[Paper Review] Investigations of Natural Radioactivity levels and Assessment of radiological hazard of Tea samples collected from local market in Ethiopia

Tadelech Sisay, Tilahun Tesfaye|arXiv (Cornell University)|Jan 14, 2020

Radioactivity and Radon Measurements4 citations

TL;DR

This study measured natural radioactivity (²³⁸U, ²³²Th, ⁴⁰K) and artificial ¹³⁷Cs in six tea brands from Addis Ababa markets using HPGe gamma spectroscopy. Results showed average activity concentrations of 3.66 ± 0.47 Bq/kg (²³⁸U), 18.28 ± 2.4 Bq/kg (²³²Th), and 582.59 ± 29.64 Bq/kg (⁴⁰K), with all radiological hazard indices below safe limits, indicating tea consumption poses no significant radiological risk in Ethiopia.

ABSTRACT

In this study, the activity concentration of natural ( 238 U, 232 Th, 40 K) and artificial radionuclides (137 Cs) were measurements in six different brands of tea have been collected from local market in Ethiopia (Addis Ababa city). have been analyzed by a detection system consisting of High Purity Germanium (HPGe) detector and multichannel analyzer. The average activity concentrations were nuclide M D A report 238U, 232Th and 40 K respectively. The mean values were found 3.66$ \\pm$0.47, 18.28$\\pm $2.4 and 582.59$ \\pm $29.64 Bq/kg respectively. The activity concentration of 40K is increasing faster than the other NORM for Tea. In order to evaluate the radiological hazard of the natural radioactivity, radium equivalent (Raeq ), the external hazard index (Hex), internal hazrd index (Hin) , the total absorbed dose rate (D), the annual effective dose equivalent (AEDE) have been calculated and compared with the international acceptable value.

Motivation & Objective

• To measure natural (²³⁸U, ²³²Th, ⁴⁰K) and artificial (¹³⁷Cs) radionuclide activity concentrations in tea samples from Addis Ababa markets.
• To evaluate radiological hazards associated with tea consumption using standard radiological indices.
• To compare measured activity concentrations and hazard indices with international safety standards.
• To assess the radiological safety of tea consumption in Ethiopia based on empirical data.
• To determine if tea poses a health risk due to natural or artificial radioactivity in the local food chain.

Proposed method

• Collected six tea samples from local markets in Addis Ababa and dried them at 150 °C to constant mass.
• Sealed samples in 0.5 L Marinelli beakers and allowed to reach secular equilibrium with ²²⁶Ra decay products over 30 days.
• Performed gamma-ray spectroscopy using a high-purity germanium (HPGe) detector coupled with a multichannel analyzer and Genie 2000 software.
• Calculated activity concentrations using net count rates, gamma transition probabilities, detector efficiency, and sample weight via the formula: A = N / (Pγ × ε × W).
• Computed radiological hazard indices: radium equivalent (Raeq), external (Hex) and internal hazard indices (Hin), absorbed dose rate (D), and annual effective dose equivalent (AEDE).
• Applied standard equations: D = 0.427ARa + 0.623ATh + 0.043AK; AEDE = D × 0.7 Sv/Gy × 0.2 × 8760 h/y; Raeq = ARa + 1.43ATh + 0.077AK.

Experimental results

Research questions

• RQ1 What are the activity concentrations of ²³⁸U, ²³²Th, ⁴⁰K, and ¹³⁷Cs in tea samples from Addis Ababa markets?
• RQ2 How do the measured radiological hazard indices (Raeq, Hex, Hin) compare to international safety thresholds?
• RQ3 What is the annual effective dose equivalent from tea consumption, and does it exceed the 1 mSv/year limit?
• RQ4 Are there significant variations in radioactivity levels among different tea brands?
• RQ5 Is there any presence of artificial radionuclides such as ¹³⁷Cs in the tea samples?

Key findings

• The average activity concentration of ²³⁸U in tea samples was 3.66 ± 0.47 Bq/kg, well below the recommended limit of 35 Bq/kg.
• The average ²³²Th activity concentration was 18.28 ± 2.4 Bq/kg, below the acceptable limit of 40 Bq/kg.
• The average ⁴⁰K activity concentration was 582.59 ± 29.64 Bq/kg, exceeding the typical world average of 400 Bq/kg but still within safe radiological limits.
• Radium equivalent activity (Raeq) averaged 75.53 Bq/kg, significantly below the international limit of 370 Bq/kg.
• The external hazard index (Hex) averaged 0.19, and the internal hazard index (Hin) also averaged 0.19, both well below the safe threshold of 1.0.
• The annual effective dose equivalent (AEDE) ranged from 43.43 to 48.82 μSv/y, with an average of 46.62 μSv/y, well under the 1 mSv/year public dose limit.
• No artificial radionuclides, including ¹³⁷Cs, were detected in any of the tea samples.