ABSTRACT
Prompt gamma-ray neutron activation analysis method (PGNAA) was used to measure the talc content in flour. Neutron activation prompt gamma spectrum measured by NaI(Tl) detector has complex components, poor energy resolution, and high Compton plateau, how to obtain accurate element content from the prompt γ spectrum is one of the core problems of PGNAA. To reduce the systematic uncertainty caused by the variation of the neutron energy spectrum and γ self-absorption in different samples, the spectral decomposition method based on library least-squares was improved. As a result, the average relative deviation between the calculated values from measured spectra and the theoretical values based on the known composition was reduced from 6.1% to 0.3%. The relative uncertainty of 30 measurements on the same sample was reduced from 4.8% to 3.0%. The detection time can be reduced to 1 min, which meets the requirement of on-line measurement for talc in flour.
Subject(s)
Flour/analysis , Food Contamination/analysis , Gamma Rays , Neutron Activation Analysis/methods , Talc/analysis , Algorithms , Least-Squares AnalysisABSTRACT
To measure the neutron yield of D-T neutron generator, the activation foils of iron, copper and aluminum were used to be irradiated in the neutron field. The 14.1â¯MeV neutron yield was deduced by counting the characteristic γ-rays of radioisotopes produced by five nuclear reactions [56Fe(n,p)56Mn, 65Cu(n,2n)64Cu, 63Cu(n,2n)62Cu, 27Al(n,α)24Na, 27Al(n,p)27Mg]. The relationship between the neutron yield and the deuteron beam energy, beam current of the D-T neutron generator was measured by the BF3 proportional counter and the fluctuation of neutron yield under specified parameters was evaluated. Eleven activated iron foils were used to measure 14.1â¯MeV neutron yield at different angles of D-T neutron generator. The direction with the highest neutron flux is 30∘-45∘ along the beam direction and the neutron flux decreases gradually with the increase of angle. The measurements of neutron yield, stability and angular distribution of D-T neutron generator are significant for improving the accuracy of neutron activation analysis and neutron irradiation efficiency, as well as optimizing the neutron shielding design.
ABSTRACT
In this paper, we use a model modified from classic corticothalamic network(CT) to explore the mechanism of absence seizures appearing on specific relay nuclei (SRN) of the thalamus. It is found that typical seizure states appear on SRN through tuning several critical connection strengths in the model. In view of previous experimental and theoretical works which were mainly on epilepsy seizure phenomena appearing on excitatory pyramidal neurons (EPN) of the cortex, this is a novel model to consider the seizure observed on thalamus. In particular, the onset mechanism is different from previous theoretical studies. Inspired by some previous clinical and experimental studies, we employ the external stimuli voltage on EPN and SRN in the network, and observe that the seizure can be well inhibited by tuning the stimulus intensity appropriately. We further explore the effect of the signal transmission delays on seizures, and found that the polyspike phenomenon appears only when the delay is sufficiently large. The experimental data also confirmed our model. Since there is a complex network in the brain and all organizations are interacting closely with each other, the results obtained in this paper provide not only biological insights into the regulatory mechanisms but also a reference for the prevention and treatment of epilepsy in future.
Subject(s)
Cerebral Cortex/physiology , Epilepsy, Absence/etiology , Models, Neurological , Thalamic Nuclei/physiology , Action Potentials/physiology , Electroencephalography , Epilepsy, Absence/diagnosis , Humans , Neural Pathways/physiology , Neurons/physiology , Thalamic Nuclei/cytologyABSTRACT
Based on a classical model of the basal ganglia thalamocortical network, in this paper, we employed a type of the deep brain stimulus voltage on the subthalamic nucleus to study the control mechanism of absence epilepsy seizures. We found that the seizure can be well controlled by turning the period and the duration of current stimulation into suitable ranges. It is the very interesting bidirectional periodic adjustment phenomenon. These parameters are easily regulated in clinical practice, therefore, the results obtained in this paper may further help us to understand the treatment mechanism of the epilepsy seizure.
