Photon fluence

Chloroplasts. Intact chloroplasts were isolated from freshly harvested growth chamber-grown spinach (Splnacla oleracea L.) as described by Lilley and Walker (10). Thylakoids were prepared by the method of Armond t al. (11). Chlorophyll concentrations were determined by the method of MacKinney (12). Photochemical reactions yere conducted at 25°C with a photon fluence rate of 750... 

Wave- length Photon energy Relation between energy fluence and photon fluence ... 

Hence, in the epilimnion of Greifensee, for light with A = 330 nm and 400 nm, the average photon fluence rate is only about 4 and 13%, respectively, of the nearsurface photon fluence rate. Insertion of these values into Eqs. (5) and (6) together with the kp values calculated above (case a) yields ... 

Fluxes must be specified during each phase of device operation including startup, heating, burn, fueling, shutdown and failure modes. Plasma failure modes, such as instabilities which cause much of the stored plasma energy to be dumped in a short time may result in large particle or photon fluences to selected small areas of surfaces exposed to the plasma. 

Since the Y-photon ionization rate is R = aN F, where ionization cross-section and Fthe photon fluence, both the electron and ion signals can be increased by tight focussing of the laser. Because the ion yield should increase as the Y-th power of the intensity, focussed lasers tuned to an intermediate resonance will ionize virtually every atom in the focal volume. For a typical dye laser with 0.5-mrad divergence, the spot size for a 5-cm focal length lens is 25 /mi which, for an assumed energy of ca 10 mJ per 10 ns pulse (i.e. 1 MW of power), yields a flux p of ca 1011 W cm-2. This power density corresponds, for 500-nm photons, to a fluence of ca 5 x 1022 photon cm-1. Since the peak electric field, E V cm 1, is related to p by... 

Cleavage of chemical bonds by adequate photon fluence Hp o/mol uT ... 

Photon exposure (Hp) The photon irradiance, Ep, integrated over the time of irradiation (f Epdt, simplified expression Hp = Ept when the photon irradiance is constant over the time considered). The SI unit is uT. Alternatively, the term can be used with the amount of photons (mol or its equivalent einstein), the SI unit then being mol uT. For a parallel and perpendicularly incident beam not scattered or reflected by the target or its surroundings photon fluence (H ) is an equivalent term. 

Photon fluence rate ( ) The rate of photon fluence. Four times the ratio of the photon flow, volume element containing the point under consideration divided by the surface of that sphere, Sk. (f,f Lpdm, simphfied expression F = 4 constant over the sohd angle considered). The SI unit is m s. ... 

Fluencerate is the fluence per unit time,e.g., the photon fluence rate (mol m-2 s-1) is thesameas the photon flux density. 

Gamma-rays follow the inverse square law over a wide range of exposure rate and distance. Suppose that a point gamma ray source is uniformly emitting S photons of energy E (MeV) per second in every direction. The photon fluence rate d> (photons/ cmVs) at a distance of d cm from the source is represented by... 

It is conveniently expressed as a plot of photoreaction per fixed number of photons vs the wavelength of radiation to which the sample was exposed. The use of a fixed total photon fluence at each wavelength avoids the need to make the assumptions involved in calculating effectiveness on a per photon basis. Action spectrum will therefore not depend on the spectral irradiance distribution of the source used in its determination. 

Both reactions yield an unsaturated chain end and a propagating radical. The quantum yield for scission, was determined from viscometric data on irradiated films and known photon fluence levels, using an expression similar to the one below ... 

The same group [110] has recently investigated the photodegradation of PMMA films containing a benzophenone sensitizer in low concentrations (0.05, 0.10 and 0.23 moI%). Gravimetrically determined gel fraction in samples exposed to equal photon fluences showed marked wavelength dependence with a maximum at approximately X = 340 nm. This maximum was independent of the concentration of sensitizer but the amount of gel formation increased with its concentration in the polymer. 

---