PEN dosimeters are direct reading radiation dosimeters that measure and display accumulated dose of gamma and x-ray exposure. They are designed to be rugged and reliable, and are often used in military and industrial applications to monitor radiation exposure. The dosimeters typically consist of a metal clip that attaches to a pocket or other object for easy monitoring, and are hermetically sealed and immersion proof for durability. Overall, PEN dosimeters provide accurate measurements of radiation exposure, making them an important tool for protecting personnel in potentially hazardous environments.