Irradiation of the Sample

Depending on the selected reaction, irradiation of the sample may take place in a reactor, in an accelerator, or with an isotopic source. After the selection of an irradiation facility, the next step is a decision about the irradiation time. If the sample contains known isotopes at approximately known amounts, it is easy to estimate the proper irradiation time. If, on the other hand, the sample is completely unknown, one irradiates the sample for an arbitrary time, checks some of the isotopes present (from the emitted radiations), and then irradiates the sample again for a time that will provide enough activity for proper isotope identification with the desired accuracy. 

Since neutrons are, by far, more frequently used for activation analysis than other particles, neutrons will be assumed to be the projectiles for the equations discussed next. However, it should be noted that the same equations apply when some other radiation is used as the bombarding particle. 

The equation that gives the activity produced after irradiating the sample for time fg is (for derivation, see Sec. 14.4) 

The number of target nuclei stays essentially constant, i.e., r, / r 1. 

The radioisotope produced has such a small reaction cross section that 

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Silicone acrylates (Fig. 5) are again lower molecular weight base polymers that contain multiple functional groups. As in epoxy systems, the ratio of PDMS to functional material governs properties of release, anchorage, transfer, cure speed, etc. Radiation induced radical cure can be initiated with either exposure of photo initiators and sensitizers to UV light [22,46,71 ] or by electron beam irradiation of the sample. 

The principles behind MAP liquid-phase and gas-phase extractions are fundamentally similar and rely on the use of microwaves to selectively apply energy to a matrix rather than to the environment surrounding it. MAP gas-phase extractions (MAP-HS) give better sensitivity than the conventional static headspace extraction method. MAP-HS may also be applied in dynamic applications. This allows the application of a prolonged, low-power irradiation, or of a multi-pulse irradiation of the sample, thus providing a means to extract all of the volatile analytes from the matrix [477]. 

The lateral structure was studies by optical microscopy, and contrast arises from the fact that after irradiation of the samples with the ion beam in the TOF-ERDA apparatus, the PBrxS-rich structures appear darker than those rich in dPS, giving an excellent contrast (Figure 4.30). 

Figure 9.13 compares X-band EPR spectra of Fe-MCM-41 before (a) and after (b) and (c) carotenoid adsorption. The sample with incorporated Car exhibits a signal with g=2.0028 + 0.0002, characteristic of carotenoid radical cation prior to irradiation (Figure 9.13b). Irradiation of the samples at 365 nm (77 K) increases the Car 1 signal intensity (Figure 9.13c). The X-band experiments (Figure...

A detailed study of the C02- species on MgO has been carried out by Lunsford and Jayne 26). Electrons trapped at surface defects during UV irradiation of the sample are transferred to the CO2 molecule upon adsorption. By using 13C02 the hyperfine structure was obtained. The coupling constants are axx - 184, am = 184, and a = 230 G. An analysis of the data, similar to that carried out in Section II.B.2 for N02, indicates that the unpaired electron has 18% 2s character and 47% 2p character on the carbon atom. An OCO bond angle of 125° may be compared with an angle of 128° for CO2- in sodium formate. 

The microwave photochemical reactor is an essential tool for experimental work in this field. Such equipment enables simultaneous irradiation of the sample with both MW and UV/VIS radiation. The idea of using an electrodeless lamp (EDL), in which the discharge is powered by the MW field, for photochemistry was bom half a century ago [46, 68]. The lamp was originally proposed as a source of UV radiation only,... 

Cirkva and Hajek have proposed a simple application of a domestic microwave oven for microwave photochemistry experiments [86]. In this arrangement, the EDL (the MW-powered lamp for this application was specified as a microwave lamp or MWL) was placed in a reaction vessel located in the cavity of an oven. The MW field generated a UV discharge inside the lamp that resulted in simultaneous UV and MW irradiation of the sample. This arrangement provided the unique possibility of studying photochemical reactions under extreme thermal conditions (e.g. Ref. [87]). 

Simultaneous UV and MW irradiation of the sample Possibility of performing photochemistry at high temperature Good photochemical efficiency — the EDL is inside the sample Simplicity of the experiment and the low cost of the EDL Use of a commercially available microwave oven Wireless EDL operation... 

Alternatively, arene displacement can also be photo- rather than thermally-induced. In this respect, we studied the photoactivation of the dinuclear ruthenium-arene complex [ RuCl (rj6-indane) 2(p-2,3-dpp)]2+ (2,3-dpp, 2,3-bis(2-pyridyl)pyrazine) (21). The thermal reactivity of this compound is limited to the stepwise double aquation (which shows biexponential kinetics), but irradiation of the sample results in photoinduced loss of the arene. This photoactivation pathway produces ruthenium species that are more active than their ruthenium-arene precursors (Fig. 18). At the same time, free indane fluoresces 40 times more strongly than bound indane, opening up possibilities to use the arene as a fluorescent marker for imaging purposes. The photoactivation pathway is different from those previously discussed for photoactivated Pt(IV) diazido complexes, as it involves photosubstitution rather than photoreduction. Importantly, the photoactivation mechanism is independent of oxygen (see Section II on photoactivatable platinum drugs) (83). 

These workers distinguished between inorganic mercury obtained by direct analysis on the sample as received, and organic mercury (the difference between total mercury obtained upon ultraviolet irradiation of the sample and inorganic mercury). 

Most of the methods of analysis for mercury actually measure inorganic mercury to measure either organic or total mercury by such methods, it is necessary to decompose any organic mercury compounds present. This decomposition can be effected by ultraviolet irradiation of the samples. Systems of this sort have been described [46-48]. Since as much as 50% of the mercury maybe present in organic form [46] the differentiation between inorganic and organic mercury can be of considerable importance. 

Several other light-induced phenomena associated with spin transition systems have recently been reported. These include light induced thermal hysteresis (LITH), which is another example of light induced bistability, discovered for the SCO compound [Fe(PMBiA)2(NCS)2] which undergoes a very abrupt thermal ST around 170 K with hysteresis [174]. Irradiation of the sample at 10 Kwith green light resulted in the population of the LIESST state. When the temperature was raised to 100 K and lowered back to 10 K under continuous irradiation a wide thermal hysteresis loop resulted. The... 

Fig. 10 57Fe Mossbauer spectra of (bpym, Se) recorded at 4.2 K in zero-field after irradiation of the sample (a) and in a magnetic field of 50 kOe (b). Mossbauer subspectra correspond to LS in [HS-LS] (grey), HS in [HS-LS] pairs (light grey), HS in [HS-HS] pairs (dark grey)...

The main objective in carrying out LIESST experiments on (bt, S) was to elucidate the nature of excitations (metastable pairs) which appear at low temperatures after light irradiation of a ground [LS-LS] state. As is illustrated in Fig. 11a, at 4.2 K before irradiation the Mossbauer spectrum of a sample, which was enriched with 20% of 57Fe, reflects the presence of mainly LS species. The Mossbauer parameters obtained from the fitting of the spectrum are dLs=0.357(l) mms, AEq(ls)=0.452(2) mms. After irradiation of the sample for one hour (2=514 nm) at 4.2 K, the Mossbauer spectrum of (bt, S) shows a decrease in the intensity of the LS species (62.0%) in favour of an increase of the HS species (38.0%) (Fig. lib). Time-dependent measurements revealed the decay of the HS component (Fig. 11c, d), which... 

It involves the simultaneous irradiation of the sample and a standard known mass of the same element to produce a radioactive isotope of the element. The activities of both the sample and the standard are then determined and, because their specific activities will be the same, it is possible to calculate the mass of the unknown sample. 

Using as the background continuum the short-lived spontaneous fluorescence of rhodamine B or 6 G, McLaren and Stoicheff 233) developed this method further to obtain inverse Raman spectra over the range of frequency shifts 300-3500 cm" in liquids and solids in a time of 40 nsec The stimulating monochromatic radiation at 6940 A is provided by a giant-pulse ruby laser. A small part of the main laser beam is frequency-doubled in a KDP-crystal and serves to excite the rhodamine fluorescence, thus ensuring simultaneous irradiation of the sample by both beams. 

In order to obtain a date from the measurement of an irradiated sample, it is necessary to know the proportion of 39K that was converted to 39Ar. The number of39Ar atoms formed by irradiation of the sample is given by... 

A rapid preseparation technique was developed for the extraction of SAL from various chicken tissues using the irradiation of the sample in EtOH-2-PrOH for 9 s in a common household microwave oven. The extract was analyzed without further cleanup and detected via postcolumn reaction with DMABA at 86°C. Recoveries ranged between 87% and 100% (105). 

Increase of the stable Frenkel-pair concentration under irradiation of the samples is saturated (Fig.6) when the trapping of excitons at defects exceeds the exciton self-trapping in the perfect lattice. Further long-time irradiation of the samples results in an aggregation of vacancies and interstitials, which results in decrease of intensity of defect subbands (Fig.6e). 

In routine analytical laboratories, the use of advanced oxidation processes (AOPs) is an emerging alternative to conventional sample treatments2 for analytical and environmental chemists. AOPs involve the in situ generation of highly potent chemical oxidants, such as the hydroxyl radical (OH ). Several processes have been applied in analytical sample pretreatment homogenous UV irradiation, either by direct irradiation of the sample or photolysis mediated by an appropriate chemical reagent ozone and ultrasonic irradiation. A variety of AOPs ensures compliance of specific treatment requirements with optimum treatment technologies (Table 5.1). 

Irradiation of the samples was performed at the Institut Armand-Frappier (IAF). Four irradiators with different dose rates were used. In all instances, Cobalt-60 ( Co, half-life 5.26 years, 1.25 MeV yray photon) was used as the gamma ray source. The GammaCell I, n, HI and the Calibrator emit y rays at 107,350,700 and 3000 krad/h respectively. At the end of the experimental runs, the 107 and 350 krad/h dose rates of the GammaCell I and n were down to 85 and 265 krad/h respectively, due to the Co half-life. The calibrator was kept constant at 3000 krad/h. The exact value of the various dose rates was constantly monitored during the experiments. 

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