Simultaneous measurement of radon, radon progeny and thoron concentrations using Makrofol-DE detectors

In this study we describe the set-up of a new passive integrating system to measure simultaneously ²²²Rn, ²²²Rn progeny (²¹⁸Po and ²¹⁴Po) and ²²⁰Rn concentration indoors. It consists of four Makrofol-DE (polycarbonate) circular foils. Two are enclosed within two diffusion chambers—each one with a different filter membrane—to measure ²²²Rn and ²²²Rn+²²⁰Rn. The other two foils are kept in direct contact with air and are electrochemically etched at different conditions to obtain the ²²²Rn daughters. Theoretical sensitivities of each Makrofol-DE foil are calculated using Monte-Carlo technique. The calculations are performed taking into account: (1) the Bethe–Bloch's expression for the stopping power of heavy charged particles in a medium, (2) the properties and behaviour of ²²²Rn, ²²⁰Rn and their progeny in the open air and within the diffusion chamber and (3) the etching conditions used to visualise -particles tracks.     

Interlaboratory comparison of microphone calibration

The results of an interlaboratory comparison on microphone calibration involving five National Metrology Institutes (NMIs) are presented. The Institute for National Measurement Standards (INMS-Canada), was the pilot laboratory that provided the data analysis for this investigation. The final results presented here were discussed and agreed upon by all participants. The maximum rms deviation for the two LS1P laboratory standard microphones measured by the above participants is 0.037 dB, which may be considered as the key comparison reference value.     

Effect of environmental conditions on radon concentration-track density calibration factor of solid-state nuclear track detectors

In this work, the effect of environmental conditions viz., temperature (T) and relative humidity (RH) on the track density-radon concentrations calibration factor (K) has been studied for CR-39 and LR-115 track detectors. The factorK was determined using a reference radon chamber in the National Institute for Standards (NIS) in Egypt. Track detectors were etched at the recommended optimum etching conditions. It is found that, the calibration factorK varies with bothT and RH, so they should be considered for the sake of uncertainty reduction. Good agreement is found between the calculated and measured values ofK and the compatibility between them is in the range of experimental uncertainty.     

Comparison of seasonal and yearly average indoor radon levels using CR-39 detectors

In order to assess the effect of long term exposure, CR-39 based radon dosimeters were exposed to indoor radon in the drawing rooms (living room) of 200 selected houses of the districts of Swabi, Mardan and Charsadda in the North West Frontier Province (NWFP) as well as in the Mohmand and Bajuar Agencies of the federally administered tribal areas (FATA), Pakistan. Dosimeters were exposed to the indoor radon during each season as well as throughout the year. From the measured indoor radon data it was observed that seasonal yearly average value were higher than that of the 12 months average indoor radon concentration values. The overall seasonal average was found to be 13% higher than that of the 12 months exposed CR-39 based dosimeters. However after the removal of the worst differences, seasonal average remains only 8 % higher than the 12 months averaged value.     

Upgrading of LET track-etch spectrometer calibration: Calibration and uncertainty analysis

The spectrometer of linear energy transfer (LET) was developed several years ago. It is based on the chemically etched polyallyldiglycolcarbonate (PADC) track-etch detector. LET spectra are determined through track parameters determination and analysis by an automatic optical image analyser LUCIA G. For the past few years, we have used three materials, Page, 0.5 mm thick and Tastrak, 1 and 0.5 mm thick. To upgrade and determine their calibration curves, we have performed irradiation in high-energy heavier charged particle beams at Dubna, Russia and at Chiba, Japan. We were able to irradiate detectors by means of particles from ¹²C to ⁵⁶Fe with LET in water from 7.9 to . Upgraded calibration curves were obtained through a regression analysis, including systematic uncertainty estimation. The results obtained were combined with statistical uncertainty treatment and were used to analyse recently and previously obtained data. Examples of the results are presented and analysed.     

紫外探测器的辐射定标及标准传递

针对定量化遥感的深入研究和探测器测量精度的提高,本文对紫外波段探测器的标定方法和标准的传递进行了研究。介绍了紫外探测器低温辐射计的工作原理、标准建立过程及发展现状,探讨了美国国家标准研究院（NIST）传递标准探测器的选取和标准传递过程。文中的研究为探测器定标方法的研究提供了理论基础,对提高标准探测器定标精度,促进其工程化应用具有借鉴意义。     

Comparative measurements between NTD and GEL detectors for radon gas

Because of the interest in an inexpensive radon monitoring technique and the use of new materials and new methods, this work presents comparative measurements between traditional passive radon detector using nuclear track detector (NTD), and a new method based on the diffusion of radon gas in gels, measuring the quantity of the remainder radioactive solids by the analysis of the gamma radiation from the decay of radon daughters. The methodology of the new detectors is introduced. The preliminary results show a measurable response of the gel material detectors to radon gas. The measurements are compared with those using NTDs CR-39 type for calibration purposes. Both the detection systems, the passive close-end cup system with NTDs and the passive close-end cup gel material detector, were exposed at the same time in the radon calibration chamber to different radon exposition levels from 150 to 3000 Bq/m⁻³.     

Monte Carlo simulation of radon SSNT detectors

A Monte Carlo based software for the computation of the sensitivity of etched radon track detectors was developed. It can be applied to the measurement of radon and radon daughters in free air or inside of a measurement chamber. LR 115 and CR-39 detectors, with or without an attenuator, are specifically addressed. Various etching conditions and observation criteria for counting the track density may be specified. The latent track formation and the etching process are realistically modelled. The dependence of the etch-rate ratio on the energy is taken into account. The plate-out phenomenon is included in the model. An inhomogeneous source distribution in the detector cup can be considered.     

Measurement of indoor radon levels in Erbil capital by using solid state nuclear track detectors

Radon alpha activity concentration has been measured in 28 homes in the Erbil Capital-Iraqi Kurdistan region during the autumn season by using time-integrated passive radon dosimeters containing CR-39 solid state nuclear track detectors “SSNTDs”. The radon activity concentrations in these homes range from (10.33–90.34) with an average of . The average absorption effective dose equivalent for a person living in homes for which the investigation were done was found to be , obtained by using an equilibrium factor of 0.5 and an occupancy factor of 0.8. The average lung cancer cases per year per 10⁶ person was found to be 23±12.     

About ageing and fading of Cr-39 PADC track detectors used as air radon concentration measurement devices

PADC detectors are widely used as air radon concentration measurement devices and the typical procedure that a Radon Service Laboratory uses to manage the detectors provides a calibration phase followed by the field measurement. The calibration is performed in a reference radon concentration atmosphere, using high radon concentration values in order to achieve typical exposure values of few MBq h m^?3 with an exposure time of few days. On the other hand the field measurement is characterized by long term exposures lasting up to six months and by radon concentrations that are quite lower than the ones used in the calibration.The aim of this study is to check whether the calibration procedure is actually representative of a field measurement, or, in other words, whether and how much ageing or fading can affect the calibration factor.We found that the ageing and fading effect can produce a decrease in the detector sensitivity leading to an underestimation of the radon concentration up to 40% for exposure lasting few months. An important issue is that both ageing and fading can be ascribed to a decrease in the track etching velocity V_t.In the paper we also provide an algorithm to compensate for the sensitivity variation due to fading/ageing effect.     

Further studies on ageing and fading of CR39 PADC track detectors used as air radon concentration measurement devices

PADC detectors are commonly used both as radon detectors and as personal dosemeters for neutron radiation. In both cases the measurement in workplace fields are characterized by long term irradiations, lasting up to several months. During this period the detectors undergo to uncontrolled and unmonitored environmental conditions. In a recent work the same authors demonstrated that the environmental conditions, mainly temperature, can seriously affect the detector sensitivity. The temperature effect is to reduce the V ratio by decreasing the track etching velocity V_t. This causes a decrease in limit angle and efficiency.This paper describes the same ageing/fading test made with CR39 from a different supplier. In this case it seems that the temperature has a negligible effect, so no compensation algorithm is needed.     

LET calibration for CR-39 detectors in different oxygen environments

High LET (linear energy transfer) radiation is the main contributor to the radiation field in low Earth orbit (LEO) in terms of dose equivalent. CR-39 plastic nuclear track detectors (PNTDs) can measure the LET spectrum and charge spectrum for the complicated radiation field in space. Previous research indicated that the sensitivity of CR-39 is different for CR-39 PNTDs working in different oxygen environments. LET calibration for CR-39 detectors in different oxygen environments is needed. Almost all the previous LET calibration work was carried out for CR-39 detectors in good-oxygen condition, LET calibration work for CR-39 in poor-oxygen condition has not been conducted until our work. Systematic LET calibrations were carried out by JSC-SRAG (Space Radiation Analysis Group) for CR-39 detectors working in different oxygen environments and abundant results of LET calibrations were obtained. This paper introduces the method for CR-39 LET calibration, presents and discusses the calibration results and some applications.     

Design, construct and test of a calibration radon chamber

A new radon chamber has been designed, constructed, and tested. The design was chosen to meet the needs of several different radon detection techniques, both active and passive. The chamber is a cubic shape made of pixy glass with volume about . On top, it has a circular opening with double lock system for entering and removing samples without significant disturbance of the inside concentration. It also has the possibility to expose passive radon detectors at different levels inside the chamber. In addition, two fans, with variable speeds, were fitted in two opposite corners to maintain the uniformity of radon gas inside the volume. This calibration chamber can be used to perform researches and studies on radon behavior, in addition to calibrating different types of detectors (passive and active) which are used for measuring radon and its daughters. Solid radium-226 source with activity of 122 kBq was placed at the bottom of the chamber to generate radon.     

High sensitivity detectors for measurement of space potentialfluctuations

A detection technique yielding an order of magnitude increase in the sensitivity of a Proca-Green type energy analyzer to beam energy fluctuations has been demonstrated. A sensitivity of <1 part in 10 ⁶ is possible. The technique can be used to increase the sensitivity of a Heavy Ion Beam Probe (HIBP) to space potential fluctuations in a plasma. The increase in sensitivity is achieved by splitting the detected ion beam into 10 smaller beamlets and summing the signals produced by the beamlets. Experimental results from an ion beam test facility are presented along with the projected results if implemented on the 2 MeV HIBP on the TEXT-Upgrade tokamak     

Studies on radon adsorption characteristics of different charcoals used as amplifiers for the track detectors

Ten sorts of charcoals were studied regarding their use as amplifier in the design of a personal dosimeter. It consists of a combination of a Makrofol detector and activated charcoal. The calibration factor for the Makrofol using the charcoals as an amplifier is about ten times higher comparing with an exposure without charcoal. The best results were obtained with Carboxen 563. The background radioactivity of charcoals must also be considered in the dosimeter's design.     

The calibration of the solid state nuclear track detector LR 115 for radon measurements

An experimental calibration of indoor room and outdoor soil detector devices which are based on LR 115 as sensitive element has taken place at the Swedish Radiation Protection Institute in Stockholm (Sweden) in 1994 and 1996, at the Physikalisch-Technischen Bundesanstalt in Braunschweig (Germany) in 1997 and at the Umweltforschungszentrum Leipzig-Halle (Germany) in 1997. Special properties of the used solid state nuclear track detector (SSNTD) material LR 115^* have been measured to define the application of the experimental calibration.     

Measurements of radon concentration in soil gas by CR-39 detectors

A miniature diffusion chamber with a 25 × 4 × 0.5 mm CR-39 track etch detector (Pershore Moulding Ltd.), mounted on the 1.1 m long pole has been developed for radon gas measurements at 1 meter depth in the soil. For chemically etched CR-39 (7h, 70°C NaOH) and automatic track analysis the lowest detection limit of the chamber was found to be 0.5 MBq h m⁻³ and the useful exposure range from 2 to 20 MBq h m⁻³. The typical exposure time in the soil is between 2 to 14 days. The chamber was tested against the active AlphaGUARD PQ-2000 (Genitron Instruments GmbH) probe. The test yielded consistent results for soils with typical values of permeability and which are not miniature with water. The pilot measurements of radon gas in soil conducted with the miniature diffusion chambers around 48 buildings in Kraków and Silesia regions yielded an average radon concentration of 13 kBq m⁻³. The chambers are to be applied to measure radon concentration in soil before constructing new houses in order to avoid high radon risk areas.     

Long-term measurements of radon progeny concentrations with solid-state nuclear track detectors

In this paper, we review existing methods for long-term measurements of radon decay products with solid-state nuclear track detectors. We then propose a method to determine the equilibrium factor using the bare LR 115 detector. The partial sensitivities p_i of the LR 115 detector to and its α-emitting short-lived progeny, and , were investigated. We determined the distributions of lengths of major and minor axes of the perforated α-tracks in the LR 115 detector produced by , and through Monte Carlo simulations. The track parameters were first calculated using a track development model with a published V function, and by assuming a removed active layer of . The distributions determined for different α-emitters were found to be completely overlapping with one another. This implied equality of partial sensitivities for radon and its progeny.Equality of partial sensitivities makes convenient measurements of a proxy equilibrium factor F_p possible which is defined in the present work as (f₁+f₃) and is equal to the ratio between the sum of concentrations of the two α-emitting radon progeny to the concentration of radon gas . In particular, we have found F_p=(ρ/ρ_itC₀)-1, where ρ (track/m²) is the total track density on the detector, (for the V function mentioned above and for a removed active layer of ), t is the exposure time and C₀ (Bq/m³) is the concentration of . If C₀ is known (e.g., from a separate measurement), we can obtain F_p. The proxy equilibrium factor F_p is also found to be well correlated with the equilibrium factor between radon gas and its progeny through the Jacobi room model. This leads to a novel method for long-term determination of the equilibrium factor.Experimental irradiation of LR 115 detectors to known concentrations as well as known equilibrium factors were carried out to verify the present method. The relationship between ρ_i and the removed layer was then derived for the V function specifically determined for the LR 115 detectors we were using for the experiments. The actual removed layers for individual detectors after etching were measured accurately using surface profilometry. A curve showing the relationship between the removed layer and the track diameter of normally incident 3 MeV α-particles is also provided for other researchers, who do not have access to surface profilometry, to use the present technique conveniently.     

Ion-pulse ionization chamber for direct measurement of radon concentration in the air

A large-volume (24.8l in total volume, 16.8l in fiducial volume) multiwire pulse ion collection ionization chamber was examined as a detector of α particles from radon decays in the air inside the chamber. The possibility of obtaining spectrometric information from slow ion pulses was tested. An energy resolution of 3.9% for 5.49-MeV α particles was obtained in preliminary measurements. It was shown that a detector of this kind could be used for direct measurements of radon activities in flowing air at a level less than 1 Bq/m³. A radon concentration at a level of 10 Bq/m³ can be measured with an accuracy better than 10 % for a counting time of 10³ s. The detector will be used for continuous accurate monitoring of the ²²²Rn concentration in the air of low-background laboratories.     

System for calibration of track detectors used in gaseous and solid alpha radionuclides monitoring

A laboratory system for the calibration of track detectors and charcoal detectors used in monitoring of radon and its decay products/their aerosols in air, is proposed. The system consists of three main components: (i) the alpha exposure chambers, including alpha monitoring devices and the connection with the ²²⁶Ra radioactive source. The CR-39 track detectors are mounted in the monitoring devices pre-equipped or not with paper filter; (ii) the calibrated  ²²⁶Ra source. Among the three tested sources: ²²²Rn, ²²⁶Ra+²²²Rn and ²²⁶Ra, the ²²⁶Ra source is considered the most appropriate radon source for our calibration system. It is kept into an airtight flat bottom flask, the radionuclide ²²⁶Ra being always in the radioactive equilibrium with their descendants. In the alpha exposure chambers, the source assures the radon at a constant rate; (iii) the ALFAUURASE program for the computation of radioactive accumulation of the alpha ²²⁶Ra descendants. For any initial mass of the parent, the amount and the activity of each alpha decay product and of all the decay products can be calculated by this computation program. Each component of the calibration system is described in the paper. The use of the system for the calibration of CR-39 track detectors in radon measurements is tested.