  It is believed that type II radio bursts are generated by shock waves. In
order to understand the generation conditions of type II radio bursts, in this
paper, we analyze the physical parameters of a shock front. The type II radio
burst we selected was observed by Siberian Solar Radio Telescope (SSRT) and
Learmonth radio station and was associated with a limb CME occurring on 2014
January 8 observed by the Atmospheric Imaging Assembly (AIA) on board the Solar
Dynamics Observatory (SDO). The evolution of the CME in the inner corona
presents a double-layered structure that propagates outward. We fit the outer
layer of the structure with a partial circle and divide it into 7 directions
from -45$^\circ$ to 45$^\circ$ with an angular separation of 15$^\circ$. We
measure the outer layer speed along the 7 directions, and find that the speed
in the direction of -15$^\circ$ with respect to the central direction is the
fastest. We use the differential emission measure (DEM) method to calculate the
physical parameters at the outer layer at the moment when the type II radio
burst was initiated, including the temperature ($T$), emission measure ($EM$),
temperature ratio ($T_{d}/T_{u}$), compression ratio ($X$), and Alfv\'en Mach
number ($M_{A}$). We compare the quantities $X$ and $M_{A}$ to that obtained
from band-splitting in the radio spectrum, and find that this type II radio
burst is generated at a small region of the outer layer that is located at the
sector in 45$^\circ$ direction. The results suggest that the generation of type
II radio bursts (shock) requires larger values of $X$ and $M_{A}$ rather than
simply a higher speed of the disturbance.
