The maximum and the minimum diameter of the disk were
measured, and the overall diameter was determined by the average
of the maximum and minimum values. Rectangular wood samples
were cut from the disks along a straight line via the pith. In the
Kawamata area, two sapwood samples (2e3 cm wide 2e3 cm
long 5 cm thick) were obtained from the both sides of the disk,
and one heartwood sample was obtained at the center of the disks.
In the Yamakiya area, the rectangular wood samples (1 cm
wide 3 cm long 5 cm thick) were obtained from the edge to the
center of the disk in succession. Samples were dried at 105 C for
24 h, and 137Cs concentration per kilogram of dry weight of wood
samples were measured with a Germanium semiconductor detector
(SEG-EMS: SEIKO EG&G Inc., GC2513: CANBERRA) using a 100-
ml container, and measured with a NaI Spectrometer
(2480WIZARD2: Perkin Elmer) using a 20-ml container with the
accumulation time from 3600 to 80,000 s. The measurement error
by the Germanium semiconductor detector was less than 3e5 Bq
kg1
, and the relationships of 137C concentration measurement by
the Germanium semiconductor detector (CG) and by the NaI
Spectrometer (CN) were shown as a linear equation with slope of
unity (linear approximation: CN ¼ 1.0183 CG, R2 ¼ 0.9387). 137Cs
concentration was determined after decay compensation on March
15, 2011.