Lanny Ray McHargue

Enhanced cosmic‐ray production of 10Be coincident with the Mono Lake and Laschamp Geomagnetic Excursions

The cosmogenic isotope 10 Be , total Be, and Al were measured in partly varved sediments from the upper 50 m of core 480, leg 64 (DSDP), Gulf of California. The concentration of 10 Be from 1 to 50 kyr is in general agreement with estimates of the geomagnetic dipole moment obtained from archaeomagnetic and marine core research. 10 Be anomalies were also found at 32 kyr and 43 kyr, contemporaneous with the Mono Lake and Laschamp excursions, respectively. The production of 10 Be required to explain these anomalies is too high, particularly for the Mono Lake excursion, to be produced by a combination of decreased geomagnetic field and unprecedented long-term solar activity. We conclude that the cause is a change in the galactic cosmic-ray flux consistent with a supernova event. The coincidence with the two excursions remains a paradox.

Geomagnetic modulation of the late Pleistocene cosmic-ray flux as determined by 10Be from Blake Outer Ridge marine sediments

Abstract The cosmic-ray flux incident upon the Earth during the late Pleistocene, 20–60 kyr B.P., was studied by measuring the cosmogenic radionuclide 10 Be from a marine sediment core at site CH88-10P on the Blake Outer Ridge. The paleointensity of the geomagnetic field for this core was determined by various methods. The variance in the concentration of 10 Be in the authigenic fraction of the sediments from Blake Ridge closely correlates with the inverse of the variance in the paleointensity of the geomagnetic field. The 10 Be signal lags, up to 1000 years of sedimentation, the measured paleointensity of the sediments. In contrast, the data from several other elements, some climatically sensitive, and from beryllium show relationship neither to 10 Be nor to the paleomagnetic data. The relationship between 10 Be concentration and the dipole field intensity ( M / M o ) as measured in the sediments is consistent with theoretical models.

MEASUREMENT OF PROTON PRODUCTION CROSS SECTIONS OF 10BE AND 26AL FROM ELEMENTS FOUND IN LUNAR ROCKS

Cosmic rays penetrate the lunar surface and interact with the lunar rocks to produce both radionuclides and stable nuclides. Production depth profiles for long-lived radionuclides produce in lunar rocks are measured using Accelerator Mass Spectrometry (AMS). For a particular radionuclide these production depth profiles can be interpreted to give an estimate for the solar proton flux over a time period characterized by the half life of the radionuclide under study. This analysis is possible if and only if all the cross sections for the interactions of all cosmic ray particles with all elements found in lunar rocks are well known. In practice, the most important cross sections needed are the proton production cross sections, because 98% of solar cosmic rays and {similar_to}87% of galactic cosmic rays are protons. The cross sections for the production of long-lived radionuclides were very difficult to measure before the development of AMS and only in recent years has significant progress been made in determining these essential cross sections. Oxygen and silicon are major constituents of lunar rocks. We have reported already {sup 14}C production cross sections from O and Si for proton energies 25-500 MeV, and O(p,x){sup 10}Be from 58 160 MeV[6]. Here we present new measurements for the cross sections O(p,x){sup 10}Be,O(p,x){sup 7}Be, Si(p,x){sup 7}Be,Si(p,x){sup 26}Al, and Si(p,x){sup 22}Na from {approximately}30 - 500 MeV.

Accelerator mass spectrometry at Arizona: geochronology of the climate record and connections with the ocean.

There are many diverse uses of accelerator mass spectrometry (AMS). Carbon-14 studies at our laboratory include much research related to paleoclimate, both with 14C as a tracer of past changes in environmental conditions as observed in corals, marine sediments and many terrestrial records. Terrestrial records such as forest fires can also show the influence of oceanic oscillations, whether they are short-term such as ENSO, or on the millennial time scale. In tracer applications, we have developed the use of 129I as well as 14C as tracers for nuclear pollution studies around radioactive waste dump sites, in collaboration with IAEA. We discuss some applications carried out in Tucson for several of these fields and hope to give some idea of the breadth of these studies.

STATUS OF THE NSF-ARIZONA AMS LABORATORY

Abstract The operation of the NSF-Arizona Laboratory is summarized. The methods used to determine accuracy and precision of radiocarbon measurements, and to make corrections for background contaminations are presented. An insulating support which has been installed, and a new heavy-ion beam line which is under construction, are described.

Accelerator mass spectrometry of long-lived light radionuclides

Abstract Many different kinds of paleoclimatic, geological and archaeological records can be characterized by measuring their radionuclide concentrations using accelerator mass spectrometry (AMS). The purpose of this paper is to highlight some applications of AMS, using studies conducted at the Arizona AMS Facility as examples. These include studies of 14 C, 10 Be, 26 Al, and 129 I. The work can be generally divided into two types: (1) methodological studies designed to refine and improve the capabilities of AMS, and (2) studies which utilize radiogenic isotopes as geochronometers or as geochemical tracers. Studies of the first type include the development of our 26 Al measurement capabilities, the construction on an automated sample preparation line and the construction of a plasma oxidation line. Studies of the latter type include 14 C dating of corals, speleothems and bones; new records of 10 Be from marine sediments and extraterrestrial materials; and 129 I studies of the pathways of this isotope in the surface ocean.

Cosmogenic and implanted radionuclides studied by selective etching of lunar soils

Abstract We have made new measurements of the concentrations of 14C and 10Be in lunar surface soils. We discuss the results of these new studies based on different acid etching methods, which provide useful information for future experiments. We also discuss the implications of these results for the production of these radionuclides by galactic and solar cosmic radiation, and the direct implantation of solar-energetic particles into lunar surface material.

Cold‐nuclear fusion within the core of the Earth?

It is proposed that the core of the Earth where metal hydrides are subject to high pressure and temperature conditions is a suitable site for ‘‘cold‐nuclear’’ fusion to proceed. This is compatible with recent experimental evidence, that shows that low levels of cold‐nuclear fusion may take place in hydrides, that hydrogen is soluble in iron at high pressures, and in some models up to 0.4% by weight of the core of the Earth may be hydrogen. If it is assumed that 3He is produced within the Earth by cold‐nuclear fusion, and production and escape to the atmosphere has attained steady‐state, the terrestrial fusion rate λf is between 0.3×10−25 to 4.4×10−25 fusions per second, per deuteron. In contrast to terrestrial radiogenic heat production, cold‐nuclear fusion can produce only 10−5 of the observed terrestrial heat flow.

Accelerator mass spectrometry at Arizona: geochronology of the climatic record and connections with the ocean.

There are many diverse uses of accelerator mass spectrometry (AMS). C studies at our laboratory include much research related to paleoclimate, with C as a tracer of past changes in environmental conditions as observed in corals, marine sediments, and many terrestrial records. Terrestrial records can also show the influence of oceanic oscillations, whether they are short term, such as ENSO (El Niño/Southern Oscillation), or on the millennial time scale. In tracer applications, we have developed the use of I as well as C as tracers for nuclear pollution studies around radioactive waste dump sites, in collaboration with IAEA. We discuss some applications carried out in Tucson, AZ, for several of these fields and hope to give some idea of the breadth of these studies.