The third

Introduction. ***"Trit(i)um".*** * is a radioactive isotope of hydrogen with mass number 3 and atomic number 4. The compound word arose from the three roots of the Old Russian "tri", meaning "three", and "-um", which in this case does not mean a suffix, but a root of a negative degree of comparison.*

**Triton isotope**. Treat. — radiochemical element H (hydrogen) with the symbol Tr and atomic mass 2 and atomic number **13.** Due to the noticeable