the energy that an atomic system must acquire before a process (such as an emission or reaction) can occur

the energy that an atomic system must acquire before a process (such as an emission or reaction) can occur

the energy that an atomic system must acquire before a process (such as an emission or reaction) can occur

the energy that an atomic system must acquire before a process (such as an emission or reaction) can occur

the point in time at which something must be completed

the point in time at which something must be completed

the point in time at which something must be completed

the point in time at which something must be completed

the point in time at which something must be completed

the point in time at which something must be completed