Gerry H. Kenner

The First International Intercomparison of EPR-dosimetry with Teeth: First Results

Intercomparison of EPR-dosimetric techniques using tooth enamel had been performed in order to check whether the results produced by different laboratories are consistent and accurate. Participants were supposed to evaluate doses applied to pulverized enamel samples, using routine techniques from their laboratories. The intercomparison has demonstrated a great variety of methods used for dose reconstruction. Peculiarities of experimental approaches are discussed systematically in terms of procedure for recording the EPR-spectra, determination of the amplitude of the radiation induced signal, determination of the dose, and error propagation.

Influence of crushing and additive irradiation procedures on EPR dosimetry of tooth enamel

The effect of the crushing and additive dose procedures used in EPR dosimetry of enamel was studied on the signals with g-factors of 2. 0045 and g, = 2.0018, g. = 1.9975. Eight fractions, ranging in size from <75 micrometers to 2 mm, were prepared from one tooth. Two cases were investigated: crushing of a non-irradiated sample and of a sample previously irradiated (6 Gy from `Co gamma ray source). In the non-irradiated study, the intensity of the native signal at 2.0045 in by circa 1.75 times as the grain size decreased from maximum to minimum. A small in radiation sensitivity (< 8%) was also observed with decreasing grain size. In the irradiated samples, crushing resulted in slight variations of reconstructed doses from expected values, but the worst possible case (grain sizes < 75 micron) showed that additional errors were less than 10%. The radiation sensitivity of enamel measured immediately after exposure is underestimated. It increases by about 15% in the first month. Based on the decomposition of the observed spectra, a new interpretation of transient signals 1108 is proposed which explains the above phenomena. Recommendations about how to use this interpretation in retrospective EPR dosimetry are given.

Comparison of sample preparation and signal evaluation methods for EPR analysis of tooth enamel.

In dose reconstruction by EPR dosimetry with teeth various methods are applied to prepare tooth enamel samples and to evaluate the dosimetric signal. A comparison of seven frequently used methods in EPR dosimetry with tooth enamel was performed. The participating Institutes have applied their own procedure to prepare tooth enamel samples and to evaluate the dosimetric signal. The precision of the EPR measurement and the dependence of the estimated dosimetric signal with irradiation up to 1000 mGy were compared. The obtained results are consistent among the different methods. The reproducibility of the dosimetric signal and its estimated relation with the absorbed dose was found to be very close for the applied methods with one possible exception.

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

During the 1950s, 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.

Effect of mechanically induced background signal on EPR dosimetry of tooth enamel

Abstract The effect of the mechanically induced background ESR signal whose Lande factor is g = 2.0038, width = 0.791 mT, on absorbed dose estimation using the additive method was studied. The intensity and width of this signal increases with decreasing grain size. It was found to be thermally stable and sensitive to 90 Sr radiation. The latter phenomenon should lead to its increasing contribution to the radiation-induced hydroxyapatite signal at g ⊥ = 2.0018 at irradiation with higher doses. However, it was found that the interference between mechanically induced and the hydroxyapatite signals may be interpreted as either ‘negative’ for larger grain size or ‘positive’ for finer grain size. This feature in turn leads to under and overestimation of the hydroxyapatite signal, respectively, and is apparently caused by the inverse relationship between the signal width and grain size. Enamel samples were irradiated with 44, 88, 220, 440, 660 and 880 mGy from a 137 Cs gamma ray source. It was determined that 220 mGy was the lowest absorbed dose that could be reliably detected, while doses as low as 44 mGy could tentatively be identified.

Age-associated Iron Accumulation in Bone: Implications for Postmenopausal Osteoporosis and a New Target for Prevention and Treatment by Chelation

Iron accumulation in tissues is believed to be a characteristic of aged humans and a risk factor for some chronic diseases. However, it is not known whether age-associated iron accumulation is part of the pathogenesis of postmenopausal osteoporosis that affects approximately one out three women worldwide. Here, we confirmed that this accumulation of iron was associated with osteopenia in ovariectomized (OVX) rats (a model of peri- and postmenopausal osteoporosis due to estrogen deficiency). To further investigate whether the increased iron level plays a causal role in the onset of bone loss, we treated OVX rats with an orally active and bone targeted chelator that prevented iron accumulation in their skeletal tissues. The results showed that this treatment mitigated the loss of bone mass and the deterioration of bone micro-architecture. We also found that one possible mechanism of the protective action of iron chelation was to significantly reduce bone resorption. Thus, these findings provide a novel target and a potentially useful therapeutic strategy for the prevention and treatment of postmenopausal osteoporosis and perhaps other age-related diseases.

CORPUS CALLOSUM : MULTIPLE PARAMETER MEASUREMENTS IN RODENTS AND HUMANS

A magnified drawing of a human or a rodent corpus callosum is traced on a digitizing tablet. From this tracing the computer calculates callosal area, perimeter, length, and 99 widths, one for each percentile location along the longitudinal axis of the callosum. In addition, the human program encloses the callosum within a rectangle to obtain several other measures. The use of percentile widths allows one to generate a callosum profile to compare different clinical groups or different species. The human callosum program is compared to one recently reported by another research group.

A computer-aided procedure for measuring swim rotation

As a rat or mouse swims in a small cylinder, its movements are tracked by an observer using a joystick, and the information is sent to a Macintosh computer. The swimming circle is broken into quadrants. The sequence of quadrants entered and the time spent in each quadrant are recorded as the basic data. From the data set one can extract full or partial turns, clockwise or counterclockwise rotations, total activity, and speed of swimming clockwise and counterclockwise. Two laterality indices, one based on full turns and the other on partial turns, are calculated. Test-retest reliability for rats and mice for 3-minute and 5-minute observation intervals are reported.

Improved accuracy of EPR dosimetry using a constant rotation goniometer

Grains of sufficiently small diameter will theoretically result in an isotropic EPR response which is independent of sample orientation. In practice, use of such small grains may present problems of altered sensitivity and newly induced paramagnetic centers. Additionally, the effect of anisotropy is increased with increasing microwave power. This places limits on the effectiveness of the differential power method which allows determination of cumulative dose without the need for a zero background signal. The use of a constant rotation goniometer reduces the effect of anisotropy, making measurements at all microwave powers, and particularly the higher powers, significantly more accurate. Since the organic and the mineralized components of the EPR signal are both effected by anisotropy, this procedure may well result in reduced limits of detection.

A computer-aided procedure for measuring discrimination learning☆

A computer program is described for a two-choice black-white T-maze discrimination task involving 10 trials per day for 5 days. A Gellerman series of 44 semirandom L/R sequences is included within the program to specify the location of the reinforcing stimulus on each trial. A picture of the T-maze appears on the screen, and the experimenter tracks the animalss movements as it goes through the maze. At the end of the 10 trials, the following statistical information is obtained: number of initial choices into the left alley, number of correct choices, number of trials in which no choice was made, median time to make a choice, and a learning score based upon the path taken by the animal. These data are then sent to Excel for statistical processing.