No, the atomic mass number, also known as the mass number or nucleon number, is always a whole number. The mass number represents the total number of protons and neutrons in an atomic nucleus. Since both protons and neutrons have nearly equal masses and each has a mass of approximately 1 atomic mass unit (u), the mass number is the sum of these whole numbers.
For example, if an atom has 6 protons and 8 neutrons, the mass number would be 6 + 8 = 14. It is not possible to have a fraction or a decimal in the mass number because it represents a count of discrete particles (protons and neutrons) in the nucleus.