<?xml version="1.0" encoding="utf-8"?><mads xmlns="http://www.loc.gov/mads/" xmlns:mods="http://www.loc.gov/mods/v3" xmlns:xlink="http://www.w3.org/1999/xlink" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://www.loc.gov/mads/
mads.xsd"><authority><topic authority="http://AATesaurus.cultura.gencat.cat/aat/getty_en">hydrogen isotopes</topic></authority><related type="broader"><topic>hydrogen and hydrogen isotopes</topic></related><variant type="other"><topic>hydrogen isotope</topic></variant><variant type="other"><topic>isotopes of hydrogen</topic></variant> <note xml:lang="en"><![CDATA[ Chemical elements of hydrogen having the same atomic number but different mass. Three of them are naturally occuring: 1H (protium), 2H (deuterium), and 3H (tritium). ]]></note></mads>