Alpha-particle spectroscopy

A p-type material is one with positive holes and an n-type material is one with electrons in excess. To create these types of matrices, small amounts of impurities are incorporated into some host materials. For example, if the host material is silicon, which has four valence electrons, it may be doped with boron, which has three valence electrons. This creates regions in the matrix where there are holes for electrons to occupy it becomes a p-type material. The energy for creating an electron-hole pair is 3.7 eV in silicon and 3.0 eV in germanium (Knoll 1989). Thin wafers of silicon diode surface barrier detectors that have a very thin layer of gold on the surface are used for alpha-particle spectroscopy. Hyperpure germanium detectors, typically a closed-end coaxial, 6 cm in... 

The use of nuclear techniques allows the determination of C, N, H, O, and heavier contaminants relative fractions with great accuracy, and of the elements depth profile with moderate resolution (typically 10 nm). Rutherford backscattering spectroscopy (RBS) of light ions (like alpha particles) is used for the determination of carbon and heavier elements. Hydrogen contents are measured by forward scattering of protons by incident alpha particles (ERDA) elastic recoil detection analysis [44,47]. 

Radioactive plutonium isotopes emit alpha particles. The amount of radioactive plutonium in a sample can be measured by alpha spectroscopy, a technique for counting the alpha radiation. The technique is used at the Los Alamos National Laboratory (LANL) in New Mexico in order to monitor employees for exposure. 

Sample preparation is rather involved. A sample of urine or fecal matter is obtained and treated with calcium phosphate to precipitate the plutonium from solution. This mixture is then centrifuged, and the solids that separate are dissolved in 8 M nitric acid and heated to convert the plutonium to the +4 oxidation state. This nitric acid solution is passed through an anion exchange column, and the plutonium is eluted from the column with a hydrochloric-hydroiodic acid solution. The solution is evaporated to dryness, and the sample is redissolved in a sodium sulfate solution and electroplated onto a stainless steel planchette. The alpha particles emitted from this electroplated material are measured by the alpha spectroscopy system, and the quantity of radioactive plutonium ingested is calculated. Approximately 2000 samples per year are prepared for alpha spectroscopy analysis. The work is performed in a clean room environment like that described in Workplace Scene 1.2. 

A series of episodes in the historical development of our view of chemical atoms are presented. Emphasis is placed on the key observations that drove chemists and physicists to conclude that atoms were real objects and to envision their stracture and properties. The kinetic theory of gases and measmements of gas transport yielded good estimates for atomic size. The discovery of the electrorr, proton and neutron strongly irtfluenced discttssion of the constitution of atoms. The observation of a massive, dertse nucleus by alpha particle scattering and the measrrrement of the nuclear charge resrrlted in an enduring model of the nuclear atom. The role of optical spectroscopy in the development of a theory of electronic stracture is presented. The actors in this story were often well rewarded for their efforts to see the atoms. 

The upcoming Antiproton Decelerator (AD) [1] at CERN allows the formation and precision spectroscopy of antiprotonic atoms. Among the three approved experiments, the ASACUSA collaboration [2] will as part of its program continue experiments with antiprotonic helium that were previously performed by the PS205 collaboration [3] at the now closed Low Energy Antiproton Ring (LEAR) of CERN. Antiprotonic helium consisting of an alpha particle, an antiproton, and an electron (He++ —p — = pHe+), was found to have lifetimes in the... 

The Curiosity rover has a whole suite of chemistry tools on board. The laser-induced breakdown spectroscopy (LIBS) tool is probably the coolest. This instrument breaks down rocks and bits of soil by firing a (freaking) laser at the target. The elements that made up that rock are then detected by atomic emission spectroscopy. Curiosity also contains an alpha particle (He + ion) X-ray spectrometer (APXS), which is also used to measure what elements make up a sample. If the NASA scientists want to know more... 

The Si ( a) AP reaction has been studied with deuterons of energy from 5 to 7 MeV, and with magnetic analysis of the alpha particles by Browne in order to identify T = 0 levels of AP . The energy release in the reaction SP (dcf) AP has also been measured by magnetic spectroscopy S1. ... 

Alpha spectroscopy is a more selective technique, since alpha particles are emitted with characteristic energies, which facilitate simultaneous determination of alpha radionuclides with good-quality energy resolution. Therefore it could be used directly as detection technique for some alpha radionuclides. Nevertheless, various alpha emitters can be affected by the presence of spectral interferences, e.g. " Am/ Pu and and by auto-absorption effects, requiring carefiil... 

The short range of alpha particles (25-30 pm) and their significant absorption by detector windows make the measurement of such particles more difficult. The use of samples with a thickness greater than 6mg/cm is a well-established technique but gives poor energy resolution. Thin window proportional counters and pulse ionization chambers have also been used, but the methods of choice today are the surface-barrier and p-n junction detectors. These detectors usually require vacuum and very thin electrodepo-sited samples for spectroscopy measurements. Surface-barrier detectors usually exhibit better energy resolution than the diffused p-n junction devices of similar size. The surface-barrier detectors are more sensitive to the ambient atmosphere and they need an atmosphere free of chemical fumes and water vapor. 

On-line particle sizing by ultrasonic (acoustic attenuation) spectroscopy was developed for use during batch crystallization processes.14 Crystallization of the alpha polymorph of (l) -glutamic acid from aqueous solution was monitored by continuously pumping the crystallizing solution through an on-line ultrasonic spectrometer. The method enabled measurement of the crystal size distribution and solid concentration throughout the... 

Fig. 2.6. Top section of computational domain for TEXTOR model, showing also the cross-section of the toroidal ALT-II limiter 45 degrees underneath the outer mid-plane. Bottom computed Balmer-alpha emission profile (photons/s/cm3, logarithmic colour scale) in the TEXTOR edge plasma, as used for interpretation of visible spectroscopy [26] and determination of plasma particle confinement...

The basic information in the study of sorption processes is the quantity of substances on the interfaces. In order to measure the sorbed quantity accurately, very sensitive analytical methods have to be applied because the typical amount of particles (atoms, ions, and molecules) on the interfaces is about I0-5 mol/m2. In the case of monolayer sorption, the sorbed quantity is within this range. As the sorbed quantity is defined as the difference between quantities of a given substance in the solution and/or in the solid before and after sorption processes (surface excess concentration, Chapter 1, Section 1.3.1), all methods suitable for the analysis of solid and liquid phases can be applied here, too. These methods have been discussed in Sections 4.1 and 4.2. In addition, radioisotopic tracer method can also be applied for the accurate measurement of the sorbed quantities. On the basis of the radiation properties of the available isotopes, gamma and beta spectroscopy can be used as an analytical method. Alpha spectroscopy may also be used, if needed however, it necessitates more complicated techniques and sample preparation due to the significant absorption of alpha radiation. The sensitivity of radioisotopic labeling depends on the half-life of the isotopes. With isotopes having medium half-time (days-years), 10 14-10-10 mol can be measured easily. 

Usually, direct analysis of alpha, beta and some gamma emitters is impossible if the sample is not previously isolated and preconcentrated. There is little use of direct radiometric detection of beta emitters by beta spectroscopy or liquid scintillation because of its low capacity to discriminate between different beta particles. This is because beta particles from a single isotope are emitted with a range... 

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