The femtochemistry of the ferrioxalate actinometer

The ferrioxalate actinometer is widely used as an analytical standard to determine the photon flux of light sources in photochemical reactors. Yet, the underlying mechanistic functioning of the actinometer at the molecular level is entirely unknown. Here, we present results from femtosecond UV-pump/mid-infrared-probe spectroscopy to reveal the elementary events including the primary C–C and Fe–O-bond breakages that follow an initial photon absorption by the ferrioxalate complex.

Universal dependence of the total number albedo of photons on the mean number of photon scatterings

This paper presents the results of research on photon reflection from plane targets based on Monte Carlo simulations performed by the MCNP code. Five materials (water, concrete, aluminum, iron, and copper) are examined in the area of initial photon energies of up to 200 keV. The values of the total number albedo for photons dependent on the initial photon energy or the mean number of photon scatterings are calculated and graphically presented. We have shown that the values of the total number albedo for different target materials, expressed as a function of the mean number of photon scatterings, are in good agreement with each other and can be approximated by simple, universal analytic functions obtained by the least squares method. The accuracy of these analytic appoximations is confirmed by their comparison with the results of PENELOPE and FOTELP Monte Carlo codes.

STUDY OF THE THRESHOLD BEHAVIOR OF THE ηN SCATTERING AMPLITUDE THROUGH THE ASSOCIATED PHOTOPRODUCTION OF ϕ- AND η-MESONS

We suggest that the γp → ϕηp reaction cross section, in the kinematics where the ηp invariant mass in the final state lies between the threshold value ( m p+ m η) and the N *(1535) resonance mass, is largely determined by the ηN scattering amplitude close to threshold. The initial photon energy is chosen in the range [Formula: see text], in order to reach low (absolute) values of the squared 4-momentum transfer from the initial photon to the final ϕ-meson. In these conditions, we expect the t-channel π0- and η-meson exchanges to drive the dynamics underlying the γp → ϕηp process. We show that the η-exchange is the dominating contribution to the cross section while the π0-exchange is negligible. The η-π0 interference is of the order of 20 – 30%. The sign of this term is not known and alters significantly our results. Data on the γp → ϕηp process would be therefore very useful to help unravelling the behavior of the ηp scattering amplitude close to threshold and assessing the possibility of producing η-nucleus bound states.

Number albedo of low-energy photons for water, aluminum, and iron

Number albedo of water, aluminum, and iron for incident photons in the energy range from 20 keV to 100 keV is presented in this paper. The results are obtained through Monte Carlo simulations of photon reflection by using MCNP-4C, FOTELP-2K3, and PENELOPE-2005 computer codes. The calculated values are compared with the classical data published by B. P. Bulatov and his collaborators. The influence of fluorescence yield to the photon number albedo of an iron target at the initial photon energies below 40 keV is detected and analyzed.

Spectral albedo of photons of initial energies below 100 keV

This paper shows the results of Monte Carlo simulations of the photon reflection from homogenous plates of the shield materials made of water, aluminum, and iron. Perpendicular incidence of a monoenergetic photon beam of the initial energy of 20 keV up to 100 keV is considered. The numerical experiments were performed using the verified Monte Carlo programs MCNP-4C, FOTELP-2K3, and PENELOPE-2005. As the result, the values of difference number albedo distributed in ten even intervals according to the energy and nine even intervals according to the polar angle of reflected photons were obtained. Out of these data, the spectral albedo coefficients for all three materials and three initial photon energies of 40 keV, 60 keV, and 100 keV were calculated, graphically presented, and analyzed. The values of the spectral albedo determined on the basis of MCNP-4C code were compared to the results of the early simulations of the photon reflection performed in Russia and in the USA. Also, with the help of MCNP-4C program, the yield of fluorescent photons to the spectrum of the reflected radiation was registered, which can be seen in the graphs in the form of the peak at the energy of 7.112 keV only at the shielding plates made of iron.

Total number albedo and average cosine of the polar angle of low-energy photons reflected from water

The total number albedo and average cosine of the polar angle for water and initial photon energy range from 20 keV to 100 keV are presented in this pa per. A water shield in the form of a thick, homogenous plate and per pendicular incidence of the monoenergetic photon beam are assumed. The results were obtained through Monte Carlo simulations of photon reflection by means of the MCNP computer code. Calculated values for the total number albedo were compared with data previously published and good agreement was confirmed. The dependence of the average cosine of the polar angle on energy is studied in detail. It has been found that the total average cosine of the polar angle has values in the narrow interval of 0.66-0.67, approximately corresponding to the reflection angle of 48?, and that it does not depend on the initial photon energy.