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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.

A pilot program has been initiated at Kirtland AFB, New Mexico to study new methods of environmental characterization and restoration of sites contaminated with potential mixed wastes. The initial program studied four sites whose primary radioactive contaminant was thorium. Geophysical, nuclear, and chemical analyses were performed during the initial phase, with the program currently expanding to include biochemical studies. The entire program was conducted on-site to eliminate public health concerns about hazardous waste movement and to provide a more efficient and effective way to collect and process characterization samples. Chemical analyses showed no significant chemical contamination by metals, semi-volatile organic compounds, and total petroleum hydrocarbons by EPA standards and thus indicated that the soil would not have to be treated as mixed waste. Radioactivity analysis showed a 232 Th activity that ranged from background levels to over 1000 pCi/g. Additionally, using dry sieving, a correlation was found between sample radiation content and soil grain size. It is planned to exploit this effect later in the program when site remediation strategies are developed.

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 cameras use the kinematics of Compton scattering to construct a source image without the use of collimators or masks. Compton telescopes were first built in the 1970s for astronomical observations. The first laboratory instrument was designed for medical imaging. Recently, three dimensional imaging has been demonstrated using an array of high resolution germanium detectors for characterization of mixed radioactive waste containers. Image resolution depends on the detector accuracy in both energy and position and on the image reconstruction algorithm. Advantages of Compton imaging include a wide field of view, background suppression, the ability to image high energy gamma rays (up to 10 MeV) and the ability to obtain three dimensional images from a fixed position on one side of the source without the need for tomography. The operation of Compton cameras will be reviewed along with recent results and future prospects.

A Compton camera was constructed using four individual high-purity germanium (HPGe) coaxial detectors in the front plane and four elements of a 15 element HPGe coaxial array in the back plane. 60Co, 133Ba, and 137Cs sources were used in configurations that included single sources in positions covering the intended field-of-view and multiple sources of both identical isotopes and different isotopes. Experiments were also conducted with sources in waste-container sized attenuating media. This proof-of-concept experiment was designed to demonstrate non-tomographic three-dimensional imaging for the characterization of mixed waste containers. The present analysis demonstrates three-dimensional imaging of multiple sources at multiple energies and the imaging of sources within a waste-container sized attenuating medium.

Cosmic ray interactions with materials result in secondary neutrons which are easily measurable. The magnitude of this neutron flux depends on geomagnetic latitude, altitude, and on the materials that constitute the local environment. In general the neutrons produced by cosmic rays in a given object depend on the atomic number, density, and total mass of the elements which constitute that object. Any massive object will have a unique “neutron signature” depending on its materials and structure. To test if this phenomenon might be used to determine if a closed canister contains a specific object, such as a missile, we conducted a proof of concept study. The study had two parts, experimental and Monte Carlo simulations. The object was to perform measurements and simulations of a “block missile mockup”. We constructed the mockup at approximately one-sixth the mass of a real missile. A clear neutron signature was observed from this mockup experimentally, and modeling predictions agreed well with the data. Predictions from our results indicate that a full sized missile should produce a very distinct signature.

In our previous work, a 1 mm thick 238U (uranium) disk backed by a charged-particle detector, when exposed to the neutron flux from a 252Cf (californium) source (mean neutron energy of 2.2 MeV), showed a count-rate increase that was higher than can be accounted for by the detection of short-range primary fission fragments. Electrons resulting from fission product decays were seen as a more plausible reaction mechanism. The current study extends the investigation of this phenomenon by using six 238U disks ranging in thickness from 100 μm to 1 mm in order to discern the relationship between disk thickness and neutron detection efficiency. Also considered is the effect of using thin foils of nonfissionable material in order to suppress the α-particle background from the 238U disks. The exact isotopic composition of these 238U samples is known, which eliminates a source of ambiguity in the previous study. With these samples we find that the excess neutrons found in the previous study are not seen. This forces us to conclude that the results reported in our previous work were not due to the detection of electrons resulting from β-decay of the fission products of 238U, but were most likely the result of the interaction of a neutron with an impurity in the previous samples.

Currently, the detection of ambient levels of tritium in the atmosphere using beta decay techniques is limited by the need for large sample volumes and long sampling and processing times. Accelerator mass spectrometry (AMS) can significantly reduce both the counting time and the sample size in tritium measurements. Using the Crocker Nuclear Laboratory (CNL) cyclotron we have achieved an efficiency of 1.8 × 10−5 with a T/H ratio of 2.2 × 10−13 using a sample size of 32 mBq (0.85 pCi). Counting times were between 4 to 6 min. An analysis of the current results as well as future improvements will be discussed. The current research demonstrates the great potential for a dedicated, monoenergetic, low energy AMS system to meet the needs of low-level tritium detection.

A rugged HPGe detector capable of taking high resolution data in a vibrational environment has been developed. The objectives included a detector with 35% gamma efficiency and 1.90 keV energy resolution (both quantities measured at 1332.5 keV), a dewar with a capacity of 1.2 l and a hold time of 24 h. Results of vibration tests performed on large HPGe detectors hard mounted on a shake table were used to guide detector modifications in this program. Severe resonances were found in the low frequency region for transverse vibrations for commercial hand-held detectors. These were eliminated in a redesigned rugged detector with a stiffened dewar and a solid cold finger. This detector with a further improved dewar has a hold time of nearly 40 h and a better performance in a vibrational environment. To fabricate rugged detectors, crucial components in the dewar-cryostat arrangement must be stiffened and all components mounted securely.

Commonly used least-squares fitting procedures can lead to strongly biased results when fitting peaks with very low statistics. The problem has been identified as being due to large statistical fluctuations in the data, leading to large variations in the weights used for the fit. Several modifications to the least-squares method are investigated for efficiency in eliminating the bias. These are tested on a set of gamma-ray spectra constructed in the laboratory and variously summed so as to give results with statistics increasing from very low to good. Three-point averaging or five-point smoothing of the data for calculating the weights are found to give consistent, unbiased results on these data. Other modifications of the least-squares method are shown to give less satisfactory results. When applicable, a simple “hand analysis” gives more consistent results than any of the fitting methods.

A review is given of techniques for the complete automatic analysis of multichannel gamma-ray spectra from high-resolution germanium detectors, and a FORTRAN computer program is described. Previously reported fitting methods, peak shape functions, and peak search techniques are discussed. A semi-empirical peak shape is presented which gives a good fit to the variety of peak shapes and intensities which may be found in a spectrum. Equivalence is shown between a peak search using the covariance of a general peak shape with the data and a search using a general zero-area transform on the data. A comparison is made of the sensitivities of four different transforms when used in a peak search.

The detection of very low concentrations of tritium in the atmosphere requires rather large samples and counting times using conventional radioactive decay techniques. Substantial reductions in both sample size and counting time can be realized using accelerator mass spectrometry techniques. We have used the sector-focused cyclotron at the Naval Research Laboratory to detect tritium in hydrogen at the level of 1 part in 1012 in a 4 ml sample of hydrogen at 1 atm pressure and 15 min counting time. The detection techniques as well as improvements in beam transport efficiency and elimination of memory effects in the accelerator will be presented.

The peak-to-total ratio and absolute efficiency of a 5″ dia. × 5″ NaI crystal for gamma-ray energies from 0.4 to 9.2 MeV have been measured by using a magnetic spectrometer to isolate nuclear states which decay by only one gamma transition. Particle-gamma-ray coincidence measurements provide the pulse-height spectrum for a single gamma-ray energy. The detector efficiency is determined by detecting only those particles leading to the nuclear state which provides the desired gamma ray. The efficiency is given by the ratio of the coincidence counts in the gamma-ray spectrum to the particle counts in the spectrometer. The peak-to-total ratio data were supplemented by singles measurements from some gamma-ray sources and (p,γ) and (p,αγ) reactions.

A fast approximation to the complementary error function has been programmed and tested for use in the peak-shape function for fitting peaks in gamma-ray spectra. The function was compared for speed and accuracy on the NRL ASC 7 computer to the mathematical library version of the complementary error function. The approximation has resulted in a 50% time savings in the computer program HYPERMET which was developed at NRL for automatic analysis of gamma-ray spectra from germanium detectors.

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.

Symptoms associated with one unit of solution of posterior pituitary extract given intravenously occur frequently but are transient, variable, and do not contraindicate the use of the drug. Injections have been given to thousands of patients and only one in over 28 years was found to be unusually susceptible, and while she was sick for several hours, she was never critically ill. She also consented to two subsequent studies. Death is usually due to hemorrhage and shock from the ruptured uterus following the injection of from 5 to 10 units of the pituitary solution. There are numerous subjective symptoms in postpartum patients receiving oxytocic medication intravenously. In 2 groups of patients totaling 37 who received intravenous injections of ergonovine maleate 0.4 mg., there were 57 per cent who experienced cramping; 19 per cent dizziness; 14 per cent nausea (one case associated with emesis); 14 per cent flushing; and small numbers who complained of cardio- or laryngospasm, headache, desire to defecate or to urinate, tingling of breasts, tinnitus, and palpitation. Very few of the symptoms can be attributed to the psychic effect of an intravenous injection. Also, there were 58 per cent who developed a transient rise in blood pressure after intravenous ergonovine. Thus, one must conclude that a therapeutic dosage of ergonovine given intravenously can produce definite, distressing symptoms which are transient and variable.