  We have investigated the stability limits of small spin-polarized clusters
consisting of up to ten spin-polarized tritium T$\downarrow$ atoms and the
mixtures of T$\downarrow$ with spin-polarized deuterium D$\downarrow$ and
hydrogen H$\downarrow$ atoms. All of our calculations have been performed using
the variational and diffusion Monte Carlo methods. For clusters with
D$\downarrow$ atoms, the released node procedure is used in cases where the
wave function has nodes. In addition to the energy, we have also calculated the
structure of small clusters using unbiased estimators. Results obtained for
pure T$\downarrow$ clusters are in good accordance with previous calculations,
confirming that the trimer is the smallest spin-polarized tritium cluster. Our
results show that mixed T$\downarrow$-H$\downarrow$ clusters having up to ten
atoms are unstable and that it takes at least three tritium atoms to bind one,
two or three D$\downarrow$ atoms. Among all the considered clusters, we have
found no other Borromean states except the ground state of the T$\downarrow$
trimer.
