Water Content and Beta Ray Transmission of Various Leaves

The mass thickness and the moisture ratio of various plant leaves were measured with the beta radiation transmission method using a G-M detector and 14C source. Since beta rays transmitted by leaf are diffuse, the placement of the detector with respect to the leaf was a primary limiting factor on the transmitted beta rays that would be detected. It was recognized that the distance between leaf and detector or source, should be kept as short as possible. The transmission of beta rays decreased with increasing mass thickness of a leaf. The mass thickness of the leaf made the mass absorption coefficient almost independent of the nature of the leaf. Although the absorption curve was not linear under a wide range of the mass thickness, the curve was approximately linear for thin leaves. The low-energy beta ray source, such as 14C, is to be used only for thin leaves of mass thickness smaller than 20mg/cm2. On the contrary, the high-energy beta ray source, such as 204Tl, should be used for thick leaves of mass thickness larger than 30mg/cm2.