Modeling Study of a Proposed Field Calibration Source Using K-40 and High-Z Targets for Sodium Iodide Detectors.

Calibration sources based on the primordial isotope potassium-40 (K) have reduced controls on the source's activity due to its terrestrial ubiquity and very low specific activity. Potassium-40's beta emissions and 1,460.8 keV gamma ray can be used to induce K-shell fluorescence x rays in high-Z metals between 60 and 80 keV. A gamma ray calibration source that uses potassium chloride salt and a high-Z metal to create a two-point calibration for a sodium iodide field gamma spectroscopy instrument is thus proposed. The calibration source was designed in collaboration with the Sandia National Laboratory using the Monte Carlo N-Particle eXtended (MCNPX) transport code. Two methods of x-ray production were explored. First, a thin high-Z layer (HZL) was interposed between the detector and the potassium chloride-urethane source matrix. Second, bismuth metal powder was homogeneously mixed with a urethane binding agent to form a potassium chloride-bismuth matrix (KBM). The bismuth-based source was selected as the development model because it is inexpensive, nontoxic, and outperforms the high-Z layer method in simulation. Based on the MCNPX studies, sealing a mixture of bismuth powder and potassium chloride into a thin plastic case could provide a light, inexpensive field calibration source.

Terrestrial radioactivity of the Jabal Eghei area in southern Libya and assessment of the associated environmental risks.

Activity concentrations of main terrestrial radioisotopes (226)Ra, (232)Th and (40)K were measured in geological samples collected in Libya's Jabal Eghei area, in order to contribute to the establishment of a baseline map of the environmental radioactivity levels and to estimate the associated environmental risk to the population. Activity concentrations ranged from 22 to 5256 Bq kg(-1) for (226)Ra, from 11 to 221 Bq kg(-1) for (232)Th and from 132.0 to 2304 Bq kg(-1) for (40)K. Using these results, representative risk factors were calculated: the total absorbed gamma dose rate in air (ranged from 25.5 to 2434.3 nGy h(-1) with a mean value of 251.8 nGy h(-1)), the radium equivalent activity (55-5281 Bq kg(-1), with the mean value of 537 Bq kg(-1)), external hazard index (0.149-14.24, with a mean value of 1.451) and annual outdoor effective dose (31.3-2985.4 µSv, with a mean value of 308.9 µSv). Accordingly, the radiation risk is above the world average, mainly as the consequence of discovered uranium anomalies.

Subcellular imaging of RNA distribution and DNA replication in single mammalian cells with SIMS: the localization of heat shock induced RNA in relation to the distribution of intranuclear bound calcium.

The subcellular localization of RNA for understanding transcriptional activity by using RNA precursors, like 5-bromouridine (BrU), generally requires chemical fixation and staining of cells with monoclonal antibody for imaging BrU-containing RNA in individual cells. Although effective for RNA localization, the native chemical composition of diffusible ions and molecules is destroyed in this approach and one cannot study their spatial relationship with RNA localization sites in this sample type. This work presents a novel secondary ion mass spectrometry approach in cryogenically prepared cells, which allows the same cell imaging of RNA (and/or replicating DNA) distribution in relation to intracellular chemical composition. The heat shock treatment of HeLa cells was used as a model system because the transcription of heat shock genes is activated during heat shock while other transcriptional activities of the cell are suppressed. The HeLa cells were heat-shocked for 1 h at 42 degrees C in presence of 100 muM BrU and/or 100 microM IdU (5-iododeoxyuridine). Following the heat shock treatments, the cells were cryogenically prepared with our sandwich freeze-fracture method and freeze-dried prior to secondary ion mass spectrometry analysis. A CAMECA IMS 3f secondary ion mass spectrometry ion microscope (CAMECA, Paris, France) capable of producing elemental (isotopic) distributions with a spatial resolution of 500 nm was used in the study. Secondary ion mass spectrometry analysis of fractured freeze-dried HeLa cells revealed well-preserved intracellular (39)K and (23)Na concentrations in heat-shocked cells. Both DNA replication and RNA distribution (total RNA) were imaged directly in the same cell by secondary ion mass spectrometry imaging of masses (127)I (from IdU) and (81)Br (from BrU), respectively. Surprisingly, the nucleus of heat-shocked cells contained spatially resolved regions with elevated levels of bound calcium (approximately 0.75 mM total calcium instead of 0.50 mM total calcium in the nucleoplasm). These regions spatially correlated with depleted levels of BrU-RNA in (81)Br secondary ion mass spectrometry images. The remainder of intranuclear regions displayed the presence of BrU-RNA with heterogeneous distribution. These observations indicate that calcium in its bound form may play a fundamental role in processes such as transcription and/or processing and storage of RNA. The shape of intranuclear regions with elevated levels of bound calcium resembled the heat shock induced nuclear bodies in HeLa cells. The analysis of cryogenically prepared frozen freeze-dried cells provides an ideal sample type for further understanding of the role of bound calcium in transcription of genes under physiological and pathological conditions.

The new IAEA-372 grass-certified reference material for (40)K and (137)Cs.

A new grass-certified reference material characterized for (137)Cs and (40)K has been issued by the International Atomic Energy Agency. Characterization of this material was conducted by a group of national metrological institutes and expert laboratories. The paper describes the process for assigning the certified reference value to the material.

Body composition during GH replacement in adults - methodological variations with respect to gender.

OBJECTIVE: Men with growth hormone deficiency (GHD) may be more sensitive to GH treatment than women in terms of changes in body composition. We have studied whether age, body-mass index (BMI) and the different types of methodology used to assess body composition may explain these differences. DESIGN: Forty-four men and forty-four women with GHD, closely matched for age and BMI, were studied before and after 6 months of GH replacement. The dose of GH was individually adjusted. Body composition was assessed by measurements of potassium-40, total body nitrogen (TBN), tritiated water dilution, dual-energy X-ray absorptiometry (DXA) and bioelectrical impedance analysis (BIA). Four- and five-compartment models for body composition were also calculated. RESULTS: The total daily dose of GH was similar in men and women at 6 months. Serum insulin-like growth factor-I (IGF-I) was higher in men than women at baseline and after 6 months of treatment (P = 0.01, paired t-test). The increment was, however, similar. In women, GH treatment reduced body weight and increased TBN. In both men and women, total body water and body cell mass increased, while total body fat (BF) mass decreased. At baseline, mean total BF varied considerably depending on the methodology used, with the highest value obtained from DXA. The changes in BF were, however, less dependent on the methodology, but DXA and BIA demonstrated the largest inconsistency between men and women. CONCLUSIONS: These results suggest that gender differences in body composition in response to GH treatment are small, if adjustments are made for baseline factors such as age, BMI and dose of GH. Different methods of body composition measurements produce different results, but changes in response to GH administration are less inconsistent.

The measurement of total body potassium in patients on peritoneal dialysis.

OBJECTIVES: To assess the validity of measuring total body potassium (TBK) to estimate fat-free mass (FFM) and body cell mass (BCM) in patients on peritoneal dialysis (PD). METHODS: We studied 29 patients on PD (14 men, 15 women) and 30 controls (15 men, 15 women). We calculated TBK by using a whole-body counter to measure 1.46 MeV gamma-ray emissions from naturally occurring 40K. We measured total body water (TBW) by deuterium oxide dilution, and extracellular water (ECW) from bromide dilution. These measurements allowed us to estimate intracellular water (ICW), fat-free mass dilution (FFM(Dilution)), and body cell mass dilution (BCM(Dilution)). RESULTS: The FFM(TBK) in male PD patients (55.7 +/- 7.0 kg) did not differ from that in male controls (57.0 +/- 10.9 kg). The FFM(TBK) in female PD patients (38.4 +/- 6.8 kg) was less than that in female controls (44.7 +/- 4.5, p < 0.01). The FFM(Dilution) did not differ from the FFM(TBK). Correlation of FFM(TBK) and FFM(Dilution) was r = 0.90, p < 0.0001 for all subjects; r = 0.90, p < 0.0001 for PD patients; and r = 0.90, p < 0.0001 for controls. Bland-Altman comparison of FFM(Dilution) with FFM(TBK) in individuals showed bias 0.6 kg, range -8.5 kg to 9.7 kg for the whole group; bias 1.4 kg, range -7.9 kg to 10.7 kg for PD patients; and bias -0.2 kg, range -9.0 kg to 8.6 kg for controls. The BCM(TBK) in male PD patients (30.1 +/- 4.5 kg) did not differ from that in male controls (31.9 +/- 6.2 kg). The BCM(TBK) in female PD patients (19.0 +/- 4.4 kg) was less than that in female controls (23.1 +/- 2.9 kg, p < 0.01). The BCM(Dilution) results did not differ from those for the BCM(TBK). Correlation of BCM(TBK) and BCM(Dilution) was r = 0.90, p < 0.0001 for all subjects; r = 0.87, p < 0.0001 for PD patients; and r = 0.93, p < 0.0001 for controls. Bland-Altman comparison of BCM(Dilution) with BCM(TBK) in individuals showed bias 0.1 kg, range -5.9 kg to 6.1 kg for the whole group; bias 0.0 kg, range -6.9 kg to 6.9 kg for PD patients; and bias 0.1 kg, range -5.0 kg to 5.2 kg for controls. The [K+]ICW did not differ between PD patients and controls (148.0 +/- 25.1 mmol/L vs 148.1 +/- 14.3 mmol/L, p = nonsignificant). CONCLUSIONS: Total body potassium is a valid, noninvasive technique for measuring FFM and BCM in PD patients. In our PD patient group, depletion of FFM and BCM as compared with controls was identified in the women but not in the men.