Five hot springs called ‘Abegarm-e-Mahallat’, located in the central part of Iran, have a mean water temperature of 46 ± 1°C and are used by visitors as spas. This is an area of high natural radiation background due to the presence of ²²⁶Ra and its decay products in the deposited travertine (CaCO₃). The mean concentration of ²²⁶Ra in these hot springs, measured by the emanation method, ranged from 0.48 ± 0.05 to 1.35 ± 0.13 Bq l⁻¹. ²²²Rn concentrations measured in the hot springs using a liquid scintillation counter ranged from 145 ± 37 to 2731 ± 98 Bq l⁻¹. Mean radon concentrations in air were 487 ± 160 and 15.4 ± 2.7 Bq m⁻³ for indoor and outdoor, respectively. Radiation levels above that of normal background (∼100 nGy h⁻¹) were mainly limited to the Quaternary travertine formations in the vicinity of the hot springs. The results of environmental radiological studies in this region are presented and discussed.

IGBT is widely applied in converter circuit because of its highly switching speed and easy driving, which brings severe electromagnetic interference (EMI). High and low of the gate drive circuit performance affects the level of EMI. This paper proposed a novel three stage gate control technology for IGBT. It is based on an optimal combination of several requirements necessary for good switching performance under snubberless operation conditions. The control scheme specifically combines together the slow drive requirements for low electromagnetic interference and switching stress and the fast drive requirements for high-speed switching and low switching losses. The gate drive can also effectively dampen current and voltage oscillations generated during turn-on and turn-off respectively. This paper looks at the conflicting requirements of the conventional gate drive circuit design and demonstrates using experimental results that the proposed three-stage gate drive scheme obtains an optimal between switching speed, power dissipation and electromagnetic interference