Open chain intermediates from the ring-opening reaction of aqueous sodium deuteroxide (2 mol) with 2-chloro-5-nitropyridine (1 mol) and 2-chloro-3-nitropyridine (1 mol) were isolated. These intermediates were purified, analyzed for elemental composition, and characterized by various spectrophotometric techniques. The intermediate formed from 2-chloro-5-nitropyridine and two equivalents of deuteroxide ion reacts with additional deuteroxide in D2O in various polar solvents to reclose the pyridine ring. The kinetics of the ring closure reaction are reported and are supplemented with observations of salt and solvent effects upon the rate of closure. In addition, a mechanism for the ring closure is presented. The intermediate formed from 2-chloro-3-nitropyridine did not undergo a similar ring closure when reacted with additional deuteroxide, but instead formed various decomposition products. A reason for the failure of this ring closure is suggested.

Purpose: To estimate in-patient KERMA for specific organs in computed tomography (CT) scanning using ratios to isocenter free-in-air KERMA obtained using a Rando phantom. Method: A CT scan of an anthropomorphic phantom results in an air KERMA K at a selected phantom location and air kerma K CT at the CT scanner isocenter when the scan is repeated in the absence of the phantom. The authors define the KERMA ratio (R K ) as K= K CT , which were experimentally determined in a Male Rando Phantom using lithium fluoride chips (TLD-100). R K values were obtained for a total of 400 individual point locations, as well as for 25 individual organs of interest in CT dosimetry. CT examinations of Rando were performed on a GE LightSpeed Ultra scanner operated at 80 kV, 120 kV, and 140 kV, as well as a Siemens Sensation 16 operated at 120 kV. Results: At 120 kV, median R K values for the GE and Siemens scanners were 0.60 and 0.64, respectively. The 10th percentile R K values ranged from 0.34 at 80 kV to 0.54 at 140 kV, and the 90th percentile R K values ranged from 0.64 at 80 kV to 0.78 at 140 kV. The average R K for the 25 Rando organs at 120 kV was 0.61 6 0.08. Average R K values in the head, chest, and abdomen showed little variation. Relative to R K values in the head, chest, and abdomen obtained at 120 kV, R K values were about 12% lower in the pelvis and about 58% higher in the cervical spine region. Average R K values were about 6% higher on the Siemens Sensation 16 scanner than the GE LightSpeed Ultra. Reducing the x-ray tube voltage from 120 kV to 80 kV resulted in an average reduction in R K value of 34%, whereas increasing the x-ray tube voltage to 140 kV increased the average R K value by 9%. Conclusions: In-patient to isocenter relative KERMA values in Rando phantom can be used to estimate organ doses in similar sized adults undergoing CT examinations from easily measured air KERMA values at the isocenter (free in air). Conversion from in-patient air KERMA values to tissue dose would require the use of energy-appropriate conversion factors.

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KERMA ratios may be combined with air KERMA measurements at the isocenter to estimate organ doses in pediatric CT patients.

Purpose: To develop an efficient annealing/readout protocol for TLD dosimetry that will maximize the accuracy and precision in radiographic dosimetry measurements. Method and Materials: 500 TLD chips were grouped in batches of 100 and subjected to varying annealing protocols and then irradiated to varying exposure levels. Three different annealing/readout protocols were tested. In protocol ♯1, the chips were annealed at 400 C for 1 hour followed by 2 hours at 100 C. The chips were exposed, and then allowed to rest for 24 hours before reading. In protocol ♯2, the anneal cycle was 400 C for 1 hour followed with a 30 minute cool‐down, followed by 20 hours at 80 C. Immediately after exposure, the TLD's were heated to 120 C for 10 minutes, then read. In protocol ♯3, the anneal cycle was 400 C for 1 hour followed by a 30 minute cool‐down, then 100 C for 2 hours. After exposure, the TLDs were pre‐heated and read as in protocol ♯2. Results: For protocol ♯1, the inter‐exposure uncertainty in the response (nC/mR) was approximately 4.2%. Using protocol ♯2, the intra‐batch uncertainty was reduced to 4.0%, and for protocol ♯3 the uncertainty was reduced to ∼3.7%. By using individual chip calibrations, the intra‐batch uncertainty for estimating consecutive exposures was reduced to 3.5%, 1.8%, and 1.7% for protocols ♯1, 2, and 3, respectively. By binning TLD signals over groups of 3 chips, the uncertainty in estimating exposures was reduced to ∼1.1% for protocol ♯3. Conclusion: With careful calibration and binning of results, an accuracy approaching 1% is readily obtained. The anneal/readout protocol that yielded the highest accuracy also required the least time for a complete cycle, with a batch of 100 chips being processed in <1 working day using a single furnace for annealing and a single‐chip reader.