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Three-dimensional optical random access memories (3D ORAMs) are a new generation of high-density data storage devices. Binary information is stored and retrieved via a light induced reversible transformation of an ensemble of bistable photochromic molecules embedded in a polymer matrix. This paper describes the application of 3D ORAM materials to radiation dosimetry. It is shown both theoretically and experimentally, that ionizing radiation in the form of heavy charged particles is capable of changing the information originally stored on the ORAM material. The magnitude and spatial distribution of these changes are used as a measure of the absorbed dose, particle type and energy. The effects of exposure on 3D ORAM materials have been investigated for a variety of particle types and energies, including protons, alpha particles and 12C ions. The exposed materials are observed to fluoresce when exposed to laser light. The intensity and the depth of the fluorescence is dependent on the type and energy of the particle to which the materials were exposed. It is shown that these effects can be modeled using Monte Carlo calculations. The model provides a better understanding of the properties of these materials. which should prove useful for developing systems for charged particle and neutron dosimetry/detector applications. c2001 Published by Elsevier Science B.V.

The status of pollution of the Arctic basin is studied in ecological terms, and the interactions of the Arctic ecosystem with the global system are estimated. A spatial simulation model for the kinetics of pollutants in the Arctic basin is proposed in which the ecological and spatial distribution of the hydrological parameters is taken into account. The model includes blocks describing the flows of pollutants in the trophic chains, the exchange between the water–ice system and the atmosphere and the interaction of the water ecosystem with the global biosphere–climate system. A global model controls the inputs of the simulation model and makes it possible to compute the dynamics of the distribution of pollutants between the Arctic aquatories, which include the Central basin and the peripheral seas. The model uses both published data and the data of the US/Russian expedition to Siberia accomplished in the summer of 1995. Climatic and anthropogenic processes are described in the form of scenarios. The results of computer experiments are given demonstrating the advantages of the simulation model to forecast and to estimate the dynamics of radionuclides, heavy metals and oil hydrocarbons in the Arctic Seas. The total and local pictures of the spatial distribution of pollutants in the Arctic basin are given as functions of various environmental and anthropogenic parameters. It is concluded that the use of the global biospheric model enables the consideration of the interactions between the Arctic basin environment and adjoining territories. This allows estimates to be made of the consequences of the anthropogenic impact on the Arctic ecosystem.

The first experimental investigation has been performed of radiation effects on three-dimensional optical random-access-memory materials. Thin films of poly(methyl methacrylate) doped with spirobenzopyran were irradiated with uniform fluxes of protons, α-particles and 12 C +3 ions, at fixed energies per nucleon from 0.5 to 2.5 MeV and fluences from 10 10 to 10 14 cm −2 . The exposed films were examined under a confocal laser scanning microscopy system which is capable of optically sectioning the materials. The irradiation resulted in a permanent change in the materials from a nonfluorescent form to a form which is fluorescent under both 488 and 514 nm excitation. Profiles were measured of fluorescent intensity versus depth, and of intensity versus dose. It was found that both the particle energy and the dose can be obtained from measuring the width of the depth profile and the fluorescent intensity. These properties are very promising for dosimetry applications since they allow calculation of an accurate dose equivalent.

This paper considers the problem of the origin of the pollution level in the Yenisey river estuary which is located in north-central Siberia and empties into the Kara sea. In the framework of this problem, a joint American–Russian environmental and hydrophysical expedition to the Angara and Yenisey rivers of Siberia was accomplished in the summer of 1995. Using the results of the pollution measurements taken during this expedition, it becomes possible to begin the synthesis of the spatial mathematical model for pollution transport in the Angara–Yenisey river system. The model includes blocks describing the flows of pollutants from biogeochemical, hydrophysical and anthropogenic sources. The influence of soil–plant formations are considered. The model is designed for interactive use in the mode of a computer experiment. The results of model calculations and of the expedition are given.

Compton imaging systems have a number of advantages for characterization of nuclear waste, such as identifying hot spots in mixed waste in order to reduce the volume of high-level waste requiring extensive treatment or long-term storage, and imaging large objects or contaminated areas. Compton imaging also has potential applications for monitoring production, deployment, shipping and storage of nuclear warheads and components in the verification of treaties such as START I and II, the Comprehensive Test Ban Treaty and the Non-Proliferation Treaty. This article presents a brief historical perspective and discusses system design requirements and performance specifications for these applications. The advantages of Compton imaging are compared to competing imaging technologies.

Germanium detector systems with both high spectral resolution and good imaging capabilities to the problems of environmental remediation. Over the last year, much progress has been made. We have (1) developed and built amorphous-contact germanium detectors of increasing sophistication, (2) built and tested an array of four position sensitive germanium detectors, (3) demonstrated spectroscopy and imaging uses with 235U, and Results from this research were presented at the EMSP's first workshop in Chicago in 1998, at the SPIE Session in July 1999, and at the IEEE Nuclear Science Symposium in November 1998 and 1999. AMORPHOUS CONTACTS The goal of the amorphous contact effort was to extend the single element (pixel) amorphous technology developed by Luke et al. (1994) to double-sided orthogonal strip detectors. Amorphous contact provides multiple advantages over the current lithium contact technology. We have fabricated the first orthogonal strip detector with dimensions appropriate for field use. The detector has an active volume of 50 mm x 50 mm x 10 mm and has 25 x 25 strips (see Figure 1). It is currently undergoing tests. The resolution is {approx}12 keV FWHM, which is dominated by electronic noise. The noise was high because of the large capacitance and the non-optimal electronics used with the test cryostat.

Significant quantities of Be-7 have been found on the leading edge of the Long Duration Exposure Facility (LDEF), which was returned to earth after almost six years in space. Although the absolute atmospheric concentration of Be-7 needed to explain this detection is extremely small, its concentration at LDEF's altitude must be several orders of magnitude higher than in the stratosphere below, where it is produced by cosmic-ray reactions with atmospheric nitrogen and oxygen nuclei. The detection may lead to the use of Be-7 as an exoatmospheric tracer as well as to studies of surface interactions in space.

The goal of this project is the development of field portable gamma-ray detectors that can both image gamma rays from radioactive emission and determine the isotopic composition by the emitted spectrum. Most instruments to date have had either very good imaging with no spectroscopy, or very good spectroscopy with no imaging. The only instruments with both imaging and spectroscopy have had rather poor quality imaging and spectroscopy (e.g. NaI Anger Cameras). The technology would have widespread applications, from laboratory nuclear physics, to breast cancer imaging, to astronomical research. For this project, we focus on the applications in the field of fissile materials, spent nuclear fuels and decontamination and decommissioning.

'The objective of this research is the development of high resolution germanium detector systems for direct imaging of spent nuclear fuels and fissile materials and Compton scatter imaging of large objects of arbitrary size. A small configuration of detectors shall be assembled to demonstrate the performance of such a system. The efforts in this first year of a three year program have been focused on the design and procurement of a four detector array of germanium strip detectors. The basic detector is a 5 cm x 5 cm x 1 cm thick planar germanium detector with segmented anode and cathode. These segmentations are in the form of strips with a pitch of 2 millimeters. The strips on the anode side run orthogonal to the strips on the cathode side so that, in a gamma-ray interaction, the collection of electrons and holes on opposite electrodes produces signals which identify the interaction position in two dimensions. Each detector in the array has 25 anode contacts and 25 cathode contacts. The detector array has been designed as a planar array providing 100 square centimeters of active area mounted in a single cryostat. To reduce electronics channel count, parallel strips from adjacent detectors are electrically joined together effectively making strips that are 10 cm long. In this configuration, 100 channels of electronics are required to readout the array. In a related project, the authors are investigating processes to produce improved contacts for germanium strip detectors which would offer both more reliable extended use and the potential for finer strip pitch or position resolution. Investigating amorphous contacts, they have, to date, prepared two Ge test detectors. One was produced using n-type Ge and the other p-type Ge. The p-type detector has a Li diffused contact on one side while the n-type detector has a B ion-implanted contact. Amorphous contacts have been formed on the opposite side of each detector by RF sputtering. They are currently conducting a series of leakage current versus operating temperature measurements in order to determine the barrier heights of the amorphous contacts. The use of n and p type detectors will allow us to measure the electron and hole blocking behavior of the contacts respectively. This will provide important information on the nature of these contacts and will determine if double-sided strip detectors can be produced using only amorphous contacts.'

A prototype electronics package of amplifier, ADC, pulser, data-bus interface, bias supply and low voltage supply has been developed to process high resolution data from rugged intrinsic germanium detectors with high reliability in a harsh environment. This sturdy modular package attachable to the dewar of a rugged detector oriented horizontally or downward degrades detector energy resolution at 1332 KeV less than 0.25 KeV.

The γ-ray decay of neutron particle-hole states in 140 Ce has been studied with the reaction 140 Ce(p,p′γ o ) 140 Ce. Evidence is presented that the strong ground-state γ rays observed from some of these states are E1 transitions. This allows the identification of 1 − states.

Proton resonance structure was observed in the 205Tl(d, p) reaction at single-particle energies for out-going protons leading to all strongly excited states below 3 MeV excitation in 206Tl. Decay of the isobaric analog of the 207Tl ground state was not observed.

This report describes the results of an experiment to measure the natural gamma radiation emitted from the earth's surface with the aid of radiation detectors mounted in an aircraft. For comparison, two detector systems were used: an array of intrinsic germanium detectors with a total active volume of 0.4 liter and a single NaI(Tl) scintillation detector 30.5 cm diam X 30.5 cm long. Data were recorded on flights at altitudes of 60, 120, 240, 300 and 5100 meters and with average airspeed of 200 knots. A discussion is presented on the application of germanium detectors to the atmospheric radon problem; in particular, on the use of the photons with energy 295, 352 and 609 keV to determine the respective contributions from the air and the surface.