Ne Isotopes Research Articles

Production of stable and radioactive nuclides in thick stony targets ( R = 15 and 25 cm) isotropically irradiated with 600 MeV protons and simulation of the production of cosmogenic nuclides in meteorites

Two artificial meteoroids made out of gabbro with a density of 3 g cm −3 with radii of 15 and 25 cm were isotropically irradiated with 600 MeV protons in order to simulate the production in meteoroids of cosmogonie nuclides by galactic cosmic ray protons. The depth dependent production of a wide range of radionuclides from target elements O, Mg, Al, Si, Ti, Fe, Co, Ni, Cu, Ba, Lu, and Au was measured. Furthermore, the production of He and Ne isotopes from Al, Mg, Si as well as from degassed meteoritic material was determined. Together with earlier results on an artificial meteoroid with a radius of 5 cm, and with data derived from thin-target experiments, the depth dependence of production rates is investigated for radii from 0 to 75 g cm −2. 60Co from Co shows the strongest size dependence; the center production rates differ by a factor of 100 for radii of 5 and 25 cm. Other low-energy products, like 58Co from Co and 24Na produced from Al, increase only up to a factor of 3.5 over the entire range of radii. For extreme high-energy products, in contrast, the center production rates decrease by up to a factor of 10. The observed depth profiles show a wide varity of shapes. Low-energy products have pronounced maxima in the center, high-energy products exhibit strong decreases from surface to center and, in between, essentially flat profiles are seen as well as such with a transition maximum. The spectra of primary protons and of secondary protons and neutrons in the artificial meteoroids were calculated using Monte Carlo techniques. The fluxes of secondary protons and neutrons depend strongly on depth and size, the spectral shapes being different for protons and neutrons. Calculating also the nucleon spectra which result from irradiation with real GCR p-spectra, the differences between simulation experiments and cosmic irradiation conditions are quantitatively described. On the basis of all these spectra and of thin-target excitation functions, production rates were calculated and compared with the experimental ones. The theoretical depth profiles allow to distinguish the different contributions of primary and secondary particles and to unravel the various production modes of cosmogenic nuclides in meteoroids. Our investigation shows that it is possible to model the production of residual nuclides in artificial meteoroids with excellent accuracy by thin-target calculations, provided that reliable thin-target excitation functions are at hand.

Measurements of 22Ne-20Ne Isotope Shifts by Laser-Induced Line Narrowing in Three-Level Systems

Application of laser-induced absorption line narrowing (ALN) to neon isotope shift investigations in the stretched three-level systems 1 s5-2p4-3 s2 and 1 s4-2 p4-3 s2 is reported. The measurements have been performed with a frequency and intensity-stabilized 633-nm He-Ne probe laser and with a tunable single-mode R6G dye laser. Utilization of longitudinal magnetic modulation to the neon gas absorber yields background-free resonance signals. Measurements of 594.5-, 609.6-, and 633-nm 22Ne-20Ne isotope shifts result in (1712 ± 8) MHz, (1753 ± 8) MHz, and (904 ± 8) MHz, respectively. These values agree with previous data.

Proton-induced spallation at 600 MeV

In the course of a systematic investigation of proton-induced reactions up to p-energies of 3000 MeV, the target elements O, Mg, Al, Si, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Y, Zr, Rh, Ba, Lu and Au were irradiated with 600-MeV protons at the CERN synchrocyclotron. A consistent set of more than 200 thin-target cross-sections for the production of radionuclides and stable He, Ne and Xe isotopes has so far been measured. Here, 199 cross-sections for the production of radionuclides are presented. On the basis of the new data the quality of existing semi-empirical equations for the calculation of spallation cross-sections is discussed. In a more physical approach, the production of residual nuclides in the course of the intranuclear cascade was calculated using Monte Carlo techniques and compared with experimental cross-sections.

Exposure History of H5 Chondrite Gujargaon

Abstract— Cosmic ray produced tracks, He and Ne isotopes and radionuclides have been studied in the recently fallen H5 chondrite Gujargaon. The results indicate an exposure age of about 7 Ma. The high track production rates of 0.25 to 0.69 × 106 cm−2 Ma−1 suggest that the Gujargaon meteoroid had a small size (Re = 9–10 cm) in space and suffered 1–3 cm ablation in the atmosphere. The conclusion about the meteoroid size is supported by the low activity of neutron capture isotope 60Co and high spallogenic 22Ne/21Ne ratio of about 1.25. The data on long lived isotopes 10Be, 53Mn and 26Al are used to derive production rates of these isotopes in a rock having a radius of 9 cm and the activity levels of the short lived isotopes 22Na and 54Mn are used to estimate the effect of modulation of galactic cosmic rays at the time of solar maximum of 1982.

Isotope enrichment in Ne clusters

Clusters of Ne atoms produced by adiabatic nozzle expansion have been studied with a high resolution double focusing sector field mass spectrometer. Analysis of the isotopic composition of these clusters (up to n=22) showed instead of the expected statistical distribution a pronounced shift to the heavier neon isotope 22Ne. The shift was found to correspond to an increase of the isotope ratio of 22Ne from 8.7% in the monomer to ∼12.5% in the clusters with n>4 (enrichment factor of ∼1.5.)

On the scissors type mode in 46Ti and lighter nuclei

A microscopic formulation of the scissors mode, based on the angular-momentum projected Hartree-Fock Bogoljubov approximation, is applied to the Ti and Ne isotopes. Results for M1 transition strengths and form factors are presented and compared to available experimental data and shell model calculations. For 46Ti the B( M1)↑ value obtained is in excellent agreement with the experimental data for the 1 + state at 4.3 MeV.

Giant resonance decays in 20Ne, 22Ne and interference effects with quasifree scattering processes

The charged particle (c) decay from excited states up to the giant quadrupole resonance (GQR) in 20Ne has been studied in a kinematically complete 20Ne(α, α′ c) coincident experiment at E α = 155 MeV. Angular correlation functions and branching ratios are extracted for the α 0, α 1 and p 0 decay channels. The ( α, α′ α 0) angular correlation functions are analysed in PWBA in terms of coherent interference with the quasifree scattering process leading to the same final states. Good fits to the data are achieved over a large range of excitation energies. Branching ratios have been extracted and compared to results of Hauser-Feshbach calculations. Above E x = 12.5 MeV excitation energy a discrepancy was found between the experimentally observed α 0 branching ratios and the HF predictions. These results yield evidence for a direct α 0 decay mechanism of the split isoscalar giant quadrupole resonance in 20Ne. Some results are presented also for a 22Ne(α, α′ c) coincidence experiment. Qualitative comparison has been made between the general decay behaviour of the two Ne isotopes.

Noble gas studies on the host phase of high [formula omitted] ratios in deep-sea sediments

Elemental abundances and isotopic compositions of noble gases were determined for a magnetic separate and chemically leached samples from deep-sea sediments (14°29.61′S, 158°52.98′W). High 3He 4He ratios suggesting the presence of cosmic material were observed in all samples, and especially enriched in magnetic fractions. Ne isotopes and light noble gas abundances suggested that the high 3He 4He ratio was of solar wind origin and not due to cosmic ray spallation. However, heavy noble gases (Kr and Xe) were of atmospheric origin. Altogether the noble gases were well explained by a mixture of solar wind implanted on interplanetary dust particles (IDPs) and terrestrial noble gas fractionated from the atmosphere. The degree of contamination of IDPs in the magnetic fractions was estimated to be about 100 ppm.

On the depth dependence of spallation reactions in a spherical thick diorite target homogeneously irradiated by 600 MeV protons: Simulation of production of cosmogenic nuclides in small meteorites

An artificial meteorite made out of diorite with a radius of 5 cm was irradiated isotropically with 600 MeV protons in order to simulate the production of cosmogenic nuclides in small meteorites by galactic cosmic ray protons. The primary proton dose of 4.82 × 10 15 cm −2 is equivalent to a some 50 Ma of cosmic ray exposure. The depth dependent production of a wide range of radionuclides from target elements O, Mg, Al, Si, Ti, Fe, Co, Ni, Cu, Ba, and Lu was measured. Furthermore, the production of He and Ne isotopes from Al, Mg, Si, as well as from glass and meteoritic material was determined. Thick-target data are compared with thin-target production rates measured simultaneously, thus allowing to separate the contribution of secondary protons and neutrons. The results demonstrate that, in contrast to present presumptions, even in small meteorites secondary particles have to be considered and that the depth profiles show differences in production of up to 30% between surface and center. The experimental data are discussed with respect to cosmic irradiation conditions of real meteorites. Using Monte Carlo techniques depth dependent nucleon spectra were calculated. On the basis of these spectra and of thin-target excitation functions theoretical production rates were derived and compared with the experimental ones. This comparison shows that it is possible to reproduce the experimental depth profiles quite well by thin-target calculations provided reliable excitation functions are at hand. The thick-target measurements and the thin-target calculations provide a basis for an advanced modelling of the production of cosmogenic nuclides in small meteorites, which strictly differentiates between all contributing production modes.

Can intrasolar diffusion contribute to isotope anomalies in the solar wind?

The possible role of intrasolar diffusion is examined for the isotopes of He, Ne, and Xe to see if there is a theoretical basis for an empirical mass fractionation relationship between the isotopic compositions of planetary and solar‐wind‐implanted elements. It is shown that if diffusion is responsible, even in part, for the observed depletion of 4He in the solar wind, then significant fractionation effects across the isotopes of Ne and Xe as well as He can be predicted. It is also shown that isotopic fractionation need not necessarily infer extreme elemental abundance patterns in the solar interior.

Intensive sampling of noble gases in fluids at Yellowstone: I. Early overview of the data; regional patterns

The Roving Automated Rare Gas Analysis (RARGA) lab of Berkeley's Physics Department was deployed in Yellowstone National Park for a 19 week period commencing in June, 1983. During this time 66 gas and water samples representing 19 different regions of hydrothermal activity within and around the Yellowstone caldera were analyzed on site. Routinely, the abundances of five stable noble gases and the isotopic compositions of He, Ne, and Ar were determined for each sample. In a few cases the isotopes of Kr and Xe were also determined and found to be of normal atmospheric constitution. Correlated variations in the isotopic compositions of He and Ar can be explained within the precision of the measurements by mixing of only three distinct components. The first component is of magmatic origin and is enriched in the primordial isotope 3He with 3He 4He ≥ 16 times the air value. This component also contains radiogenic 40Ar and possible 36Ar with 40Ar 36Ar ≥ 500 , resulting in a 3He 36Ar ratio ≥ 41,000 times the air value. The second component is assumed to be purely radiogenic 4He and 40Ar ( 4∗He 40∗Ar = 4.08 ± .33 ). This component is the probable carrier of observed excesses of 21∗Ne, attributed to the α,n reaction on 18O. Its radiogenic character implies a crustal origin in U. Th, and Krich aquifer rocks. The third component, except for possible mass fractionation, is isotopically indistinguishable from the noble gases in the atmosphere. This component originates largely from infiltrating run-off water saturated with atmospheric gases. In addition to exhibiting nucleogenic 21∗Ne, Ne data show anomalies in the ratio 20Ne 20Ne , which correlate roughly with the 21Ne 22Ne anomalies for the most part, but not as would occur from simple mass fractionation. Some exaggerated instances of the 20Ne 22Ne anomaly occur which could be explained by combined mass fractionation of Ne and Ar isotopes to a severe degree coupled with remixing with normally isotopic gases. Otherwise exotic processes have to be invoked to explain the 20Ne data. Relative abundances of the non-radiogenic and non-nucleogenic noble gases ( 22Ne, 36Ar, 84Kr, and 132Xe) are highly variable but strongly correlated. High Xe/Ar ratios are always accompanied by low Ne/ Ar ratios and vice versa. Except for water from the few cold ( T < 20° C) springs analyzed, none of the samples have relative abundances consistent with air saturated water and the observed variations are not readily explained by the distillation of air saturated water. In characterizing each area of hydrothermal activity by the highest 3He 4He ratio found for that area, we find that within the caldera this parameter is somewhat uniform at ~7 ± 1 times the air value. There are exceptions, most notably at Mud Volcano, an area located along a crest of recent and rapid uplift. Here the maximum 3He 4He ratio is ~ 16 times the air value. Also noteworthy is Gibbon Basin which is in the vicinity of the most recent rhyolitic volcanism and exhibits a 3He 4He ratio ~ 13 times the air value. Immediately outside the caldera the maximum sol 3He 4He ratio decreases rapidly to values < ~3 times the air value.

Solar-flare produced 3He in lunar samples

Lunar rocks and soils undergo long-term irradiation by solar and galactic cosmic rays (SCR and GCR) leading to compositionally-distinct spallation spectra for noble gases1,2 and leaving behind fossil records characteristic of different irradiation features. Because the SCR effects are restricted to the first few millimetres of rocks and soils in contrast to GCR, various studies based on solar flare tracks3,4, thermoluminescence5, and radionuclides3,6 over the past decade have aimed to decipher these fossil records bearing the imprints of the low (SCR) and high (GCR) energy irradiation phenomena. These studies have greatly helped our understanding of the energy spectra and fluxes of charged particles streaming out of the Sun. We have already reported quantitative studies, aimed at isolating the SCR and GCR produced Ne and Ar isotopes in several lunar soils and rocks1,2 and have calculated their solar flare exposure ages which agree with the ‘surface’ exposure ages based on 26Al and particle track studies3. We describe here, for the first time, using 3He in samples from three different depths of lunar rocks, a method for deducing the absolute SCR (flare) proton fluxes in the past few million years which compare favourably with those derived from 26Al and 53Mn studies3,6 of other lunar samples.

The neutron-rich isotopes of cosmic-ray neon and magnesium

A balloon-borne detector flown during the period of minimum activity in the last solar cycle has been used to observe the isotopes of Ne, Na, Mg, and Al in the cosmic radiation, over an energy range approx.390--530 MeV/n. The detector has a mass resolution of 0.4--0.55 amu in this charge range and was calibrated in flight by fast particles. While the Al and Na nuclei are consistent with essentially pure /sup 23/Na and /sup 27/Al beams, both Ne and Mg show appreciable abundances of neutron-rich isotopes. We find relative abundances corrected to the top of the atmosphere for /sup 20/Ne:/sup 21/Ne:/sup 22/Ne of 57:17:26 and for /sup 24/Mg:/sup 25/Mg:/sup 26/Mg of 59:21:20. The neon abundances are in good agreement with those found from three different satellite experiments. The abundances of magnesium are more controversial, and these measurements add evidence that magnesium is also neutron rich. Our ability to reproduce the neon abundances found by others enhances our confidence in the measurement of magnesium, but the statistical weight is still marginal. These abundances, corrected for interstellar propagation, appear significantly different from those of solar-system material, and reflect the special nature of the cosmic-ray sources.

Total muon capture rates in neon

We report here the results of the calculation of total muon capture rates (${\ensuremath{\Lambda}}_{\ensuremath{\mu}\mathrm{c}}$) in Ne isotopes using Hartree-Fock wave functions. These wave functions are generated from (a) a phenomenological set of interaction matrix elements and (b) a microscopic set derived from the Reid soft core potential. Satisfactory agreement with the experiment both for the spectra of and the ${\ensuremath{\Lambda}}_{\ensuremath{\mu}\mathrm{c}}$ in $^{20}\mathrm{Ne}$ is obtained. The trend of the variation of ${\ensuremath{\Lambda}}_{\ensuremath{\mu}\mathrm{c}}$ in Ne isotopes as predicted by the empirical formulas is explained by incorporating the oblate admixture in the ground states of $^{22}\mathrm{Ne}$ and $^{24}\mathrm{Ne}$.

High resolution measurements of galactic cosmic-ray neon, magnesium, and silicon isotopes

The individual isotopes of galactic cosmic-ray Ne, Mg, and Si at ~0.20 amu. Our results suggest that the cosmic ray source is enriched in ^(22)Ne, ^(25)Mg, and ^(26)Mg when compared to the solar system. In particular, we find (^(25)Mg + ^(26)Mg)/^(24)Mg = 0.49(+0.23, -0.14) compared with the solar system value of 0.27, suggesting that the cosmic-ray source and solar system material were synthesized under different conditions.

He, Ne and Ar composition in a neutron activated sea-floor basalt glass

We have measured the composition of He, Ne and Ar in the glassy rim of a fresh oceanic basalt from the East Pacific Rise. Three splits of the sample were subjected to neutron irradiation prior to analysis to investigate the noble gas release as a function of different neutron doses. The shapes of the observed 39Ar- 40Ar degassing profiles depend critically on the irradiation dose due to a severe redistribution of excess 40Ar. This shows that the application of the 39Ar- 40Ar method for dating of glassy samples requires the utmost care. Including the He and Ne results from the irradiated specimens, it was possible to determine the concentrations of Li and Mg and to estimate upper limits for Na and F in addition to the concentrations of K, Ca and Cl which are measured routinely as a byproduct of the 39Ar- 40Ar dating method. This provides a useful extension of the 39Ar- 40Ar technique since it may help to identify the outgassing sites during stepwise heating experiments. Furthermore it allows one to study the diffusion behavior of He and Ne isotopes artificially produced during irradiation. In our samples the activation energies of 3He and 21Ne tend to increase with growing neutron doses.

Triton emission in the interactions of fast neutrons with nuclei

Cross sections have been measured for the formation of tritium in the interactions with Li, Be, B, C, N, O, F, Ne, Na, Mg, Al, Si, P, S, Cl, Ar, Ca, V, Co, As, Y, La, Pr, Tb, Ho and Tl of fast neutrons produced via break-up of 53 MeV deuterons on a Be target ( E n = 11.5–43.5 MeV; I max at 22.5 MeV; FWHM = 15.8 MeV). The activation technique in combination with vacuum extraction and low-level gas phase β − counting of tritium was employed. Furthermore, cross sections were measured for isotopes of the elements Ne, Mg, Ar, Ca, Ti, Cr, Fe, Ni, Zn, Ge, Se, Zr, Mo, Pd, Te, Ba, Pr, Dy, W, Tl and Pb by γ-ray spectroscopic analysis of the radioactive reaction products. A comparison of the two sets of cross sections shows that for nuclei with A > 40 the emission of three single particles (lp2n) is much more probable than the emission of a bound tri-nucleon ( 3H). The cross-section data obtained via tritium counting show that the (n, t) cross sections for the lightest nuclei are exceptionally large, probably due to direct interactions, and the process competes with other modes of de-excitation; for elements with Z > 20, on the other hand, the cross section is low (< 0.25 % of σ n.e.) and practically constant, showing thereby that in the medium and heavy mass regions the probability of emission of a triton is relatively independent of the target nucleus. A comparison of the cross-section systematics at E n = 14.6 MeV and for the neutron spectrum described above is presented; the trends are somewhat similar.

Diogenite exposure ages

He, Ne and Ar isotopes have been measured in six, and 26Al in two diogenites. Cosmic-ray exposure ages corrected for shielding effects using 22Ne/ 21Ne ratios are generally concordant. Five diogenites have a group age of 14 Myr and three others may have a group age of 24 Myr, implying that two collisions may have produced 8 of the 9 diogenites.

Progress report on separators sidonie and Paris

Our isotope separators are used full-time for isotope separations. The only study made on them deals with the use of a curved emitting slit in order to reduce the beam height inside the magnetic gap. Many rare gas separations have been performed yielding more than 1 g of 10 isotopes of Ne, Kr and Xe. The isotopic purities lie between 99% and 99.99%, while chemical purities are always better than 99.9%. Some technical details on these separations are given. Some of them include separations in a “closed loop circuit”; then the efficiency reaches approximately 30%. Some examples of the use of highly enriched isotopes (nuclear physics and atomic physics) are given.

Cross sections for He and Ne isotopes in natural Mg, Al, and Si, He isotopes in CaF2, Ar isotopes in natural Ca, and radionuclides in natural Al, Si, Ti, Cr, and stainless steel induced by 12-to 45-MeV protons

Stacks of thin Mg, Al, Si, Ca, CaF2, Ti, and stainless steel foils were bombarded in twelve irradiations by a variable energy cyclotron. Cross sections are reported for He and Ne in natural Mg, Al, and Si, and for He in CaF2, and for Ar in natural Ca, as determined from mass spectrometer analysis of the inert gases. In addition, cross sections of Na-22 in natural Al and Si, of V-48 in natural Ti, and of Cr-51, Mn-52, and Co-57 in stainless steel are reported. From these were deduced Cr-51 and Mn-52 cross sections in natural Cr.