the total mass of a helium nucleus is not equal to the mass of its individual parts because of mass defect.
the total mass of a helium nucleus is not equal to the mass of its individual parts because of mass defect.
why is the total mass of a helium nucleus not equal to the mass of its individual parts?
mass defect
mass defect is the difference between the mass of an object and the sum of the masses of its constituent particles. discovered by albert einstein in 1905, it can be explained using his formula "e" = "mc", which describes the equivalence of energy and mass. the decrease in mass is equal to the energy given off in the reaction of an atom's creation divided by "c". by this formula, adding energy also increases mass (both weight and inertia), whereas removing energy decreases mass. for example, a helium atom containing four nucleons has a mass about 0.8% less than the total mass of four hydrogen nuclei (which contain one nucleon each). the helium nucleus has four nucleons bound together, and the binding energy which holds them together is, in effect, the missing 0.8% of mass.
nuclear binding energy
these exotic atoms can be produced by simply mixing antiprotons with ordinary helium gas; the antiproton spontaneously removes one of the two electrons contained in a normal helium atom in a chemical reaction, and then begins to orbit the helium nucleus in the electron's place. this will happen in the case of approximately 3% of the antiprotons introduced to the helium gas. the antiproton's orbit, which has a large principal quantum number and angular momentum quantum number of around 38, lies far away from the surface of the helium nucleus. the antiproton can thus orbit the nucleus for tens of microseconds, before finally falling to its surface and annihilating.
antiprotonic helium