light spectrum, observed in the Hessdalen lights might be explained through a dust plasma model. Radon decay produces alpha particles (responsible by helium emissions in spectrum) and radioactive elements such as polonium. In 2004, Teodorani showed an occurrence where a higher level of radioactivity on rocks was detected near the area where a large light ball was reported. Computer simulations show that dust immersed in ionized gas can organize itself into double helixes like some occurrences of the Hessdalen lights; dusty plasmas may also form in this structure. Another hypothesis explains Hessdalen lights as a product of piezoelectricity generated under specific rock strains, because many crystal rocks in Hessdalen valley include quartz grains which produce an intense charge density. Piezoelectricity In a 2011 paper, based on the dusty plasma theory of Hessdalen lights, Gerson Paiva and Carlton Taft suggested that piezoelectricity of quartz cannot explain a peculiar property assumed by the Hessdalen lights phenomenonthe presence of geometrical structures in its center. Paiva and Taft have shown a mechanism of light ball cluster formation in Hessdalen lights by nonlinear interaction of ion-acoustic and dusty-acoustic waves with low frequency geoelectromagnetic waves in dusty plasmas. The theoretical velocity of ejected light balls is about , in good agreement with the observed velocity of some ejected light balls, estimated at . The central ball is white, while the ejected balls that are observed are always green in colour. This is ascribed to radiation pressure produced by the interaction between very low frequency electromagnetic waves (VLF) and atmospheric ions (present in the central white-coloured ball) through ion-acoustic waves. O ions (electronic transition ), with green emission lines, are probably the only ones transported by these waves. Electronic bands of O ions occur in auroral spectra. The estimated temperature of Hessdalen lights is about . At this temperature, the rate coefficients of dissociative recombination will be for the oxygen ions, and for the nitrogen ions. Thus, in the Hessdalen lights plasma, the nitrogen ions will decompose more rapidly than oxygen ions. Only ionic species are transported by ion acoustic waves. Therefore, oxygen ions will dominate in the ejected green light balls in Hessdalen lights, presenting a negative band of O with electronic transition after ion-acoustic wave formation. Paiva and Taft presented a model for resolving the apparently contradictory spectrum observed in Hessdalen lights. The spectrum is nearly flat on the top with steep sides, due to