Question

1. Tritium (3H) decays by negative beta decay with a half-life of 12.26y.
   1. To what nucleus does 3H decay to – show the equation for the decay mode;
   2. Calculate the number of Curies of activity in 1g of 3H.

Answer 1

In negative beta decay () decay The mass number (A) remains same but atomic number increase by 1

in negative beta decay 1 of the neutron is changing to 1 proton , electron and an anti-neutrino

General expression for negatron emission ( negative beta decay) is given by

Here we have Tritium

A=3 and Z=1 so

So the nucleus to which the Tritium transforms by negative decay is Helium (³He)

PART B

Activity is given by the formula

where R is the activity in Becquerel

N is the number of atoms/nucleus remaining

is the decay constant

Given half-life of tritium t_1/2 as 12.26 years

we know

so

Given 1 gram of tritium number of atoms in 1 gram of tritium is

Atomic massof tritium is 3 amu

therefore

Activity

Activity in terms of unit curie (Ci) is  

Therefore Activity of 1gram tritium is