New calculations of neutron kerma coefficients and dose equivalent.

For neutron energies ranging from 1 keV to 20 MeV, the kerma coefficients for elements H, C, N, O, light water, and ICRU tissue were deduced respectively from microscopic cross sections and Monte Carlo simulation (MCNP code). The results are consistent within admitted uncertainties with values evaluated by an international group (Chadwick et al 1999 Med. Phys. 26 974-91). The ambient dose equivalent generated in the ISO-recommended neutron field for an Am-Be neutron source (ISO 8529-1: 2001(E)) was obtained from the kerma coefficients and Monte Carlo calculation. In addition, it was calculated directly by multiplying the neutron fluence by the fluence-to-ambient dose conversion coefficients recommended by ICRP (ICRP 1996 ICRP Publication 74 (Oxford: Pergamon)). The two results agree well with each other. The main feature of this work is our Monte Carlo simulation design and the treatments differing from the work of others in the calculation of neutron energy transfer in non-elastic processes.     

Evidence of a neutron RBE of 70 (+/- 50) for solid-tumor induction at Hiroshima and Nagasaki and its implications for assessing the effective neutron quality factor.

Carcinogenic and genetic effects in the cohort of A-bomb survivors are the main source of information on radiation effects on humans. A detailed analysis of the age-specific mortality rates for solid tumors as a group using the widely accepted linear-quadratic cum cell-killing dose-effect model reveals that the Hiroshima-Nagasaki data are statistically consistent with a limiting, low-dose neutron RBE of about 70. This value, although consistent with a wide range of neutron RBEs, is about 3.5 times higher than the current effective quality factor for neutrons. The data on leukemia mortality do not support the notion of a difference in effectiveness between neutron and gamma radiation; however, these two radiation sources appear to act synergistically. For both types of tumors, the commonly used concepts of constant, dose-independent RBE and "gamma effective dose" cannot be justified other than at very low neutron doses.     

Sample size calculations for evaluating a diagnostic test when the gold standard is missing at random

Performance of a diagnostic test is ideally evaluated by a comparison of the test results to a gold standard for all the patients in a study. In practice, however, it is common for a subset of study patients to have the gold standard not verified (missing) due to ethical or expense considerations. Sensitivity and specificity are often used as the relevant test performance measures and a joint confidence region (CR) for sensitivity and specificity can summarize the precision of estimates. In this paper, we present an approach to sample size computations when designing a study in which the gold standard is considered to be missing at random (MAR). We calculate the needed increase in sample size to ensure that the joint CR under MAR falls inside the boundaries of the joint CR derived for data with no missingness present. Copyright © 2010 John Wiley & Sons, Ltd.     

Accelerator mass spectrometry of 63Ni at the Munich Tandem Laboratory for estimating fast neutron fluences from the Hiroshima atomic bomb

After the release of the present dosimetry system DS86 in 1987, measurements have shown that DS86 may substantially underestimate thermal neutron fluences at large distances (>1,000 m) from the hypocenter in Hiroshima. This discrepancy casts doubts on the DS86 neutron source term and, consequently, the survivors' estimated neutron doses. However, the doses were caused mainly by fast neutrons. To determine retrospectively fast neutron fluences in Hiroshima, the reaction 63Cu(n, p)63Ni can be used, if adequate copper samples can be found. Measuring 63Ni (half life 100 y) in Hiroshima samples requires a very sensitive technique, such as accelerator mass spectrometry (AMS), because of the relatively small amounts of 63Ni expected (approximately 10(5)-10(6) atoms per gram of copper). Experiments performed at Lawrence Livermore National Laboratory have demonstrated in 1996 that AMS can be used to measure 63Ni in Hiroshima copper samples. Subsequently, a collaboration was established with the Technical University of Munich in view of its potential to perform more sensitive measurements of 63Ni than the Livermore facility and in the interest of interlaboratory validation. This paper presents the progress made at the Munich facility in the measurement of 63Ni by AMS. The Munich accelerator mass spectrometry facility is a combination of a high energy tandem accelerator and a detection system featuring a gas-filled magnet. It is designed for high sensitivity measurements of long-lived radioisotopes. Optimization of the ion source setup has further improved the sensitivity for 63Ni by reducing the background level of the 63Cu isobar interference by about two orders of magnitude. Current background levels correspond to a ratio of 63Ni/Ni<2x10(-14) and suggest that, with adequate copper samples, the assessment of fast neutron fluences in Hiroshima and Nagasaki is possible for ground distances of up to 1500 m, and--under favorable conditions--even beyond. To demonstrate this capability, we have measured successfully 6Ni/Ni ratios as low as (3.5 +/- 0.6) x 10(-13). The latter are, based on DS86, representative of a ratio expected from a typical Hiroshima copper sample at about 1,300-m ground range.     

Mercury intolerance and lymphocyte transformation test with nickel sulfate, palladium chloride, mercuric chloride, and gold sodium thiosulfate

The peripheral lymphocytes of 10 patients referred to as mercury intolerant and 9 patients referred to as tolerant with regard to presence or absence of psychosomatic symptoms when percutaneously exposed to low patch test doses of mercury were stimulated in vitro with four metal salts. In addition, cells from 7 subjects with no anamnestic mercury intolerance or allergy to metals as well as free from dental alloys were included as controls. Lymphocyte transformation test was done by in vitro challenge with five concentrations of gold sodium thiosulfate, nickel chloride, palladium chloride, and seven concentrations of mercuric chloride. Stimulation with palladium chloride and mercuric chloride showed a difference between the mercury-intolerant and -tolerant patients on one hand and the controls on the other, but there was no difference between the two patient groups. With regard to nickel sulfate, there was a significant dose-dependent stimulation in all the three groups but no difference between the groups could be seen. Gold sodium thiosulfate did not stimulate the lymphocytes at all. Based on these results, we therefore conclude that lymphocyte transformation test performed with the four metal salts cannot be used to further differentiate between mercury-intolerant and -tolerant patients.     

Simulations of neutron transport at low energy: a comparison between GEANT and MCNP

The use of the simulation tool GEANT for neutron transport at energies below 20 MeV is discussed, in particular with regard to shielding and dose calculations. The reliability of the GEANT/MICAP package for neutron transport in a wide energy range has been verified by comparing the results of simulations performed with this package in a wide energy range with the prediction of MCNP-4B, a code commonly used for neutron transport at low energy. A reasonable agreement between the results of the two codes is found for the neutron flux through a slab of material (iron and ordinary concrete), as well as for the dose released in soft tissue by neutrons. These results justify the use of the GEANT/MICAP code for neutron transport in a wide range of applications, including health physics problems.     

Meteorological observations at Hiroshima on days with weather similar to that of the atomic bombing.

An attempt to explain discrepancies between measured neutron-induced radioactivities (i.e., 152Eu, 60Co) and calculated yields based on the Dosimetry System 1986 was made by considering moist air densities at different altitudes over Hiroshima, Japan. The investigation checked the validity of moist air density estimates used in the Dosimetry System 1986 computer codes. Meteorological observations were conducted to obtain atmospheric temperature and pressure profiles for the Hiroshima area. By coupling these observations with surface measurements taken on 6 August 1945 at Ebayama Park (3.6 km from the hypocenter), estimates of temperature, pressure, and humidity at the time of detonation were derived. This allowed the calculation of densities for dry air, moist air, and water vapor. The results proved similar to the Dosimetry System 1986 estimates. Water vapor density calculations showed the largest difference (at most 7%). These results imply that the 152Eu yield contradiction in the Dosimetry System 1986 calculations vs. real measurements for large ground distances (> 900 m) is not the result of an erroneous estimate of moist air density in Hiroshima.     

Development and test of a GEM-based TEPC for neutron protection dosimetry

A novel tissue-equivalent proportional counter (TEPC) based on a gas electron multiplier (GEM) for measuring H*(10) for neutrons was designed and constructed. The pulse height spectra (PHS) of two different neutron sources (a 252Cf source and a AmBe source) were measured using the new TEPC. The measurements were made with the TEPC filled with two different gases (10P gas and a propane-based tissue-equivalent gas) at various pressures. A computer simulation of the new TEPC, based on the Monte Carlo method, was performed to obtain the PHS for the two neutron sources. It is shown that the experimental results agree well with the simulation results for both 252Cf and AmBe neutron sources. Several outstanding problems are discussed and suggestions are made to make the GEM-based TEPC a practical neutron rem meter. The potential advantage of this novel neutron rem meter would be its low weight and compactness.     

Mixtures of nickel and cobalt chlorides induce synergistic cytotoxic effects: implications for inhalation exposure modeling.

Workers are often simultaneously exposed to two or more chemicals, yet little is known about the toxicity of most chemical mixtures. The traditional assumption, in the absence of further information, has been that the chemical components of a mixture have mutually independent effects, and the toxic response to multiple chemicals is additive. The data presented here show that mixtures of NiCl(2) and CoCl(2) induce a synergistic (that is, greater than additive) toxic response in cell culture. Immortalized alveolar epithelial type II cells were incubated for 4 h with various concentrations of either NiCl(2), CoCl(2), or NiCl(2) and CoCl(2) together, and cell viability assessed 24 h later. The LD(50) for NiCl(2) was 5.7 mM. CoCl(2), with an LD(50) of 1.1 mM, was about five times more potent than NiCl(2). Mixtures of NiCl(2) and CoCl(2) decreased cell viability synergistically. For example, a mixture of 750 microM NiCl(2) and 750 microM CoCl(2) reduced cell viability by more than three times the value predicted by the additive approach. We used concentration-response data from these studies in a mathematical model; this model describes the equivalent inhalation exposure to an aerosol composed of a mixture of chemicals with different toxicities and also accounts for synergistic responses to these chemicals. Our results along with previous studies using an animal model suggest that these synergisms should be taken into account when conducting future exposure assessments.     

Interpretation of erythrocyte glutathione reductase activation test values for assessing riboflavin status.

The erythrocyte glutathione reductase activation test (EGR-AC) is considered to be the best method to assess riboflavin nutritional status. Riboflavin supplementation studies carried out in India have raised doubts about the validity of currently available interpretive guidelines for interpreting the EGR-AC test. Changes in EGR-AC values in response to graded doses of riboflavin supplementation were investigated in schoolchildren, aged 7-11 years, belonging to the low-income group. For comparison, unsupplemented well-to-do schoolchildren of similar age group were also examined. The results of the study based on the measurement of EGR-AC by the procedure of Bayoumi and Rosalki (Clinical Chemistry, 1976, Vol. 22, pp. 327-335) with an incubation period of 15 min suggest that the cut-off value for EGR-AC to discriminate between riboflavin-deficient and normal children cannot be less than 1.5.     

Student perceptions of the progress test in two settings and the implications for test deployment

Background The Progress Test (PT) was developed to assess student learning within integrated curricula. Whilst it is effective in promoting and rewarding deep approaches to learning in some settings, we hypothesised that implementation of the curriculum (design and assessment) may impact on students’ preparation for the PT and their learning. Aim To compare students’ perceptions of and preparations for the PT at two medical schools. Method Focus groups were used to generate items for a questionnaire. This was piloted, refined, and then delivered at both schools. Exploratory factor analysis identified the main factors underpinning response patterns. ANOVA was used to compare differences in response by school, year group and gender. Results Response rates were 640 (57%) and 414 (47%) at Schools A and B, respectively. Three major factors were identified: the PT’s ability to (1) assess academic learning (2) support clinical learning; (3) the PT’s impact on exam preparation. Significant differences were found between settings. In the school with early clinical contact, more frequent PTs and no end of unit tests, students were more likely to appreciate the PT as a support for learning, perceive it as fair and valid, and use a deeper approach to learning—but they also spent longer preparing for the test. Conclusion Different approaches to the delivery of the PT can impact significantly on student study patterns. The learning environment has an important impact on student perceptions of assessment and approach to learning. Careful decisions about PT deployment must be taken to ensure its optimal impact.     

Lymphocyte transformation test with nickel in hard metal asthma: another sensitizing component of hard metal.

To determine cell-mediated immunity to nickel, another matrix in hard metal besides cobalt, lymphocyte transformation tests (LTT) with nickel were carried out in seven hard metal asthma patients all of who had reacted to cobalt chloride in the bronchial provocation tests (BPT). Immunoallergic studies prior to the present study revealed that three of the seven generated a simultaneous positive reaction in the BPT with nickel and the allergosorbent test with nickel-conjugated human serum albumin (Ni-HSA). A stimulation index in LTT indicating a positive response was defined on the basis of results from the studies in the controls. Data revealed that two of the three who showed a combination of positive bronchial and immunological reactions with nickel had a positive LTT with nickel. In the other five, peripheral lymphocytes did not proliferate in response to nickel. Thus it is suggested that cell-mediated immunity to nickel as well as cobalt is implicated in some cases associated with hard metal asthma.     

Radiological implications of inhaled 239Pu and 241Am in dusts at the former nuclear test site in Maralinga.

The biokinetics of 239Pu and 241Am present in three dust samples obtained from Maralinga were investigated after their deposition in the rat lung. Results were used as an experimental basis for assessing the radiological implications for human exposure. The transfer rates of these actinides to blood in the various dusts differed by 50-fold. The most transportable forms were compatible with a material that had 25% class W and 75% class Y characteristics. The doses per unit intake for adults, children, and infants exposed to an aerosol of 5 microns AMAD were calculated to be, respectively, 0.059, 0.076, and 0.140 mSv Bq-1. The corresponding doses for the least transportable forms were the same as those calculated for a class Y compound, namely 0.036, 0.049, and 0.096 mSv Bq-1. The behavior of the actinides in humans was predicted by combining the transfer rates to blood with mechanical clearance data obtained after volunteers had inhaled 85Sr or 88Y labeled fused aluminosilicate particles. The results suggested that monitoring of 241Am in the chest could be used to advantage for assessing intakes incurred by workers involved with any further decontamination procedures but would be of little practical value for assessing inadvertent public exposure. The paper includes comments on the relevance of the 1990 ICRP recommendations and the proposed new dosimetric model for the respiratory tract.     

Atmospheric aerosol measurements of 238U and 232Th at Fernald,Ohio, and implications on inhalation dose calculations

Measurements of the aerosol size distribution of 238U and 232Th at the U.S. Department of Energy's Fernald Environmental Management Project site were made to improve the inhalation dose calculations to off-site individuals. For approximately 1 y an 8-stage cascade impactor was co-located with a high volume sampler and operated at the Fernald Environmental Management Project site to collect aerosol samples. During most of the year, the site was dominated by giant particles with more than 70% of the mass of 238U above 15 microm. The seasonal average of the activity median aerodynamic diameter, based on the impactor samples, which excluded particles >15 microm, for both uranium and thorium was approximately 6.5 microm. These numbers reflect the activities at the site and the domination of the resuspension processes. During most sampling periods the size distribution was bimodal. Thorium concentrations were comparable to the uranium concentrations during the late spring and summer period and decreased to approximately 25% of the 238U concentration in the late summer. Fernald Environmental Management Project is required to calculate the maximum allowable dose from airborne emissions, excluding radon, to meet NESHAP compliance. These calculations assume an AMAD of 1 microm. We found that if you combine size distribution information with the latest ICRP 66 lung model you reduce the estimated dose by a factor of 7. Inclusion of the size distribution of radionuclides at any sampling site would substantially improve the dose estimates to the population.