Mixed radiation fields

In this region, there is a linear relationship between the number of ion pairs collected and applied voltage. A charge amplification of 104 can be obtained in the proportional region. By proper functional arrangements, modifications, and biasing, the proportional counter can be used to detect alpha, beta, gamma, or neutron radiation in mixed radiation fields. 

Since the single channel analyzer can be set so that an output is only produced by a certain pulse size, it provides for the counting of one specific radiation in a mixed radiation field. 

Nielsen F, Jonsson M. (2008) Simulations of HjOj concentration profiles in the water surrounding spent nuclear fuel taking mixed radiation fields and bulk reactions into account. J Nucl Mater 374 281-285. 

ESR dosimetry in neutron beams has been reported recently using alanine, ammonium tartate, and lithium formate ESR dosimeters [58-60]. A sensitivity improvement by gadolinium addition was observed experimentally and examined theoretically by Monte Carlo simulations. Those materials have also been considered for dosimetry in a mixed radiation field of photons and neutrons. 

The values of the voltage intersection are compiled in Table 8. This observation may be used to conclude from the measured current/voltage curve on the quality of radiation. Especially in mixed radiation fields of fast neutrons and y-rays, from the value of the intersection the relative contribution of the two types of radiation to the total dose can be estimated (Blanc et al., 1964). 

Ionization chambers filled with liquid hydrocarbons have been developed as dosimeters for mixed radiation fields of low LET radiation and fast neutrons (Blanc et al., 1963). Use is made of the fact that the slope of the ionization current vs. voltage curve depends on the LET of the radiation (see Section 5.7). 

Page DJYS, Bonin HW, Bui VT, Bates PJ (2002) Mixed radiation field effects on the morphology and viscoelastic behavior of poly (ether ether ketone). J Appl... 

It is very important, in the theory of quantum relaxation processes, to understand how an atomic or molecular excited state is prepared, and to know under what circumstances it is meaningful to consider the time development of such a compound state. It is obvious, but nevertheless important to say, that an atomic or molecular system in a stationary state cannot be induced to make transitions to other states by small terms in the molecular Hamiltonian. A stationary state will undergo transition to other stationary states only by coupling with the radiation field, so that all time-dependent transitions between stationary states are radiative in nature. However, if the system is prepared in a nonstationary state of the total Hamiltonian, nonradiative transitions will occur. Thus, for example, in the theory of molecular predissociation4 it is not justified to prepare the physical system in a pure Born-Oppenheimer bound state and to force transitions to the manifold of continuum dissociative states. If, on the other hand, the excitation process produces the system in a mixed state consisting of a superposition of eigenstates of the total Hamiltonian, a relaxation process will take place. Provided that the absorption line shape is Lorentzian, the relaxation process will follow an exponential decay. 

Although two-photon transitions were the first multiphoton transitions to be considered, there is no reason to limit studies of atomic response to just two optical waves, once the possibility of nonlinear coupling between the atoms and the radiation field has been recognised. Indeed, one of the most important processes involves the generation of a higher frequency lo by the superposition of three waves oq, ll>2 and 0J3, a process referred to as four-wave mixing. 

In some nonlinear wave-mixing schemes, all energy and momentum remains in the radiation field, but in others (e.g., Stokes Raman shifting, optically pumped lasers) some energy and momentum is exchanged between the radiation field and the material medium. 

The H2 molecule acts as a nonlinear medium for stepwise addition and subtraction of the v = 1 — 0 frequency to u>i. Since the four-wave mixing process conserves both the energy and momentum of the radiation field, no net excita-tion of the nonlinear medium results. 

It should be specially noted that average values of reaction rates are needed because under no circumstances can photons be very well mixed consequently, since in the radial direction in particular the photon concentration is normally non-uniform, usually, the reaction rate will be a strong function of the radial position. This consideration is also important if the reaction involves highly reactive intermediates, because very often their reaction characteristic time is much smaller than the hydrodynamic mixing time and the well-mixed condition cannot be extended to all the species participating in the reaction. Hence, even in approximate models, as is the case for the plug flow simplification, the radiation field non-uniformities cannot be ignored. 

Even in well-mixed photochemical reactors, the volume average of the reaction rate must always be calculated because usual experimental measurements never represent local values. Note that the volume of connecting lines in Figure 6.2 has been considered negligible. This stirring mechanism is suggested for laboratory reactors to avoid the effects produced by the presence of a stirrer inside the reactor thus producing a distortion of the radiation field inside the reaction space. 

A small molecule has been previously defined as a system of discrete molecular levels interacting with a radiation field in the absence of other dissipative continua (predissociation, preionization, collisional relaxation). The excited system may thus decay uniquely by the radiative path, and the emission quantum yield Q must be equal to one if measured in a sufficiently broad spectral range. On the other hand, the s-l coupling, inducing redistribution of the s) level oscillator strength, always implies a lengthening of the fluorescence lifetime of mixed levels with respect to that of a pure s> state. 

Much work has been done on Pu and other actinides with these compounds, in process and analytical applications. They have much higher distribution coefficients than TBP for U and Pu(IV), and rfiow much less deleterious effects on the distribution due to high radiation fields because the radlolysls products do not interact with the extractant to produce synergistic mixtures, ( cf Mixed Extractants, p. 71). 

---