The long-time reactor irradiation of biological material at reduced temperature

When biological material in closed quartz ampoules is irradiated gaseous reaction products are formed as a result of radiation damage and thermal decomposition. The pressure thus created in the ampoules puts a limit to the time of irradiation or the sample mass and thereby to the detection limit of neutron activation analysis. The investigation will show how the internal pressure of the ampoules is reduced by cooling the sample containers in a nitrogen bath during irradiation so that a number of trace elements also in fresh biological material can be detected by means of neutron activation analysis with long-time irradiation. It will further contain a methodical study of the mechanical strength of quartz ampoules used as sample containers and the change in sample temperature using different sample containers and cooling through different media. The results of two irradiation studies of biological material in the low temperature irradiation unit of the reactor Melusine of the CENG Grenoble will be discussed.