What is the source of longwave infrared radiation? View Available Hint(s) O Longwave infrared radiation is produced when the nucleus of an atom splits into smaller parts. Longwave infrared radiation is caused by the radioactive decay of an unstable atomic nucleus as it loses energy. Longwave infrared radiation comes from the process of joining together two or more atomic nuclei to form a single heavier nucleus. O Longwave infrared radiation is emitted from Earth's surface. Longwave infrared radiation is emitted from the Sun