Abstract—: A spectrometer based on a Si(Li) detector has been tested by exposure to α particles with the aim of determining changes in the detector characteristics versus the fluence. As a result of 60-day measurements with a total fluence of 6.2 × 10⁹ α particles, it has been established that the dependence of the deterioration in the energy resolution of α-particle peaks on the fluence is described by a linear function with a slope of Δσ/ΔФ = (8.4 ± 0.4) × 10^–10 keV/α. The measured amplitude of the α-particle momentum decreases linearly with increasing fluence with a slope of (–4.8 ± 0.6) × 10^–9 keV/α. These effects do not prevent reliable discrimination between the signals from α particles and fission fragments until the fluence reaches a value of 10¹⁰ α particles when the Si(Li) detector is a part of a neutron source for detecting fission fragments.