Soft irradiation

The calculated light efficiencies are, in general, lower than would be desirable. However, some values are quite promising but they were obtained under very peculiar circumstances, namely on a very small scale or with soft irradiation intensities. On the other hand, these values may suggest that the limitation is not biological but are explainable from an engineering point of view. And the challenge is still there ... 

In this chapter, visible light-induced radical polymerization reactions in the 380-800 nm range are reviewed. The role of the absorbing species (dye) and the complete multicomponent photoinitiating systems (PISs) (dye and additives) are then emphasized. The original works on the dye-based PISs that have been proposed over the years are also outlined. However, this chapter is mainly focused on the latest developments, in the 2010-2014 period, and the actual trends of research, in particular the novel perspectives of applications under soft irradiation conditions. 

Photoinitiation under soft irradiation conditions novel three-component systems... 

In the past 3-4 years, huge efforts have been deployed to develop PISs able to initiate the polymerization of low-viscosity matrices (radical or cationic) under soft irradiation conditions, i.e. visible lights, low intensity (2-30 mW/cm ) and under air [LAL 14a]. They require the design of particularly reactive systems and involve novel strategies for an efficient production of radical or cationic initiating species. Such systems can successfully operate in high-viscosity media or/and under intense light sources. 

A recent research direction was focused on the use of the photoredox catalysis (well-known and largely employed in organic synthesis [XIA 15, SHI 10]) in the pol5mierization area where the development of sustainable radical-mediated chemical processes under very soft irradiation conditions can be of interest (see a review in [LAL 14b]). The goal is twofold ... 

It was found that that in the case of soft beta and X-ray radiation the IPs behave as an ideal gas counter with the 100% absorption efficiency if they are exposed in the middle of exposure range ( 10 to 10 photons/ pixel area) and that the relative uncertainty in measured intensity is determined primarily by the quantum fluctuations of the incident radiation (1). The thermal neutron absorption efficiency of the present available Gd doped IP-Neutron Detectors (IP-NDs) was found to be 53% and 69%, depending on the thicknes of the doped phosphor layer ( 85pm and 135 pm respectively). No substantial deviation in the IP response with the spatial variation over the surface of the IP was found, when irradiated by the homogeneous field of X-rays or neutrons and deviations were dominated by the incident radiation statistics (1). 

Precisely controllable rf pulse generation is another essential component of the spectrometer. A short, high power radio frequency pulse, referred to as the B field, is used to simultaneously excite all nuclei at the T,arm or frequencies. The B field should ideally be uniform throughout the sample region and be on the order of 10 ]ls or less for the 90° pulse. The width, in Hertz, of the irradiated spectral window is equal to the reciprocal of the 360° pulse duration. This can be used to determine the limitations of the sweep width (SW) irradiated. For example, with a 90° hard pulse of 5 ]ls, one can observe a 50-kHz window a soft pulse of 50 ms irradiates a 5-Hz window. The primary requirements for rf transmitters are high power, fast switching, sharp pulses, variable power output, and accurate control of the phase. 

Figure 2.11. Proton-Proton shift correlations of a-pinene (1) [purity 99 %, CDCls, 5 % v/v, 25 °C, 500 MHz, 8 scans, 256 experiments], (a) HH COSY (b) HH TOCSY (c) selective one-dimensional HH TOCSY, soft pulse irradiation at Sh = 5.20 (signal not shown), compared with the NMR spectrum on top deviations of chemical shifts from those in other experiments (Fig. 2.14, 2.16) arise from solvent effects...

The surface to be analyzed is irradiated with soft X-ray photons. When a photon of energy hv interacts with an electron in a level X with the binding energy Eg (Eg is the energy E of the K-shell in Pig. 2.1), the entire photon energy is transferred to the electron, with the result that a photoelectron is ejected with the kinetic energy... 

Plutonium has a much shorter half-life than uranium (24.000 years for Pu-239 6,500 years for Pu-240). Plutonium is most toxic if it is inhaled. The radioactive decay that plutonium undergoes (alpha decay) is of little external consequence, since the alpha particles are blocked by human skin and travel only a few inches. If inhaled, however, the soft tissue of the lungs will suffer an internal dose of radiation. Particles may also enter the blood stream and irradiate other parts of the body. The safest way to handle plutonium is in its plutonium dioxide (PuOj) form because PuOj is virtually insoluble inside the human body, gi eatly reducing the risk of internal contamination. 

Soft-pulse multiple irradiation In this method, pre-saturation is done using shaped pulses having a broader excitation profile. Therefore, it is a more suitable method for the suppression of multiplets. This technique is very effective, easy to apply and easy to implement within most NMR experiments. In aqueous solutions, however, slowly exchanging protons would be detectable due to the occurrence of transfer of saturation. In addition, the spins with resonances close to the solvent frequency will also be saturated. 

Soft pulse Pulse designed to bring about irradiation of only a selected region of a spectrum. See Hard pulse. 

In an NMR analysis of the effects of /-irradiation induced degradation on a specific polyurethane (PU) elastomer system, Maxwell and co-workers [87] used a combination of both H and 13C NMR techniques, and correlated these with mechanical properties derived from dynamic mechanical analysis (DMA). 1H NMR was used to determine spin-echo decay curves for three samples, which consisted of a control and two samples exposed to different levels of /-irradiation in air. These results were deconvoluted into three T2 components that represented T2 values which could be attributed to an interfacial domain between hard and soft segments of the PU, the PU soft segment, and the sol... 

Figure 34 Left (a) equilibrium storage modulus G as a function of y-irradiation dose determined from DMA experiments on exposed PU samples (b) 1/T2ave as a function of G. Right BC CPMAS NMR measurements on non-irradiated PU sample (a) 3 ms, (b) 0.5 ms, and (c) 100 pis. SS denotes soft segment HS denotes hard segment. Reprinted from Maxwell [87], Copyright 2003, with permission from Elsevier.

Sommermeyer and coworkers50 reported that solutions of gramicidin exhibit fluorescence when irradiated with soft x-rays. 

After the irradiation, the surface of the film was wiped with a soft cloth wetted with acetone, dried under vacuum at 40°C for 10 hours and weighed. The degree of grafting (Dg) was determined by the equation (1). 

When a sample maintained in a high vacuum is irradiated with soft X-rays, photoionization occurs, and the kinetic energy of the ejected photoelectrons is measured. Output data and information related to (he number of electrons that arc detected as a function of energy are generated. Interaction of the soft X-ray photon with sample surface results in ionization from the core and valence electron energy levels of the surface elements. 

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