What is this radical called? 
, as @songyuanyao expressed, is called 竹字头, 竹: bamboo.

篇, a quantifier, 一篇文章(an article), 一篇报道(a report), 一篇诗歌(a poem)

In ancient China, just as people of the other parts of the world did, used something instead of modern "paper" to write on, bamboo is frequently used as writing materials, it's cheap and easy to keep for a long time, people split bamboo into thin pieces, and join them together with lines, then engrave on those pieces and form a scroll, an unfolded scroll is 一篇, so that's why there is a "bamboo" on some characters like 篇.