Variation of long-lived free radicals responsible for the EPR native signal in bone of aged or diseased human females and ovariectomized adult rats.

The purpose of this study was to gain insights into the variations seen in the electron paramagnetic resonance (EPR) spectroscopy of the native signals of teeth and bones used for retrospective dosimetry measurements. We determined that changes occur in the long-lived free radicals responsible for the native signal of cortical bone in aging or diseased human females and aged ovariectomized rats. This was done by measuring the magnitude of the broad (BC) and narrow (NC) components of the native EPR signal of bone following chemical extraction, aging, crushing and thermal annealing. Bone from the upper midshaft of femora of young (17-34 years old, n=5) and elderly (70-92 years old, n=18) females was examined. The results showed that the elderly women had significantly higher BC than the younger women (P<0.01). A similar interpretation was made of the data from an aging female rat osteoporosis model. The results for the NC signals were similar. Finally, dramatic decreases in both NC and BC signals were seen in HIV positive and uncontrolled diabetic (one each) patients indicating the need for studying this signal for a broad spectrum of metabolic disorders. Experiments were performed which strongly indicate that iron liganded with organic molecules is the source of the BC signal. Finally, the accuracy achieved in this study indicates that resolving the dosimetric signal (g=2.0018) should be improved by subtraction of the deconvoluted NC and BC signals from the original spectrum.

First international intercomparison of luminescence techniques using samples from the Techa River Valley.

Bricks collected from a contaminated village (Muslyumovo) of the lower Techa river valley, Southern Urals, Russia, were measured using thermoluminescence and optically stimulated luminescence by four European laboratories and a U.S. laboratory to establish and compare the applied dose reconstruction methodologies. The bricks, collected from 60-100-year-old buildings, had accumulated a relatively high dose due to natural sources of radiation in the brick and from the surrounding environment. This work represents the results of a first international intercomparison of luminescence measurements for bricks from the Southern Urals. The luminescence measurements of absorbed dose in bricks collected from the most shielded locations of the same buildings were used to determine the background dose due to natural sources of radiation and to validate the age of the bricks. The absorbed dose in different bricks measured by four laboratories using thermoluminescence and optically stimulated luminescence at a depth of 10 +/- 2.5 mm from the exposed brick surface agreed within +/-21%. After subtraction of the natural background dose, the absorbed dose in brick due to contaminated river sediments and banks was calculated and found to range between 150 and 200 mGy. The cumulative doses in brick due to man-made sources of radiation at 100 and 130 mm depths in the bricks were also measured and found to be consistent with depth dose profiles calculated by Monte Carlo simulations of photon transport for possible source distributions.

Preliminary report on the development of a virtually nondestructive additive dose technique for EPR dosimetry.

We propose a new approach to the additive dose method in EPR dosimetry studies for tooth enamel specimens. We outline a specialized routine whereby the sample may be left for the most part unirradiated, while only a small aliquot of the sample will be additively irradiated to relatively large doses. The routine is done in such a way so as not to significantly compromise either precision or accuracy of the dose reconstruction. It is also demonstrated that the overall throughput of the dose reconstruction is not appreciably compromised. With this potential ability, the utility of an international dose/sensitivity standard for EPR dosimetry of teeth is considered.

An EPR dosimetry method for rapid scanning of children following a radiation accident using deciduous teeth.

Electron paramagnetic resonance dosimetry may be applied to whole deciduous teeth of children. This makes it feasible to make direct measurement of absorbed gamma ray dose in the days and weeks following a nuclear accident, particularly if used in conjunction with a public awareness program. The technique reported here requires little sample preparation and has resulted in precision of approximately 30 mGy (1 sigma) for a deciduous incisor. Under conditions for rapid screening procedures, the methodology is estimated to provide 0.5 Gy accuracy. The largest error in the process is the determination of an appropriate background native signal for subtraction from the whole tooth spectrum. The native signal is superimposed on the radiation-induced signal, and the subtraction requires knowledge of a sample's relative content of enamel and dentin along with their relative native signal intensities. Using a composite background standard, an equivalent absorbed dose of 70+/-38 mGy (1 sigma) was determined. The lower detection limit of the technique was achieved by the elimination of anisotropic effects through rotation of the sample during measurement, together with subtraction of the standard native background signal and empty tube background spectra from the sample spectra.

EPR properties of synthetic apatites, deorganified dentine, and enamel.

Electron paramagnetic resonance spectroscopy (EPR) was used to study synthetic hydroxyapatite and approximately 1, 2, and 6% synthetic carbonated apatites, deorganified dentine, and enamel. The carbonated apatites were synthesized by hydrolysis of dicalcium phosphate. Comparisons were made with spectra from enamel and deorganified dentine. Microwave power saturation and dose responses were determined for the synthetic materials. The Marquardt version of the Levenberg decomposition method was used to extract individual signals from the apatite data. Two samples of dentine were irradiated with 25 and 100 Gy, respectively, from a 60Co source. The first sample was then deorganified at 200 degreesC using the Soxhlet extraction technique. A third sample was irradiated with 100 Gy after deorganification. The resulting EPR spectra were then compared. It was determined that the dosimetric signal of 2% synthetic carbonated apatite was approximately the same as that of enamel. It was also verified that the dosimetric signal saturates at about 2% in synthetic carbonated apatites. The study established that the precenters responsible for the dosimetric signal (g perpendicular = 2.0018, g parallel = 1.9985) are preferentially concentrated in the surface-accessible region of the mineral component, as shown by the approximately 80% attenuation of the dosimetric signal in dentine following deorganification. The precenters responsible are not destroyed by the deorganification since the magnitude of the dosimetric signal from the dentine specimen irradiated following deorganification was approximately twice that of the comparable untreated, irradiated sample. Finally, the dose response of 2 and 6% synthetic carbonated apatites was determined.

Electron paramagnetic resonance techniques and space biodosimetry.

This paper was presented at a workshop addressing the potential of biodosimetry techniques for use in the interplanetary space program. Some of the concerns for adequate dosimetry in space include: (1) a dosimeter that provides a permanent record of the cumulative dose and can be read independently on return to Earth; (2) a dosimeter which cannot be lost, forgotten or inadvertently removed by an individual; and (3) appropriate assessments of radiation exposures that pose an acute health risk and could jeopardize the success of an interplanetary mission. Tooth enamel is a permanent, stable biological dosimeter showing great promise in retrospective dosimetry of radiation accidents. With a proper technique, the minimum detectable dose can be in the range of tens of milligrays in extracted, prepared teeth. In addition to transient accidental doses, the cumulative dose from chronic low-level exposures (which individually may be below reportable limits) is recorded in the enamel of teeth. While many teeth remain with an individual over all or most of a lifetime, one or more are often removed due to dental problems and provide an opportunity to make dosimeteric measurements. The collection and analysis of extracted teeth in later life allows measurement of cumulative lifetime dose using the high-sensitivity techniques described in this paper. The goal of a lightweight, high-sensitivity, in vivo EPR spectrometer has not yet been realized, but its benefit to all aspects of retrospective dosimetry, terrestrial or otherwise, would be great. This paper reviews the current status of EPR dosimetry of teeth as applied to retrospective measurements of accidental exposures and outlines future research directions which will further reduce the limits of detection.

Emerging technological bases for retrospective dosimetry.

In this article we discuss examples of challenging problems in retrospective dosimetry and describe some promising solutions. The ability to make measurements by accelerator mass spectrometry and luminescence techniques promises to provide improved dosimetry for regions of Belarus, Ukraine and Russian Federation contaminated by radionuclides from the Chernobyl accident. In addition, it may soon be possible to resolve the large neutron discrepancy in the dosimetry system for Hiroshima through novel measurement techniques that can be used to reconstruct the fast-neutron fluence emitted by the bomb some 51 years ago. Important advances in molecular cytogenetics and electron paramagnetic resonance measurements have produced biodosimeters that show potential in retrospective dosimetry. The most promising of these are the frequency of reciprocal translocations measured in chromosomes of blood lymphocytes using fluorescence in situ hybridization and the electron paramagnetic resonance signal in tooth enamel.

Preparation-induced errors in EPR dosimetry of enamel: pre- and post-crushing sensitivity.

Polyakov et al. (1995) showed errors in dose estimation as a function of grain size for enamel grains given beta irradiation after crushing. We tested the effect of gamma irradiation applied to the specimens before and after crushing. We confirmed Polyakov's observations and found that post-crushing irradiation altered the slope of the dose-response curve of the hydroxyapatite signal and produced a grain-size-dependent offset. No changes in the slope of the dose-response curve were seen in enamel caps irradiated whole before crushing.

Electron paramagnetic resonance dosimetry of dentine following removal of organic material.

The feasibility of using dentine from surgically extracted human teeth as in vivo dosimeters was investigated. The organic fraction of human dentine was removed by Soxhlet extraction with diethylenetriamine. The specimens were then crushed and 75 to 250 microns granules were given doses of gamma radiation ranging from 50 mGy to 8 Gy. Following irradiation, electron paramagnetic resonance spectra were collected. Signals were detected with Lande factors of g = 2.0018, line width = 0.903 mT; and g = 1.9961, line width = 0.444 mT. These signals have both been reported for hydroxyapatite of bone and enamel. Several other signals were also seen but not characterized. It was concluded that doses of 500 mGy or less may be resolved with prior removal of the organic component of dentine.

Thermoluminescence measurements of gamma-ray doses attributable to fallout from the Nevada test site using building bricks as natural dosimeters.

During the 1950's, the U.S. Government conducted an intensive atmospheric nuclear testing program in Nevada. Fallout from these atmospheric tests was measured throughout the U.S. with some of the heaviest concentrations to populated areas falling east of the test site in Washington County, UT. External exposures from 6.5 x 10(-4) C kg-1 to 26 x 10(-4) C kg-1 (2.5-5.0 R) were reported for this region. This study provides an independent measurement of fallout radiation doses to selected communities in Utah using a thermoluminescence technique originally developed for the dating of ancient pottery. The application of the predose thermoluminescence technique to fallout dosimetry is described. A mean dose of 38 +/- 15 mGy (4.4 +/- 1.7 R), attributed to fallout radiation, was measured in quartz grains extracted from the outer centimeter of bricks removed from six communities in Washington and Kane Counties in Utah.

Application of optically stimulated luminescence to the dosimetry of recent radiation events involving low total absorbed doses.

We determined the suitability of optically stimulated recombination luminescence in quartz for low-level dosimetry of recent events such as radiation accidents. Minimum detectable doses were determined for both fired and unfired quartz. Using a single aliquot technique, good detection of doses on the order of 0.01 Gy in fired quartz was achieved. In unfired quartz, the minimum dose detected was an order of magnitude larger. Using single aliquot optically stimulated regeneration of a natural quartz sample, a dose of 0.18 +/- 0.02 Gy was measured and was in good agreement with the dose determined by multiple-activation thermoluminescence. Delayed measurements of radiation doses on the order of 1 Gy were shown to be feasible in an emergency response situation when measured up to 7 wk following the irradiation event, using a regeneration-ratio technique. Our conclusions are based on observations of 100 degrees C isothermal decay of the luminescence, high-temperature preheating experiments, thermal fading after prolonged room temperature storage, and observations of the relationship between post-annealing residual luminescence and the TL glow curve. We were able to correlate the optically stimulated recombination luminescence of quartz extracted from building tile with the sample's 278 degrees C TL emission.

Metabolism and thermoregulation during stages of sleep in humans exposed to heat and cold.

Electrophysiological stages of sleep, oxygen consumption (VO2), and skin (Tsk) and rectal (Tre) temperatures were recorded from six virtually naked male subjects exposed to ambient temperatures (Ta) of 21, 24, 29, 34, and 37 degrees C. VO2 increased during sleep as a whole as Ta departed from thermoneutrality (29 degrees C) and was significantly greater during rapid-eye-movement (REM) sleep than during adjacent nonrapid-eye-movement (NREM) periods at low and high Ta but not at 29 degrees C. Tsk showed small but significant increases during REM sleep at 29, 34, and 37 degrees C, but Tre did not change during REM sleep at any Ta. Shivering was present during wakefulness at 21 and 24 degrees C but occurred only occasionally during stages 1 and 2 sleep at 21 degrees C. The increases in VO2 and the absence of marked changes in vasomotor tone during REM sleep in the cold were unexpected and possibly indicate that REM sleep is not as thermally disruptive in humans as in other mammals.

Hibernation at moderate temperatures: a continuation of slow wave sleep.

Golden-mantled ground squirrels (Citellus lateralis) displayed virtually continuous electrophysiological states of sleep when hibernating at moderate ambient temperatures (22 degrees C). Rapid-eye-movement sleep progressively diminished with the fall in body temperature so that at a body temperature of 23 degrees C it was completely absent. At this temperature hibernation was characterized by slow wave sleep isomorphic with slow wave sleep episodes at non-hibernating (euthermic) body temperatures.

The effects of high and low ambient temperatures on human sleep stages.

Six male subjects slept nude except for shorts on a bed made from nylon webbing at 5 different ambient temperatures (TaS): 21, 24, 29 (thermoneutrality), 34 and 37 degrees C. Standard electrophysiological recordings were obtained and analyzed for sleep stages. Temperature displayed a significant quadratic trends for nearly every sleep variable, such that TaS above or below thermoneutrality had similar effects on sleep patterns. Multiple comparisons showed that 21 degrees C was the most disruptive condition, and that cold TaS were generally more disruptive to sleep than warm TaS. There were marked individual differences in sensitivity of sleep to cold. Decreases in REM sleep in humans produced by heat or cold probably result from a general disruption of sleep processes rather than being specifically related to the status of the thermoregulatory system during REM sleep.

Pre-fork synthesis: a model for DNA replication.

A model of DNA replication is presented in which DNA synthesis is continuously initiated from parental strand nicks and occurs, with conservation of helix winding number, ahead of the so-called replicating fork. The fork in this model is the locus of unwinding of already replicated, but presumably unstable, DNA. The model, involving Okazaki's notion of multiple initiation, is based upon the properties of Kornberg's DNA polymerase and accounts for the presence of single-stranded nascent DNA fragments in cell lysates. In addition to acting as sites of initiation, the parental strand nicks are implicated as sites of free rotation allowing unwinding of the replicated DNA.