--------------------- Any result in a Monte Carlo calculation is obtained by adding up the contributions to the "score", or "tally" of a detector defined by the user. A detector is the Monte Carlo equivalent of a measurement instrument. Each "estimator" (detector type) is designed to estimate one or more radiometric quantities, and the final score is a statistical estimation of the average value of the corresponding population. As in experimental measurements, it is possible to calculate a standard deviation by running several independent calculations. No default detector is available: each scoring option must be explicitly requested. There are different input options corresponding to different types of detector. The simplest is SCORE which provides energy deposition (proportional to dose) or star density in every region of the geometry. "Stars" is an old name for inelastic hadron reactions which derives from early experiments with nuclear emulsions. The same quantities can be scored in a uniform spatial mesh independent of geometry, called a "binning", by means of option USRBIN. There are several types of binnings: Cartesian, 2D-cylindrical, 3D-cylindrical and even more complex phase space structures. In addition to dose and star density, it is possible to use USRBIN to score particle fluence distributions in space. USRBIN results are often displayed as colour plots where each colour corresponds to a pre-defined range of values. A post-processing program for this purposes (PAWLEVBIN) is available in the directory $FLUPRO/flutil, and a GUI interface can be downloaded from the FLUKA website www.fluka.org. Fluence, averaged over the volume of a given geometry region, can be calculated with options USRTRACK and - less often - USRCOLL. The first is a "track-length estimator" (it estimates fluence as volume density of particle trajectory lengths), and the second is a "collision estimator" (fluence is estimated as volume density of collisions weighted with the particle mean free path). Of course, USRCOLL can be used only in a region of matter, while USRTRACK works also in vacuum. Both options provide fluence differential energy spectra. Another common scoring option is USRBDX, which also calculates fluence, but averaged over the boundary between two geometry regions. It is a "boundary crossing estimator", which estimates fluence as the surface density of crossing particles weighted with the secant of the angle between trajectory and normal to the boundary at the crossing point. Option USRBDX can also calculate current, i.e. a simple counter of crossings, not weighted by inverse cosine: but despite a widespread credence, current is only seldom a quantity worth calculating. The results of USRBDX can account on request for particles crossing the boundary from either side or from one side only, and are in the form of double-differential energy and angular spectra. The angle considered is again that with the normal at the crossing point. USRYIELD is a multi-purpose estimator option, which can estimate several different double-differential quantities. The main one is an energy-angle double-differential yield of particles escaping from a target, the angle in this case being with respect to a fixed direction. Energy and angle can be replaced by many other variables which are mostly of the same kind, such as momentum and rapidity. But it is possible also to score yields as a function of charge and LET (linear energy transfer). Production of residual nuclei can be obtained with command RESNUCLEi. The results, which are closely related to induced activity and dose rate from activated components, may include nuclei produced in low-energy neutron interactions, provided the corresponding information is available in the neutron cross section library for the materials of interest.
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