Rare cosmological events recorded in muscovite mica.
F. M. Russell, School of Computing and Engineering University of Huddersfield, HD1 3DH, U.K. https://uploads.disquscdn.com/images/2f7ad4fe6232404eca928274d022ca00dbd699f1790550d820b93ccbca7c61a7.png Figure 1. Scan of sheet of muscovite showing the fossil tracks of charged particles. The diagram identifies the relevant parts of the fossil tracks resulting from a nuclear star. The directions of the principal atomic chains are shown.Most of the tracks lying in these directions are due to quodons.Some tracks can be channelling relativistic particles but these usually show fans from nuclear scattering events, which quodons cannot create. The direction of flight of the particle causing the star is unknown. It results in at least eighttracks. When tracks lie in the (001)-plane they are usually continuous. For those moving at an angle to this plane they will intersect the potassium sheets, where the recording occurs, at separated points. The long vertical chains of dots are of this type. The fan shaped patterns are caused by nuclear scattering events that produced atomic cascades in which kink-like lattice excitations are created. These fans are clustered around the principal crystal directions.The sheet of mica is 15cm x 29cm. <strong>Abstract.</strong> A study of fossil tracks of charged particles recorded in crystals of muscovite has revealed evidence of rare events of cosmological origin. The events are not compatible with known particle interactions with matter. They were recorded during a period when the crystals were in a metastable state during cooling after growth 13km water equivalent underground. In this state a phase transition can be triggered by low energy events in the range 1eV to 10keV, when the crystals effectively behave as solid-state bubble chambers. At higher energies the chemical etching technique can be used to reveal massive damage to the lattice. The rare events show evidence of interaction with the crystal over a great range of energies. They leave a distinctive record that is easily recognised. <strong>Introduction.</strong> The search for evidence of exotic events of cosmological origin usually starts with assumptions about possible interactions with ordinary matter. Irrespective of these the detector should offer a large sensitive volume and a moderately long recording time.Ideally, it also should enable detailed study of individual recorded events. An interesting approach looked for fossil evidence of scattering of WIMPs in crystals of muscovite [1,2].It was based on the possibility that an atom recoiling from a scattering event might cause sufficient damage to a lattice that it could be revealed by the technique of chemical etching. This technique is limited by the extent of damage needed to allow etching and by background recoils generated over geologic time scales from radioactivity, nuclear fission and cosmic radiation.Ifatomic force microscopy is used to determine the depth of etch pits thenthe lower limit on recoil energies to give an etchable track is a few tens of keV.This contrasts with the lower limit of about 1eV for recording in muscovite when in the metastable state considered here. Crystals of muscovite often show visible defectsconsisting of a hatch-work of black lineslying in the cleavage (001)-plane. Many of these lines lie in principal crystallographic directions at 60ointervals but not all.A study of the properties of these exceptions showed that some were the fossil tracks of charged leptons. In particular, somewere the tracks of positrons emitted from the isotope 40K that occursin the monatomic sheets of potassium forming part of the crystalstructure. It was found that the recoil of the nucleus arising from the dominant beta decay channelcreated a mobile lattice excitation called a quodon. These quodons cantrap a charge and propagate unimpeded along chains of potassium atoms for great distances.They move at ~3km/s and are the cause of the majority of lines lying in the 60o directions.Evidence also was found for fossil tracks due to e-p showers[3]. These showed that the tracks were recorded after the crystal had grown but the temperature was still above 700K, which allowed migration of atoms to formthe black lines.Therecording process operating in the metastable state does not depend on ionisation. It arises from a phase transition triggered by the presence of a positive charge when the crystal is in a metastable state during cooling.In this state the lattice needs nucleation sitesto expel excess iron to form the black ribbons of magnetite. The sensitivity of this process is shown by the lower limit of energy of a quodon of about 1eV for it to be recorded.In effect, the crystals behave as a solid-state bubble chamber.In common with many silicate minerals the composition of muscovite is variable, as is the impurity content. This results in variability of the recording sensitivity for different causesof the nucleation sites. One consequence is the extent to which the initial delineation of a track at nanometre-scale subsequently growsby lateral accretion to become several orders of magnitude wider. This decoration does not change the occurrence, origin, orientation and physical properties of the initial fossil trackbutaffects their visibility. Clearly, in a perfect crystal the recording process cannot operate. The most finely decorated tracks are caused by charged relativisticparticles, such as muons,passing through crystals with little iron and few other impurities.The tracks of quodons are seldom found in these crystals even though they are created copiouslyin beta decay of 40K. As the iron content increases the recording sensitivity also increases allowing quodons to be recordedas well. Eventually, when the ironcontent has risen to about 6 atomic percent the decoration is extensive. It is then possible for laterally unstable kink-like excitations of the lattice, created in atomic cascades caused by nuclear scattering events, also to be recorded. Their fossil tracks are distinctive because of their fan-shape. Almost all the decoration is composed of the black mineral magnetite in the form of very thin ribbons. These ribbons are intrusive in the potassium (001)-planes, where the lattice is weakest and easily cleaved.Figure 1 shows the scan of a sheet of muscovite containing a nuclear star and illustrates the detail that can be recorded by the phase transition recording process. The sensitivity is similar to that of photography. continued at: https://arxiv.org/pdf/1902.00354.pdf https://uploads.disquscdn.com/images/8ec79c395b462ebb0c2b5cd85c1066353444f5788590b5a41d9bcd9c35f8b41c.png
