Question

does critical mass has different ranges. i mean different packets of critical masses

Answer 1

Due to definition, critical mass is the smallest mass of a fissionable
material that will sustain a nuclear chain reaction at a constant level.
The point and therefore the mass where criticality occurs may be
changed
by modifying certain attributes such as fuel, shape, temperature,
density and the installation of a neutron-reflective substance.For given
conditions (shape, temperature etc.) there is single value of critical
mass.