Age versus length of horizontal fission tracks represented by 3D-Histograms

The code calculates the age distribution of horizontal fission tracks versus their lengths. The code is for tracks measured in the modern way where the angles to the c-axis are considered. 3D-histograms of track length versus angle is the basis for inversion.  Equations relating track length histograms and associated surface track densities to track ages are given in an early version in Jensen et al. (1992) and illustrated in a poster (Jensen and Hansen, 2018). The present code is based on further development (Jensen, 2021) and inversion is now performed using a probabilistic theory (Tarantola, 2005). The code is developed for the examples given in Jensen and Hansen (2021). A code for 2D-histograms where the angles to the c-axis are not considered is given by Jensen (2021).