87Sr has 38 protons and 49 neutrons.
87Sr is a stable isotope.
The mass excess of 87Sr is -84880.07643 with an uncertainty of ±0.00513.
The mass was measured using a Penning Trap and the related equations include:
Influence Equations
58.9% 87Sr-86Kr1.012 1
41.1% 87Sr-84Kr1.036 1
Reference
1. R. Rana, M. Hocker, E.G. Myers (2012) Atomic masses of strontium and ytterbium
Physical Review A 86(5)
https://journals.aps.org/pra/abstract/10.1103/PhysRevA.86.050502