  Dielectric spectroscopy is used to investigate fundamental length scales of
146 bp short-fragment (nucleosomal) dilute Na-DNA solutions. Two relaxation
modes are detected: the high- and the low-frequency mode. Dependence of the
corresponding length scales on the DNA and on the (uni-valent) salt
concentration is studied in detail, being different from the case of long,
genomic DNA, investigated before. In low added salt regime, the length scale of
the high-frequency mode scales as the average separation between DNAs, though
it is smaller in absolute magnitude, whereas the length scale of the
low-frequency mode is equal to the contour length of DNA. These fundamental
length scales in low added salt regime do not depend on whether DNA is in a
double stranded or single stranded form. On the other hand, with increasing
added salt, the characteristic length scale of low-frequency mode diminishes at
low DNA concentrations probably due to dynamical formation of denaturation
bubbles and/or fraying in the vicinity of DNA denaturation threshold.
