Mook has conducted neutron scattering research on a broad spectrum of materials. He is best known for his pioneering research on the magnetic excitations of transition metal ferromagnets and the observation of itinerant electron effects in these materials.
For applying molecular beam techniques to study chemically reactive collisions, helping to lay the foundation for the present field of chemical dynamics, and for pioneering studies in accelerator-based atomic physics, ion-solid interactions, and the channeling of ions, electrons and positrons in crystalline solids.
For discoveries of fundamental importance in mammalian genetics, as well as for studies of genetic and developmental effects in mice, which have provided a broad basis for assessment of the genetic risk to humans from radiation and chemicals, including the development of genetic and early developmental tests now used worldwide.
For original studies of the genetic effects of radiation in mammals. A world authority on mammalian mutagenesis, he and co-workers provided the experimental basis for estimating the genetic hazards of radiation to man and for the corresponding recommendations of national and international standards bodies