Mixed Gamma Research Articles

Modified bile acid profiles in mixed neutron and gamma-irradiated pigs

Purpose:To determine the effect of mixed neutron and gamma irradiation on the bile acid pool, which may be a key factor in radiation-induced diarrhoea. Materials and methods:The bile duct of pigs was catheterized to derive bile over several experimental weeks, both before and after a 5.9Gy neutron and gamma-irradiation. After measurement of the volume and sampling, bile was returned to the pig via a duodenal catheter. Samples of bile were analysed by HPLC for their individual and total bile acid content. Blood samples were also collected for total bile acid determination. Results:Bile flow was significantly decreased during the first 24h and after the fifth day post-irradiation. Whereas total bile acid concentration in bile was not altered, profiles of individual bile acids were significantly altered as early as the first post-irradiation day. Such modifications in these profiles resulted in a change of the properties of the bile acid pool. An increased proportion of dihydroxylated bile acids known to be more deleterious for the intestine was observed. Conclusions:Neutron and gamma-irradiation leads to modifications of bile acid profiles, which may partly explain radiation-induced diarrhoea by a coherent physiopathological mechanism.

Anti-Emetic Effect of Ondansetron and Granisetron after Exposure to Mixed Neutron and Gamma Irradiation

The anti-emetic efficiency of orally administered ondansetron and granisetron has been tested in macaques exposed to a mixed y and neutron radiation (6 Gy) with a high neutron/gamma-ray ratio. Our experiments reveal that a single delivery of ondansetron (1 or 2 mg kg(-1)) or of granisetron (0.25 mg kg(-1)) 45-90 min before irradiation or 35-45 min after irradiation was not totally effective. Conversely, the delivery of two doses with the same delay prior to and after exposure led to a complete prevention of vomiting and retching. These observations can be explained by the dual mechanism of radiation-induced emesis: an early peripheral mechanism and a later central mechanism. Two deliveries of 5-HT3 receptor antagonists seem to disrupt serotonergic transmission at the brain stem structures and to affect the peripheral release of serotonin from the gut, thus completely preventing radiation-induced vomiting. This study confirms that the 5-HT3-dependent mechanisms that mediate emesis are similar for both neutron and gamma radiation.

Chromosome Aberrations Scoring for Biological Dosimetry in a Criticality Accident

During an international intercomparison of dosimetry systems for the simulation of a criticality accident which took place at the SILENE Reactor (Valduc, France), whole blood was exposed to reference pulses of mixed gamma and neutron irradiation. This was done with specimens supported free-in-air and attached to a phantom. Each blood sample was shared between the NRPB and IPSN laboratories, cultured and scored for chromosomal aberrations. Each laboratory made estimates of the neutron and gamma components of dose by reference to their own pre-existing in vitro calibration curves. It was necessary to have an estimate of the ratio of the neutron to gamma dose for this purpose. Good agreement was obtained between the results from both laboratories and with the reference doses. The conclusion is that biological dosimetry using peripheral lymphocytes gives credible estimates of personal doses in criticality accidents.

Use of a scintillation spectrometer-dosimeter for separately determing doses under conditions with mixed beta and gamma radiation

We consider the separate determination of irradiation doses in fields with mixed beta and gamma radiation. This measurement problem arises when estimating the degree of gravity of radiation injury to people who have been irradiated with ionizing radiation as a result of a nuclear accident (explosion). It is shown to be possible in principle to utilize a spectrometer—dosimeter with a phoswich scintillator for these purposes.

Heat Deposition Rate Measurements Using a Graphite Quasi-Adiabatic Calorimeter and Thermoluminescent Dosimeters in a Fusion Environment of the LOTUS Facility

Heat deposition rate measurements are made by an extremely sensitive quasi-adiabatic graphite calorimeter and thermoluminescent dosimeters (TLDs) in the fusion environment of the LOTUS facility. The response of a bare calorimeter and the response inside a large graphite cylindrical block are measured by irradiating with a mixed neutron and gamma field of the Haefely neutron generator. The reproducibility of these measurements is found to be better than 1% for a dose rate more than 60 cGy/min and better than 3.8% for dose rates in the range of 6 to 60 cGy/min. The heating rates are found to vary linearly with neutron source strength. The calculation to experiment (C/E) for the bare calorimeter is found to be 1.05, whereas inside the graphite block, C/E varies from 1.11 to 1.32. These measurements are analyzed by the MCNP Monte Carlo neutron and photon transport code using the BMCCS2, PHOTXS2, and EL2 cross-section libraries. The influence of wall-returned neutrons and gammas is found to be negligible. The origin of the discrepancies is found by measuring the gamma component of the heating at identical locations by conducting special geometry irradiation using several TLDs-700. The conditions that are employed considerably simplify the transformation of the TLD results to that of the graphite medium. A detailed data treatment is done with the TLD outputs to arrive at the gamma heating component at different locations in the graphite by employing the Burlin theory. The gamma production is found to be well represented in the calculations. On the other hand, measured and calculated net nuclear heating in the graphite differ considerably. A downward revision of the neutron kerma factor would be desirable.

A climatic index for soil erosion potential (CSEP) including seasonal and vegetation factors

The concept of Cumulative Erosion Potential (CEP) proposed by De Ploey, Kirkby and Ahnert in 1991 ( Earth Surf. Process. Landforms, 16: 399–409) provides a simple climatic index of erosion potential based on annual rainfalls and their distribution, which is assumed to be exponential (or gamma with shape parameter 1). A modified CEP (CSEP) is presented here, extending the original in three ways. First, the index is disaggregated by month to include the effects of seasonality. Second, a mixed gamma(1) distribution is used to provide a better fit to the whole of the daily rainfall distribution. Third, the index is calculated both for a bare soil and for a natural vegetation cover, giving an additional index to the potential for managing erosion through landuse change. For the natural vegetation, the index is based on an estimate of equilibrium soil organic matter which is associated with differences in soil moisture storage capacities and derived from monthly rainfall and temperature values. The index thus remains a measure of climatic potential only, based on widely available monthly data on temperature, rainfall and number of rain days. It may be compared with the patterns shown by the European Soil Erosion Map and by the CORINE classification, which are dominated by a combination of climate and lithology.

Model Studies of the Beam-Filling Error for Rain-Rate Retrieval with Microwave Radiometers

Low-frequency (less than 20 GHz) single-channel microwave retrievals of rain rate encounter the problem of beam-filling error. This error stems from the fact that the relationship between microwave brightness temperature and rain rate is nonlinear, coupled with the fact that the field of view is large or comparable to important scales of variability of the rain field. This means that one may not simply insert the area average of the brightness temperature into the formula for rain rate without incurring both bias and random error. The statistical heterogeneity of the rain-rate field in the footprint of the instrument is key to determining the nature of these errors. This paper makes use of a series of random rain-rate fields to study the size of the bias and random error associated with beam filling. A number of examples are analyzed in detail: the binomially distributed field, the gamma, the Gaussian, the mixed gamma, the lognormal, and the mixed lognormal ('mixed' here means there is a finite probability of no rain rate at a point of space-time). Of particular interest are the applicability of a simple error formula due to Chiu and collaborators and a formula that might hold in the large field of view limit. It is found that the simple formula holds for Gaussian rain-rate fields but begins to fail for highly skewed fields such as the mixed lognormal. While not conclusively demonstrated here, it is suggested that the notionof climatologically adjusting the retrievals to remove the beam-filling bias is a reasonable proposition.

A displacement model for thermoluminescent dosimetry in radioimmunotherapy

A model is developed to enable dose determination for thermoluminescent dosimeters immersed in a radioactive solution such as used in radioimmunotherapy. For low energy beta emitters used in such therapy the size of the dosimeter results in a much lower light output than when irradiated with an external Cobalt-60 (60Co) beam to the same dose as delivered to the medium. The model takes the size of the dosimeter into account and hence allows calculation of the dose in the actual medium. The application to different dosimeter sizes as well as different radionuclide energies is also illustrated. Finally, the model can be extended to dose calculation in a mixed gamma and beta irradiation geometry.

Additional Evidence for Errors in DS86 Neutron Kerma for Hiroshima Based on Biological Dosimetry and Implications for Radiation Protection and Attributable Risk Evaluation

Results of neutron activation measurements in Hiroshima indicate that calculated neutron doses based on the DS86 dosimetry system may be too low. In this study, adjusted radiation doses (neutron dose multiplied by neutron RBE, plus gamma ray dose) to bone marrow in units of equivalent gamma ray Gy were estimated as a function of distance from the hypocentre using data for fatalities occurring between 2 days and 2 months after exposure to mixed neutron and gamma radiations, among people inside Japanese-style wooden houses. A Weibull dose-response model was used to relate mortality frequency to the adjusted dose to bone marrow. Adjusted doses calculated based on DS86 neutron and gamma kerma were compared to estimates based on biological dosimetry

The mixed gamma ageing model in life data analysis

Parametric and non-parametric lifetime data analyses in practical applications require sensitive tools if non-monotonic ageing properties (trend changes) are to be examined. The well known bathtub-shaped hazard rate is a special model for describing a trend change in ageing properties over time. The identification of trend changes in the hazard rate can be supported by graphical tools. This paper discusses the combined application of graphical tools and parametric estimation in the flexible mixed gamma distribution family to identify trend changes and model bathtub-shaped hazard rates.

A BCCD-based dosimeter for mixed radiation fields

The development of a personal dosimeter based on a BCCD-detector for mixed neutron and gamma radiation in the energy range from thermal energy to 20 MeV for neutrons respectively 30 keV to a few MeV for gammas will be presented. The detector has to give information on the total radiation dose, D, and on the radiation quality. Both peaces of information are required to determine the directional dose equivalent. The basic radiation physics requirements for the detector as well as a concept of a buried channel CCD-matrix for radiation applications including the technology process will be described. A two dimensional device simulation package was used for both optimization of the charge storage nodes including free charge transfer and the basic electronic processes depending on radiation interaction with silicon.

Nondestructive Testing of Materials and Components by Computerized Tomography with Fast and Thermal Reactor Neutrons

The interaction of neutrons over a wide energy range with matter can be applied in computerized tomography (CT) to obtain nondestructive insight into objects, which is highly complementary to the information obtained by the classical method of X-ray tomography. Systematic tomography studies with thermal neutrons, fast neutrons of different spectral composition, and mixed neutron and gamma fields have been done in recent years. The experiments were performed at the Munich research reactor (Forschungsreaktor Munchen (FRM)) of the Technical University of Munich. Examples of CT measurements demonstrate the manifold possibilities of the interdisciplinary cooperation of neutron physics and materials research. IN this paper the necessary equipment and some specific problems in the processing of measured transmission rates for image reconstruction are described.

Crossing Properties of Mixture Distributions

Mixture distributions are a frequently used tool in modelling random phenomena. We consider mixtures of densities from a one-parameter exponenvial family of distributions. Using the tools of totally positive functions and the variation-diminishing property of such, we study the effect of sign-crossing properties of two mixing densities μ1 and μ2 on the resulting mixture distributions f1 and f2. The results enable us to make stochastic and variability cornparisons for binomial-beta, mixed Weibull, and mixed gamma distributions.

Measurement of depth doses in rat and mouse phantoms exposed to 252Cf mixed neutron and gamma radiations.

Measurement of depth doses in rat and mouse phantoms exposed to 252Cf mixed neutron and gamma radiations.

Lithium Fluoride (TLD-700) Response to a Mixed Thermal Neutron and Gamma Field

Irradiation studies of TLD-700 dosemeters in a mixed gamma and thermal neutron field show that TLD-700 responds to thermal neutron exposure. The results indicate that the error in estimating gamma dose in a mixed field by assuming that the TLD-700 response measures only the gamma dose can be significant in a mixed field with a high thermal neutron component.

A mixed gamma ARMA(1, 1) Model for river flow time series

In this paper we consider a time series model which can easily be used for simulating stationary river flow sequences with high skewness and the long‐term correlation structure of an ARMA(1, 1) model. The model is fitted to monthly streamflows taken from a river in Malaysia. The simulated data bear a close resemblance to the historical sequence in terms of the mean, variance, skewness, and autocorrelation coefficients.

Short term probabilities of rainfall in a semi-arid monsoonal climate

Application of Binomial distribution to the long term rainfall probabilities offers a method of estimating short term probabilities for periods like 4 out of 5 years, 2, 3 or 5 successive years etc. In view of their importance in irrigation scheduling, short term hydrological and agricultural planning, short term probabilities for the south west monsoon rainfall distribution over weekly periods in the Delhi region with a semi-arid monsoon climate based on data for the period 1941–1970 have been estimated. These are compared with the long term probability values derived using mixed gamma distribution. Probability values have been derived for occurrence of rainfall > Potential Evapotranspiration (PET) representing humid conditions and for rainfall < PET/2 representing drought conditions.

The Mixed Gamma Model for channel link lengths

An investigation of the lengths of exterior and interior links in 12 disparate areas suggests that link length distributions for most, if not all, natural landscapes represent a mixture of link length populations from different parts of the landscape characterized by different ground slope and/or environmental conditions. The mixed gamma density is derived for link lengths by assuming that both the component link length distribution for each relatively homogeneous part of the landscape and the mixing distribution of weights assigned to the various component distributions can be represented by gamma distributions. The mixed gamma density satisfactorily fits 84% of the 70 link length distributions examined, compared with 67% fitted by the log normal and 59% fitted by the gamma density. Deviations from the mixed gamma density are largely ascribed to spatial distributions of slope and environmental conditions which give rise to nongamma‐mixing distributions.

Fluctuations in the deficiency of the summer monsoon over India, and their effect on economy

To assess the deficiency in the activity of the monsoon over India during the season, an index for the country based on the percentage area with a specified percentage seasonal rainfall deficiency and termed the Monsoon Deficiency Index (MDI), has been utilized. The statistical properties of the MDI series for the period 1871–1978 have been examined. The series which can be taken to be homogeneous and random has a high variability. MDI is generally not observed to persist at a high level; a high value is invariably followed by a low value. The deficiency over the country is considered as largescale and is termed as monsoon failure when the MDI value equals or exceeds the nineth decile viz. 40, of the mixed gamma distribution fitted to the MDI series. Using this criterion, the years of monsoon failure have been identified. The monsoon failures are found to occur randomly. The effect of monsoon deficiency on the Indian economy has been assessed.

Parotid gland pathophysiology after mixed gamma and neutron irradiation of cancer patients

Electrolyte and protein concentrations were measured in parotid saliva samples obtained from patients receiving localized, fractionated, neutron and gamma irradiation for the treatment of cancer. Salivary sodium chloride concentration increased transiently but then usually decreased to preirradiation values after 2 weeks of therapy. There were concurrent decreases in salivary flow rate, pH, and bicarbonate concentration. The decreases in sodium chloride concentration and flow rate are inconsistent with a previously suggested, irradiation-induced ductal sodium resorption defect. The findings contribute toward understanding how salivary gland physiology is altered in irradiation injury.