X-Ray and Gamma Ray Spectrometers for Environmental Studies in Tanzania

The book titled, X-Ray and Gamma Ray Spectrometers for Environmental Studies in Tanzania is written with the aim of disseminating knowledge about the Gamma and x-rays, detectors, the measurements and the results of a research work done. These include Shell Fish in the vicinity of the port of Zanzibar, Vegetables and radionuclides of polluted air, all in Tanzania.

The X-ray analysis in its Energy Dispersive X-ray fluorescence (EDXRF) and Wavelength Dispersive X-ray fluorescence (WDXRF) techniques for investigations of different types of samples are described. Samples with radionuclides have been analysed by Gamma-ray Spectroscopy. The process in the radionuclides begins with the nucleus of an unstable atom losing energy by emitting radiation. The elements or isotopes that emit radiation and go through radioactivity are known as radioactive elements. There are many of these particles in the air, water and even food that we eat. The aim of chapter one is to highlight the procedures, methodologies and facilities that are used in the analysis of the coming chapters.

The report on the existence of a link between seafood and toxic heavy metals in human beings is given. The aim of this chapter is to assess the metal concentration of shellfish along the Sea Port of Zanzibar. The shellfish include; oysters, mussels, clams and crabs. They were collected at the Sea Port and the concentrations were determined using Energy Dispersive X-ray Fluorescence (EDXRF). In Zanzibar, the major source of food for a large number of populations comes from the sea like many coastal area residents. Concentrations range in clams, crabs and for Cr, Mn, Fe, Ni, Cu, Zn, Cd and As were found. The concentrations of heavy metals in most different species of shellfish could be attributed to water from sewage, marine activities, paints and human activities from the ship.

Chapter three reports on the results of vegetables from Dar es Salaam are given using Wavelength Dispersive X-ray fluorescence (WDXRF). The sample analyzer machine is equipped with an Rh anode tube with spot focus operating under vacuum conditions. The operating voltages vary from 20 kV to 60 kV with current from 50 mA to 5 mA. The characteristic x-rays from the sample were collimated before arriving at the analyzing crystal under a vacuum of 0.05 mB and detected using a proportional counter and NaI (Tl) x-ray detector biased at -1000V. The net peak is as of the characteristic lines was determined using a non-linear least square fitting procedure. The whole detection and crystal system was shielded by a 10 mm lead shield. Analysis time ranged between 20-50 seconds for each element and about 100 for the standard sample. Elements in the material range from C, N, O, Na, Mg, Al, Si, P, S, Cl, K, Ca, Ti, Ni, Mn, Fe, Cu, Zn, Br, Rb, and Sr. The values obtained are within range of those published as essential as foodstuff.

Chapter four of this book focuses on the activity concentrations data of radionuclides 7Be and 212Pb. These are from the CTBTO radionuclides monitoring station located in Dar es Salaam where for the first time is measured and analyzed. In Tanzania, the data were used together with the meteorological one to investigate the mechanism that governs radionuclide concentration levels in the atmosphere. The two radionuclides of different origins showed different periodic patterns of atmospheric concentration for the past 11 years (2008 – 2018). No correlation was found between 7Be and 212Pb activity concentration. This suggests that the surface air concentration between 212Pb (was a terrestrial radionuclide) and 7Be (was cosmogenic radionuclide), was affected differently by local conditions of atmospheric processes. The mean values of both 7Be and 212Pb were higher in dry seasons and lower in rain seasons due to vertical mixing and greater deposition of radionuclides. It was also observed that, both 7Be and 212Pb decrease with the increase in rainfall and humidity.