The largest geomagnetic disturbance caused by a coronal mass ejection (CME) of solar cycle 24 recorded on both 17 March and 22 June 2015 with minimum disturbance storm time values of −223 and −195 nT, respectively, was investigated. This study examines the effect of CME on Earth’s geomagnetic field, which includes the time derivatives of horizontal (H) and vertical (Z) components of the geomagnetic field and the rate of induction ΔZ/ΔH at African longitudes (AAE, MBO, HBK, HER, and TAM). The results demonstrated enhancement of dH/dt and dZ/dt in the daytime over the equatorial zone (AAE and MBO) and mid-latitudes (TAM, HER, and HBK) on 17 March 2015. Nighttime enhancement was observed on 22 June 2015 over the equatorial zones and mid-latitudes. Wavelet spectrum approach is used to investigate ΔZ/ΔH variation observed at AAE, MBO, HBK, HER, and TAM. The CME may have influence on time derivatives of geomagnetic field H, Z, and electromagnetic induction at the African longitudes, which may be associated with perturbations in electric fields and currents in the equatorial and low-latitude magnetic field linked with the changes in magnetospheric convection.
The study assessed the environmental impact of selected market waste dumpsites in soil samples in Ikorodu metropolis in order to determine the effect of the level of health hazard on the residents of Ikorodu community. The measurement was carried out using a Gamma ray Spectrometer NaI (TI)detector coupled to a Multichannel analyser for spectral analysis. Results revealed that the activity concentration of 40K in soil samples ranged from 14.84±1.07 BqKg−1 to 82.01±5.54 BqKg−1 with the highest found in Adamo Market and the lowest was found in Benson market. The activity concentration of 238U ranged from 0.029±0.05 BqKg−1 to 7.65±0.9 BqKg−1 with the highest found in Agunfoye Market and the lowest found in Benson Market. The activity concentrations of 232Th ranged from 1.68±0.14 BqKg−1 to 3.93±0.28 BqKg−1, the highest concentration was found in Agunfoye Market and the lowest was found in Ayangburen Market. The values were within the safety limit recommended by the United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR) with mean value of 13.5 - 69.8 BqKg−1. The Absorbed Dose Rate, Outdoor, Annual Effective Dose Rate, and the Internal and External Hazard Index was also calculated from the activity concentrations which shows that the absorbed dose rates due to gamma rays at 1m above the ground in the study area were within the range of 1.99 nGyh−1 to 7.06 nGyh−1 with an average of 4.08 nGyh−1 which is lower than the UNSCEAR average value of 59 nGyh−1. The annual effective doses are within the range of 0.00 to 0.01 mSvy−1 with an average value of 0.01 mSvy−1 which were lower when compared with the UNSCEAR value of 0.5 mSvy−1 and 0.07 mSvy−1 respectively. The External Hazard Index in the soil samples ranges from 0.01 to 0.04 with an average value of 0.02 and the Internal Hazard Index ranges from 0.01 to 0.06 with an average value of 0.03 both of which were below the permissible limit respectively, and less than 1. However, the values of the radiological parameters were below the UNSCEAR recommended international limits of 370Bq/kg and within the tolerance level indicating minimal radiological health burden on the people living in the study areas.
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