High-energy particles are detected from spontaneous processes in an ultra-dense deuterium D(0) layer. Intense distributions of such penetrating particles are observed using energy spectroscopy and glass converters. Laser-induced emission of neutral particles with time-of-flight energies of 1-30 MeV u(-1) was previously reported in the same system. Both spontaneous line-spectra and a spontaneous broad energy distribution similar to a beta-decay distribution are observed. The broad distribution is concluded to be due to nuclear particles, giving straight-line Kurie-like plots. It is observed even at a distance of 3 m in air and has a total rate of 10(7)-10(10) s(-1). If spontaneous nuclear fusion or other nuclear processes take place in D(0), it may give rise to the high-energy particle signal. Low energy nuclear reactions (LENR) and so called cold fusion may also give rise to such particles. Copyright (C) 2015, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.