After absorbring a slowly moving neutron of Mass mN (momentum $\approx$ 0) a nucleus of mass M breaks into two nuclei of masses $m_1$ and $5m_1$ ($6\, m_1 = M + mN$ ) respectively. If the de Broglic wavelength of the nucleus with mass $m_1$ is $\lambda$, the de Broglie wevelength of the nucleus will be: