With no explanation, label text_A→text_B with either "not_related" or "related".
text_A: North Korea is bordered by China.
text_B: Iron-55 or 55Fe is a radioactive isotope of iron with a nucleus containing 26 protons and 29 neutrons .. radioactive isotope. radioactive isotope. iron. iron. nucleus. atomic nucleus. protons. protons. neutrons. neutrons. It decays by electron capture to manganese-55 and this process has a half-life of 2.737 years .. electron capture. electron capture. manganese-55. manganese-55. The emitted X-rays can be used as an X-ray source for various scientific analysis methods , such as X-ray diffraction .. X-ray. X-ray. X-ray diffraction. X-ray diffraction. Iron-55 is also a source for Auger electrons , which are produced during the decay .
not_related.