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A dying massive star ends in a supernova explosion ejecting a large fraction of its mass into the interstellar medium. If this happens nearby, part of the ejecta might end on Solar System bodies and, in fact, radioactive ^{60}Fe has been detected on the Pacific ocean floor in about 2 Ma old layers. Here, we report on the detection of this isotope also in lunar samples, originating presumably from the same event. The concentration of the cosmic ray produced isotope ^{53}Mn, measured in the same samples, proves the supernova origin of the ^{60}Fe. From the ^{60}Fe concentrations found we deduce a reliable value for the local interstellar fluence in the range of 1×10^{8} at/cm^{2}. Thus, we obtain constraints on the recent and nearby supernova(e).

The age of the surface of Europa is probably tens of Myr or less, but is poorly constrained. Two different geochronology schemes could potentially be applied to near-surface samples to provide far more precise ages. First, the surface salts apparently contain enough potassium to make potassium–argon dating feasible. Second, the bombardment of the surface with both galactic cosmic rays and protons trapped within the jovian magnetosphere will cause nuclear reactions that can lead to measurable buildups of cosmogenic noble gases, which can be used to determine both cosmic-ray exposure ages and erosion, deposition, or mixing rates for surface modification. The major differences between Europa's salt-rich ice and the rocks (meteorites, lunar samples and terrestrial rocks) in which cosmogenic noble gases are normally measured are that the abundance of target elements for nuclear reactions creating neon and argon are lower (because of the high water content), but neutron-capture reactions, particularly 35 Cl( n , γ ) 36 Cl( β − ) 36 Ar, are enhanced because of the thermalizing effects of the water. As well as presenting calculations of noble gas production near the surface of Europa, we also show that the measurements required to determine ages are within reach of technology in the near future, if an instrument can be landed on the surface of Europa.

Using the Gamma-Ray Spectrometer on the Mars Odyssey, we have identified two regions near the poles that are enriched in hydrogen. The data indicate the presence of a subsurface layer enriched in hydrogen overlain by a hydrogen-poor layer. The thickness of the upper layer decreases with decreasing distance to the pole, ranging from a column density of about 150 grams per square centimeter at –42° latitude to about 40 grams per square centimeter at –77°. The hydrogen-rich regions correlate with regions of predicted ice stability. We suggest that the host of the hydrogen in the subsurface layer is ice, which constitutes 35 ± 15% of the layer by weight.

Long-lived cosmogenic radioisotopes, 10Be, 26Al, 36Cl, 41Ca and 59Ni, have been measured in five samples from the Campo del Cielo iron meteorite by accelerator mass spectrometry (AMS). The 36Cl activities were significantly above the background. For the concentrations of the other four radioisotopes, only upper limits were obtained that were, however, consistent with the 36Cl result. The measured 36Cl activity allowed an estimate of the meteoroid's preatmospheric size: a radius larger than 300 cm and a mass of at least 840 000 kg. We conclude that this meteorite might be one of the largest meteorites to have been recovered.

The energies and intensities of prompt gamma rays produced by the radiative capture of thermal neutrons have been compiled and evaluated for elements with atomic numbers Z=1–30. These elements are important for many applications, including well logging, planetary remote sensing, and other analytic and diagnostic applications. Experimental data for 70 isotopes from 1H to 68Zn were compiled and evaluated. Published thermal-capture cross sections were used to convert the isotopic gamma-ray intensities to elemental intensities. The evaluated energies and absolute intensities of these capture gamma rays are presented by element and a subset is sorted by gamma-ray energy. The literature has been covered to August 2000.

— Elemental composition and composition ratios derived from gamma-ray measurements collected by the NEAR-Shoemaker spacecraft while on the surface of 433 Eros are reported. Performance of the gamma-ray spectrometer (GRS) during cruise and orbit is reviewed. The best gamma-ray data were collected on the surface of Eros after the spacecraft's controlled descent on 2001 February 12. Methods used in spectral analysis, to convert peak areas to incident photons, and photons to elemental composition are described in some detail. The elemental abundance of K and the Mg/Si, Fe/Si, Si/O and Fe/O abundance ratios were determined. The Mg/Si and Si/O ratios and the K abundance are roughly chondritic, but the Fe/Si and Fe/O ratios are low compared to expected chondritic values. Three possible explanations for the apparent Fe depletion are considered.

The production of 3 He, 21 Ne, and 22 Ne in meteoroids of various sizes and in the lunar surface was investigated. The LAHET code system, a purely physical model for calculating cosmic- ray particle fluxes, was used to simulate cosmic-ray particle interactions with extraterrestrial matter. We discuss the depth and size dependence of the shielding parameter 22 Ne/ 21 Ne, which is used for reconstruction of pre-atmospheric sizes, depth, and exposure histories. The 22 Ne/ 21 Ne ratio decreases with increasing depth or pre-atmospheric size but then increases with depth in very large objects. This increase with depth in the 22 Ne/ 21 Ne ratio means that this ratio is a poor indicator of shielding in some large objects. The dependence of 3 He/ 21 Ne as function of 22 Ne/ 21 Ne was also calculated, and differences between the calculations and the Bern line are discussed.

The determination and some uses of production rates of cosmogenic nuclides are reviewed. Emphasis is on work done since 1993 for long-lived cosmogenic radionuclides in extraterrestrial matter. Several Monte Carlo computer codes are being used to numerically simulate the interactions and transport of cosmic-ray particles. Thin- and thick-target irradiations have been done with protons to determine reaction cross sections and to experimentally simulate cosmic-ray bombardments. Cross sections for some neutron-induced reactions are being measured or inferred from thick-target irradiations. Some other works involving cosmogenic-nuclide production rates are discussed.

Modern solar energetic particles (SEPs) have been studied for about 50 years by satellites and ground-based observations. These measurements indicate much about the nature of SEPs but cover too short a period to quantify the probabilities of very large solar particle events. Many SEPs have high enough energies to make nuclides in material in which they interact. Some nuclides measured in lunar samples have been used to extend the record about SEPs back several million years. Some new measurements of modern SEPs during the last solar cycle and new results for nuclides made by SEPs in lunar samples are presented and their implications discussed. Both the modern and ancient records need to be improved, and methods to get a better understanding of solar energetic particles are discussed. The SEP average fluxes from both sets of records are similar, and both sets can be used to show that huge fluxes of SEPs are very rare.

We studied the effect of Bi incorporation on the hole mobility in the dilute bismide alloy GaAs${}_{1\ensuremath{-}x}$Bi${}_{x}$ using electrical transport (Hall) and photoluminescence (PL) techniques. Our measurements show that the hole mobility decreases with increasing Bi concentration. Analysis of the temperature-dependent Hall transport data of $p$-type GaAsBi epilayers along with low-temperature PL measurements of $p$-doped and undoped epilayers suggests that Bi incorporation results in the formation of several trap levels above the valence band, which we attribute to Bi-Bi pair states. The decrease in hole mobility with increasing Bi concentration can be explained as being caused by scattering at the isolated Bi and the Bi-Bi pair states. We also observed a decrease in hole concentration with Bi incorporation. We believe that Bi${}_{\mathrm{Ga}}$ heteroantisite defects compensate the acceptors, thus reducing the effective hole concentration.

On Oct. 17, 2002, the ESA INTEGRAL observatory was launched into a highly elliptical orbit. SPI, a high resolution Ge spectrometer covering an energy range of 20-8000 keV, is one of its two main instruments. We use data recorded early in the mission (i.e. in March 2003) to characterize the instrumental background, in particular the many gamma-ray lines produced by cosmic-ray interactions in the instrument and spacecraft materials. More than 300 lines and spectral features are observed, for about 220 of which we provide identifications. An electronic version of this list, which will be updated continuously, is available for download at CESR. We also report first results from our efforts to model these lines by ab initio Monte Carlo simulation.

Energetic particles from the Sun have only been studied in detail during the last three decades. The modern record is good, although the number of the largest solar particle events are very few. The nuclides made by solar energetic particles in lunar rocks have been used to extend the record of these particles back /spl sim/10/sup 7/ years. The modern and ancient records are similar. By combining both sets of data, it has been inferred that solar particle events much larger than the largest events observed during the last four solar cycles are very rare.

Global distributions of thermal, epithermal, and fast neutron fluxes have been mapped during late southern summer/northern winter using the Mars Odyssey Neutron Spectrometer. These fluxes are selectively sensitive to the vertical and lateral spatial distributions of H and CO 2 in the uppermost meter of the martian surface. Poleward of ±60° latitude is terrain rich in hydrogen, probably H 2 O ice buried beneath tens of centimeter-thick hydrogen-poor soil. The central portion of the north polar cap is covered by a thick CO 2 layer, as is the residual south polar cap. Portions of the low to middle latitudes indicate subsurface deposits of chemically and/or physically bound H 2 O and/or OH.

In this paper, we present methods for the quantitative secondary ion mass spectrometry (SIMS) characterization of amorphous SiGe:H alloy materials. A set of samples was grown with germanium content ranging from 5% to 77% and was subsequently analyzed by electron probe X-ray microanalysis (EPMA) and nuclear reaction analysis (NRA). Calibration of the SIMS quantification was performed with respect to EPMA data for germanium and NRA data for hydrogen.

The Burst Detector X-Ray (BDX) instrument for the Block IIR series of Global Positioning System satellites is described. The BDX instrument can locate and characterize exoatmospheric nuclear detonations by using four sensors consisting of sets of filters over silicon diodes to detect x rays of various energies from the burst. On the BDX-IIR, a fifth sensor with a response spanning those of the other sensors confirms coincidences among the four main channels. The mechanical and electronic features of the BDX-IIR and its sensors are described. The calibrations and the system tests used in flight are presented. The commands for the BDX-IIR are given. The messages sent from the BDX-IIR are described in detail.

Hydrogen out-diffusion from the n/i interface region plays a major role in controlling the fill factor (FF) and resultant efficiency of n-i-p a-Si:H devices, with the i-layer deposited at high substrate temperatures by the hot wire technique. Modeling calculations show that a thin, highly defective layer at this interface, perhaps caused by significant H out-diffusion and incomplete lattice reconstruction, results in sharply lower device FF's due to the large voltage dropped across this defective layer. One approach to this problem is to introduce trace dopant tailing to ‘compensate’ these defects, but the resultant cells exhibit a poor red response. A second approach involves the addition of buffer layers designed to retard this out-diffusion. We find that an increased H content, either in the n-layer or a thin intrinsic low temperature buffer layer, does not significantly retard this out-diffusion, as observed by secondary ion mass spectrometry (SIMS) H profiles on devices. All these devices have a defect-rich i-layer region near the n/i interface and a poor device efficiency. However, if this low temperature buffer layer is thick enough, the outdiffusion is minimized, yielding nearly flat H profiles and a much improved device performance. We discuss this behavior in the context of the H chemical potentials and H diffusion coefficients in the high temperature, buffer, n-, and stainless steel (SS) substrate layers. The chemical potential differences between the layers control the direction of the H flow and the respective diffusion coefficients, which depend upon many factors such as the local electronic Fermi energy and the extent of the H depletion, determine the rate. Finally, we report a 9.8% initial active area device, fabricated at 16Å/s, using the insights obtained in this study.

Radionuclides produced in lunar rocks by cosmic ray interactions are measured using Accelerator Mass Spectrometry or gamma-ray spectroscopy. From these measurements, estimates of the solar proton flux over time periods characterized by the half-life of the isotope under study can be made, if all the cross sections for all the reactions of all cosmic ray particles with all elements found in lunar rocks are known. Proton production cross sections are very important because ∼98% of solar cosmic rays and ∼87% of galactic cosmic rays are protons in the lunar environment. Many of the needed cross sections have never been measured. Targets of C, Al, Si, SiO2, Mg, K, Ca, Fe and Ni have been irradiated using three accelerators to cover a proton energy range of 25–500 MeV. Excitation functions for 7Be, 10Be, 22Na, and 26Al production from Mg and Al will be reported, and the consequences of using these new cross section values to estimate solar proton fluxes discussed.

This paper details preliminary results obtained in incorporating low H content, high substrate temperature hot wire (HW) deposited amorphous silicon material into a substrate solar cell structure. By necessity, since the learning curve for this complete structure involves metal/n‐i/Schottky barrier structure optimization, a large part of the results are focused on this (partial) structure. We have found that the treatment of the top surface of the HW i layer during cooling is crucial to device performance. Without any particular attention paid to the treatment of this surface while the sample is cooling from its high deposition temperature, a significant amount of H diffuses out of the sample during the cooling process, particularly near the surface, resulting in devices with very poor photovoltaic properties. By designing a surface treatment to address this problem, we have been able to deposit HW Schottky structures with device characteristics as good as the best glow discharge devices produced in our l...

GaInNAs solar cells could be useful in next-generation multijunction solar cells if issues surrounding low photocurrents and photovoltages are surmounted. Wide-depletion-width devices generate significant photocurrent using a p-i-n structure grown by molecular beam epitaxy, but these depletion widths are only realized in a region of parameter space that leads to rough surface morphologies. Here, bismuth is explored as a surfactant for the growth of GaInNAs solar cells. Very low fluxes of Bi are effective at maintaining smooth surfaces, even at high growth temperatures and In contents. However, Bi also increases the net donor concentration in these materials, manifested in our n-on-p device structures as a pn-junction that moves deeper into the base layer with increasing Bi fluxes. Quantum efficiency modeling and scanning kelvin probe microscopy measurements confirm the type conversion of the base layer from p type to n type. Bi incorporation in GaAsBi samples shows signs of surface segregation, leading to a finite buildup time, and this effect may lead to slow changes in the electrical properties of the GaInNAs(Bi) devices. Bi also appears to create a defect level, although this defect level is not deleterious enough to increase the dark current in the devices.

The Cameca IMS-3F secondary ion mass spectrometry (SIMS) instrument, now three generations old, is still considered quality surface-analysis equipment. It was designed more than two decades ago, at a time when power transistors were the means of rastering high voltages at high frequencies. In our modification, we have replaced the high-frequency amplifiers with a simple operational amplifier (op amp) circuit that greatly enhances the capabilities of this instrument. In a Cameca dynamic SIMS instrument, the primary ion beam is focused into a small spot (∼5–100 μm) and then is rastered over an area generally between 25 μm×25 μm and 500 μm×500 μm. The raster signal is a sawtooth waveform with separate high and low-frequency components for X and Y, respectively. The transistor design of the raster amplifier does not produce a sharp waveform at high frequencies. Instead, the signal appears rounded at the top and bottom. This, in turn, allows the ion beam to spend more time at the edges of the rastered area, et...

Beryllium-10 contents in the 20-28 dpm/kg range, averaging 24.5 + or - 0.9 dpm/kg, have been obtained for 11 samples taken from along the 35-cm core AIII of the St. Severin LL chondrite. Be-10 content increases with depth in the outermost 8 cm, and there is little change in content at greater depths. Significant disagreement is noted between the measured values and the results of calculations based on the cross sections for proton-induced Be-generating reactions. Cosmogenic Be-10 in stony meteorites is better described as a medium-energy product than a high energy one.

The production rate of Ar-38 in meteorites P(38), has been determined, as a function of the sample's chemical composition, from Kr-81-Kr exposure ages of four eucrite falls. The cosmogenic Kr-78/Kr-83 ratio is used to estimate the shielding dependence of P(38). From the 'true' Ar-38 exposure ages and the apparent Kr-81-Kr exposure ages of nine Antarctic eucrite finds, terrestrial ages are calculated. They range from about 300,000 ages (Pecora Escarpment 82502) to very recent falls (Thiel Mountains 82502). Polymict eucrites from the Allan Hills (A78132, A79017, and A81009) have within the limits of error the same exposure age (15.2 x 10 to the 6th ages) and the same terrestrial age (110,000 ages). This is taken as strong evidence that these meteorites are fragments of the same fall. A similar case is the Elephant Moraine polymict eucrites A79005, A79006, and 82600 with an exposure age of 26 x 10 to the 6th ages and a terrestrial age of 180,000 ages. EETA 79004 may be different from this group because its exposure age and terrestrial age are 21 x 10 to the 6th ages and 250,000 ages, respectively. The distribution of terrestrial ages of Allan Hills meteorites is discussed. Meteorites from this blue ice field have two sources: directly deposited falls and meteorites transported to the Allen Hills inside the moving Antarctic ice sheet. During the surface residence time meteorites decompose due to weathering processes. The weathering 'half-life' is about 160,000 ages. From the different age distributions of Allan Hills and Yamato meteorites, it is concluded that meteorite concentrations of different Antarctic ice fields need different explanations.

The interaction of galactic cosmic rays (GCR) and solar cosmic rays (SCR) with bodies in the solar system is discussed, and what the record of that interaction reveals about the history of the solar system is considered. The influence of the energy, charge, and mass of the particles on the interaction is addressed, showing long-term average fluxes of solar protons, predicted production rates for heavy-nuclei tracks and various radionuclides as a function of depth in lunar rock, and integral fluxes of protons emitted by solar flares. The variation of the earth's magnetic field, the gardening of the lunar surface, and the source of meteorites and cosmic dust are studied using the cosmic ray record. The time variation of GCR, SCR, and VH and VVH nuclei is discussed for both the short and the long term.

Gamma-ray spectrometers on the Apollo 15 and Apollo 16 missions have been used to map the moon's radioactivity over 20 percent of its surface. The highest levels of natural radioactivity are found in Mare Imbrium and Oceanus Procellarum with contrastingly lower enhancements in the eastern maria. The ratio of potassium to uranium is higher on the far side than on the near side, although it is everywhere lower than commonly found on the earth.

Calculation of the rates of formation of radionuclides as a function of depth in the moon for bombardments by galactic-cosmic-ray particles and by solar protons. The fluxes and spectra of galactic-cosmic-ray particles and of solar protons as a function of depth in the moon are first determined semiempirically. For galactic cosmic rays, the model emphasizes the production of secondary particles and the attenuation of particles by nuclear interactions. Solar proton calculations cover a range of observed spectral parameters, and only ionization energy losses need be considered. The excitation functions for the nuclear reactions used in these calculations are presented. The calculated production rates are given for a range of depths in the moon and are compared with experimental results and with earlier calculations. The model can also be applied to other effects of particle bombardment.

The basis for transphosphorylation between nucleotides and hydroxyapatite (HA) has been explored. Using a recently-proposed model for the surface of HA and the structure of 2- and 3-membered polyphosphates, a reasonable atomic explanation can be shown for this reaction. Transphosphorylation has been found to result in a pyrophosphate on HA which is distinctive from pyrophosphate absorbed onto HA from solution. The models suggest that this distinction is due to a different orientation of the pyrophosphate on the surface of the HA depending on the origin of the pyrophosphate.

Cosmic‐ray primary and secondary particles induce characteristic gamma‐ray and neutron emissions from condensed bodies in our solar system. These characteristic emissions can be used to obtain qualitative and quantitative elemental analyses of planetary surfaces from orbital altitudes. Remote sensing gamma‐ray spectroscopy has been successfully used to obtain elemental composition of the Moon and Mars during United States Apollo 15 and 16 missions and the Soviet Luna and Mars missions. A remote sensing gamma‐ray and neutron spectrometer will be included aboard the United States Mars Observer Mission. If proper care is not taken in the design of the spectrometer and choice of materials in the construction of the detector system and spacecraft, the sensitivity of these remote sensing spectrometers can be greatly degraded. A discussion of these design and material selection problems is presented.

A model is presented for the differential fluxes of galactic-cosmic-ray (GCR) particles with energies above 1 MeV inside any spherical stony meteorite as a function of the meteorite's radius and the sample's depth. This model is based on the Reedy-Arnold equations for the energy-dependent fluxes of GCR particles in the moon and is an extension of flux parameters that were derived for several meteorites of various sizes. This flux is used to calculate the production rates of many cosmogenic nuclides as a function of radius and depth. The peak production rates for most nuclides made by the reactions and energetic GCR particles occur near the centers of meteorites with radii of 40 to 70 g/cm (2). Although the model has some limitations, it reproduces well the basic trends for the depth-dependent production of cosmogenic nuclides in stony meteorites of various radii. These production profiles agree fairly well with measurments of cosmogenic nuclides in meteorites. Some of these production profiles are different than those calculated by others. The chemical dependence of the production rates for several nuclides varies with size and depth.

This paper presents solar-flare-associated proton and alpha-particle fluxes determined for major events from October 1972 through March 1987 (the period that represents the last part of solar cycle 20 and the whole of solar cycle 21), using data obtained by detectors on board the IMP-7 and IMP-8 satellites, along with earlier obtained data for cycle 20. It was found that the average omnidirectional flux of protons with kinetic energy above 10 MeV for cycle 21 (64/sq cm per sec) is lower than the corresponding number for cycle 20 (92/sq cm per sec) and for the cycle 19 (378/sq cm per sec). No definitive correlation was found to exist between cycle-averaged solar flare proton fluxes and peak sunspot numbers.

The spectrum of the total (diffuse and discrete sources) cosmic gamma-ray background over the 0.3 to 27 MeV range was measured with a 7.0 cm diameter x 7.0 cm long uncollimated NaI(Tl) scintillation counter located on a boom 7.6 m from the Apollo 15 service module. Data on cosmic gamma-rays were taken during transearth coast at various boom extensions, detector gains, and with the plastic anticoincidence scintillator enabled and disabled.