Five Eyes, refers to an intelligence sharing agreement between the United States, Canada, United Kingdom, Australia, and New Zealand, essentially all the countries which share a common English-speaking heritage.
When Jack is coming up with super powers that the radiation could give them, he says Mac would get telekinesis, because, "You're practically Professor X as it is." Lucas Till played Havoc in X-Men movies X-Men: First Class (2011), X-Men: Days of Future Past (2014) and X-Men: Apocalypse (2016).
In the opening scene, Mac & Jack were wearing a camouflage or "Ghillie" suit. These suits originated in Scotland, and were used to catch poachers or predators, by blending into the environment.
The date of the Chernobyl Disaster in Ukraine is April 26, 1986.
To reiterate, Mac said that Strontium-90 dissipates in about 30 years, and depending on the isotope of Plutonium, the half-life is anywhere from 80-24,000 years.