Theoretical basis for long-term measurements of equilibrium factors using LR 115 detectors

In this paper, we propose a method to determine the equilibrium factor using a bare LR 115 detector. The partial sensitivities ρ_i of the LR 115 detector to ²²²Rn and its alpha-emitting short-lived progeny, ²¹⁸Po and ²¹⁴Po, were investigated. We first determined the distributions of lengths of major and minor axes of the perforated alpha tracks in the LR 115 detector produced by ²²²Rn, ²¹⁸Po and ²¹⁴Po through Monte Carlo simulations. The track parameters were calculated using a track development model with a published V function, by assuming a removed active layer of 6.54 μm. The distributions determined for different alpha emitters were found to completely overlap with one another. This implied equality of partial sensitivities for radon and its progeny, which was also confirmed through analytical considerations. Equality of partial sensitivities makes possible convenient measurements of the proxy equilibrium factor F_p, which is defined in the present work as (F₁+F₃) and is equal to the ratio between the sum of concentrations of the two alpha emitting radon progeny (²¹⁸Po+²¹⁴Po) to the concentration of radon gas (²²²Rn). In particular, we have found F_p=(ρ/ρ_itC₀)−1, where ρ (track/m²) is the total track density on the detector, ρ_i=0.288×10⁻² m, t is the exposure time and C₀ (Bq/m³) is the concentration of ²²²Rn. 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.     

Comparison of outdoor activity size distributions of Rn and Rn progeny

Inhalation of ²²²Rn and ²²⁰Rn progeny from the domestic environment contributes the greatest fraction of the natural radiation exposure to the public. Dosimetric models are most often used in the assessment of human lung doses due to inhaled radioactivity because of the difficulty in making direct measurements. These models require information about the parameters of activity size distributions of thoron and radon progeny. The present study presents measured data on the attached and unattached activity size distributions of thoron and radon progeny in outdoor air in El-Minia, Egypt. The attached fraction was collected using a low-pressure Berner cascade impactor technique. A screen diffusion battery was used for collecting the unattached fraction. Most of the attached activities for ²²²Rn and ²²⁰Rn progeny were associated with aerosol particles of the accumulation mode. The activity size distribution of thoron progeny was found to be shifted to slightly smaller particle size compared to radon progeny.     

Effects of heating on the emanation rates of radon-222 from a suite of natural minerals

The emanating power of radon provides information on the internal structure of a mineral and the radiation damage caused by the decay of ²³⁸U, ²³⁵U and ²³²Th (and their daughters) that are present in the mineral. The concentration of ²²²Rn in groundwater is primarily controlled by the concentration of U and Th in the underlying rocks, as well as the emanation coefficient for that particular rock. The variations in the emanation coefficient for ²²²Rn caused when subsurface rocks are subjected to tectonic forces results in changes in ²²²Rn in groundwater. Increased emanation rates of radon from a mineral grain can potentially alter the ²³⁸U–²⁰⁶Pb, ²³⁵U–²⁰⁷Pb and ²³²Th–²⁰⁸Pb chronological clocks.

We have measured radon emanation coefficients on a suite of minerals comprised of one oxide (uraninite), three silicates (thorite, zircon, and cerite) and one phosphate (monazite) at room temperature and after heating at 200°C and 600°C. Annealing of some of the nuclear tracks within a mineral significantly reduces the emanation rates of radon in these minerals, suggesting that the tracks created by decay events serve as conduit pathways for the release of ²²²Rn. Higher emanation rates of ²²²Rn from mineral grains that are surrounded by liquid as compared to air indicate that a major portion of the escaping ²²²Rn in air gets embedded into adjacent mineral grains and/or opposite walls of a pore.     

Unattached fraction and size distribution of aerosol-attached radon progeny in the open air

Unattached fractions of the radon progeny ²¹⁸Po and ²¹⁴Pb, size distributions for both unattached ²¹⁸Po and ²¹⁴Pb, and attached ²¹⁴Pb and ²¹⁴Bi, along with condensation nuclei (aerosol-particle concentrations), were measured in the open air of the city of El-Minia, Egypt. The measurements were performed with a wire-screen diffusion battery and a low-pressure Berner cascade impactor using standard methodologies. The results for parameters of derived distributions demonstrate that the distributions for the former (unattached ²¹⁸Po and ²¹⁴Pb) are nearly similar. The diffusion equivalent diameters (d_f) of ²¹⁸Po and ²¹⁴Pb were determined to be 1.4 and 1.55 nm with relative geometric standard deviations (σ_g) of 1.65 and 2.1, respectively. The latter distributions (attached ²¹⁴Pb and ²¹⁴Bi) are nearly identical. Most of the activities were associated with the aerosol particles of the accumulation mode. The mean activity median aerodynamic diameters (AMAD) of ²¹⁴Pb and ²¹⁴Bi have the same value of 380 nm but the relative geometric standard deviation of the log-normal distribution of ²¹⁴Pb shows a broader activity distribution than ²¹⁴Bi (σ_g = 2.2 for ²¹⁴Pb and σ_g = 2.05 for ²¹⁴Bi).     

Measurement of Pu γ-ray intensities between 148 and 161 keV

Utilizing Pu isotopic standards characterized by the Institute for Nuclear Materials and Measurement (IRMM), New Brunswick Laboratory (NBL) measured the γ-ray branching ratios of the 148.567-keV ²⁴¹Pu, the 152.72-keV ²³⁸Pu, the 159.995-keV ²⁴¹Pu and the 160.28-keV ²⁴⁰Pu γ-rays. The study reported here includes the measurement of four IRMM standards, utilizing three different detectors for a total of 16 spectra, finding branching ratios of (1.863 ± 0.008) × 10⁻⁶, (9.230 ± 0.068) × 10⁻⁶, (6.321 ± 0.040) × 10⁻⁸ and (4.065 ± 0.017) × 10⁻⁶, γ/disintegration, respectively.     

Measurement of the half-life of Lu

The half-life of ¹⁷⁶Lu was determined by measuring the disintegration rate of a solution of lutetium oxide, using a calibrated HPGe detector, and found to be (3.69±0.02)×10¹⁰ y. It is recommended that the current adopted value be calculated from the grouping of three published values since 1983, including our value, the weighted mean of which is (3.73±0.01)×10¹⁰ y.     

Effect of pH and concentration on the diffusion of radiostrontium in compacted bentonite—a capillary experimental study

The effects of pH and Sr²⁺ solution concentration on diffusion and sorption of Sr²⁺ in compacted bentonite (ρ_b=1000±30 kg/m³) were studied using an “in-diffusion” method at an ionic strength of 0.1 M NaClO₄. The results (distribution coefficients, K_d, apparent and effective diffusion coefficients, D_a and D_e) derived from the capillary method are in good agreement with the literature data obtained for similar bentonite dry densities and fit Fick's second law very well. The results suggest that the diffusion of Sr²⁺ in compacted bentonite decreases slightly with increasing pH values and also increases slightly with increasing Sr²⁺ solution concentration. The distribution coefficients are weakly dependent on the solution concentrations and show a slight increase with increasing pH values. The average effective diffusion coefficient of Sr²⁺ in compacted bentonite is (1.2±0.2)×10⁻⁹ m²/s, surface diffusion effects are found for the diffusion of Sr²⁺ in compacted bentonite.     

Echo-planar and gradient-echo diffusion MRI of normal brain iron in the globus pallidus

The purpose of this study was to investigate effects of normal brain iron on proton diffusion and its quantification by diffusion MRI. The studies were undertaken in 24 cases ages ranging from 15 to 74 years (mean=45 years) with normal iron deposition in the globus pallidus to characterize the appearances on diffusion imaging with differing b values and on apparent diffusion coefficient (ADC) maps. Diffusion MRI was obtained by the spin-echo echo-planar imaging sequence (n=20 patients) or by the gradient-echo diffusion sequence, PSIF (n=4). In the PSIF sequence, pixel lens calculations were performed. In the echo-planar sequence, ADC value calculations were performed by using Stejskal–Tanner formula and by direct reading from automatically generated ADC maps. ADC values obtained from the normal appearing parenchyma were used as controls. Twenty patients with acute cerebral infarction were included for comparison of ADC values with those of iron deposition. The mean ADC value in the normal cerebral parenchyma was 0.85±0.11×10⁻³ mm²/s. In the globus pallidus, mean ADC value was 48±0.12×10⁻³ mm²/s. That of regions with acute infarction was 0.34±0.11×10⁻³ mm²/s. On b=0 or 50, b=500 and b=1000 s/mm² images of the echo-planar diffusion imaging globus pallidus appeared hypointense compared to surrounding parenchymal structures. Low signal and low pixel values were evident on the PSIF imaging. This study indicates that, on diffusion MRI, normal iron deposition reveals prominent low signal on all the images of the echo-planar diffusion imaging sequence with differing b values, as well as on the gradient-echo diffusion, PSIF sequence. Low signal on ADC maps and low ADC values are evident. These represent characteristic diffusion MRI features of normal iron deposition in the brain, reflecting susceptibility effects.     

Evaluation of Dosimetric Parameters for Various Ir Brachytherapy Sources Under Unbounded Phantom Geometry by Monte Carlo Simulation

As per TG-43 dose calculation formalism, it is essential to obtain various dosimetric parameters such as the air-kerma strength, dose rate constant, radial dose function, and anisotropy function, as they account for accurate determination of dose rate distribution around brachytherapy sources. Most of the available reported Monte Carlo simulations were performed in liquid water phantoms with a bounded region of 30-cm diameter. In this context, an attempt was made to report the dosimetric parameters for various commercially available pulsed-dose rate (PDR) and high-dose rate (HDR) sources under unbounded phantom conditions, as the data may be used as input to treatment planning systems (TPSs) for quality control assistance. The air-kerma strength per unit activity, S_k/A, was computed for various Iridium-192 (¹⁹²Ir) sources in dry air medium. The air-kerma strength and dose rate constant for old PDR is (9.77 ± 0.03) 10⁻⁸ U/Bq and 1.124 ± 0.001 cGyh⁻¹U⁻¹; for new PDR, the values are (9.96 ± 0.03) 10⁻⁸ U/Bq and 1.124 ± 0.001 cGyh⁻¹U⁻¹; for old MHDR, the values are (9.80 ± 0.01) 10⁻⁸ U/Bq and 1.115 ± 0.001 cGyh⁻¹U⁻¹; for new MHDR, (9.80 ± 0.01) 10⁻⁸ U/Bq and 1.112 ± 0.001cGyh⁻¹U⁻¹; for old VHDR, the values are (10.32 ± 0.01) 10⁻⁸ U/Bq and 1.035 ± 0.002 cGyh⁻¹U⁻¹; for new VHDR, the values are (10.34 ± 0.02) 10⁻⁸ U/Bq and 1.096 ± 0.001 cGyh⁻¹U⁻¹. The computed radial dose function values and anisotropy function values are also in good agreement with available data.     

Purification and activity standardisation of a Ho solution

As part of a project to use the long-lived (T_1/2=1200a) ^166mHo as reference source in its reference ionisation chamber, IRA standardised a commercially acquired solution of this nuclide using the 4πβ–γ coincidence and 4πγ (NaI) methods. The ^166mHo solution supplied by Isotope Product Laboratories was measured to have about 5% Europium impurities (3% ¹⁵⁴Eu, 0.94% ¹⁵²Eu and 0.9% ¹⁵⁵Eu). Holmium had therefore to be separated from europium, and this was carried out by means of ion-exchange chromatography. The holmium fractions were collected without europium contamination: 162 h long HPGe gamma measurements indicated no europium impurity (detection limits of 0.01% for ¹⁵²Eu and ¹⁵⁴Eu, and 0.03% for ¹⁵⁵Eu). The primary measurement of the purified ^166mHo solution with the 4π (PC) β–γ coincidence technique was carried out at three gamma energy settings: a window around the 184.4 keV peak and gamma thresholds at 121.8 and 637.3 keV. The results show very good self-consistency, and the activity concentration of the solution was evaluated to be 45.640±0.098 kBq/g (0.21% with k=1). The activity concentration of this solution was also measured by integral counting with a well-type 5″×5″ NaI(Tl) detector and efficiencies computed by Monte Carlo simulations using the GEANT code. These measurements were mutually consistent, while the resulting weighted average of the 4π NaI(Tl) method was found to agree within 0.15% with the result of the 4πβ–γ coincidence technique. An ampoule of this solution and the measured value of the concentration were submitted to the BIPM as a contribution to the Système International de Référence.     

Radon in groundwaters from Guarany aquifer, South America: environmental and exploration implications

Groundwater and sandstone samples were analyzed for radon in Guarany aquifer, Paraná sedimentary basin, South America. The dissolved radon ranged between 3 and 3303 pCi/l, being lognormally distributed, with a modal value of 1315 pCi/l, and a median value of 330 pCi/l. ²²²Rn leakage experiments for sandstones yielded a theoretical value of 1390 pCi/l for ²²²Rn in water, showing that theoretical modeling can reliably be used to interpret laboratory and field data.     

Investigation of the NMR relaxation rate dose-response of a ceric sulphate dosimeter

The relationship between the radiation absorbed dose and the NMR longitudinal and transversal relaxation rates, R₁ and R₂, respectively, of a ceric sulphate dosimeter was examined. By adding copper sulphate, the R₁ and R₂ dose-responses were found to be linear up to 60 kGy with dose sensitivities of 13×10⁻⁶ and 15×10⁻⁶ s⁻¹ Gy⁻¹, respectively. There is thus the potential for a three-dimensional ceric dosimeter for high dose applications, provided a suitable gelling substance is used.     

Ultra-low-level determination of U in IAEA marine reference materials by ICPMS and AMS

The development of analytical procedures for the measurement of ultra-low levels of ²³⁶U in marine samples using high-resolution inductively coupled plasma mass spectrometry (HR-ICPMS) and accelerator mass spectrometry (AMS) techniques are discussed and results are presented for IAEA reference materials—marine sediments (IAEA-135, 306, 384 and 385), marine biota (IAEA-134 and 414) and seawater (IAEA-381), collected in areas affected by nuclear reprocessing plants and nuclear weapons tests. The obtained minimum detection limit of the ²³⁶U/²³⁸U atom ratio was 1×10⁻⁸ for AMS and 1×10⁻⁶ for HR-ICPMS.     

Study of scattering effects in low-energy gamma-ray spectrometry

The photon-scattering effect was studied in the low-energy range 15–80 keV with planar and coaxial germanium detectors.

Different experimental tests have been conducted with a point source, progressively reducing the matter around the radioactive deposit, to investigate the origin and characteristics of the different spectrum components due to scattered photons (bumps). These tests were completed by Monte Carlo simulations.

Finally, a peak-shape calibration was performed using several radionuclides (¹⁰⁹Cd, ²⁴¹Am, ¹³³Ba, ¹³⁷Cs and ¹⁵²Eu). This allowed in identifying the main contributions to the bumps and improving the spectra processing.     

Alternative quality control for technetium-99m IDA complexes

A quality control procedure for ^99mTc-IDA complexes based on the use of C₁₈ Sep-pak^TM cartridges is developed and the validation of the procedure presented. C₁₈ Sep-pak^TM cartridges are pretreated by washing with 95% ethanol followed by 10⁻³ N hydrochloric acid. A small amount of the ^99mTc-IDA complex is applied, washed with 10⁻³ N hydrochloric acid and eluted with 95% ethanol. The radiochemical purity values obtained for ^99mTc-mebrofenin and ^99mTc-disofenin using this Sep-pak^TM procedure are comparable to those obtained using the standard two strip (ITLC-SG/100% methanol, ITLC-SA/20% saline) procedure.     

Radiochemical purification of no-carrier-added scandium-47 for radioimmunotherapy

A procedure, adaptable to large-scale remote operation, was developed to purify no-carrier-added (NCA) ⁴⁷Sc from irradiated Ti targets. Methods based on extraction chromatography and cation-exchange chromatography were compared. Results of this comparison led to the development of an optimized procedure based on cation-exchange with Dowex AG 50W-X4 and ⁴⁷Sc elution with HCl/HF. This method gave 90–97% overall ⁴⁷Sc recovery, with a Ti separation factor greater than 2.4×10⁻⁵, and specific activities ≥0.9 GBq μg⁻¹. Use of the ⁴⁷Sc product, for labeling monoclonal antibodies, resulted in consistent labeling yields of ≥90%.     

A liquid-scintillation-based primary standardization of Pb

A new radioactivity solution standard of ²¹⁰Pb has been developed and will be disseminated by the National Institute of Standards and Technology (NIST) as standard reference material (SRM) 4337. This new ²¹⁰Pb solution standard is contained in a 5 mL flame-sealed borosilicate glass ampoule, consists of (5.133±0.002) g of a nominal 1 mol L⁻¹ nitric acid solution, has a density of (1.028±0.002) g mL⁻¹ at 20 °C, has carrier ion concentrations of about 11 μg Pb²⁺ and 21 μg Bi³⁺ per gram of solution, and is certified to contain a massic activity (9.037±0.22) kBq g⁻¹ as of the reference time 1200 EST, 15 June 2006. All of the uncertainties cited above correspond to standard uncertainties multiplied by a coverage factor k=2. The standardization for the ²¹⁰Pb content of the solution was based on 4πβ liquid scintillation (LS) measurements using CIEMAT/NIST ³H-standard efficiency tracing (CNET). Confirmatory determinations were also performed by high-resolution HPGe γ-ray spectrometry, by 2π spectrometry with a Si surface barrier detector of separated ²¹⁰Po, and by 4πβ(LS)–γ(NaI) anticoincidence counting.     

Radiotracer technique in adsorption study: Part XVII. Removal Behaviour of Alkali Metal (K- and Li-) Titanates for Cd(II)

Alkali metal (potassium and lithium) titanates were synthesized and employed for the efficient removal of Cd(II) ions from aqueous solutions using the radiotracer technique. The possible mechanism involved at the solid/solution interface was deduced with the help of various physico–chemical data, i.e. effect of adsorptive concentration temperature and pH. The effect of added cations and H⁺ (HCl/H₂SO₄) in the uptake process was also seen. The radiation stability of these materials in the adsorption process was assessed by employing a 11.1 GBq (Ra–Be) neutron source having an integral neutron flux of 3.85×10⁶ n·cm⁻² s⁻¹ and associated with a nominal γ-dose of ca. 1.72 Gy/h.     

Accuracy of the convolution/superposition dose calculation algorithm at the condition of electron disequilibrium

Using Monte Carlo simulation and the convolution/superposition algorithm, this work examines percent depth dose curves of the central axis in an acrylic phantom (20×20×20 cm³) with variously sized air cavities (20×20×1.0, 20×20×2.0, 20×20×3.0, 20×20×4.0 and 20×20×4.95 cm³ for study of longitudinal electron disequilibrium (ED) and 3.6×3.6×4.95, 4.5×4.5×4.95, 5.4×5.4×4.95 and 20×20×4.95 cm³ for study of lateral ED). Radiochromic film samples are also measured to verify the Monte Carlo results. The Monte Carlo simulation is performed using OMEGA/BEAM and DOSXYZ codes, and the convolution/superposition calculation relies on an ADAC commercial treatment planning system.

Underestimating the dose kernel expansion leads to overestimating the dose of what was found in the air cavity of ED using the convolution/superposition algorithm. Consequently, the dose in the rebuild-up region is influenced. The influenced region is on the acrylic phantom surface to a depth of about 0.5 cm. The density scaling method of the convolution/superposition algorithm, applied to heterogeneous media, should be enhanced to account for the over-expansion of the dose kernel in the cavity of ED.     

Determination of 4.438 MeV γ-ray to neutron emission ratio from a Am–Be neutron source

Gamma-ray (γ-ray) spectra of a 1.49×10¹¹ Bq ²⁴¹Am–⁹Be source and background were measured using a 2 in×2 in, NaI(Tl) detector. Backgrounds due to the neutron interactions and energy deposition were calculated with MCNP4C. By subtracting the backgrounds from the experimental spectra, the S_γ is obtained and the R=S_γ/S_n was estimated. The final result of R=S_γ/S_n=0.596 is in agreement with result reported in literature.