 After he had completed his doctoral study , he was offered a job at EG & G Corporation Energy Measurements in Goleta , California , to work on crystal growth . EG & G was a defense contractor of the United States government and dealt with sensitive information and science . In 1975 , this required Van den Berg to become a naturalized U.S. citizen . Van den Berg gathered years of research and management experience in the preparation of crystalline materials — in particular , the growth of single crystals of chemical compounds , and the investigation of associated defect chemistry and electronic properties . He became an international authority on vapor growth techniques with an emphasis on mercuric iodide crystals and its application in the nuclear industry as gamma ray detectors . During his work at EG & G , Van den Berg asked NASA for permission to conduct crystal growth experiments in space , which NASA approved . 
