Michael J. Tobin

Bone lead levels in adjudicated delinquents: A case control study

BACKGROUND Lead exposure shares many risk factors with delinquent behavior, and bone lead levels are related to self-reports of delinquent acts. No data exist as to whether lead exposure is higher in arrested delinquents. The goal of this study is to evaluate the association between lead exposure, as reflected in bone lead levels, and adjudicated delinquency. METHODS This is a case-control study of 194 youths aged 12-18, arrested and adjudicated as delinquent by the Juvenile Court of Allegheny County, PA and 146 nondelinquent controls from high schools in the city of Pittsburgh. Bone lead was measured by K-line X-ray fluorescence (XRF) spectroscopy of tibia. Logistic regression was used to model the association between delinquent status and bone lead concentration. Covariates entered into the model were race, parent education and occupation, presence of two parental figures in the home, number of children in the home and neighborhood crime rate. Separate regression analyses were also conducted after stratification on race. RESULTS Cases had significantly higher mean concentrations of lead in their bones than controls (11.0+/-32.7 vs. 1.5+/-32.1 ppm). This was true for both Whites and African Americans. The unadjusted odds ratio for a lead level > or =25 vs. <25 ppm was 1.9 (95% CL: 1.1-3.2). After adjustment for covariates and interactions and removal of noninfluential covariates, adjudicated delinquents were four times more likely to have bone lead concentrations >25 ppm than controls (OR=4.0, 95% CL: 1.4-11.1). CONCLUSION Elevated body lead burdens, measured by bone lead concentrations, are associated with elevated risk for adjudicated delinquency.

In vivo X-ray fluorescence of lead in bone using K X-ray excitation with 109Cd sources : radiation dosimetry studies

Independent experiments have been performed at two centers, to evaluate the dosimetric properties of their respective 109Cd K X-ray fluorescence (XRF) bone lead measurement systems. Measurements were made of the dose to several points on the skin on the lower leg, at the surface of the tibia, in the red marrow tibia cavity, at the midcalf, and in the abdominal region occupied by the conceptus. Overall agreement between the two data sets was found. Similarities and differences are discussed. The effective dose values for an in vivo measurement of tibia lead concentration in 1-, 5-, and 10-year-old and adult subjects were calculated from one data set to be 1100, 420, 190, and 34/38 (male/female) nSv, respectively, for an in vivo median precision (one standard deviation) of 4.9 micrograms Pb (g bone mineral)-1 for a 30-min adult measurement.

Bone lead levels and language processing performance

The relation between bone lead absorption and language processing abilities in 156 randomly selected 11- to 14-year-old boys who were asymptomatic for lead toxicity is examined. Tibial lead concentrations were measured by X-ray fluorescence spectroscopy. The language processing outcome variables consisted of the least and most difficult subtests from the Nonword Repetition Task, Competing Language Processing Task, and the Revised Token Test. Participants were classified by quartiles according to bone lead concentrations, and analysis of variance and analysis of covariance measured the impact on language processing scores. Results showed that children in the highest bone lead quartile displayed decreased language processing performance on the most difficult language processing tasks but not on the easier tasks.

Measurement of fission product gases in the atmosphere

Abstract The ability to quickly detect and assess the magnitude of releases of fission-produced radioactive material is of significant importance for ongoing operations of any conventional nuclear power plant or other activities with a potential for fission product release. In most instances, the control limits for the release of airborne radioactivity are low enough to preclude direct air sampling as a means of detection, especially for fission gases that decay by beta or electron emission. It is, therefore, customary to concentrate the major gaseous fission products (krypton, xenon and iodine) by cryogenic adsorption for subsequent separation and measurement. This study summarizes our initial efforts to develop an automated portable system for on-line separation and concentration with the potential for measuring environmental levels of radioactive gases, including 85 Kr, 131,133,135 Xe, 14 C, 3 H, 35 S, 125,131 I, etc., without using cryogenic fluids. Bench top and prototype models were constructed using the principle of heatless fractionation of the gases in a pressure swing system. This method removes the requirement for cryogenic fluids to concentrate gases and, with suitable electron and gamma ray detectors, provides for remote use under automatic computer control. Early results using 133 Xe tracer show that kinetic chromatography, i.e., high pressure adsorption of xenon and low pressure desorption of air, using specific types of molecular sieves, permits the separation and quantification of xenon isotopes from large volume air samples. We are now developing the ability to measure the presence and amounts of fission-produced xenon isotopes that decay by internal conversion electrons and beta radiation with short half-lives, namely 131m Xe, 11.8 d, 133m Xe, 2.2 d, 133 Xe, 5.2 d and 135 Xe, 9.1 h. The ratio of the isotopic concentrations measured can be used to determine unequivocally the amount of fission gas and time of release of an air parcel many kilometers downwind from a nuclear activity where the fission products were discharged.

Past occupational exposure to lead: association between current blood lead and bone lead.

Mobilization of lead from bone is known to increase with age. The authors performed the current study to determine whether there was an association between current blood lead and bone lead in workers with no current exposure but with significant past workplace exposure. The authors assessed 58 men, aged 40 to 76 years, who had earlier exposure to lead and determined both current blood lead levels and bone lead levels. At the time of the current assessment, the average blood lead level was 10.9 μg/dL and tibia bone lead concentrations ranged from -12.5 to 223.3. The authors divided workers into 3 groups by age (40-49, 50-59, and 60-76). Correlations between blood lead and bone lead were highest in the 2 oldest age groups (.49 and .75, respectively). Hierarchical regression analysis was significant for an interaction between bone lead and age in predicting blood lead (the combination of age and bone lead significantly predicted an increase in current blood lead levels). The results support the hypothesis that lead stored in bone is a significant source of blood lead later in life. Older workers with past occupational exposure may face a particular risk for recirculation of lead in blood with advancing age.

The integral catcher analysis of nuclear recoil experiments

Abstract The integral thick target thick catcher equations for extracting excitation and relaxation recoil velocities of nuclear reaction products have been reformulated. The new data analysis scheme corrects certain limitations and deficiencies inherent in the conventional procedure. Like the latter, our integral catcher analysis uses forward and backward recoil fractions F and B , but has no constraints on target thickness. The utility of the method may be extended with advantage to thinner targets. Additionally, there are no restrictions on the form of the range-velocity relationship that can be employed. Finally, the procedure inherently provides an excellent evaluation of the statistical uncertainties in the derived velocities based on the experimental uncertainties in F and B .

Estimation of carbon‐11 in the atmosphere

The production of 20 minute C‐11 by interactions of cosmic ray primary and secondary particles with atmospheric nitrogen and oxygen is calculated. We estimate unmeasured C‐11 to be the fifth most active cosmogenic radionuclide in the lower atmosphere with a disintegration rate of 0.014 dpm/m3. Nevertheless, its actual measurement will not prove an easy task.

A crystal detector for measuring beta and internal conversion electrons in flowing air containing fission gases

Abstract Low levels of radioactive gases are released from nuclear electric power generation, nuclear fuel reprocessing plants, nuclear weapons tests and from diagnostic medical uses of radioactive gas tracers. A prototype model of an inorganic scintillator – Crystal Gas Electron Detector (CGED) – was built for measurements of xenon isotopes in-line by detecting the beta and internal conversion (IC) electrons present in atmospheric samples. The detection and quantification of the radionuclide spectra are accomplished, during air flow, without complete purification of the fission gases. Initial operational tests and calibrations made permit the integration of the CGED into a portable Gas Analysis, Separation and Purification (GASP) system [1–3] . The CGED detector, Pulse Shaping and Timing (PSA) electronics, and mathematical treatment of the accumulated spectra are used to resolve the K and LMNO-IC electrons and beta continuum. These data are used, in-line, for dating the age of an air parcel containing fission gases released from nuclear reactors and/or from nuclear weapons tests, as part of the monitoring equipment required to enforce the Comprehensive Test Ban Treaty, CTBT. This report is one of a series of papers providing the design features, operational methods, calibration, and applications of radioactive gas analysis system to the International CTBT.

A PDP-12 system for on-line acquisition of heart rate data

A research program for investigating the responsiveness of infants at high risk for developing schizophrenia is described briefly. Two measures of reactivity to brief auditory stimuli, the evoked heart-rate response and the evoked potential of the brain, are recorded for analysis by the PDP-12 computer. An interface to the PDP-12, called the R peak detector and R-R interval counter, is used for reducing the EKG to R-R intervals, with an accuracy of ± 1 msec. The current usage of the PDP-12 and its IBM-compatible tape transports is discussed, and proposed developments for on-line statistical analyses of the physiological data and real-time control of the experiment are presented.

Calculated 118Te production rates from enriched 122,123Te targets

Abstract The 118 Te/ 118 Sb generator has potential application for positron emission tomography. In this study, we modelled the production of the 118 Te precursor via proton activation of 122 Te and 123 Te targets. 118 Te excitation functions were calculated for the (p, xn) and (p, pxn) production channels using a compound nucleus/statistical evaporation approach. These calculations indicate that 118 Te can be produced in GBq (100 mCi) quantities by the irradiation of a thin (0.4 g/cm 2 ) enriched 122 Te target with 62 MeV protons. This corresponds to a cumulative 118 Te production rate in the 62-60 MeV proton energy region of 16 GBq/C (1.6 mCi/μA-h). In this proton energy range, 118 Te production is maximized while the production of such contaminant nuclides as 119 Te is relatively low. In view of the sizable 118 Te production rate estimate, we are proceeding with the development of optimal Te/Sb separation chemistry applicable to a generator system.