 After returning to Earth , Van den Berg continued to work on crystal growth experiments at EG & G in California and he became the head for the section of materials science . At a later time he moved to Florida to become a chief scientist at the Constellation Technology Corporation . At age 72 , he continued to work up to 40 hours a week and grow crystals , a process he compares to gardening . The crystals he grows ( <unk> Iodide crystals ) are used to make precision detectors for nuclear radiation . These detectors are used in medical applications , by the defense industry and the International Atomic Energy Agency . 
