How long will it take for half of bismuth-214 to decay to lead? (refer to the uranium-238 decay chain series.)

5 min
13 min
20 min
27 min

Answer is: 20 min.

Bismuth 214 decay mode to lead is beta minus decay and alpha decay.

Beta decay is radioactive decay in which a beta ray and a neutrino are emitted from an atomic nucleus.

There are two types of beta decay: beta minus and beta plus. In beta minus decay, neutron is converted to a proton and an electron and an electron.

Alpha decay is radioactive decay in which an atomic nucleus emits an alpha particle (helium nucleus) and transforms into an atom with an atomic number that is reduced by two and mass number that is reduced by four.