▁the ▁ 1 9 6 3 ▁Part ial ▁Test ▁Ban ▁Tre aty , ▁in ▁which ▁D ys on ▁was ▁involved ▁and ▁which ▁he ▁supported , ▁permitted ▁only ▁under ground ▁nuclear ▁weapons ▁testing , ▁and ▁the ▁project ▁was ▁abandoned ▁in ▁ 1 9 6 5 . ▁ ▁In ▁ 1 9 5 8 ▁D ys on ▁was ▁a ▁member ▁of ▁the ▁design ▁team ▁under ▁Edward ▁T eller ▁for ▁T RI GA , ▁a ▁small , ▁inher ently ▁safe ▁nuclear ▁re actor ▁used ▁throughout ▁the ▁world ▁in ▁hosp it als ▁and ▁univers ities ▁for ▁the ▁production ▁of ▁medical ▁is ot op es . ▁ ▁In ▁ 1 9 6 6 , ▁independently ▁of ▁Elli ott ▁H . ▁Lie b ▁and ▁Walter ▁Th ir ring , ▁D ys on ▁and ▁Andrew ▁Len ard ▁published ▁a ▁paper ▁prov ing ▁that ▁the ▁Paul i ▁ex clusion ▁principle ▁plays ▁the ▁main ▁role ▁in ▁the ▁stability ▁of ▁bulk ▁matter . ▁Hence ▁it ▁is ▁not ▁the ▁elect romagnet ic ▁rep ulsion ▁between ▁outer - shell ▁orb ital ▁electrons ▁that ▁prevents ▁two ▁stack ed ▁wood ▁blocks ▁from ▁co ales cing ▁into ▁a ▁single ▁piece , ▁but ▁the ▁ex clusion ▁principle ▁applied ▁to ▁electrons ▁and ▁pro tons ▁that ▁generates ▁the ▁classical ▁macro scop ic ▁normal ▁force . ▁In ▁cond ensed ▁matter ▁physics , ▁D ys on ▁also ▁anal ys ed ▁the ▁phase ▁transition ▁of ▁the ▁Is ing ▁model ▁in ▁one ▁dimension ▁and ▁spin ▁waves . ▁ ▁D ys on ▁also ▁did ▁work ▁in ▁a ▁variety ▁of ▁topics ▁in ▁mathematics , ▁such ▁as ▁topology