Groundwater age,defined as the mean subsurface residence time spent isolated from the atmosphere,is of crucial significance for managing water resources and industrial waste.It is also very useful for understanding subsurface contaminant transport,and for paleoclimate reconstruction.It is an important parameter
Jie LiZhonghe PangGuo-Min YangJiao TianAmin L.TongXiang-Yang ZhangShui-Ming Hu
The Boltzmann constant kB is a fundamental physical constant in thermodynamics. The present CODATA recommended value of kB is 1.3806488（13） × 10^-23 J/K （relative uncertainty 0.91 ppm）, which is mainly determined by acoustic methods. Doppler broadening thermometry （DBT） is an optical method which determines kBT by measuring the Doppler width of an atomic or molecular transition. The methodology and problems in DBT are reviewed, and DBT measurement using the sensitive cavity ring-down spectroscopy （CRDS） is proposed. Preliminary measurements indicate that CRDS- based DBT measurement can potentially reach an accuracy at the 1 ppm level.
