Answer:
Gallium memory aid
6-7-7-8-9-0 (add the extra 7)
Galium (atomic # 67)
half-life (78 hours)
energy (90 keV)
BUT for each energy level add a 0 then 1 then a 2 then a 3 in front of it
energy 1 : add a 0 = 090 kEv = 90 keV
energy 2: add a 1 = 190 keV
energy 3: add a 2 = 290 keV
energy 4: add a 3 = 390 kEv
