Calibration of Electret-Based Integral Radon Monitors Using NIST Polyethylene-Encapsulated 226Ra/222Rn Emanation (PERE) Standards

The recently developed ²²²Rn emanation standards that are based on polyethylene-encapsulated ²²⁶Ra solutions were employed for a first field-measurement application test to demonstrate their efficacy in calibrating passive integral radon monitors. The performance of the capsules was evaluated with respect to the calibration needs of electret ionization chambers (E-PERM^®, Rad Elec Inc.). The encapsulated standards emanate well-characterized and known quantities of ²²²Rn, and were used in two different-sized, relatively-small, accumulation vessels (about 3.6 L and 10 L) which also contained the deployed electret monitors under test. Calculated integral ²²²Rn activities from the capsules over various accumulation times were compared to the averaged electret responses. Evaluations were made with four encapsulated standards ranging in ²²⁶Ra activity from approximately 15 Bq to 540 Bq (with ²²²Rn emanation fractions of 0.888); over accumulation times from 1 d to 33 d; and with four different types of E-PERM detectors that were independently calibrated. The ratio of the electret chamber response E_Rn to the integral ²²²Rn activity I_Rn was constant (within statistical variations) over the variables of the specific capsule used, the accumulation volume, accumulation time, and detector type. The results clearly demonstrated the practicality and suitability of the encapsulated standards for providing a simple and readily-available calibration for those measurement applications. However, the mean ratio E_Rn/I_Rn was approximately 0.91, suggesting a possible systematic bias in the extant E-PERM calibrations. This 9 % systematic difference was verified by an independent test of the E-PERM calibration based on measurements with the NIST radon-in-water standard generator.     

U.K. National Radiological Protection Board Radon Calibration Procedures

A procedure for the calibration of instruments for the detection of ²²²Rn in air is described. The method is based on the alpha-spectrometric determination of the concentration in air of ²¹⁸Po in the calibration chamber. The calibration chamber is described, together with the method of maintaining a high aerosol concentration. The ²¹⁸Po concentration at steady state in the chamber is found to be 98% of the ²²²Rn concentration typically. An assessment of the sources of uncertainty in the method presented indicate that the ²²²Rn concentration in the chamber can be determined with an overall uncertainty of about 7% at the 95% confidence level.     

An International Marine-Atmospheric 222Rn Measurement Intercomparison in Bermuda Part I: NIST Calibration and Methodology for Standardized Sample Additions

As part of an international ²²²Rn measurement intercomparison conducted at Bermuda in October 1991, NIST provided standardized sample additions of known, but undisclosed (“blind”) ²²²Rn concentrations that could be related to U.S. national standards. The standardized sample additions were obtained with a calibrated ²²⁶Ra source and a specially-designed manifold used to obtain well-known dilution factors from simultaneous flow-rate measurements. The additions were introduced over sampling periods of several hours (typically 4 h) into a common streamline on a sampling tower used by the participating laboratories for their measurements. The standardized ²²²Rn activity concentrations for the intercomparison ranged from approximately 2.5 Bq · m⁻³ to 35 Bq · m⁻³ (of which the lower end of this range approached concentration levels for ambient Bermudian air) and had overall uncertainties, approximating a 3 standard deviation uncertainty interval, of about 6 % to 13 %. This paper describes the calibration and methodology for the standardized sample additions.     

An International Marine-Atmospheric 222Rn Measurement Intercomparison in Bermuda Part II: Results for the Participating Laboratories

As part of an international measurement intercomparison of instruments used to measure atmospheric ²²²Rn, four participating laboratories made nearly simultaneous measurements of ²²²Rn activity concentration in commonly sampled, ambient air over approximately a 2 week period, and three of these four laboratories participated in the measurement comparison of 14 introduced samples with known, but undisclosed (“blind”) ²²²Rn activity concentration. The exercise was conducted in Bermuda in October 1991. The ²²²Rn activity concentrations in ambient Bermudian air over the course of the intercomparison ranged from a few hundredths of a Bq · m⁻³ to about 2 Bq · m⁻³, while the standardized sample additions covered a range from approximately 2.5 Bq · m⁻³ to 35 Bq · m⁻³. The overall uncertainty in the latter concentrations was in the general range of 10 %, approximating a 3 standard deviation uncertainty interval. The results of the intercomparison indicated that two of the laboratories were within very good agreement with the standard additions, and almost within expected statistical variations. These same two laboratories, however, at lower ambient concentrations, exhibited a systematic difference with an averaged offset of roughly 0.3 Bq · m⁻³. The third laboratory participating in the measurement of standardized sample additions was systematically low by about 65 % to 70 %, with respect to the standard addition which was also confirmed in their ambient air concentration measurements. The fourth laboratory, participating in only the ambient measurement part of the intercomparison, was also systematically low by at least 40 % with respect to the first two laboratories.     

Radiochemical evaluation of groundwater around Mika uranium mineralization and environs

Seventeen groundwater samples around Mika uranium mineralization were collected, and the ²²²Rn concentrations were measured using a DURRIDGE RAD7 electronic radon detector. The ²²²Rn concentrations in the groundwater ranged from 2350 to 46200 Bq m^–3 with an average of 29 400 Bq m^–3. The results show that 76.5% of the groundwater samples collected have ²²²Rn concentrations far above the US EPA maximum contaminant level (MCL) of 11.1 Bq L^–1 (for states without radon monitoring policy and enhanced indoor air programs), and only 23.5% have lower values. On the other hand, all the ²²²Rn levels were below the MCL of 100 Bq L^–1, recommended by EU as the level that warrants consideration of possible remedial actions. Borehole samples show relatively higher ²²²Rn concentrations than samples collected from open wells. The annual effective dose due to ingestion (H _ing) of ²²²Rn in the groundwater ranged from 0.05 to 0.92 mSv, with an average of 0.59 mSv. These values are within the ICRP recommended reference level of 1 mSv year^–1 for the intake of the radionuclide in water by the general public for a prolonged exposure.     

A New Method for Precision Cold Neutron Polarimetry Using a 3He Spin Filter

We present a new method for precision measurement of the capture flux polarization of a polychromatic (white), continuous cold neutron beam, polarized by a ³He spin filter. This method allows an in situ measurement and does not require knowledge of the neutron beam wavelength distribution. We show that a polarimetry precision of 0.1 % is possible.     

<Superscript>220</Superscript>Rn as an additional factor of radiation hazard in the Shelter

In 2003–2007, the content of ²¹²Pb (²²⁰Rn daughter product) inside the Shelter was, as a rule, in the range 0.5–5 Bq m⁻³. No seasonal and time dynamics of the ²¹²Pb concentration and no relationship with the technical activity were revealed. At simultaneous sampling of aerosols, the volume activities of ²¹²Pb in the bypass were higher by 1–2 orders of magnitude than in the surrounding medium (local zone). Hence, the sources of ²²⁰Rn emanation, in particular, ²³²U are inside the Shelter. Among 220 samples taken in the bypass, 94% had the activity median aerodynamic diameter of aerosol particles bearing ²²²Rn and ²²⁰Rn daughter products in the range from 0.05 to 0.4 μm. For the Shelter staff members, ²²²Rn and ²²⁰Rn daughter products, and also submicron size of their carriers are negative factors which were not taken into account previously when determining ionizing irradiation doses. The additional inhalation doses can reach tens of percents of the permissible annual dose.     

The NIST Primary Radon-222 Measurement System

Within the United States, the national standard for radon measurements is embodied in a primary radon measurement system that has been maintained for over 50 years to accurately measure radon (²²²Rn) against international and national radium (²²⁶Ra) standards. In turn, all of the radon measurements made at the National Institute of Standards and Technology (NIST) and the radon transfer calibration standards and calibration services provided by NIST are directly related to this national radon standard. This primary radon measurement system consists of pulse ionization chambers and ancillary gas handling and gas purification equipment. The system is currently undergoing a significant upgrading and expansion which will replace the extant outdated system.     

Measurement of small friction moments

Conclusions The most widespread methods of those examined by us for measuring small friction moments consist at present of the pendulum and calibrated spring methods for laboratory research, and of the self-braking method for industrial use. This difference is due to the fact that the self-braking method is speedier, but it can only determine the mean value of the friction moment over a given time interval, which is often insufficient for research work.The pendulum method possesses a theoretically high sensitivity; however, the measurement of small moments entails several technical difficulties, the most important of which is the impossibility of evaluating the moment due to the system's residual unbalance and to the error in determining arml. For measuring friction moments of 10^–3–10^–4g·cm preference should be given to the calibrated spring method with the rotation axis of the system beingplaced in the vertical position.An essential defect of mechanical methods for determining the instantaneous values of the friction moment consists in the limited range of the measured moments.By means of electromechanical methods it is possible to measure arbitrarily small friction moments. However, they have to be calibrated by means of mechanical instruments. Induction instruments are considerably simpler in design than those of the moving-coil type, but they are less sensitive and have a large relative error. The use of electromechanical instruments is most suitable for comparison measurements and for production testing, due to their high productive capacity.     

Compressing Spin-Polarized 3He With a Modified Diaphragm Pump

Nuclear spin-polarized ³He gas at pressures on the order of 100 kPa (1 bar) are required for several applications, such as neutron spin filters and magnetic resonance imaging. The metastability-exchange optical pumping (MEOP) method for polarizing ³He gas can rapidly produce highly polarized gas, but the best results are obtained at much lower pressure (~0.1 kPa). We describe a compact compression apparatus for polarized gas that is based on a modified commercial diaphragm pump. The gas is polarized by MEOP at a typical pressure of 0.25 kPa (2.5 mbar), and compressed into a storage cell at a typical pressure of 100 kPa. In the storage cell, we have obtained 20 % to 35 % ³He polarization using pure ³He gas and 35 % to 50 % ³He polarization using ³He-⁴He mixtures. By maintaining the storage cell at liquid nitrogen temperature during compression, the density has been increased by a factor of four.     

Variations of radon and thoron concentrations in different types of dwellings in Mysore city, India

²²²Rn and ²²⁰Rn, the immediate decay products of radium isotopes,are causative agents of lung cancer. ²²²Rn and ²²⁰Rn concentrationsin houses with different floorings, roofs and walls and in differentrooms of houses have been measured in Mysore city, Karnatakastate, India, using solid-state nuclear track detectors. Theradon and thoron concentrations in dwellings with granite flooringsare found to be higher compared with other types. A correlationbetween the indoor radon concentration and dose in air fromterrestrial gamma radiation is observed.     

The direct measurement of Ba activity by the sum-peak method

The subject is a direct measurement of the activities of ¹³³Ba sources by application of the theoretical count rate expressions recently developed by Novković et al.The total uncertainties of the activity of the measured sources, obtained in two manners, are described in this paper. The presented method is successfully tested using a germanium spectrometer with efficiencies of 50%. The accuracy of this method is proved to be comparable with the present methods of the activity measurement of ¹³³Ba.     

New National Air-Kerma-Strength Standards for 125I and 103Pd Brachytherapy Seeds

The new U.S. measurement standard for the air-kerma strength from low-energy photon-emitting brachytherapy seed sources is formally described in detail. This instrument-based standard was implemented on 1 January 1999, with its salient features and the implications of differences with the previous standard given only through a series of informal communications. The Wide-Angle Free-Air Chamber (WAFAC) is specially designed to realize air kerma from a single-seed source emitting photons with energies up to about 40 keV, and is now used to measure the wide variety of seeds used in prostate-cancer therapy that has appeared in the last few years. For the two ¹²⁵I seed models that have been subject to both the old and new standards, the new standard reduces the air-kerma strength by 10.3 %. This change is mainly due to the removal of the influence on the measurement of the Ti K x rays produced in the source encapsulation, a component with no clinical significance.     

C* estimation for cracks in mismatched welds and finite element validation

A C^* integral estimation method is proposed for a crack located in the weld with a mismatch in mechanical properties from the surrounding base material. The method involves the definition of an equivalent stress-creep strain rate (ESCSR) relationship based on the mechanical properties of both the weld and base materials and the geometrical dimension of welding seam. The value of creep fracture mechanics parameter C^*, for the mismatched weldment, is then estimated using the proposed ESCSR in conjunction with the reference stress (RS) method where the reference stress is defined based on the plastic limit load and the GE/EPRI estimation scheme. Referring to the equivalent stress-plastic strain (ESPS) curve in R6 and SINTAP procedures, an approximate solution for the ESCSR relationship has been obtained. Detailed formulae for the compact tension (CT) specimens have been derived on the basis of limit load solutions. Nonlinear finite element analysis of 48 cases with various degrees of mismatch in creep behaviour and different dimension of welding seam has been performed for CT specimens. Overall good agreement between the ESCSR method and the FE results provides confidence in the use of the proposed method in practice.     

Quantification of compaction-induced crystallinity reduction of a pharmaceutical solid using 19F solid-state NMR and powder X-ray diffraction

¹⁹F solid-state nuclear magnetic resonance (NMR) was investigated as an analytical technique to quantify the amorphous phase in a fluorine-containing pharmaceutical candidate. The crystallinity of Compound 1 was calculated using two ¹⁹F T₁ relaxation-based methods. The first method employs both the pure amorphous and the crystalline reference standards while the second method is model independent and utilizes a single standard. The ¹⁹F solid-state NMR results were confirmed with powder X-ray diffraction methods. From X-ray diffraction data, two linear calibration curves were obtained from blends of crystalline and amorphous Compound 1: one is based on the total integrated intensity of selected diffraction peaks and the other on the total intensity of the amorphous halo at 2θ positions that have no interference from crystalline diffraction peaks. The crystallinity of Compound 1 after compaction calculated by both ¹⁹F solid-state NMR methods was in excellent agreement with the results from the X-ray calibration curves. ¹⁹F solid-state NMR was shown to be a powerful technique in determining the amount of amorphous phase present in a pharmaceutical solid.     

Determination of Young's modulus and Poisson's ratio of thin films by combining sinψ X-ray diffraction and laser curvature methods

In this study, we have proposed a nondestructive method to simultaneously determine the Young's modulus (E) and Poisson's ratio (ν) of polycrystalline thin film materials. The method involved independent stress measurement by laser curvature technique and strain components determination by sin²ψ X-ray diffraction (XRD) method, and afterward, elasticity theory was employed to calculate E and ν. The proposed method was applied on two model specimens, TiN and ZrN thin films, using synchrotron X-ray and laboratory X-ray sources, respectively. The cos²αsin²ψ XRD method which measured the strain for diffraction planes at different location was performed on the same film, and the previously determined E and ν were used to calculate the stress. The residual stresses derived from cos²αsin²ψ method were close to the stresses from laser curvature measurements, which validated the measured values of E and ν. The depth profile of residual stress of the TiN thin film was assessed using cos²αsin²ψ method by appropriately adjusting the X-ray incident angle. In addition, the E value determined from nanoindentation (NIP) may depend on the indentation depth. Therefore, one should be cautious when employing the NIP-determined E in sin²ψ or cos²αsin²ψ methods to calculate the residual stress because the modulus may not always give correct stress value.     

医用诊断半值层测量仪校准影响因素的研究

在各种诊断X射线辐射源检定规程或校准规范中都对半值层测量提出了要求,半值层测量仪也得到广泛应用,但半值层测量仪的校准方法一直未明确。探讨在校准半值层测量仪过程中的主要影响因素,结果表明探测器角度对测量结果影响最大,因此校准时要将被校半值层测量仪置于测试平面中心位置,角度偏差不应超过±1°。     

Traceability of photocurrent measurements to electrical standards

In detector output-signal measurements, where the measurement uncertainty critically impacts the total uncertainty of a detector-based radiometric scale realization, traceability of the photocurrent measurement to SI traceable electrical standards is needed. A reference photocurrent-to-voltage conversion scale has been developed and described here. The new standard has internal reference resistors for all signal-gain selections to decrease noise pickup of traditionally used external reference resistors. The internal resistors were calibrated by the NIST Quantum Electrical Metrology Division against standard resistors. Using the substitution method, the reference photocurrent-to-voltage conversion scale was transferred from the converter standard to other converters up to a maximum signal-gain of 10¹⁰ V/A with an expanded uncertainty of 0.013% (k=2). The DC conversion scale was extended to AC mode signal-gain calibrations where the photocurrent measurement uncertainty is 0.05% (k-2).     

Bose-Einstein Condensation of Magnons in Superfluid 3He

The possibility of Bose-Einstein condensation of excitations has been discussed for a long time. The phenomenon of the phase-coherent precession of magnetization in superfluid ³He and the related effects of spin superfluidity are based on the true Bose-Einstein condensation of magnons. Several different states of coherent precession has been observed in ³He-B: homogeneously precessing domain (HPD); persistent signal formed by Q-balls at very low temperatures; coherent precession with fractional magnetization; and a mode of the coherent precession in compressed aerogel. The coherent precession has been also found in ³He-A in compressed aerogel. Here we demonstrate that all these cases are examples of a Bose-Einstein condensation of magnons, with the magnon interaction term in the Gross-Pitaevskii equation being provided by different types of spin-orbit coupling in the background of the coherent precession.      

Non-linear fracture mechanics analyses of part circumferential surface cracked pipes

This paper provides engineering estimates of non-linear fracture mechanics parameters for pipes with part circumferential inner surface cracks, subject to internal pressure and global bending. Solutions are given in the form of two different approaches, the GE/EPRI approach and the reference stress approach. For the GE/EPRI approach, the plastic influence functions for fully plastic J solutions are tabulated based on extensive 3-D FE calculations using deformation plasticity, covering a wide range of pipe and crack geometries. The developed GE/EPRI-type fully plastic J estimation equations are then re-formulated using the concept of the reference stress approach for wider applications. The proposed reference stress based estimates are validated against detailed 3-D elastic-plastic and elastic-creep FE results. For a total of 26 cases considered in this paper, agreement between the proposed reference stress based J and C ^* estimates and the FE results is excellent. An important aspect of the proposed estimates is that they not only are simple and accurate but also can be used to estimate J and C ^* at an arbitrary point along the crack front.