FIRST STAGE OF AGGLOMERATION OF IRRADIATED HELIUM IN REFRACTORY METALS.

Thermal desorption spectrometry has been applied to the study of the agglomeration of irradiated helium in refractory metals - vanadium, niobium, molybdenum and tungsten. After single crystals are irradiated with 100 kev helium ions with fluences of 2 multiplied by 10**1**3 to 2 multiplied by 10**1**5 ions/cm**2 at room temperature, thermal desorption spectra and absolute partial pressure of reemitted helium are measured with a calibrated quadrupole mass filter. Values of helium dissociation energy are calculated by a computer-simulation method in the case of vanadium. With the aid of the values of dissociation energy obtained, desorption peaks are assigned to the trapped modes of irradiated helium. In the low-fluence irradiation experiments, helium atoms agglomerate in the stage of subsequent annealing.