isotopes

Given a predicate that represents a relationship or action between entities, generate a one-sentence description explaining its meaning.  
# Instructions
Focus on describing the relationship, not the entities themselves. 
# Response Format
Begin the description with \' Indicates...\'

Predicate: isotopes

Indicates that two or more atomic nuclei are variants of the same chemical element that differ in neutron number (and thus mass number) but share the same number of protons.