'a radical turn' is correct and can be used in written English.
You can use it to refer to a major change or shift in some situation, for example: "The introduction of a new policy has taken the company in a radical turn."
His politics took a radical turn in 2006-2007.
But the new Graduate Transportation Design program has taken a radical turn from previous curricula.
They don't want to be told that such a radical turn to the right is not, in fact, necessary.
But the suggestion last summer that Tony Stark might be making a radical turn towards China never quite transpired.
After intermission, Mr. Woodiel said, the concert will take a "radical turn," offering contrasting versions of Scottish and Irish songs found among Jefferson's extensive collection of scores.
When Mao's policies began to take a radical turn, for instance, Deng ran a front-page editorial in People's Daily opposing "impetuosity".
His conversion signified a radical turning and a free acceptance of God's favour "in Christ".
The latest focuses on the 17th century, which he argues marked a radical turning point in human history.
It was decided that the next of these meetings – on 8 June 2014 – had to produce a radical turning point in Miliband's leadership.
Joe Louis, "the Brown Bomber", enjoyed the fervent support of Americans of all colours when he defended the same title against Germany's Max Schmeling in a fight billed as a contest between democracy and Nazism.Their successor, Mr Ali, a radical turned patriot, became a thoroughly establishment figure.
This marked something of a radical turning point: we'd gone from claiming land by clearing trees in the colonial era to claiming land by planting them.
