S.G. Stetsenko

Fission track age and cooling rate of the Marjalahti pallasite

Abstract Nuclear tracks were studied in olivine and merrillite (phosphate previously called whitlockite) from the Marjalahti pallasite. The merrillite contains an important fission contribution due mainly to the spontaneous decay of now extinct 244 Pu. The U contents of 29 merrillite grains range from 60 to 140 ppb (median value: 85 ppb). Assuming a reasonable fractionation temperature of ∼ 1750 K for the pre-pallasitic material, a lower limit of ∼ 5 K/Myr is obtained for the cooling rate, in strong contrast with the previous metallographic result (∼ 0.5 K/Myr). This disagreement, together with those observed in the case of mesosiderites, strengthens the need for a revision of the metallographic method of retracing the cooling histories of meteorites, as suggested by Narayan and Goldstein [31].

Estimation of soil surface alpha activity and alpha contamination by polymer track detectors

Abstract Estimations are presented for surface alpha contamination and alpha activity of Kiev soil samples. They were obtained in 1986 by means of CR-39 polymer track detectors and chemical etching. Parameters are given for “hot particles” from fallout after the Chernobyl accident. The hypothetic content of transuranium radionuclides (TUR) is evaluated for “effectively emitting layer” of the sample.

Tracks of heavy charged particles in some natural minerals

Abstract We assess the possibilities of registering and analysing heavy charged particles in some naturally occurring minerals from the earth and from meteorites. Using tracks of fission fragments we determine the uranium concentration of the examined minerals, as well as the radiation age in some cases. Based upon the density of the iron-group nuclei of galactic cosmic rays in meteorite minerals, information is obtained concerning their duration in the cosmos and the possible use of these meteorites for analysing the heavy components of galactic cosmic rays.

A TECHNIQUE FOR PARTIAL ANNEALING OF TRACKS IN OLIVINE TO DETERMINE THE RELATIVE ABUNDANCES OF GALACTIC COSMIC RAY NUCLEI WITH Z≥50

ABSTRACT Results on track length measurements and partial annealing of tracks in meteoritic olivine crystals are presented. Implications for determination of ultraheavy galactic cosmic ray abundances are discussed.

Revelation of heavy ion tracks in olivine: Orientation dependent annealing or etching?

Abstract The revelation of heavy ion tracks in olivine after partial annealing has been studied by the TINT technique. Large variations of track lengths have been found for given ion and annealing conditions. While this is most certainly related to the orientation of the tracks with respect to the crystallographic system, it has not been possible, up to now, to discriminate between orientation dependent annealing, and orientation dependent etching. These observations are of direct interest to studies of ultraheavy cosmic ray tracks in meteorites.

Track length of very heavy ion tracks in olivines

Abstract The lengths of etched tracks in meteoritic olivine crystals have previously been used to investigate the charge spectra of heavy galactic cosmic ray nuclei. Etchable track lengths up to 350 μm (after annealing the crystals for 32 hours at 430°C) were observed in olivines and the longest tracks have been interpreted to be possibly due to superheavy elements (SHE). For the purpose of calibration, artificial olivines were irradiated with a large variety of heavy ions including high energy (∼ 1 AGeV) uranium ions from the BEVALAC (Berkeley). The crystals were annealed under several different conditions and etched using standard procedures. After applying the above-mentioned annealing procedure, we measured in a very preliminary experiment uranium track lengths. Further results will be presented. At present, the question whether long tracks in meteoritic olivines are due to SHE or not remains open.

Study of fossil tracks due to VH and VVH groups of cosmic ray nuclei in olivine crystals from Luna-16 and Luna-24

Abstract The olivine crystals from lunar regolith samples taken by the Soviet unmanned spacecrafts Luna-16 and Luna-24 were investigated. Eleven 0.5 –1.0 mm size olivine crystals were mounted in epoxy, polished and then etched in modified WO 4 solution. The Fe-group track densities up to 10 8 tracks.cm −2 (Fe-group) were measured under optical microscope. The tracks of length greater than 30 microns due to Z ≥ 36 cosmic ray nuclei are counted for VVH tracks density for all the crystals. The VVH / VH track densities ratio for these lunar olivine crystals varies from 1.25×10 −4 to 2×10 −3 . It corresponds to the averaged depth of these crystals in lunar soil of 2–8 cm during galactic cosmic ray exposure. Lunar crystals are well suited for VVH track studies due to a very high track density. Two crystals were annealed at 430°C for 32 hrs. This procedure eliminates iron group tracks completely and leaves etchable tracks of nuclei with Z ⩾ 50 even in the olivine crystals with Fe-group tracks up to 1–2×10 8 tracks cm −2 . We were able to measure two tracks with the length 195 and 210μm which were produced by ThU group of Galactic cosmic ray nuclei.

On fission track dating of the terrestrial apatite crystals

Abstract The study of “fossil” and “fresh” tracks of apatite sample from East Siberia has been performed. We use the partial annealing procedure of “fossil” and “fresh” tracks (at 330°C during 24h) to determine the tracks age of that apatite and also to try to find the group of tracks longer that 238 U s.f. tracks.

On identification of the galactic cosmic-ray nuclear tracks due to Th-U in olivine crystals from meteorites

Abstract Earlier, in 1980–1987, during the investigations of fossil tracks in 12 cm3 of olivine crystals from the meteorites Marjalahti and Eagle Station the abundant groups of tracks with lengths of 120–140 μm, 200–220 μm and also a few tracks with L 350 μm have been measured. These crystals were annealed at 430°C during 32 h before etching. The necessary calibrations of olivine crystals with 25 and 70 MeV/N 238U nuclei were carried out at the Bevalac accelerator (LBL, Berkeley) and with 19 MeV/N 208Pb nuclei at UNILAC (GSI, Darmstadt). The subsequent annealing at 430°C during 32 h results in shortening down of 238U nuclei tracks to 230±25 μm (Marjalahti olivines) and 220±20 μm (Eagle Station olivines), which agrees with the data on the 210±20 μm fossil track group within the experimental error bar. The annealing of crystals at 450°C during 32 h provides the shortening down of the 208Pb tracks to 60–70 μm, on the 238U tracks to 120±20 μm. This can be compared with corresponding fossil track length spectra (the ∼ 50–60 μm and ∼ 115 μm groups).

Study of VVH galactic nuclei using meteoritic and moon crystal detectors

Abstract The crystal detectors developed from eight meteorites and two different moon samples (Luna-12 and Luna-16) have been used for the measurement of VH (Fe-group) and VVH galactic nuclei tracks. The partial annealing technique has been used to eliminate tracks formed due to charges around Z