Movement of Radioactive Isotopes in Yellow Birch and White Pine as Detected With a Portable Scintillation Counter

Movement of rubidium86 and calcium45 injected into the trunks of yellow birch and white pine was followed with a newly-developed portable scintillation counter. Maximum rate of upward movement of the rubidium86 in the xylem of yellow birch approximates one foot per minute along a narrow channel spiralling upward (usually dextrally) from the point where the isotope was first introduced. Movement in decadent yellow birch was very slow with an apparent increase of permeability of the bark tissue as indicated by lateral diffusion of the isotope. In October no upward movement was discerned in healthy trees but rather an active downward translocation in the phloem.