 Some radioactive isotopes of xenon , for example , 133Xe and 135Xe , are produced by neutron irradiation of fissionable material within nuclear reactors . 135Xe is of considerable significance in the operation of nuclear fission reactors . 135Xe has a huge cross section for thermal neutrons , 2 @.@ 6 × 106 barns , so it acts as a neutron absorber or " poison " that can slow or stop the chain reaction after a period of operation . This was discovered in the earliest nuclear reactors built by the American Manhattan Project for plutonium production . Fortunately the designers had made provisions in the design to increase the reactor 's reactivity ( the number of neutrons per fission that go on to fission other atoms of nuclear fuel ) . 135Xe reactor poisoning played a major role in the Chernobyl disaster . A shutdown or decrease of power of a reactor can result in buildup of 135Xe and getting the reactor into the iodine pit . 
 Some radioactive isotopes of xenon , for example , 133Xe and 135Xe , are produced by neutron irradiation of fissionable material within nuclear reactors . 135Xe is of considerable significance in the operation of nuclear fission reactors . 135Xe <a href='got' title='1'><mark>has</mark></a> a huge cross section for thermal neutrons , 2 @.@ 6 × 106 barns , so it <a href='uninflect' title='2'><mark>acts</mark></a> as a neutron absorber or " poison " <a href='null_relcl' title='3'><mark>that</mark></a>can slow or stop the chain reaction after a period of operation . This was discovered in the earliest nuclear reactors built by the American Manhattan Project for plutonium production . Fortunately the designers <a href='been_done' title='4'><mark>had</mark></a> made provisions in the design to increase the reactor <a href='null_genetive' title='5'><mark>'s</mark></a>reactivity ( the number of neutrons per fission <a href='null_relcl' title='6'><mark>that</mark></a>go on to fission other atoms of nuclear fuel ) . 135Xe reactor poisoning played a major role in the Chernobyl disaster . A shutdown or decrease of power of a reactor can result in buildup of 135Xe and getting the reactor into the iodine pit . 
Some radioactive isotopes of xenon , fir example , 133Xe and 135Xe , are produced by neutron irradiation of fissionable material within nuclear reactors . 135Xe is of considerable significance in da operation of nuclear fission reactors . 135Xe got a huge cross section for thermal neutrons , 2 @.@ 6 × 106 barns , so it act as a neutron absorber or " poison " can slow or stop tdachain reaction after a period of operation . This was discovered in the earliest nuclear reactors built by thdamerican Manhattan Project fir plutonium production . Fortunately the designers done made provisions in the design to increase the reactor  reactivity ( the number of neutrons per fission go on to fission other atoms of nuclear fuel ) . 135Xe reactor poisoning played a major role in thedaernobyl disaster . A shutdown or decrease of power of a reactor can result in buildup of 135Xe and getting the reactor into the iodine pit .