Do you want to explain to me how it will DECAY to a heavier element.
Tritium is, chemically speaking, hydrogen. On the nuclear level, it consists of one proton and two neutrons. Therefore, it is not a stable nucleus; its half-life is 12.3 years. It decays to helium-3 by releasing an electron and an electron antineutrino. This turns one of the neutrons into a proton, thus leaving a nucleus with 2 protons and 1 neutron, which is helium-3.
Decay is not just heavy elements to lighter elements; it's also lighter elements to heavier ones..
For example, a deuteron (the nucleus of deuterium, one proton and one neutron--what most people think of as "heavy hydrogen") has an atomic mass of 2.013553. But if you add the mass of a proton (1.007276) and a neutron (1.008665), you get 1.007276 + 1.008665 = 2.015941. Subtract the actual mass of a deuteron from the sum of its parts, and you get: 2.015941 - 2.013553 = 0.002388. The "missing mass" is actually the binding energy of the deuteron (since mass and energy are the same by the formula E = MC^2). When the deuteron is split up, that energy is released.