the total number of neutrons and protons in the nucleus of a particular atom
WordReference Random House Learner's Dictionary of American English © 2025
WordReference Random House Unabridged Dictionary of American English © 2025
mass′ num′ber, [Physics.]
- Physicsthe integer nearest in value to the atomic weight of an atom and equal to the number of nucleons in the nucleus of the atom. Symbol: A
- 1920–25
Collins Concise English Dictionary © HarperCollins Publishers::
'mass number' also found in these entries (note: many are not synonyms or translations):
A, a
- actinium series
- antimony 124
- barium 140
- beta decay
- carbon 13
- cesium 137
- chlorine 36
- chromium 51
- cobalt 60
- heavy nitrogen
- iodine 131
- ionium
- isobar
- isomerism
- neutron number
- nucleon number
- nuclide
- packing fraction
- plutonium
- protium
- radioactinium
- radiocarbon
- thorium series
- uranium 235
- uranium 238
- uranium 239
- uranium series