at measure 6 , the soprano starts with the G so shouldn't the alto not go over the G till the next measure ? but you could see the alto is getting higher then the G through the measure.. is this a part interrupt ?
I believe you're discussing what is commonly called a voice overlap. A voice overlap occurs when, from one chord to the next, a voice moves into the register of a neighboring voice. In the example below, a voice overlap occurs on beat 4 because the bass is higher than the tenor was in the previous chord.
Your example would be a voice overlap if the chords moved immediately from beat 1 to beat 3. However, since your example has beat 2 between those two chords, it is no longer a voice overlap. Voice overlap occurs over the span of two chords. Since your example occurs over the span of three chords, it is acceptable.
Voice overlap is not to be confused with a voice crossing, which is when voices move into the register of a neighboring voice in the same chord. In the example below, a voice crossing occurs on beat 4 when the soprano line (the stemmed-up E) moves below the alto (the stemmed-down A).