The de Broglie wavelength \( \lambda \) is given by:
\[
\lambda = \frac{h}{p}
\]
where \( p \) is the momentum of the particle. The momentum \( p = mv \), and for a particle moving at \(\frac{1}{10}\) of the velocity of light:
\[
v = \frac{c}{10}
\]
Thus, the momentum is:
\[
p = m \times \frac{c}{10} = \frac{mc}{10}
\]
Substituting this into the de Broglie formula:
\[
\lambda = \frac{h}{\frac{mc}{10}} = \frac{10h}{mc}
\]