sampling. In this work, the flow rate of the sampling (90.4%) and charge effect of the filter (6.7%) had the major contribution in the total uncertainty budget of PM10 mass measurement. Rest of the uncertainty components, e.g., balances (0.39%) and conditioning of filter (2.39%), had the least contribution.

P123] Reference dosimetry in flattening filter-free beams: Experience with IPSM-1990/IPEM Topical Report 1–2016 and IAEA TRS-398

Introduction Flattening Filter Free beams have become widespread in current radiotherapy practice; therefore, an assessment of different dosimetric approaches is necessary. The British Institute of Physics and Engineering in Medicine (IPEM) Topical Report 1 (2016) recommendations include a FFF spectral correction. IAEA TRS-398 has not yet included this type of correction. Materials and methods Three Varian Truebeam linacs were used, with 6FFF and 10FFF beams. A PTW Semiflex thimble chamber and an IBA CCU electrometer were used for PDD measurements for IPSM 1990, a PTW Roos and an IBA CCU electrometer were used for IAEA TRS-398 PDD measurements. For absolute dose measurements, a NE 2571 Farmer chamber and a PTW Unidos E electrometer were used. Absolute dose was measured following both protocols recommendations: 5 cm (IPSM 1990) and 10 cm (TRS-398) deep. Polarity and recombination factors were also measured at each recommended depth. Our secondary standard chamber and electrometer were calibrated at the National Physical Laboratory (UK), and all our measurements are subsequently traceable to NPL. Ion chamber intercomparisons, using the replacement method recommended for FFF beams by IPEM Topical Report 1, were performed with our secondary standard (NE 2561) and NE 2571 at each of the recommended depth and for both beam qualities. Results NPL N D , w calibration factors were used for each beam quality for IPSM 1990; whereas for TRS-398, the recommended option of using N D , w for Co-60 along with its tabulated k q factors was utilized. TRS-398 and IPSM 1990/IPEM Topical Report 1 absolute dose measurements are within 0.5%, falling well within uncertainty estimates. Conclusions A detailed and thorough absolute dose study was carried out according to the two above mentioned codes of practice: correction factors, ion chamber intercomparisons and absolute dose measurements at recommended depths. All experimental results are accompanied by a rigorous uncertainty analysis, according to ISO GUM. Our results for 6 FFF and 10 FFF show that, within uncertainty, absorbed dose to water according to both codes of practice agree.

NPL Kibble balance bifilar coil design and evaluation. XXII IMEKO World Congress, Belfast, 3 - 6 September 2018

A novel design of Kibble (watt) balance has been designed and is being constructed at the National Physical Laboratory. Lheory predicts that this type of balance will be simpler to construct and operate due to the removal of many of the alignment sensitivities present in existing balances. The balance uses a compact twisted pair coil in both the weighing and moving modes. This paper describes the design and manufacture of the coil and presents results of outgassing measurements made on the coil using a vacuum mass comparator.

OA154] A comparison of dosimetry codes practice for FFF beams: IAEA TRS-398 and IPSM 1990

Purpose Flattening Filter Free beams have become widespread in current radiotherapy practice; therefore, an assessment of different dosimetric approaches is necessary. The British Institute of Physics and Engineering in Medicine (IPEM) recommendations, Topical Report 1 (2016), include a FFF spectral correction. IAEA TRS-398 has not yet included this type of correction. A comparison of IAEA TRS-398 and the British IPSM 1990 codes of practice (including recent IPEM recommendations) was carried out. Methods Three Varian Truebeam linacs were used, with 6FFF and 10FFF beams. A PTW Semiflex thimble chamber and an IBA CCU electrometer were used for PDD measurements for IPSM 1990, a PTW Roos and an IBA CCU electrometer were used for IAEA TRS-398 PDD measurements. For absolute dose measurements, a NE 2571 Farmer chamber and a PTW Unidos E electrometer were used. Absolute dose was measured following both protocols recommendations: 5cm (IPSM 1990) and 10 cm (TRS-398) deep. Polarity and recombination factors were also measured at each recommended depth. Our secondary standard chamber and electrometer were calibrated at the National Physical Laboratory (UK), and all our measurements are subsequently traceable to NPL. Ion chamber intercomparisons, using the replacement method recommended for FFF beams by IPEM Topical Report 1, were performed with our secondary standard (NE 2561) and NE 2571 at each of the recommended depth and for both beam qualities. Results NPL N D , w calibration factors were used for each beam quality for IPSM 1990; whereas for TRS-398, the recommended option of using N D , w for Co-60 along with its tabulated k q factors was utilized. TRS-398 and IPSM 1990/IPEM Topical Report 1 absolute dose measurements are within 0.5%, falling well within uncertainty estimates. Conclusions A detailed and thorough absolute dose study was carried out according to the two above mentioned codes of practice: correction factors, ion chamber intercomparisons and absolute dose measurements at recommended depths. All experimental results are accompanied by a rigorous uncertainty analysis, according to ISO GUM. Our results for 6 FFF and 10 FFF show that, within uncertainty, absorbed dose to water according to both codes of practice agree.

Neutron activation of NIST surrogate post-detonation urban debris (SPUD) candidate SRMs

Despite their importance, there is a dearth of post-detonation nuclear forensics standard reference materials (SRMs) suitable for analysis traceable back to a national standard. Accordingly, the nuclear forensics community has requested SRMs be produced that mimic post-detonation fallout debris that include actinides, urban materials, fission products, and activation products. The National Institute of Standards and Technology (NIST), in partnership with the National Physical Laboratory and with support from the Federal Bureau of Investigation, have developed two surrogate post-detonation urban debris (SPUD) candidate SRMs to mimic the “rubble” of a city after an improvised nuclear device detonation. NIST SPUD samples were irradiated at The University of Texas TRIGA reactor, then analyzed via gamma-ray spectroscopy for short-lived, medium-lived, and long-lived fission and activation products.

Time traders

In today’s markets, every microsecond counts. Jon Cartwright discovers how the UK’s National Physical Laboratory is keeping regulators up to speed

New Schemes of Digital Speckle Photography

This paper presents a review and an analysis of the development of speckle photography from the first experiments performed at the National Physical Laboratory of Great Britain up to the present time. The possibility of diagnosing turbulent and three-dimensional flows by the speckle photography methods has been shown. The single-exposure scheme of speckle photography has been analyzed and the possibility of using multiaspect speckle photography in reconstructive tomography of complex three-dimensional flows has been shown. Methods based on speckle technologies such as Talbot interferometry, PIV and BOS techniques have been analyzed. Particular consideration is given to the application of new measuring technologies in diagnosing turbulent flows and reconstructive tomography of three-dimensional flows.

Role of National Pressure and Vacuum Metrology in Indian Industrial Growth and Their Global Metrological Equivalence

The pressure and vacuum metrology group of National Physical Laboratory (NPL) has a strong role in metrological research and development in India because of its importance to the nation’s economy as well as the constitutional obligation following NPL charter of developing and maintaining national standards of pressure and vacuum measurements. Although, the group is successfully fulfilling its national duties, providing national calibration and measurement services since last 35 years, admittedly still there is lack of awareness, misinformation, and penetration of Calibration and Measurement Capabilities (CMCs) to the end users, grass root level industries, academician and Govt. laboratories. Occasionally, we are receiving feedbacks of such grey areas of awareness. Therefore, it was considered appropriate to compile the information of all these CMCs, expertise, training potential and available developed technologies in this article. The present paper also describes the summary of some of the results obtained in recent international key comparison exercises which have helped us to improve the quality in pressure metrology with a measure of technical efficiency.