Physics:Straggling

range of a charged particle in matter is subject to fluctuations caused by the probability distribution of energy loss. These fluctuations are called range straggling; compare this to energy loss straggling, which describes the fluctuations in energy loss. Range straggling can be described by

where R is the range, , E and M are the particle energy and mass, and f is a slowly varying function depending on the absorber (see Rossi65). For protons in liquid hydrogen, the relative error is of the order of 0.015.