Emission of light charged nuclei in the n-thermal fission of 239Pu

Various charged nuclei in the n-thermal fission of 239Pu have been detected by using a telescope consisting of two semiconductor detectors. The identified particles with the relative features are reported: Long-range alpha particles. During three independent runs 14330 particles have been detected. To evidence the low part of the energetic spectrum no absorber has been interposed between the target and the telescope: nevertheless a triple fast coincidence has been realized with the fragment and telescope detectors pulses to allow the particles to be revealed. The observed energetic interval is from 7 to 28 MeV. The most probable energy is 16 ± 1 MeV with a FWHM. of 9 MeV. The given resolution is due to the continuous damage induced on the DE detector by the fission fragments and natural alphas of 239Pu. The energy spectrum is symmetrically distributed around the peak energy spectrum of Gaussian shape. Helium-six. 250 of these events have been identified. The observed energy spectrum extends from 8 to 18 MeV with the most probable energy at 12 ± 1 MeV and an FWHM. of 7 MeV. The yield relative to 100 alphas is 1.7 ± 0.2. Helium-three. These particles have been detected during two runs with a Ni absorber interposed between the telescope and the target. The yield relative to 100 alphas is 0, 9. Owing to overlapping of the alpha-particle tail, this yield is to be considered as an upper limit. The peak energy is 16 ± 1 MeV but probably the energy spectrum is influenced by the alpha tail. Tritons. The observed energy interval is from 5.5 to 11 MeV. The peak energy is 8.2 ± 0. 7 MeV with an FWHM. of 6 ± 1 MeV. The yield relative to 100 alphas is 5.5 ± 0.5. Deuterons. Evidence has been obtained of such particles in the energy range from 4 to 7 MeV. The lower limit of the yield relative to 100 alphas is 0.3. (author)