Mass Attenuation Coefficients Of Samples Research Articles

A general function for determining mass attenuation coefficients to correct self-absorption effects in samples measured by gamma spectrometry

This work is focused on obtaining a general function for calculating the mass attenuation coefficients of samples whose compositions are known such as waste, biota or NORM (Naturally Occurring Radioactive Materials) samples. After determining the general function, it is possible to assess the self-absorption effects by the self-absorption correction factor, which is really important to consider for samples measured by gamma spectrometry. In order to obtain a general function of the mass attenuation coefficients dependent on the gamma emission energy (Eγ) and the chemical elements (Zi) with their respective concentrations (xi), it was necessary to fit the tabulated values of the mass attenuation coefficients versus gamma energy in the range of 20 keV–2000 keV for each chemical element. This is the energy range for the majority of gamma emissions of natural radionuclides. Once those fittings for each chemical element, Z, from 1 (H) to 92 (U) were done, the parameters, that resulted from those fittings, were fitted versus the atomic number, Z. This provides a general function that allows to calculate the mass attenuation coefficient by knowing the gamma emission energy and the sample composition. Finally, both the general function for calculating the mass attenuation coefficient and the self-absorption correction factor, which is used in gamma spectrometry with coaxial Ge detectors, were validated by comparisons made with the values provided by databases for several samples with widely different known densities, compositions and activity concentrations.

Fabrication of anthropomorphic thyroid-neck phantom for dosimetry study in nuclear medicine.

The aim of this study was to fabricate an anthropomorphic thyroid-neck phantom for dosimetry study in nuclear medicine. The main structures of the anthropomorphic phantom comprise of neck, thyroid, trachea, oesophagus, cervical bone and spinal canal. Several slots for Optically Stimulated Luminescent Dosimeter (OSLD) for each organ was also fabricated to measure the absorbed dose received by thyroid and other organs at risk. The phantom was made from paraffin wax and sodium chloride (NaCl) compounds. The fabricated anthropomorphic phantom was then tested by administrating 99mTc with an activity of 0.3 mCi and 2.0 mCi in thyroid and neck phantoms respectively. The phantom was scanned for 30 min with diagnostic thyroid imaging of SPECT to observe the distribution of 99mTc. A comparison analysis between mass attenuation coefficient of samples and mass attenuation coefficient of human tissue obtained from ICRU report-44 was performed to validate the mass attenuation coefficient of samples obtained in this study. Relative percentage differences of mass attenuation coefficients of samples obtained from experimental and XCOM stimulation values were evaluated respectively. The absorbed dose to thyroid and other organs at risk was evaluated from OSLDs at 6 h (first half life), 12 h (second half life) and 24 h (fourth half-life) after the injection of 99mTc.

Determination of effective atomic numbers and mass attenuation coefficients of samples using in‐situ energy‐dispersive X‐ray fluorescence analysis

The matrix effect has a major impact on energy‐dispersive X‐ray fluorescence analysis (EDXRFA) and is difficult to be evaluated due to that the contents of some low‐atomic‐number elements cannot be identified by in‐situ EDXRFA. Up to today, the fundamental parameter algorithm proposed by Rousseau has been widely applied to correct the matrix effect. Accordingly, determining the matrix and mass attenuation coefficient (μ/ρ) of sample is a key issue for the fundamental parameter algorithm. In present work, the method to deduce μ/ρ by effective atomic number (Zeff) was studied. First, the relationship between Zeff and coherence to Compton scatting ratio (R) of the incident X‐ray was determined by standard samples. Then, we deduce Zeff and their μ/ρ. The value of μ/ρ deduced by our method is in good agreement with that calculated by WinXCOM, and the relative change (Δ) is less than 7%. We also deduced Zeff and their μ/ρ of Chinese national standard soil samples employing our method and good agreement with the calculated values were also obtained. We found that the agreement between experimental values of μ/ρ with theoretical values by WinXCOM still exists when the energy of the incident X‐ray is greater than 4 keV, and the Δ is less than 10%. The result indicates that our method may be applied directly to in‐situ EDXRFA.

POTENTIAL OF RHIZOPHORA SPP PARTICLEBOARD TREATED WITH SOY FLOUR AS WATER EQUIVALENT MATERIAL

Water is a recognized tissue equivalent material. Due to some reason, water is not a suitable material to use as the daily routine in Quality Assurance assessment. In this paper, Rhizophora spp was treated with soy flour were applied to fabricate solid water equivalent material. Nine samples of three different particle sizes of Rhizophora spp as well as their treatment level were prepared. An innovative approach, x-ray fluorescence was used to measure the unknown attenuation coefficient while field emission scanning electron microscopy was presented to evaluate the microscopy structure of desired samples. Effective energy range between 15.7 to 26.7 keV was used to measure the mass attenuation coefficient of the fabricated particleboard. All the results were compared with the water value in XCOM database. This study showed that there was no significant difference (p>0.05) between mass attenuation coefficient of sample with the water value from XCOM. In addition, the morphology images were improved for post-treated compared to untreated Rhizophora spp particleboard. Based on these results, Rhizophora spp particleboard is amenable as an alternative window of purported water equivalent material.

Assessment of natural radioactivity and mass attenuation coefficients of brick and roofing tile used in Turkey

In this study the distribution of natural radionuclides ( 226 Ra, 232 Th, 40 K) in brick and roofing tile samples commonly used as building materials in Turkey was measured by using gamma spectrometry. The activity concentrations, radium equivalent activities (Ra eq ), representative level index, indoor absorbed dose rate in air values and annual effective dose due to the intake of the above-mentioned radionuclides in the brick and roofing tile samples were estimated to assess the radiation hazard for people living in dwellings made of the materials studied. The measured average activity concentrations of 226 Ra, 232 Th and 40 K were 34 ± 14, 34 ± 13 and 462 ± 175 Bq.kg −1 , respectively, for brick samples. For roofing tile, the average activity concentrations of 226 Ra, 232 Th and 40 K were measured to be 34 ± 14, 33 ± 12 and 429 ± 161 Bq.kg −1 , respectively. The concentrations for these natural radionuclides were compared with the reported data of other countries. The Ra eq values of all samples were lower than the limit of 370 Bq.kg −1 , equivalent to a gamma dose of 1.5 mSv.a −1 recommended by OECD. This study shows that the measured brick and roofing tile samples do not pose any significant source of radiation hazard and are safe to be used as building materials. Moreover, the experimental mass attenuation coefficients (μ/ρ) of brick and roofing tile samples were determined in the energy range 80–1332 keV using the gamma ray transmission method. The experimental mass attenuation coefficients were compared with theoretical values obtained using XCOM. It was found that the computed values and the experimental results of this work are in good agreement with those reported in the literature. The chemical compositions and structural analysis (XRD) of the brick and roofing tile samples are also presented. ► In this study, the distribution of natural radionuclides in brick and roofing tile samples used in Turkey were studied. ► Associated potential radiological hazards were evaluated. ► Experimental mass attenuation coefficients of these samples were determined. ► Results provide useful data for adopting safety measures, dealing with radiation emergencies.

Determination of Uranium in Rocks and Soils of South Cameroon by γ-ray Spectrometry

Analytical results of uranium concentration in rocks and soils collected in the area of Lolodorf of South Cameroon where a radiometric anomaly had been found by previous investigation are reported. The analysis has been carried out by γ-ray spectrometry using a Ge detector. Radioactivity concentration of 235U was determined by comparing peak count rates of samples with those of natural uranium standard sample. Radioactivity concentration of 238U was calculated from the 235U radioactivity concentration by assuming that the isotopic composition of 235U is 0.7200% of natural abundance. Difference of γ-ray self-absorption between the samples and uranium standard was accurately corrected by using a mass attenuation coefficient of samples and standard measured by using an external γ-ray source. The radioactivity concentrations in rocks ranged from 0.92±0.02 to 228±14Bq/kg(235U) and 20±5 to 4868±307Bq/kg(238U), while radioactivity concentrations in soils ranged from 3±1 to 63±2 Bq/kg(235U) and 71±19 to 1346±38 Bq/kg(238U). The γ-ray dose rates in air at 1m above the ground surface due to the high uranium concentration in soil samples were ranged from 33±9 to 622±18 nGy/h. The highest uranium concentration of about 0.04% in rock was found in the analysis. These results show that the uranium content in the studied areas is significantly high and the studied areas have a potential for uranium mining.