JULY 6--An explosion and three-alarm fire rips through the experimental hall of the Cambridge Electron Accelerator, injuring eight Harvard and M.I.T. scientists and technicians and causing at least $1 million in damage. The explosion blew the roof off the circular experimental hall and severely damaged the bubble chamber then being filled with 100 gallons of liquid hydrogen.

JULY 7--Preliminary investigation indicates that 95 gallons of liquid hydrogen in the bubble chamber were expelled safely and that hydrogen in the chamber filling system may have caused the explosion.

JULY 11--The Atomic Energy Commission, which provides funds for the accelerator operation, begins its investigation of the blast.

JULY 18--CEA officials predict that work will resume in parts of the experimental hall by November and confirm that the bubble chamber will be rebuilt.

JULY 20--Arthur C. Reid, 19, a laboratory technician, dies of injuries suffered in the explosion.

JULY 21--An AEC investigating team issues an interim report saying that the cause of the explosion has not been found.

AUGUST 22--Investigators say they are near to reporting on the blast's causes.