Solar cosmic ray records in lunar rock 64455

Cosmic ray produced ¹⁰Be (half-life = 1.36 × 10⁶ yr), ²⁶Al (7.05 × 10⁵ yr), and ³⁶Cl (3.01 × 10⁵ yr) were measured in a depth profile of 19 carefully-ground samples from the glass-coated lunar surface rock 64455. The solar cosmic ray (SCR) produced ²⁶Al and ³⁶Cl in this rock are present in high concentrations, which in combination with the low observed erosion rate, <0.5 mm/Myr, provide well defined depth profiles characterizing the SCR component of the cosmic rays. In conjunction with new experimentally determined excitation functions, the ³⁶Cl concentrations suggest a softer solar-proton spectral shape than that derived from most previous measurements. The fact that no SCR-produced ¹⁰Be activity could be detected in 64455 is in good agreement with observations in 68815 and also indicates a softer SCR spectrum. Comparison of observed SCR profiles in 64455 with theoretical calculations indicates that the average solar-proton spectrum over the past 2 Myr (based on ²⁶Al) has an exponential rigidity parameter (R₀) of about 90 MV with a proton flux (J) of 73 protons/cm²/s·4π above 10 MeV. Over the last ∼0.5 Myr (based on ³⁶Cl) R₀ is about 70 MV with a flux of ∼196 protons/cm²/s·4π above 10 MeV. These SCR fluxes are consistent with most previous work.     

Irradiation history and atmospheric ablation of meteorites: Results from cosmic ray track studies

The dominant component of nuclear tracks observed in meteoritic minerals poor in uranium is produced by cosmic ray very heavy (vh:Z>20) nuclei. Studies of cosmic ray tracks and other cosmogenic effects in meteorites give us information on the irradiation history of these meteorites and enable us to estimate the extent of ablation during their atmospheric transit, and hence their pre-atmospheric masses. In a specific type of meteorite, known asgas-rich meteorite, one finds individual grains and xenoliths that have received solar flare and galactic cosmic ray irradiation prior to the formation of these meteorites. Detailed studies of these exotic components give insight into the accretionary processes occurring in the early history of the solar system. Some of the important results obtained from such studies and their implications to meteoritics are summarized.     

Noble gas investigations of lunar rocks 10017 and 10071

The noble gases He, Ne, Ar, Kr and Xe and also K and Ba were measured in the Apollo 11 igneous rocks 10017 and 10071, and in an ilmenite and two feldspar concentrates separated from rock 10071. Whole rock K/Ar ages of rocks 10017 and 10071 are (2350 ± 60) × 10⁶ yr and (2880 ± 60) × 10⁶ yr, respectively. The two feldspar concentrates of rock 10071 have distinctly higher ages: (3260 ± 60) × 10⁶ yr and (3350 ± 70) × 10⁶ yr. These ages are still 10 per cent lower than the Rb/Sr age obtained by Papanastassiouet al. (1970) and some Ar⁴⁰ diffusion loss must have occurred even in the relatively coarse-grained feldspar.The relative abundance patterns of spallation Ne, Ar, Kr and Xe are in agreement with the ratios predicted from meteoritic production rates. However, diffusion loss of spallation He³ is evident in the whole rock samples, and even more in the feldspar concentrates. The ilmenite shows little or no diffusion loss. The isotopic composition of spallation Kr and Xe is similar to the one observed in meteorites. Small, systematic differences in the spallation Kr spectra of rocks 10017 and 10071 are due to variations in the irradiation hardness (shielding). The Kr spallation spectra in the mineral concentrates are different from the whole rock spectra and also show individual variations, reflecting the differences in target element composition. The relative abundance of cosmic ray produced Xe¹³¹ differs by nearly 50 per cent in the two rocks. The other Xe isotopes show no variations of similar magnitude. The origin of the Xe¹³¹ yield variability is discussed.Kr⁸¹ was measured in all the samples investigated. The Kr⁸¹/Kr exposure ages of rocks 10017 and 10071 are (480 ± 25) × 10⁶ yr and (350 ± 15) × 10⁶ yr, respectively. Exposure ages derived from spallation Ne²¹, Ar³⁸, Kr⁸³ and Xe¹²⁶ are essentially in agreement with the Kr⁸¹/Kr ages. The age of rock 10071 might be somewhat low because of a possible recent exposure of our sample to solar flare particles.     

吉林陨石的热释光剖面与母体宇宙暴露历史示踪

对３个已知取样浓度和３个未知取样部位的吉林陨石样品的热释光研究表明,其自然热释光值具有宇宙成因核素含量相似的性质即浓度分布效应,随着样品距离表面位置的增大而降低,这表征了母体暴露期间宇宙射线的分布状况。诱导热释光数据表明,母体表面部分的样品的峰温和峰宽高于较深部位样品,说明这些样品中发光体矿物由有序态向无序态转化趋势明显。表面位置样品明显高的热释光数据说明在母体暴露过程中,除了银河宇宙射线外,太阳     

Long-term galactic cosmic ray variations over the last billion years based on the cosmic-ray exposure ages of iron meteorites

The distribution of the cosmic-ray exposure ages (T) of iron meteorites was analyzed to establish the possible variations in the intensity of the galactic cosmic ray (GCR) over the last billion years. The analysis was made for the entire data set containing ~80 age values from the literature (Voshage et al., 1983) and the corrected set after the exclusions of paired meteorites (using the Akaike information criterion). The dependence of the criterion χ² in the distribution of the phase values Ph = T/t–int(T/t) on the values of the assumed period (t) of GCR variations was analyzed for both sets of meteorites. The significant deviations of these parameters from the respective average values were found for t ~ 400–500 Myr and, in part, for t ~ 150 Myr. These deviations were interpreted by numerical modeling using the values of ages randomly distributed in the range of 0–1000 Ma. It was found that for variations with a period of 450 Myr, the distribution of the phase values and cosmic-ray exposure ages in the model data set is similar to that of iron meteorites. These results testify to the existence of the GCR variations with a period of ~400–500 Myr during the last 1 Gyr. The variations in the GCR flux can be explained by periodic galactic spiral arm crossings of the solar system. The GCR variations with a period of ~150 Myr discussed in the previous studies (Shaviv, 2002; 2003; Scherer et al., 2006) appears to be less certain.     

A climatological study of the relations among solar activity,galactic cosmic ray and precipitation on various regions over the globe

We apply Fourier and wavelet analyses to the precipitation and sunspot numbers in the time series (1901–2000) over Australia (27°S, 133°E), Canada (60°N, 95°W), Ethiopia (8°N, 38°E), Greenland (72°N, 40°W), United Kingdom (54°N, 2°W), India (20°N, 77°E), Iceland (65°N, 18°W), Japan (36°N, 138°E), United States (38°N, 97°W), South Africa (29°S, 24°E) and Russia (60°N, 100°E). Correlation analyses were also performed to find any relation among precipitation, sunspot numbers, temperature, and cloud-cover at the same spatial and temporal scale. Further correlations were also performed between precipitation with electron and proton fluence at the time interval, 1987–2006. All these parameters were considered in annual and seasonal scales. Though correlation study between precipitation and other parameters do not hint any linear relation, still the Fourier and wavelet analyses give an idea of common periodicities. The 9–11 year periodicity of sunspot numbers calculated by Fourier transform is also confirmed by wavelet transform in annual scale. Similarly, wavelet analysis for precipitation also supports the short periods at 2–5 years which is verified by Fourier transform in discontinuous time over different geographic regions.     

Noble gas concentrations and cosmic ray exposure ages of eight recently fallen chondrites

Abundances and isotopic compositions of He, Ne, Ar, and Xe have been measured in eight recently fallen chondrites. Ratios of concentrations of cosmic ray-produced ³He, ²¹Ne, ²²Ne and ³⁸Ar indicate that all eight samples experienced less than average cosmic ray shielding. ³He and ²¹Ne exposure ages were calculated using shielding corrected chondritic production rates and the measured ${}^{22}\text{Ne}{}^{21}\text{Ne}$. Exposure ages calculated from ${}^{22}\text{Na}{}^{22}\text{Ne}$ and ${}^{26}\text{Al}{}^{21}\text{Ne}$ ratios and constant relative production rates show a bias between the two ages due to variations in ${}^{22}\text{Na}{}^{26}\text{Al}$. Arguments are presented that this bias is due to irradiation hardness differences, and therefore the use of constant values for both the ${}^{22}\text{Na}{}^{22}\text{Ne}$ and ${}^{26}\text{Al}{}^{21}\text{Ne}$ production ratios is not permitted. Dwaleni, Swaziland, was found to be an unusual gas-rich chondrite with high concentrations of solar-derived He and Ne and planetary-type Xe.     

Aluminous enstatites of lunar meteorites and deep-seated lunar rocks

Fragments of aluminous enstatite from lunar meteorites of highland origin were investigated. It was found that such fragments usually occur in impact breccias of troctolitic composition. The aluminous enstatite contains up to 12 wt % Al₂O₃ and shows low CaO (<1 wt %) and almost constant high Mg/(Mg + Fe) ratio (89.5 ± 1.4 at %) identical to that of the Earth’s mantle. With respect to these parameters, the aluminous enstatites are distinctly different from common orthopyroxene of lunar rocks. The aluminous enstatite associates with spinel (pleonaste), olivine, anorthite (clinopyroxene was never found), and accessory minerals: rutile, Ti-Zr oxides, troilite, and Fe-Ni metal. The same assemblage was described in rare fragments of spinel cataclasites from the samples of the Apollo missions. Thermobarometry and the analysis of phase equilibria showed that the rocks hosting aluminous enstatite are of deep origin and occurred at depths from 25 km to 130–200 km at T from 800 to 1300°C, i.e., at least in the lower crust and, possibly, in the upper mantle of the Moon. These rocks could form individual plutons or dominate the composition of the lower crust. The most probable source of aluminous enstatite is troctolitic magnesian rocks and, especially, spinel troctolites with low Ca/Al and Ca/Si ratios. The decompression of such rocks must produce cordierite-bearing assemblages. The almost complete absence of such assemblages in the surficial rocks of lunar highlands implies that vertical tectonic movements were practically absent in the lunar crust. The transport of deep-seated materials to the lunar surface was probably related to impact events during the intense meteorite bombardments >3.9 Ga ago.     

月球地质年代学研究方法及月面历史划分

介绍了确定月球地层单元相对年龄和绝对年龄的方法。建立相对年龄的方法主要有4种：地层叠置法、撞击坑大小频率分布统计法、撞击坑形态法和月壤成熟度法;研究绝对年龄的方法有两种：样品的同位素测年法和月球成坑计年法。回顾了现用月球层序划分的形成及发展过程,在此基础上,提出了改善月球年代划分的建议,分别用冥月宙、古月宙和新月宙表示月球内动力地质作用为主的时期、内外动力地质作用共同作用的时期和外动力地质作用为主的时期。推荐以南极艾肯盆地的形成为界线,将前酒海纪划分为前艾肯纪和艾肯纪,分别表示月球内动力地质作用为主的演化期和内外动力地质作用并重的演化初期。这种改进后的“三宙六纪”的月球年代划分既可以形成逻辑上更符合月球动力学演化过程的月球年代划分,同时又有助于开展在月球背面的地质研究。     

The cosmic ray record in the San Juan Capistrano meteorite

An integrated study of the cosmic ray exposure history of the San Juan Capistrano meteorite was carried out using measurements of rare gas isotopic abundances, particle track densities and radioisotope concentrations. Spallation systematics determined for Kr isotopes in lunar samples are shown to be valid also for the San Juan Capistrano and St. Severin meteorites, thus allowing us to determine a reliable ⁸¹Kr/⁸³Kr production ratio as needed for applying the ⁸¹Kr-Kr dating method. The ⁸¹Kr-Kr age of SJC is 28.7 ± 2.0 Myr, about 35% longer than ages determined by spallation He or Ne. The minimum observed track production rate (2.6 × 10⁵ tracks/cm² · Myr) sets a minimum of 8 cm for the preatmospheric radius of an assumed spherical body. Track density gradients and the low ⁶⁰Co activity (<2.9 dpm/g Co) both set an upper limit of 10 cm to the radius. Track results show that ablation losses have averaged 6cm. The relative spallation yields of ⁷⁸Kr and ⁸³Kr, and the ratios ³He/²¹Ne and ²²Ne/²¹Ne are all compatible with a hard irradiation as would be experienced by a sample depth of about 6 cm in a body of 8–10 cm. The low activities of ⁵⁴Mn, ²²Na and ²⁶Al are also consistent with these irradiation conditions.     

Records of ancient cosmic radiation in extraterrestrial rocks

Recent results on cosmic ray interactions in lunar samples and meteorites resulting in production of stable and radionuclides, particle tracks and thermoluminescence are reviewed. A critical examination of²⁶A1 depth profiles in lunar rocks and soil cores, together with particle track data, enables us to determine the long term average fluxes of energetic solar protons (>10 MeV) which can be represented by (J _s,R _o)=(125, 125). The lunar rock data indicate that this flux has remained constant for 5×10⁵ to 2×10⁶ years. Production rates of stable and radionuclides produced by galactic cosmic rays is given as a function of size and depth of the meteoroid. Radionuclide (⁵³Mn,²⁸Al) depth profiles in meteorite cores, whose preatmospheric depths are deduced from track density profiles are used to develop a general procedure for calculating isotope production rates as a function of meteoroid size. Based on the track density and²²Ne/²¹Ne production rates, a criterion is developed to identify meteorites with multiple exposure history.²²Ne/²¹Ne ratio <1·06 is usually indicative of deep shielded exposure. An examination of the available data suggests that the frequency of meteorites with multiple exposure history is high, at least 15% for LL, 27% for L and 31% for H chondrites. The epi-thermal and the thermal neutron density profiles in different meteorites are deduced from⁶⁰Co and track density data in Dhajala, Kirin and Allende chondrites. The data show that the production profile depends sensitively on the size and the chemical composition of the meteoroid. Cosmic ray-induced thermoluminescence in meteorites of known preatmospheric sizes has been measured which indicates that its production profile is nearly flat and insensitive to the size of the meteoroid. Some new possibilities in studying cosmic ray implanted radionuclides in meteorites and lunar samples using resonance ionisation spectroscopy are discussed.     

Variations of the cosmic ray fluxes as a possible earthquake precursor

Variations of the air pressure, cosmic ray fluxes, sunspot numbers, and interplanetary magnetic field in connection with strong earthquake occurrences are studied. The results of this investigation permits one to consider the variations of the cosmic rays as one of the possible cause of air pressure variations and one of the possible earthquake precursors.     

Glacial retreat history of Nanhuta Shan (north-east Taiwan) from preserved glacial features: the cosmic ray exposure perspective.

Taiwan, located at the junction of the Pacific Ocean, the Eurasian continent, and the South China marginal Sea, is of particular interest for reconstructing paleoclimate periods in Eastern Asia. This study reports the first cosmic ray exposure dating (CRE) of glacial features in Taiwan. Among the areas where glacial relicts have been described in Taiwan, the Nanhuta Shan range is probably the place where glacial landforms are best preserved. We consequently focused on this area combining glacial geomorphology observations together with CRE dating using in situ produced ¹⁰Be of erratic boulders and ice-sculpted surfaces. When combined with the geomorphic characteristics of the sampled areas, the obtained minimum CRE ages suggest that the glacial retreat in the Nanhuta Shan commenced about 10±3 ka ago and retreat was complete by 7±1 ka ago. This is consistent with the Holocene warming trend deduced from other biological and physico-chemical paleoclimatic records for the region. Estimates of local bedrock surface denudation rates either directly from in situ produced ¹⁰Be measurements or from geomorphic considerations are employed to determine the preservation of such glacial features within the highly dynamic setting of Taiwan.     

Solar modulation of galactic cosmic rays in the three-dimensional heliosphere according to meteorite data

Cosmogenic radionuclides with distinctive half-lives from chondritic falls were used as natural detectors of galactic cosmic rays (GCR). A unique series of uniform data was obtained for variations in the integral gradients of GCR with a rigidity of R > 0.5 GV in 1955–2000 on heliocentric distances of 1.5–3.3 AU and heliographic latitudes between 23° S and 16° N. Correlation analysis was performed for the variations in GCR gradients and variations in solar activity (number of sunspots, SS, and intensity of the green coronal line, GCL), the intensity of the interplanetary magnetic field (IMF), and the inclination of the heliospheric current sheet (HCS). Distribution and variations of GCR were analyzed in 11-year solar cycles and during a change in 22-year magnetic cycles. The detected dependencies of GCR gradients on the intensity of IMF and HCS inclination provided insight into the differences in the processes of structural transformation of IMF during changes between various phases of solar and magnetic cycles. The investigated relationships lead to the conclusion that a change of secular solar cycles occurred during solar cycle 20; moreover, there is probably still an increase in the 600-year solar cycle, which can be among the major reasons for the observed global warming.     

Rb-Sr age of lunar igneous rocks 62295 and 14310

We report an age of crystallization for spinel-troctolite (VHA basalt) 62295 of 4.00 ± 0.06 × 10⁹ yr (I = 0.69956 ± 6) and an age of crystallization for KREEP-rich basalt 14310 of [3.94 ± 0.03 × 10⁹yr (I = 0.70041 ± 5). The ages probably date the cooling of shock melts.     

Cosmic-ray exposure history at the Apollo 16 and other lunar sites: lunar surface dynamics

Concordant ⁸¹K-Kr exposure ages for four station 11 breccias indicate an age of 50.3 ± 0.8m.y. for North Ray Crater. Ray structures visible from orbital photography suggest that stations 8 and 9 should contain a substantial amount of South Ray ejecta. Concordant ⁸¹Kr-Kr exposure ages at these sites indicate an age for South Ray Crater of 2.04 ± 0.08m.y. Surface effects (tracks, surface angularities, and micro-crater populations) show good general agreement with this young an age, but discrepancies on a sample-by-sample basis seem to indicate that extensive pre-surface irradiations must have occurred. A detailed pre-surface exposure history is derived for the parent boulder of samples 69935 and 69955. It is suggested that secondary impacts play a major role in near-surface regolithic stirring. Widespread pre-surface irradiation would in fact be expected if most of the newly excavated material had been transported to the surface by secondary impacts rather than by the South Ray event itself.     

Surface history of some Apollo 17 lunar soils

Cosmic ray track densities in Apollo 17 soil samples are used to infer surface exposure times of soils from a trench at Van Serg Crater, from on and near a boulder at Camelot Crater, and from the position of the heat flow and neutron flux experiments (the ALSEP site). The topmost 2 cm of soil at Van Serg was exposed for 11 m.y., the top cm at Camelot for 36 m.y. A layering chronology and average deposition rate are proposed for the trench. For all soils the median track densities imply predispositional irradiation in the top 15 cm of the lunar surface for times that were long compared with the actual residence in the stratigraphic positions from which the soils were collected. Van Serg crater is inferred to have been formed approximately 24 m.y. ago.     

Surface history of lunar soil and soil columns

Measurements of cosmic ray track densities are presented for soil samples from Apollo 15, 16 and 17. Median track densities are used to infer total effective exposure times within ~15 cm of the lunar surface. Minimum track densities are used to derive the time of the last impact-produced rearrangement of soil grains. For samples from near various craters ages are derived of 40 m.y. for St. George, 6 (±3) m.y. for S. Ray, 25–90 m.y. for Plum, and 20–35 m.y. for Shorty. The material of 15003. the Apollo 15 deep core at depths of 120–160 cm, is inferred to have been deposited at an average rate of ≥0.35 cm/m.y. The Apollo 16 core at 41–47 cm depths. 60007, appears to be well mixed and was covered up by deposition at 0.3 cm/m.y. for the next few m.y. after its deposition.