We're covering tunneling in my quantum mechanics class. I did a little bit of research and was surprised to find out that Gurney and Condon made one of the first practical application of quantum tunneling to accurately predict alpha decay of various radioactive elements. They describe alpha decay as alpha particles tunneling through the attractive potential barrier of the nucleus. I found three very interesting journal articles on the subject. The first is a historical summary by Condon. The second and third are the initial journal articles by Gurney and Condon in Nature and Physical Review. All three of these articles can be accessed for free from most university libraries.
EU Condon, Tunneling - How it all Started, Am. J. Phys., 46, 319, (1978)
Gurney and Condon, Wave Mechanics and Radioactive Disintegration, Nature, 122, 439, (1928)
Gurney and Condon, Quantum Mechanics and Radioactive Disintegration, Phys. Rev., 33, 127, (1929)