Spectra alpha-particle

Gr. helios, the sun). Janssen obtained the first evidence of helium during the solar eclipse of 1868 when he detected a new line in the solar spectrum. Lockyer and Frankland suggested the name helium for the new element. In 1895 Ramsay discovered helium in the uranium mineral clevite while it was independently discovered in cleveite by the Swedish chemists Cleve and Langlet at about the same time. Rutherford and Royds in 1907 demonstrated that alpha particles are helium nuclei. 

No stable divalent salt is known. However, Am2+ has been detected in CaF2 matrix (0.1% Am) by paramagnetic resonance spectrum at low temperature. Its formation is attributed to the reduction of Am3+ by electrons in the lattice set free by the effects of alpha particle emission. 

The sample in the final counting form must be handled with care and skill. When radionuclides that emit alpha particles are poorly electrodeposited, the quality of the counting data - the alpha-particle spectrum - may be degraded due to extraneous material deposited over the active surface. The energy peak... 

Figure 15.2 Alpha particle spectrum for a purified plutonium sample.

Any other body which has absorptivity a fiw) = 1 for photons with energy Hui will emit radiation according to (4.1). Although the sun consists mainly of protons, alpha particles and electrons, its absorptivity is a(Tkj) = 1 for all photon energies tiw, by virtue of its enormous size. Its temperature is not homogeneous, but emitted photons originate from a relatively thin surface layer a few hundred kilometres thick, in which the temperature is constant and in which all incident photons are absorbed. Conversely, only photons emitted within this surface layer may reach the surface of the sun. The solar spectrum observed just outside the Earth atmosphere agrees well with (4.1)... 

Most alpha particles are in the range 4-8 MeV. There are several, discrete monoenergetic alphas emitted from most alpha emitters, not just a continuous spectrum of emissions (Harley, 2001, 2008). 

Beta particles are emitted when a neutron is converted to a proton plus an electron and the electron is lost. Unlike the discrete energy emissions from the decay of alpha particles, beta particles are emitted along a spectrum of energies, because energies are shared between positive and negative electrons. Positrons are emitted when a proton becomes a neutron and decays by beta emission or an electron is captured. These are competing processes, and both occur with about the same frequency (Harley, 2001, 2008). 

The first objective for the Sojourner was to show that it could function in the little-known environment on the surface of Mars and to observe its behavior in order to make design improvements in future rovers. Sojourner moved around the immediate area of the lander, butting the APXS up against rocks. Detectors measured interactions between a radioactive source in the APXS and the surface materials by obtaining an energy spectrum of the alpha particles, protons, and x rays produced by the exposure. This instrument could determine the chemical composition of materials, including the amounts present of most major elements except hydrogen. 

Alpha particles emitted from nuclides which decay to a single level are observed as mono-energy particles. On transitions given the branching ratio in Table 5.6, multiple alpha energies are observed. Such a fine structure in the alpha spectrum comes about because an alpha emitter may decay to any one of several discrete energy levels of its daughter. Am is commonly used as a standard source. 

An example of this situation are plutonium isotopes, Pu and Pu. They are used for estimation of a burn up of nuclear fuel. As the energy difference of these alpha emitters is only 10 keV, the alpha particle spectrum is observed as an overlapped single peak. However, when a Si detector is used, which has an energy resolution of less than 10 keV (FWHM), the overlapped peaks can be analyzed by the least squares fitting technique. 

Intermolecular forces involving sulfur hexafluoride molecules have been discussed in several papers (91, 121, 122, 194, 350, 296). Other studies include (a) molecular volume (254), (b) stopping of alpha particles (16,117), (c) transfer of energy by collision (205), (d) mutual diffusion of H2 and SF6 (291), (e) mutual solubilities of gases, including SF , in water (197), (f) salting out of dissolved gases (219), (g) compressibility (193) (h) Faraday effect (161), (i) adsorption on dry lyophilized proteins (14), (j) effect of pressure on electronic transitions (231), (k) thermal relaxation of vibrational states (232), (1) ultraviolet spectrum (295), (m) solubility in a liquid fluorocarbon (280). 

Lil(Eu). Lil(Eu) is an efficient thermal-neutron detector through the reaction jLKn, a)jH. The alpha particle and the triton, both charged particles, produce the scintillations. Lil has a density of 4.06 X 10 kg/m, decay time of about 1.1 /i,s, and emission spectrum peaking at 470 nm. Its conversion efficiency is about one-third of that for Nal. It is very hygroscopic and is subject to radiation damage as a result of exposure to neutrons. 

Figure 12-1. Tb shows the sensor head from the Mars rover missions of 2(K)4. The head contains a curium-244 source that emits X-rays and 5.81 MeV alpha particles. The X-rays cause fluorescence in Martian rock samples, and the alpha particles stimulate X-ray emission as well. X-ray emission stimulated by bombardment by alpha and other subatomic particles such as protons is called punicle induced X-ru emission, or I lXE. llie X-ray detector is a new room-temperature type, which in the low temperature of the Martian night (below 4U°C.) exhibits low noise and high signal-to noise ratio for excellent resolution and sensitivity. Note the concentric design of the sensor head with six (im-244 sources arranged around the central detector. The X-ray spectrum of Figure 12-14 was acquired with the sensor head.

In contrast to alpha emission, beta emission is characterized by production of particles with a continuous spectrum of energies ranging from nearly zero to some maximum that is characteristic of each decay process. The jS particle is not nearly as effective as the alpha particle in producing ion pairs in matte r because of its small mass (about /7(XK) that of an alpha particle), At the same time, its penetrating power is substantially greater than that of the alpha particle. Beta-particle energies are frequently related to the thickness of an absorber, ordinarily aluminum, required to stop the particle. 

The energy spectrum of a beta-particle group takes the form of a continuum that has different shapes for different radionuclides three are shown in Fig. 2.5. Because of the energy distribution of beta particles, the relationships observed for the interaction of beta particles with matter are not as simple as those of alpha particles. 

Older LS counter systems (see Section 8.3.2) have three channels for distinguishing energies new ones have full energy spectrometers. These are directly applicable for distinguishing alpha particles by energy. Because beta particles are emitted as a spectrum from zero to maximum energy, and the spectra have various shapes, identification of beta-particle emitters by energy is less feasible. 

The Si detector with spectrometer is used with thin sources to identify and quantify radionuclides that emit alpha particles. All alpha particles are in the appropriate energy range for detection unless attenuated in a thick source. Chemical separation of the element of interest and meticulous preparation of the source usually are needed to obtain well-resolved peaks. Figure 9.1 shows the spectrum of a... 

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