Namal (Gamma abundance: 35.6%) of its daughter

Namal Lake sediment samples
were measured on fully integrated HPGe based (CANBERRA, USA) gamma
spectrometer. For radioactivity measurement, the sediment samples were analyzed
with Gamma Spectrometer consisting of ORTEC GMX60P4-95-A end-window type
coaxial High-purity Germanium (HPGe) detector coupled with ORTEC
TRUMP-PCI_Multi-channel analyzer.. Detector photo peak relative efficiency was
60% with energy resolution (FWHM) of 2.3 KeV at 1.33 MeV Co-60 2.3 KeV at 1.
Spectroscopy amplifier was ORTEC model 672. Recorded spectra were evaluated
with Gamma Vision 6.2 software package. To reduce gamma ray background, the
detector was shielded by 14 cm thick lead wall with a fixed bottom and sliding
cover. The lead shield contained an inner lining of 0.5 cm copper to absorb
lead X-rays.

Ra-226
concentration was determined by analyzing its peaks at transition energy of
185.9 KeV that has gamma abundance of 3.28% 160(Nada and Ibrahim, 2013) and at 351.9 KeV (Gamma abundance: 35.6%)
of its daughter nuclide, Pb-214 in U-238 decay series after 161Ndontchueng et al., (2013). As Ra-228
belongs to the decay series of Th-232, does not emit suitable gamma rays, its
determination was carried out through its daughter products in the decay series
Ac-228 at 911 KeV with an emission probability of 29% 162,163(Semkow et al., 2002; Vasile and Benedik,
2008) and Tl-208 at 583.2 KeV with an emission probability of 84.5% 164(Ndontchueng et al., 2013). Peaks
obtained at the energy values of 1460 KeV 165(Wo and Ahmad, 2008) and 661.66 KeV 166(Hamzah et al., 2012) were analyzed for the determination of 40K
and 137Cs activity, respectively. Measurements were performed with
identical geometries as those of the reference standard sources that were also
used for energy and efficiency calibration of the Gamma Spectrometer. Standard
reference material was soil IAEA- Vienna for World-Wide Open Proficiency Test
(Table-3.2). Both standard and sample jars were placed on detector top and
analyzed for 64800 seconds (18 hrs).

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