Alpha Track Research Articles

Histological type of Thorotrast‐induced liver tumors associated with the translocation of deposited radionuclides

Exposure to internally deposited radionuclides is known to induce malignant tumors of various histological types. Thorotrast, a colloidal suspension of radioactive Thorium dioxide ((232)ThO(2)) that emits alpha-particles, was used as a radiographic contrast during World War II. Thorotrast is known to induce liver tumors, particularly intrahepatic cholangiocarcinoma (ICC) and angiosarcoma (AS), decades after injection. Therefore, patients injected with Thorotrast comprise a suitable study group to understand biological effects of internal ionizing radiation injury. Autoradiography and X-ray fluorescence spectrometry (XRF) were carried out on non-tumorous liver sections from Thorotrast-induced ICC (T-ICC) and Thorotrast-induced AS (T-AS). Autoradiography revealed that the slope of the regression line of the number of alpha tracks for the amount of deposited Thorium ((232)Th) was higher in non-tumorous parts of the liver with T-ICC than those with T-AS. XRF showed that the intensity ratio of Radium (Ra) to Thorium (Th) in non-tumorous liver tissue with T-ICC was significantly higher than that with T-AS. Furthermore, the mean (228)Ra/(232)Th radioactivity ratio at the time of death calculated was also significantly higher in T-ICC cases than in T-AS cases. These suggest that the metabolic behavior of radionuclides such as relocation and excretion, as well as the content of deposited radionuclides, is a major factor in determining the histological type of Thorotrast-induced liver tumors.

Development of Micromegas for neutrinoless double beta decay searches

The present paper is a summary of experimental tests performed with microbulk Micromegas for application in a neutrinoless double beta decay experiment based in a xenon TPC. No critical limitation related with high pressure has been detected for Micromegas, which has been tested up to 10 bar. No significant differences have been found between low energy X-rays and high energy alpha tracks regarding ionization yield and electronic transparency of Micromegas mesh. Using 5.5 MeV alphas in argon-isobutane mixtures, values as low as 1.8% FWHM have been obtained, with possible evidence that better resolutions are achievable. These results seems independent of pressure (probed up to 4.5 bar) or gas mixture (microbulks have run in xenon without quencher). The imperative necessity of high quality gas led to start on a new TPC and MPGD dedicated lab at Zaragoza.

A new CR-39 nuclear track passive thoron measuring device

220Rn monitoring in dwellings and in workplaces is seldom performed, both because usually the associated risk is considered negligible and for the difficulties of properly measuring it. As a consequence the state of art of thoron measurements by using solid-state nuclear track detectors shows a significant lag compared with radon. However the demand of determining the thoron contribution to natural dose assessment is worldwide increasing, and in the presence of some building materials as tuff, should be mandatory. To tackle this problem, the ENEA Radon Measuring Service has developed a dose evaluation procedure based on the measurement of the 220Rn concentration at a standard distance from the wall, by using a new (patent pending) CR-39 alpha track detector thoron passive device (ATD-TnPD), coupled to our own radon passive device (ATD-RnPD). The two devices are geometrically similar and their responses were extensively evaluated to optimise the uncertainty of the thoron measurement. This paper depicts the prime features of the new device, and the introduced changes aimed at reducing the device's equilibrium time constant from 20.8 min to 3.1 min. Since no reliable thoron calibration facility has resulted available up to now, we had to state the ATD-TnPD's sensitivity parameter by performing the calibration step by our own. A closed circuit thoron exposure facility was set up to provide thoron exposures at 3 different levels. The exposed detectors were chemically etched at 7 increasing etching times to study the relationship between sensitivity and etching conditions, so to optimise the detector response and the measurement uncertainty.

RADON EXHALATION RATES FROM BUILDING MATERIALS USING ELECTRET ION CHAMBER RADON MONITORS IN ACCUMULATORS

An electret ion chamber (EIC) radon monitor in a sealed accumulator measures the integrated average radon concentration at the end of the accumulation duration. Theoretical equations have been derived to relate such radon concentrations (Bq m(-3) ) to the radon emanation rate (Bq d(-1)) from building materials enclosed in the accumulator. As an illustration, a 4-L sealable glass jar has been used as an accumulator to calculate the radon emanation rate from different granite samples. The radon emanation rate was converted into radon flux (Bq mm(-2) d(-1)) by dividing the emanation rate by surface area of the sample. Fluxes measured on typical, commercially available granites ranged from 20-30 Bq m(-2) d(-1). These results are similar to the results reported in the literature. The lower limit of detection for a 2-d measurement works out to be 7 Bq m(-2) d(-1). Equations derived can also be used for other sealable accumulators and other integrating detectors, such as alpha track detectors.

Radiobarites from the Cenozoic volcanic region of the Bohemian Massif: radiochemical study, history, and lead isotopic composition

A specific, radium bearing type of barites has been known from the Ohře (Eger) Rift, a region of Cenozoic volcanic activity in northwestern Bohemia, Czech Republic, since 1904. Barites from Karlovy Vary, Teplice and Děcin areas have been studied to elucidate geochemical history of these specific samples. Low background radiometric method using high-resolution gamma-ray spectrometry has shown that radioactivity of these barites (up to 8 Bq g−1) is carried by 226Ra, which is not in equilibrium with the parent 238U. In all samples, uranium activity was below 0.005 Bq g−1––the detection limit achieved by instrumental neutron activation analysis. The alpha track method on a crystal plate has shown that 226Ra is accumulated in surface layers or crystal cracks, therefore, the crystal rims must be relatively young, not older than 10–15 thousand years. In a lead fraction isolated from the barites, concentration and isotopic composition of lead were determined by photon activation analysis and ICP MS, respectively.

Factors affecting the registration and counting of alpha tracks in solid state nuclear track detectors

In view of the fact that the radon progeny contribute the highest to the natural radiation dose to general populations, large scale and long-term measurements of radon and its progeny in the houses have been receiving considerable attention. Solid State Nuclear Track Detector (SSNTD) based systems, being the best suited for large scale passive monitoring, have been widely used for the radon gas (using a cup closed with a semi-permeable membrane) and to a limited extent, for the measurement of radon progeny (using bare mode in conjunction with the cup). These have been employed for radon mapping and indoor radon epidemiological studies with good results. In this technique, alpha tracks recorded on SSNTD films are converted to radon/thoron concentrations using corresponding conversion factors obtained from calibration experiments carried out in controlled environments.The detector response to alpha particles depends mainly on the registration efficiency of the alpha tracks on the detector films and the subsequent counting efficiency. While the former depends on the exposure design, the latter depends on the protocols followed for developing and counting of the tracks. The paper discusses on parameters like etchant temperature, stirring of the etchant and duration of etching and their influence on the etching rates on LR-115 films. Concept of break down thickness of the SSNTD film in spark counting technique is discussed with experimental results. Error estimates on measurement results as a function of background tracks of the films are also discussed in the paper.

Estimate of etched tracks by optical method and spark counting

Solid State Nuclear Track Detectors (SSNTD) are commonly used for long term measurements of radon, thoron and progeny concentrations. In the present study, we compared the optical counting method and the spark counting technique for counting the alpha tracks on LR 115 track detector films. The paper discusses the various parameters that are innate in the process. More than 300 films were counted by both optical microscope and spark counter and the results are compared. The overall results show that the tracks obtained by spark counting are marginally less compared to the optical measurement. A linear fit of the data gives a slope less that one, which indicates that both the methods are almost in good agreement for counting the tracks when the track density is low. At higher track densities the spark counter gives an underestimation with respect to actual number of tracks formed, which could be corrected using a relation obtained between the tracks measured by optical method and spark counting.

Determination of boron distribution in rat's brain, kidney and liver

To determine relative boron distribution in rat's brain, liver and kidney, a mixture of boric acid and borax, was used. After transcardial injection of the solution, the animals were sacrificed and the brain, kidney and liver were removed. The coronal sections of certain areas of the brain were prepared by freezing microtome. The slices were sandwiched within two pieces of CR-39. The samples were bombarded in a thermal neutron field of the TRR pneumatic facility. The alpha tracks are registered on CR-39 after being etched in NaOH. The boron distribution was determined by counting these alpha tracks CR-39 plastics. The distribution showed non-uniformity in brain, liver and kidney.

A simple technique for determining the equilibrium equivalent Thoron concentration using a CR-39 detector: Application in mineral treatment industry

The paper presents a simple technique for determination of the Equilibrium Equivalent Thoron Concentration (EETC). A solid-state nuclear alpha track detector (SSNATD) named CR-39 manufactured by BARYOTRAK is used as the detector. This technique can be utilized anywhere, provided that air sampling is carried out with a DC driving pump. Although the measurement of Thoron concentrations is useful enough for screening high Thoron exposure, it is still necessary to determine Thoron progeny concentrations in order to complete dose assessment. After applying this technique for determining the EETC in some selected areas in southern Thailand, it has been found that the obtained EETC values are consistent with the values presented in the report compiled by UNSCEAR in 2000.

Retrospective assessment of indoor radon exposure by measurements of embedded 210Po activity in glass objects

In most of the epidemiological studies contemporary radon measurements have been used as surrogates for radon concentrations in past decades even though changes in radon levels and residence may have occurred. Short-lived radon progeny may deposit on available surfaces in dwellings thus giving rise over time to a build up of long-lived progeny. Airborne radon decay products can be deposited and implanted through alpha recoil into the glass surfaces. On glass surface, activities of 210Po may arise as a result of the decay of recoil implanted activity following the alpha decay of surface deposited 218Po or 214Po. Measurement of 210Po implanted on a household glass is a method that can be employed to retrospectively determine the historic level of radon in dwellings. This method is based on the assumption that levels of recoil implanted 210Po in the glass provide a measure of time integrated radon concentration in the environment in which the glass has been located. The surface deposited activity of the radon progenies, which then become implanted in the glass by alpha recoil, is believed to reflect past exposure to airborne activity. Such retrospective measurements on glass are valuable in estimating the human dose derived from radon during the time of exposure. In this paper an account is given of the principles and some field applications of a retrospective technique, using the alpha track detectors, CR-39 and LR-115, to measure 210Po implanted in glass surfaces (surface traps). By using this CR–LR difference technique, the cumulative radon exposure in a dwelling in past decades may be estimated. This method provides reliable radon exposure data as a support to epidemiological studies concerning the health effects of radon exposure in the living environment.

Discrimination of nuclear recoils from alpha particles with superheated liquids

The PICASSO collaboration observed for the first time a significant difference between the acoustic signals induced by neutrons and alpha particles in a detector based on superheated liquids. This new discovery offers the possibility of improved background suppression and could be especially useful for dark matter experiments. This new effect may be attributed to the formation of multiple bubbles on alpha tracks, compared to single nucleations created by neutron-induced recoils.

Application of alpha track registration technique for plutonium estimation in bioassay samples

Bioassay monitoring is carried out for occupational workers handling plutonium (Pu) in nuclear facilities. In India, presently Pu estimation in bioassay samples is done by alpha spectrometry. The minimum detectable activity (MDA) of alpha spectrometry is 0.5 mBq for a counting period of 1 day. To reduce the load of sample counting on alpha spectrometry, an alternative method based on alpha track registration in solid state nuclear track detectors (SSNTDs) is developed in the present paper. For this purpose, few urine samples of normal subjects spiked with known amounts of Pu in the range of 0.5–5.5 mBq were exposed to CR-39 SSNTDs. The total number of alpha tracks seen in the CR-39 films of the sample and the standard were used to calculate the amount of Pu in the sample. The results of alpha track registration technique were also compared with that obtained by the well-established alpha spectrometry and were found to agree well within ±30%. The minimum amount of Pu that can be analyzed by this method is 0.18 mBq for an exposure period of 45 days.

A study of indoor radon levels in rural dwellings of Ezine (Canakkale, Turkey) using solid-state nuclear track detectors

Indoor radon activity level and radon effective dose (ED) rate have been carried out in the rural dwellings of Ezine (Canakkale) during the summer season using Radosys-2000, a complete set suitable to radon concentration measurements with CR-39 plastic alpha track detectors. The range of radon concentration varied between 9 and 300 Bq m(-3), with an average of 67.9 (39.9 SD) Bq m(-3). Assuming an indoor occupancy factor of 0.8 and 0.4 for the equilibrium factor of radon indoors, it has been found that the 222Rn ED rate in the dwellings studied ranges from 0.4 to 5.2 mSv y(-1), with an average value of 1.7 (1.0) mSv y(-1). There is a possibility that low radon concentrations exist indoors during the summer season in the study area because of relatively high ventilation rates in the dwellings. A winter survey will be needed for future estimation of the annual ED.

Radon surveys in Ajloun city using CR-39 detectors

In the present study radon ( 222Rn) concentrations in dwellings, soil and water at Ajloun city was performed by using CR-39. The detectors were chemically etched and the alpha track density was measured using an optical microscope. The average indoor radon concentration for the whole survey was 27.6 ± 1.8 Bq m - 3 . Differences were found at the different floors: 31.1 ± 4.4 , 23.8 ± 3.6 and 19.7 ± 3.2 Bq m - 3 for the 1st, 2nd and 3rd floors, respectively. Furthermore, the average concentration of radon in soil air was 3.4 ± 1.4 kBq m - 3 . In addition, the average radon level in water samples from different water springs was 2.0 ± 0.3 Bq ℓ - 1 . However, the average concentration of radon in Ajloun city is lower than the national average ( ∼ 40.0 Bq m - 3 ) .

Alpha track analysis and fission track analysis for localizing actinide-bearing micro-particles in the Yenisey River bottom sediments

Distribution of actinides in bottom sediment and flood land soil cores collected from the Yenisey River near the Krasnoyarsk Mining and Chemical Combine (MCC) were analyzed. Actinide-bearing micro-particles were localized using alpha track analysis (ATA) and fission track analysis (FTA). Different types of radioactive micro-particles were found by analysis of the ratios of fission tracks to α -tracks from single particles. The different origin of these particles was confirmed by scanning electron microscopy with energy dispersed microanalysis (SEM-EDX), secondary ion mass-spectrometry (SIMS) and single-particle α -spectrometry. It is established that for most of the radioactive micro-particles ATA and FTA are the only possible techniques to obtain information concerning their origin. For the studied samples of bottom sediments and flood land soils, it was established that 80–90% of alpha radioactivity is attributed to hot-particles with 238Pu and 239,240Pu as the major radionuclides. According to the sequential extraction data most of 238Pu and 239,240Pu is found in the residual low-soluble fraction.

Radon survey in dwellings of Gansu, China: the influence of thoron and an attempt for correction

Alpha track detectors used in a previous investigation of the US National Cancer Institute and the China Ministry of Health on indoor radon ((222)Rn) in Gansu, China, proved to be influenced by (220)Rn (thoron), thus overestimating the (222)Rn level. Therefore, the detector was improved used in the previous survey. The new detectors allow discrimination between the two isotopes without any disturbance of the (222)Rn measurement. With this detector, a semi-annual study was conducted in 49 traditional dwellings of a village in Gansu. The arithmetic (AM) and geometric (GM) mean (222)Rn concentrations were 120 +/- 61 and 105 Bq m(-3) (with geometric standard deviation GSD = 1.8), respectively, while the mean (220)Rn concentrations at 2.5 cm wall distance were 430 +/- 210 Bq m(-3) (AM) and 350 Bq m(-3) (GM) with GSD = 2.3. The high thoron concentrations demonstrate the importance of the (220)Rn contribution to radiation exposure, in the investigated area. The actual level of indoor (222)Rn was about three times lower than that in the previous investigation which was affected by (220)Rn. A correction method for the radon results of the previous study is proposed, which provides (222)Rn and (220)Rn values comparable with those obtained in the study presented here.

Are ageing and fading really a problem for the quality of the passive radon measurements?

Since ageing and fading of alpha tracks in CR-39 are acknowledged to modify the sensitivity of radon measurement by an alpha track device (ATD), a Radon Service operating under quality assurance has to state how these effects affect the uncertainty of the measurements, especially when long term exposures are met. A test lasting one year has been carried out, by using a total of 624 PADC detectors, to analyse the effects of three different treatments (temperature, light and as used inside the ENEA holder) together with the factor of the duration of the treatment (1, 3, 4, 6, 9 and 12 months) on the detector response. The replications ( N = 6 ) and the target exposure ( 4000 kBq h m - 3 ) were so set to achieve a minimum of 2% as significant statistical difference between treatment and control exposures. The shift of the track effective minor axis distribution has been investigated and related to the reduction of the sensitivity, which resulted in correlation with the surface removed layer of the bulk material. The use of a sensitivity value dependent on how fading, ageing and other factors modify the track diameter distribution was able to reduce the bias of the measurement.

Calibration factor for thoron estimation in cup dosimeter

Estimation of inhalation dose in monazite deposit areas essentially requires concentrations of both radon ( 222Rn) and thoron ( 220Rn) for computation. Solid state nuclear track detector (SSNTD) based dosimeters are often employed for the simultaneous measurements of 222Rn and 220Rn. These dosimeters have two identical cups with cellophane in one cup and glass fibre filter in the other for radon alone and radon + thoron entries into the cups, respectively [Eappen, K.P., Mayya, Y.S., 2004. Calibration factors for LR-115 (type-II) based radon thoron discriminating dosimeter. Radiat. Meas. 38, 5–17]. Alpha tracks are registered on SSNTD films inside the cups in proportion to the gas concentrations and their decay progenies. Calibration factors (CFs) are obtained experimentally for known exposure to radon or thoron concentrations that is measured outside the cups. The theoretical CFs for the respective cups are obtained by using track development models for the exposure and etching conditions. In the case of 222Rn, it is assumed that the gas inside the cup is uniformly distributed; hence, the CF can be computed with the concentration measured outside the cup. However, in the case of 220Rn, certain assumptions are required in computing the CF from the gas concentration measured outside the cup due to its short half-life and hence small diffusive length. This paper discusses the theoretical method that is used in calculating the effective concentration of 220Rn inside the dosimeter cup which is taken for computing the theoretical CF. The CF obtained through modelling is compared with experimental values. Both the values are in very good agreement.

Soil radon concentration along fault systems in parts of south eastern Ghana

Radon gas emission from soils in parts of southeastern Ghana (Accra) have been measured to find a possible correlation of the gas emanation with faults and seismic activity in the area. LR-115 alpha track sensitive plastics were used for the detection of the gas at 47 sampling points within a 500 m × 500 m spaced grid. The obtained radon data was analyzed and superimposed on the geological and structural map to highlight the correlation between the gas emission and seismicity. In the highly faulted area, radon activity up to 115.00 kBq m −3 was measured; on the contrary in non-faulted areas radon activity was less than 20.00 kBq m −3. In the highly faulted area radon activity above 50.00 kBq m −3 have been considered anomalous. The background level increased to 115.00 kBq m −3 before a magnitude 1.5 earthquake struck the area.

Comparison of retrospective and contemporary indoor radon measurements in a high-radon area of Serbia

In Niska Banja, Serbia, which is a high-radon area, a comparison was made between two retrospective radon measuring methods and contemporary radon measurements. The two retrospective methods derive the radon concentrations that occurred in dwellings over longer periods in the past, based on the amount of trapped (210)Po on the surface of glass objects (surface traps, ST) or in the bulk of porous materials (volume traps, VT). Both surface implanted (210)Po in glass objects and contemporary radon in air were measured in 46 rooms, distributed in 32 houses of this radon spa-town, using a dual alpha track detector configuration (CR-39 and LR115) and CR-39 track etched detectors, respectively. In addition to the use of surface trap measurements, in 18 rooms (distributed in 15 houses) VT samples of suitable material were also collected, allowing to compare ST and VT retrospective radon concentration estimates. For each room, contemporary annual radon concentrations (CONT) were measured or estimated using seasonal correction factors. The distribution of the radon concentration in all data sets was found to be close to lognormal (Chi-square test>0.05). Geometric means (GM) are similar, ranging from 1040 to 1380 Bq m(-3), whereas geometric standard deviations (GSD) for both the retrospective methods are greater than for the CONT method, showing reasonable agreement between VT, ST and CONT measurements. A regression analysis, with respect to the lognormal distribution of each data set, shows that for VT-ST the correlation coefficient r is 0.85, for VT-CONT r is 0.82 and for ST-CONT r is 0.73. Comparison of retrospective and contemporary radon concentrations with regard to supposed long-term indoor radon changes further supports the principal agreement between the retrospective and conventional methods.