Source code:
@Grab(group='org.openscience.cdk', module='cdk-bundle', version='2.9')
import org.openscience.cdk.interfaces.*;
import org.openscience.cdk.*;
IAtom atom = new Atom("C");
atom.setMassNumber(13)
atom.setNaturalAbundance(1.07)
atom.setExactMass(13.00335484)
println "Mass number: " + atom.getMassNumber()
println "Natural abundance: " + atom.getNaturalAbundance()
println "Exact mass: " + atom.getExactMass()
Output:
Mass number: 13
Natural abundance: 1.07
Exact mass: 13.00335484