code: private boolean isMajorIsotope(int number, int mass) {
          try {
              IIsotope isotope = Isotopes.getInstance().getMajorIsotope(number);
              return isotope != null && isotope.getMassNumber().equals(mass);
          } catch (IOException e) {
              return false;
          }
      }
docs: Utility to determine if the specified mass is the major isotope for the given atomic number.
  
  @param number atomic number
  @param mass   atomic mass
  @return the mass is the major mass for the atomic number