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Activation Techniques
Published in Frank Helus, Lelio G. Colombetti, Radionuclides Production, 2019
The entire simple target assembly shown in Figure 6 is attached to the end of the beam line. The collimator (made from aluminum, tantalum, or other materials) prevents beam from striking the beam line, electron suppressor ring, and O-ring support structure. By defocusing the beam on a small aperture a section of reasonably uniform power density is selected to fall on the target material. The beam profile behind the collimator should be, in diameter, smaller than the surface of the target material, so that the backing plate will not be irradiated. The beam should be homogen over the whole surface of the target material. It is very important to eliminate the beam hot spots which can cause local overheating of target material. The electron suppressor is used to prevent back-streaming of electrons from the target and enables exact measurements of the beam current. The foil system can be cooled by spraying the foils with pre-cooled helium gas or another gaseous medium. The advantage of helium is that no radioactive products are co-produced in the gas phase. The target backing plate is regularly cooled with water. The insulator makes the beam current measurements possible on the Faraday cup basis.
Emerging Biomedical Analysis
Published in Lawrence S. Chan, William C. Tang, Engineering-Medicine, 2019
The detection of an ion in a modern mass spectrometer is achieved by creating an electric signal. The basic ion detector is the Faraday cup. The principle of the Faraday cup is that a current is induced when a packet of ions hits the dynode surface. The number and charge of ions are determined by measuring the current.
Absolute and Reference Dosimetry
Published in Harald Paganetti, Proton Therapy Physics, 2018
The main instrument in use to measure the incident particle fluence is the Faraday cup, which enables an accurate measurement of the number of protons provided it is well designed. A typical design is shown in Figure 10.6. For broad beams, an additional major uncertainty is due to the determination of the field area. For pencil beams, this uncertainty vanishes when the derived quantity is a laterally integrated dose. A major concern is the influence of electrons generated in the entrance window that reach the collecting electrode (and thus reduce the signal) as well as electrons liberated in and escaping from the collecting electrode (which enhance the signal). Both sources of perturbation to the measurement are usually suppressed by a guard electrode with a negative potential with respect to the electrode and casing sometimes with addition of a magnetic field. The relative standard uncertainty of absorbed dose-to-water determination using a Faraday cup varies between 2% and 3% and is dominated by the collection efficiency of the Faraday cup, the determination of the area, the mass stopping power of water, and the contributions to the absorbed dose to water by secondary charged particles originating from nonelastic interactions.
Mass spectrometry in the lipid study of cancer
Published in Expert Review of Proteomics, 2021
Md. Mahamodun Nabi, Md. Al Mamun, Ariful Islam, Md. Mahmudul Hasan, A.S.M. Waliullah, Zinat Tamannaa, Tomohito Sato, Tomoaki Kahyo, Mitsutoshi Setou
The selection of the ionization source is important in MS studies of a particular group of molecules. Numerous ionization sources, including electrospray ionization (ESI) [23], chemical ionization (CI), atmospheric pressure chemical ionization (APCI), atmospheric pressure photo ionization (APPI), matrix-assisted laser desorption ionization (MALDI), desorption electrospray ionization (DESI), and secondary ion sources have been developed that are compatible with a variety of mass analyzers. Recently, rapid evaporative ionization mass spectrometry (REIMS) has emerged as an efficient technique for direct analysis of samples in near real time [24]. Time-of-flight (TOF) is the most widely used mass analyzer because of its high sensitivity and fragmentation capabilities in tandem mass spectrometry (MSn) analysis. Other commonly used analyzers are ion trap and quadrupole time-of-flight (QTOF) [25]. The Fourier-transform ion cyclotron resonance (FT-ICR) mass analyzer offers the best mass resolution and has thus far been applied in MALDI-MS. Usually, mass analyzers generate a current flow for each separated ion which is transformed digitally. The detector measures charged particles and records the abundances of each ion present in a sample. Initially, mass detectors (for example, Faraday Cup) were designed to capture and count the number of charged ions [26]. The commonly used mass detectors in the modern instrument are the secondary electron multiplier and image current. For example, FT-ICR and Orbitrap mass analyzer use image current for ion detection [27].
Organ burden of inhaled nanoceria in a 2-year low-dose exposure study: dump or depot?
Published in Nanotoxicology, 2020
Jutta Tentschert, Peter Laux, Harald Jungnickel, Josephine Brunner, Irina Estrela-Lopis, Carolin Merker, Jan Meijer, Heinrich Ernst, Lan Ma-Hock, Jana Keller, Robert Landsiedel, Andreas Luch
Reconstructed ion images and the associated mass spectra were acquired using a time of flight secondary ion mass spectrometry (ToF-SIMS) V instrument (ION-TOF GmbH, Münster, Germany) with a 30 keV nano-bismuth primary ion beam source (Mn emitter). The ion currents were 0.5 pA at 5 kHz using a Faraday cup. A pulse of 0.7 ns from the bunching system resulted in a mass resolution that usually exceeded 6000 (full width at half-maximum) at m/z <500 in positive ion mode. The primary ion dose was controlled below 1012 ions cm−2 to ensure static SIMS conditions. Charge compensation on the sample was obtained by a pulsed electron flood gun with 20 eV electrons.
A proposed explanation for thunderstorm asthma and leukemia risk near high-voltage power lines: a supported hypothesis
Published in Electromagnetic Biology and Medicine, 2018
Deposition of singly charged ultrafine particles (≤200 nm) in an experimental model were significantly higher than predicted when measured by a condensation particle counter or a Faraday Cup (Cohen et al., 1995). Here also, deposition was greater in charged than charge-neutralized particles. The authors state that deposition in humans would be further enhanced due to surface irregularities.