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During World War II, the Hanford Site in Washington became the location for U.S. plutonium production. In 2004, a bottle containing a sample of plutonium was recovered from a Hanford waste trench. Here, state-of-the-art instrumental analyses, reactor model simulations, and investigative science techniques were used to provide insights as to the origin of this unknown sample, a process collectively termed as nuclear archeology. Isotopic age dating conducted on the sample in 2007 indicated the sample was separated from the spent fuel 61.6 +/- 4.5 years earlier. The isotope (22)Na, a detectable product of a secondary nuclear reaction, proved useful as a powerful tool for nuclear forensic analysis as (1) an easily detectable signifier of the presence of alpha emitting actinides, (2) an indicator of sample splitting, and (3) a measure of the time since sample splitting. Analytical results of minor actinide isotopes and reactor model simulations confirmed the material originated from the X-10 reactor in Oak Ridge, TN. Corroborated by historical documents, we concluded this sample was part of the first batch of Pu separated at T-Plant, Hanford, the world's first industrial-scale reprocessing facility, on December 9, 1944. This sample represents the oldest known collection of man-made (239)Pu in the world.

The Tagish Lake C2 (ungrouped) carbonaceous chondrite fall of January 18, 2000, delivered 10 kg of one of the most primitive and physically weak meteorites yet studied. In this paper, we report the detailed circumstances of the fall and the recovery of all documented Tagish Lake fragments from a strewnfield at least 16 km long and 3 to 4 km wide. Nearly 1 kg of "pristine" meteorites were collected one week after the fall before new snow covered the strewnfield; the majority of the recovered mass was collected during the spring melt. Ground eyewitnesses and a variety of instrument-recorded observations of the Tagish Lake fireball provide a refined estimate of the fireball trajectory. From its calculated orbit and its similarity to the remotely sensed properties of the D- and P-class asteroids, the Tagish Lake carbonaceous chondrite apparently represents these outer belt asteroids. The cosmogenic nuclide results and modeled production indicate a prefall radius of 2.1-2.4 m (corresponding to 60-90 tons) consistent with the observed fireball energy release. The bulk oxygen-isotope compositions plot just below the terrestrial fractionation line (TFL), following a trend similar to the CM meteorite mixing line. The bulk density of the Tagish Lake material (1.64 ± 0.02 g/cm^3) is the same, within uncertainty, as the total bulk densities of several C-class and especially D- and P-class asteroids. The high microporosity of Tagish Lake samples (~40%) provides an obvious candidate material for the composition of low bulk density primitive asteroids.

On the night of March 26, 2003, a large meteorite broke up and fell upon the south suburbs of Chicago. The name Park Forest, for the village that is at the center of the strewnfield, has been approved by the nomenclature committee of the Meteoritical Society. Satellite data indicate that the bolide traveled from the southwest toward the northeast. The strewnfield has a southeast-northwest trend; however, this is probably due to the effects of strong westerly winds at high altitudes. Its very low 56Co and very high 60Co activities indicate that Park Forest had a preatmospheric mass that was at least ~900 kg and could have been as large as ~7 x 10^3 kg, of which only ~30 kg have been recovered. The average compositions of olivine and low-Ca pyroxene, Fa24.7 ± 1.1 and Fs20.8 ± 0.7, respectively, and its bulk oxygen isotopic composition, δ18O = +4.68‰, δ17O = +3.44‰, show that Park Forest is an L chondrite. The ferromagnesian minerals are well equilibrated, chondrules are easily recognized, and maskelynite is mostly ≤50 μm across. Based on these observations, we classify Park Forest as type 5. The meteorite has been strongly shocked, and based on the presence of maskelynite, mosaicism and planar deformation features in olivine, undulatory extinction in pyroxene, and glassy veins, the shock stage is S5. The meteorite is a monomict breccia, consisting of light-colored, angular to rounded clasts in a very dark host. The light and dark lithologies have essentially identical mineral and oxygen isotopic compositions. Their striking difference in appearance is due to the presence of a fine, pervasive network of sulfide veins in the dark lithology, resulting in very short optical path lengths. The dark lithology probably formed from the light lithology in an impact that formed a sulfide-rich melt and injected it into cracks.

An ordinary chondrite fall in southeast Michigan, USA (near the crossroads hamlet of Worden in northeast Washtenaw County) penetrated the garage roof of a private home on 1997 September 1. The Worden chondrite comprises silicate matrix, mineral fragments, chondrules, chondrule fragments, and opaque primary phases. Electron microprobe analyses (olivine, Fa23.9; orthopyroxene, FS20.1, En78.8, W01) indicate diagnostic L-chondrite silicate mineral compositions. Recognizable chondrules and chondrule fragments constitute up to 42 vol%. Chondrule boundaries are readily discernable (especially where chondrules have rims of opaque material) but not sharp, and discrete plagioclase crystals are visible in the devitrified mesostasis of barred olivine chondrules; together, these characteristics suggest petrologic type S. The spatially averaged ensemble of shockrelated features (optical extinction of olivine grains, minor localized shock melt) suggests assignment of a shock stage of S3. The 26 Al and 22Na activities are typical for an L chondrite. Worden fell near the most recent solar minimum in 1997, and the 22Na production rate should have been at a level approaching the maximum levels due to solar modulation of the galactic cosmic-ray flux. The low value for the Worden 22Na activity relative to those observed in chondrite falls associated with the 1969 solar maximum and 1976 solar minimum suggests a relatively small preatmospheric size. The 60Co activity confirms the indication of a small body. The 56Co activity was essentially zero, indicating that none of the recovered meteorite contained material exposed to solar cosmic rays. The Worden chondrite is the fourth documented fall in Michigan, and the fourth stony meteorite recovered in Michigan; all other Michigan meteorites are finds, not observed falls, and are iron meteorites. All Michigan falls to date are ordinary chondrites. The three falls prior to Worden were Allegan (HS) fell 1899; Rose City (HS, brecciated, black (dark matrix)) fell 1921 ; and Coleman (L6, veined (shocked); Osborn et aI., 1997) fell 1994. Worden has a much lighter matrix than Rose City, and is less extensively thermally and shock metamorphosed than either Rose City (StOffler et aI., 1991) or Coleman.

— The compositionally typical H5 chondrite St-Robert has an exposure age, 7.8 Ma, indistinguishable from that of the main cluster of H chondrites. Small values of the cosmogenic 22Ne/21Ne ratio in interior samples imply a pre-atmospheric radius on the order of 40 cm. Sample depths based on tracks and the production rates of Bhattacharya et al. (1973) range from 6 to ∼40 cm and are generally larger than depths estimated from published 60Co activities, perhaps because the track production rates adopted are too high. Depth profiles of the production rates of 14C, 36Cl, 26Al, 10Be, and 21Ne in stony material show increases with depth and reach levels 5% to 15% higher than expected from modeling calculations. The maximum concentrations in St-Robert are, however, generally comparable to those measured for the L5 chondrite, Knyahinya, whose pre-atmospheric radius of ∼45 cm is thought to lead to the maximum possible production rates in chondrites. We infer that the pre-atmospheric radius of St-Robert was within 5 cm of the value that supports maximum production rates (i.e., 45 ± 5 cm). This radius corresponds to a pre-atmospheric mass of (1.3 ± 0.4) × 103 kg. The agreement of exposure ages for St-Robert obtained in several different ways and the similarity of the depth profiles for 14C, 26Al, 10Be, and 21Ne argue against a lengthy pre-exposure of St-Robert on the parent body and against a two-stage exposure after launch from the parent body. Following Morbidelli and Gladman (1998), we suggest that St-Robert was chipped from deep in its parent body, spent the next 7–8 Ma without undergoing a major collision, was nudged gradually into an orbital resonance with Jupiter, and then traveled quickly to Earth.

— A 0.5 kg stony meteorite associated with a bright bolide seen over southeastern Michigan on 1994 October 20 has been recovered. The circumstances of the fall and recovery of this chondrite, named Coleman, are presented. The most likely trajectory from the observations of the event implies preatmospheric orbital parameters typical of meteorites. Gamma-ray spectrometry of the cosmogenic radionuclides showed that the recovered mass was an interior fragment of a larger body and revealed abnormally high 22Na and 26Al activity. Electron microprobe analysis yielded compositions of Fa24.1 and Fs20.3, which are consistent with an L-chondrite classification. Petrographically, the presence of chondrules, the observed mineralogy and the degree of chondrule-matrix integration suggests assignment to petrologic type 6.

— The Peekskill H6 meteorite fell on 1992 October 9. We report extensive measurements of cosmic-ray produced stable nuclides of He, Ne, and Ar, of the radionuclides 22Na, 60Co, 14C, 36Cl, 26Al, and 10Be, and of cosmic-ray track densities. After correction for shielding via the 22Ne/21Ne ratio, the concentrations of cosmic-ray produced 3He, 21Ne and 38Ar give an average exposure age of 25 Ma, which is considered to be a lower limit on the true value. The 10Be/21Ne age is 32 Ma and falls onto a peak in the H-chondrite exposure age distribution. The activities of 26Al, 14C, 36Cl, and 10Be are all close to the maximum values expected for H-chondrites. Together with cosmic-ray track densities and the 22Ne/21Ne ratio, these radionuclide data place the samples at a depth >20 cm in a meteoroid with a radius >40 cm. In contrast, the 60Co activity requires a near-surface location and/or a much smaller body. Calculations show that a flattened geometry for the Peekskill meteoroid does not explain the observations in the context of a one-stage irradiation. A two-stage model can account for the data. We estimate an upper bound of 70 cm on the radius of the earlier stage of irradiation and conclude that Peekskill's radius was

The St-Robert (Quebec, Canada) meteorite shower occurred on 1994 June 15 at 0h02m UT accompanied by detonations audible for >200 km from the fireball endpoint. The fireball was recorded by visual observers in Vermont, New York State, New Hampshire, Quebec and Ontario as well as by optical and infrared sensors in Earth-orbit. Penetration to an altitude of 36 km occurred ∼60 km to the northeast of Montreal, where the bolide experienced several episodes of fragmentation. A total of 20 fragments of this H5 chondrite, comprising a total mass of 25.4 kg, were recovered in an ellipse measuring 8 × 3.5 km. One fragment of the shower partially penetrated the aluminum roof of a shed. Interpretation of the visual and satellite data suggests that the fireball traveled from south-southwest to north-northeast, with a slope from the horizontal of 55°–61°. A statistical evaluation of the likely heliocentric orbits for the body prior to collision with the Earth, coupled with theoretical modeling of the entry, suggests an entry velocity in the range of 12.7–13.3 km/s; the meteoroid had moved in a low-inclination orbit, with orbital perihelion located extremely close to the Earth's orbit. From satellite optical data, it is found that the photometric mass consumed during the largest detonation is ∼1200 kg. Estimation of the amplitude of the acoustic signal detected by the most distant observer yields a source energy near 0.5 kt TNT equivalent energy, which corresponds to a mass of order 10 metric tonnes. This measure is uncertain to approximately one order of magnitude. Theoretical modeling of the entry of the object suggests a mass near 1600 kg. Cosmogenic radionuclide activities constrain the lower initial mass to be ∼700 kg with an upper limit near 4000 kg. Seismic data possibly associated with the fireball suggest extremely poor coupling between the airwave and the ground. The total mass estimated to have reached the ground is ∼100 kg (in material comprising >55 g fragments), while the preatmospheric mass is found to be most probably in the range of 1200–2000 kg.

We describe a previously unreported meteorite found in Axtell, Texas, in 1943. Based on the mineralogical composition and texture of its matrix and the sizes and abundance of chondrules, we classify it as a CV3 carbonaceous chondrite. The dominant opaque phase in the chondrules is magnetite, and that in refractory inclusions is Ni-rich metal (awaruite). Axtell, therefore, belongs to the oxidized subgroup of CV3 chondrites, although unlike Allende it escaped strong sulfidation. The meteorite bears a strong textural resemblance to Allende, and its chondrule population and matrix appear to be quite similar to those of Allende, but its refractory inclusions, thermoluminescence properties, and cosmogenic Co-60 abundances are not. Our data are consistent with a terrestrial age for Axtell of approximately 100 years and a metamorphic grade slightly lower than that of Allende.

The Noblesville meteorite is a genomict, regolith breccia (H6 clasts in H4 matrix). Moessbauer analysis confirms that Noblesville is unusually fresh, not surprising in view of its recovery immediately after its fall. It resembles 'normal' H4-6 chondrites in its chemical composition and induced thermoluminescence (TL) levels. Thus, at least in its contents of volatile trace elements, Noblesville differs from other H chondrite, class A regolith breccias. Noblesville's small pre-atmospheric mass and fall near solar maximum and/or its peculiar orbit (with perihelion less than 0.8 AU as shown by natural TL intensity) may partly explain its levels of cosmogenic radionuclides. Its cosmic ray exposure age of about 44 Ma is long, is equalled or exceeded by less than 3 percent of all H chondrites, and also differs from the 33 +/- 3 Ma mean exposure age peak of other H chondrite regolith breccias. While Noblesville is now among the chondritic regolithic breccias richest in solar gases, elemental ratios indicate some loss, especially of He, perhaps by impacts in the regolith that heated individual grains. While general shock-loading levels in Noblesville did not exceed 4 GPa, individual clasts record shock levels of 5-10 GPa, doubtless acquired prior to lithification of the whole-rock meteoroid.

Accelerator mass spectrometry (AMS) is a mass spectrometry technique making use of tandem accelerators and high-charge states for determination of very small isotopic ratios (10−10 to 10−15). The technique takes advantage of the high ion energies achieved and negative ion interferential instabilities to enable extremely low backgrounds to be achieved. AMS developments, instrumentation, and applications are reviewed.

[1] Reported Xe isotopic abundances in enstatite chondrites (EC's) show some variability, and this makes comparisons to other solar system reservoirs rather difficult. In contrast, we find uniform Xe isotopic abundances in the EC chondrite Abee for a variety of clasts, except for 128Xe and 129Xe, the isotopes affected by neutron capture in I and by extinct 129I. We report averages for the studied clasts which are consistent within error limits with OC-Xe and with the Q-Xe signature. On the other hand, the elemental abundance ratios Ar/Xe are variable between clasts. A strongly reducing environment which is indicated for enstatite meteorites was generally assumed to be consistent with conditions existing in the early inner solar system. Xe isotopic abundances in SNC meteorites from Mars and also those in some terrestrial wells show that distinct isotopic reservoirs coexisted on the same planets. In particular, the Xe isotopic signatures in terrestrial well gases show the presence of a minor distinct component in two of the reported four well gases. These authors suggested that the extra component represents solar Xe, but we show that also a meteoritic xenon reservoir of the Abee-Xe structure is an option. The reported Xe data in Ar-rich (subsolar) EC's show isotopic abundances slightly lighter than those in Abee-Xe, but the relative abundances of Ar, Kr, and Xe indicate only a minor component of elementally unfractionated solar Xe. The elemental ratios suggest rather a different origin for these gases: the loading of solar particles into grain surfaces during exposure at elevated temperatures during accretion of matter in the inner solar system. A model of this type was suggested for the accretion of gases now observed in the atmosphere on Venus. We note that disks of crystalline silicates (including enstatite and olivine) have been observed in T Tauri stars during their early evolution.

The result of a double-blind, cold fusion experiment are reported, in which six laboratories measured the helium content of five identically shaped 2-mm-diam {times} 10-cm-long palladium rods supplied by Fleischmann and Pons. Three rods were initially implanted with {sup 4}He. Before analysis, three of the rods had served as cathodes during electrolysis in cold fusion experiments: two in 0.1 M LiOD, and one in 0.1 M LiOH. The other two, one implanted and one not, served as references. The major observations reported on in this paper are as follows: All the materials, including the as-received palladium stock, contained easily measured quantities of {sup 4}He, well above amounts normally found in high-purity palladium. The {sup 4}He could be totally removed from at least two of the materials, including the as-received palladium stock, by surface etching the samples to a depth of {approximately}25 {mu}m. Helium implanted by alpha-particle bombardment remained in the electrodes through out the electrolysis. No {sup 3}He was measured above detection limits in any of the materials by any of the six laboratories.

Measurement of ionized atoms by mass spectrometry is an alternative to radiation detection for measuring radioactive isotopes. These systems are large and complex; they require trained operators and extensive maintenance. They began as research systems but have been developed commercially for measuring amounts of radioactive isotopes and their atom ratios to other isotopes. Several types of mass spectrometer systems are in use. This chapter covers the basics of mass spectrometry and surveys the application of these instruments for radionuclide detection and discusses the circumstances under which use of mass spectrometers is advantageous, the type of mass spectrometer used for each purpose, and the conditions of sample preparation, introduction and analysis.

Plutonium and other actinides represent important contaminants in the groundwater and vadose zone at Hanford and other DOE sites. The distribution and migration of these actinides in groundwater must be understood so that these sites can be carefully monitored and effectively cleaned up, thereby minimizing risks to the public. The objective of this project was to obtain field data on the chemical and physical forms of plutonium in groundwater at the Hanford site. We focused on the 100-k and 100-n areas near the Columbia River, where prior reactor operations and waste storage was in close proximity to the river. In particular, a unique set of technical approaches were combined to look at the details of Pu speciation in groundwater, as thus its chemical affinity for soil surfaces and solubility in groundwater, as these impact directly the migration rates off site and possible mitigation possibilities one might undertake to control, or at least better monitor these releases.

The preatmospheric mass of the Tagish Lake meteoroid was about 200,000 kilograms. Its calculated orbit indicates affinity to the Apollo asteroids with a semimajor axis in the middle of the asteroid belt, consistent with a linkage to low-albedo C, D, and P type asteroids. The mineralogy, oxygen isotope, and bulk chemical composition of recovered samples of the Tagish Lake meteorite are intermediate between CM and CI meteorites. These data suggest that the Tagish Lake meteorite may be one of the most primitive solar system materials yet studied.

The noble gases for unshocked ureilite ALHA 78019 and moderately shocked ureilite Kenna are measured. The preparation of the samples and the analysis procedures are described. The analyses reveal that for ALHA 78019 the residue yield equals 2.5 percent of the original mass of the meteorite and 25 percent of the gas is contained in the fine-grained amorphous carbon, and for Kenna the residue yield equals 2.9 percent and 60 percent of the noble gas is contained in the carbon. It is noted that the gases and carbon are present in the ureilites prior ot the shock that produced the diamond, and the shock has no effect on the origin of the carbon in these meteorites. The source of the gas-rich carbon in the ureilite ALHA 78019 is investigated; the Xe-130/C ratio, which equals 4.2 x 10 to the -10th, implies that the gases were acquired while the ureilite was exposed to the solar nebula.

The sorption of Ne, Ar, Kr, and Xe was studied in carbon black, acridine carbon, and diamond in an attempt to understand the origin of trapped noble gases in meteorites. The results support a model in which gases are physically adsorbed on interior surfaces formed by a pore labyrinth within amorphous carbons. The data show that: (1) the adsorption/desorption times are controlled by choke points that restrict the movement of noble gas atoms within the pore labyrinth, and (2) the physical adsorption controls the temperature behavior and elemental fractionation patterns.

The RC027 lightly-shocked ureilite contains less than 1 percent of a fine-grained interstitial silicate that has an igneous texture indicating crystallization from an interstitial liquid. RC027 is also noted to exhibit the strongest olivine preferred-orientation thus far observed in a ureilite; its fabric is characteristic of fabrics formed by tabular minerals in a fluid laminar flow regime, and is unlike those formed by synectonic recrystallization and plastic flow. The elemental and isotopic compositions of noble gases in RC027 are typical of previously analyzed ureilites.

Although the earth's atmosphere contains Ne, Ar, and Kr in about C1,2-chondrite proportions, Xe is depleted about 20-fold. To test the suggestion that the 'missing' Xe is trapped in Antarctic ice, distribution coefficients for Xe in artifically formed frost at -20 to -60 C were measured, using Xe-127 tracer. The values are 0.098 + or - 0.004 cc STP/g atm for trapping and less than 5 cc STP/g atm for trapping plus adsorption. If these results are representative of natural ice, then the Antarctic ice cap contains less than 1 percent of the atmospheric Xe inventory, or not greater than about 0.001 the amount needed for a C1,2-chondrite pattern. Two possibilities remain for the 'missing' Xe, both on the premise that the earth's noble gases, along with other volatiles, came from chondritic material: (1) xenon is preferentially retained in the mantle and lower crust, due to the strong affinity of Xe for clean silicate surfaces and amorphous carbon; and (2) the source material of the earth's volatiles had high, relatively unfractionated, Ar/Xe and Kr/Xe ratios, like the non-carbonaceous noble gas carriers in C3O and E-chondrites.

The sorption of Xe-127 at 5 x 10 to the -7th atm onto carbon black, pyrolyzed polyvinylidene chloride, and pyrolyzed acridine at 100-1000 C for 5 min-240 h is measured experimentally by gamma spectrometry. The results are presented in tables and graphs and characterized in detail. The tightly bound Xe remaining in the samples after 4000 min pumping at temperatures above 100 C is found to comprise two components: a low-temperature component attributed to physisorption within an atomic-scale labyrinth of micropores, and a high-temperature component due to volume diffusion. The implications for the trapping of noble gases near grain surfaces of amorphous carbon in meteorites are considered.

Primitive meteorites contain up to 400 ppm of a very fine-grained type of carbon tentatively called C-delta. Evidence is presented here that part of all of the C-delta is primary, not shock-produced, diamond formed by stellar condensation as a metastable phase. It appears that interstellar dust contains diamond.