Optical systems for sensing radiation emissions from radiological and nuclear matter. An example system includes a light source, a light sensor, a processing device in signal communication with the light source and the light sensor, and a fiber optic cable that receives light from the light source and delivers light to the light sensor. The fiber optic cable includes an optical fiber core region surrounded by a cladding region. The optical fiber is a single mode optical fiber having a mode field diameter greater than 25 μm. The optical fiber cladding region includes a plurality of lengthwise holes positioned to provide single mode light propagation properties. The plurality of lengthwise holes have a diameter between 0.1-5 μm.