Detector Si

Figure 24.2 Schematic diagram of the setup used to measure and control H2O concentration and gas temperature in the combustion region (in situ) of a forced 5-kilowatt combustor at Stanford University 1 — steel duct 2 — quartz duct 3 — A1 duct 4 — multiplexed beam 5 — tunable diode lasers 6 — data acquisition and control computer 7 — control signals 8 — primary air driver Aair sin(27r/of) 9 — fuel drivers Afuei sin(27r/of-f dfuei) 10 — demultiplexing box 11 — Si detector (ND filter) and 12 — laser beam...

Detectors include (1) Geiger-Mueller tube, (2) ionization chambers, (3) scintillation counters, (4) proportional counter, (5) electron-multiplier tubes, and (G) nondispersive detectors using cooled lithium-drifted Si detectors, See Fig. 3... 

Beta particles at the deposition point passed through the Mylar tape and a 0.0075 cm thick A1 vacuum window and were counted with a 450 mm2 totally depleted surface barrier Si detector 1000 Mm thick. The geometric solid angle for a point source under these conditions was estimated to be 17, however, the measured efficiency was about 14. ... 

An a-y coincidence experiment was performed using a cooled Si(Li) detector for the detection of photons and a Si detector for the detection of a-particles. Three parameter events were collected on tape and one dimensional spectra were later generated in coincidence with various gates. The spectra showed that the and a3Q are in prompt coincidence with L X-rays and the delay occurs at the 27.4 keV level. The analysis of the time spectrum between the group and the 27.4 keV photopeak gave a half-life of 38.3 - 0.3 ns, in agreement with previous measurements. 

Step 28. Count sample at specified distance from Si detector in vacuum chamber of alpha-particle spectrometer for 60,000 s. 

Step 28. Count the sample for 60,000 s at an instructor-specified distance from the Si detector in the vacuum chamber of the alpha-particle spectrometer. 

Here, AH(A-B) is the partial molar net adsorption enthalpy associated with the transformation of 1 mol of the pure metal A in its standard state into the state of zero coverage on the surface of the electrode material B, ASVjbr is the difference in the vibrational entropies in the above states, n is the number of electrons involved in the electrode process, F the Faraday constant, and Am the surface of 1 mol of A as a mono layer on the electrode metal B [70]. For the calculation of the thermodynamic functions in (12), a number of models were used in [70] and calculations were performed for Ni-, Cu-, Pd-, Ag-, Pt-, and Au-electrodes and the micro components Hg, Tl, Pb, Bi, and Po, confirming the decisive influence of the choice of the electrode material on the deposition potential. For Pd and Pt, particularly large, positive values of E5o% were calculated, larger than the standard electrode potentials tabulated for these elements. This makes these electrode materials the prime choice for practical applications. An application of the same model to the superheavy elements still needs to be done, but one can anticipate that the preference for Pd and Pt will persist. The latter are metals in which, due to the formation of the metallic bond, almost or completely filled d orbitals are broken up, such that these metals tend in an extreme way towards the formation of intermetallic compounds with sp-metals. The perspective is to make use of the Pd or Pt in form of a tape on which the tracer activities are electrodeposited and the deposition zone is subsequently stepped between pairs of Si detectors for a-spectroscopy and SF measurements. 

A rather new development in this field is energy dispersive X-ray fluorescence using energy-dispersive Si detectors with attached multichannel analysers. X-irradiation excited by radio-isotopes makes this method independent of large X-ray tubes. The application of nondispersive X-ray fluorescence is somewhat restricted by its limit of resolution. 

There are, however, three main limitations of EDX spectrometers. The resolution of characteristic peaks is poorer than with WDX spectrometers, and the background is higher. Furthermore, the efficiency of the normal Li-doped Si detector with an 8 / m thick Be window falls off dramatically for elements of low atomic number Z thus, only x-rays from Na (Z = 11) and heavier atoms can be detected. Windowless detectors are available, which can detect light elements such as B (Z = 5), but their use is not free of complications for quantitative analysis. 

Fully depleted Si detectors in which the zone of depletion extends over the whole crystal are also available. The energy loss -dE/dx in this kind of detector can be determined by means of another detector which is placed behind the first one and in which the remaining energy is measured. 

Thereafter an aliquot of each slice is analysed for plutonium isotopes and Vb. Plutonium was separated by anion exchange using " Pu as radiochemical yield determinant and measured by alpha spectrometry using solid state ion implanted Si detectors. 

The ICP-SFMS instrument was tuned using a I ng mf uranium standard solution prior to analysis. Sensitivity was about 2 x 10 cps for 1 ng g" solution. Concentrations of plutonium isotopes and " Am were calculated as a function of Pu/ Pu, Pu/ Pu, Pu/ Pu and Am/ Am ratios according to the isotope dilution method. All raw data were corrected for instrumental mass bias using linear correction. NdFs micro coprecipitated alpha sources were counted by a PIPS type alpha Si detector with a surface... 

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. 

Another more serious defect of the EDS technique concerns the inherent sensititivy of the measurements for light (low-Z) elements. Several factors prevent the efficient detection of elements within the first row of the Periodic Table and limit information from the second. Instrumentally, the efficiency of the Li-drifted Si detector, its resolution, and the transparency of the Be window commonly used between the former and the system vacuum all concern us here. Detection sensitivities may be as low as 10", thereby limiting MDM at a given S/N, whilst the resolution (typically 150— 200 eV) may make the analysis of, for example, magnesium (hco = 1253.6 eV) in the presence of aluminium (hcu = 1486.6 eV) difficult. The presence of the Be window presents a more immediate practical problem in that characteristic Z-rays softer than, say, Na Kct may be absorbed, and this certainly precludes the analysis of the majority of the first-row elements (Li to F). 

Figure 9. Side views of the sample regions of the experimental setups used on station 7.3.3 at the ALS for combined X-ray fluorescence and diffraction in transmission and reflection mode. The white wedge to the left of each frame represents the focused beam (width not to scale) coming from the vertical-focus mirror on the left. The large black object is the diffraction detector. The cylindrical object coming in from the upper left is the Si detector used for fluorescence mapping.

Figure 8.31 Artifacts in an EDXRF spectrum. The spectrum of pure iron, measured with a Si(Li) detector, shows a peak lower in energy than the Fe Kq. peak by an amount exactly equal to the energy of the Si Kq, line. Some of the Fe photon energy is transferred to the Si detector atoms the amount of energy absorbed by an Si atom has escaped from the Fe photon. This t)rpe of peak is called an escape peak. Sum peaks also appear in EDXRF spectra when two intense photons arrive at the detector simultaneously. A sum peak from two Kq, photons is shown along with a sum peak from one Kq and one Kys photon. [Courtesy of Thermo ARE (www.thermo ARL.com).]...

Samples of soil, fir, and spruce material pressed into pellets or samples of honey in native form were placed in counting vessels. Specimens were excited by a Cd annular source IPR, 25mCi. Emitted characteristic X-rays were detected by the system s Si-detector (resolution 165 eV at... 

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... 

If the gross alpha-particle activity is sufficiently high, a thin sample—of the order of 1 mg/cm —is prepared for alpha-particle spectral analysis with a Si detector plus spectrometer. The energy range of interest usually is 4-10 MeV. 

An international group (Gaggeler et al., 1992 Tiirler, 1992) used OLGA II and 35-s 262Db to perform the first online isothermal gas chromatography of the bromides of element 105. The volatile species were deposited on a moving tape and transported in front of six large area passivated implanted planar Si detectors for measurement of a-particles and SFs. The adsorption enthalpies were nearly... 

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