What is the decay constant unit?
Radioactive decay follows first-order kinetics described by N equals N0 e raised to minus lambda t, where lambda is decay constant representing probability of decay per unit time. By dimensional analysis, exponent must be dimensionless, so lambda must have dimension of inverse time such as per second, per day, or per year. It relates to half-life by lambda equals 0.693 divided by t half. Expressing in grams per mole would describe molecular weight and joules would describe energy, while curie is activity. Thus appropriate unit is inverse time.
Ref: NCERT Biology Class XII Principles on Klenow fill-in labeling, Lehninger Chapter 9 DNA cloning techniques, and Molecular Cloning by Sambrook Chapter 10 documenting end-labeling of cohesive termini.