{"id":11662,"date":"2016-03-01T15:06:43","date_gmt":"2016-03-01T15:06:43","guid":{"rendered":"http:\/\/sitepourvtc.com\/?page_id=11662"},"modified":"2022-10-13T13:12:24","modified_gmt":"2022-10-13T13:12:24","slug":"stopping-power-bethe-formula","status":"publish","type":"page","link":"https:\/\/sitepourvtc.com\/nuclear-power\/reactor-physics\/interaction-radiation-matter\/interaction-heavy-charged-particles\/stopping-power-bethe-formula\/","title":{"rendered":"Stopping Power – Bethe Formula"},"content":{"rendered":"
The stopping power<\/strong> describes specific energy losses for heavy charged particles in the surrounding medium, and the Bethe formula can express it. The stopping power<\/strong> of most materials is very high for heavy-charged particles, and these particles have very short ranges. For example, the range of a 5 MeV alpha particle is approximately only 0.002 cm in aluminium alloy.<\/div><\/div>\n

 <\/p>\n

A convenient variable that describes the ionization properties of the surrounding medium is the stopping power<\/strong>. The linear stopping power of the material is defined as the ratio<\/strong> of the differential energy loss<\/strong> for the particle within the material to the corresponding differential path length<\/strong>:<\/p>\n

\"stopping_power_formula\"<\/p>\n

Where T is the kinetic energy of the charged particle, nion<\/sub> is the number of electron-ion\u00a0pairs formed per unit path length, and I\u00a0denotes the average energy\u00a0needed to ionize an atom in the medium. For charged particles, S increases as the particle velocity decreases<\/strong>. The classical expression that describes the specific energy loss is known as the Bethe formula. The non-relativistic formula was be found by Hans Bethe in 1930. Hans Bethe also found the relativistic version (see below) in 1932.<\/p>\n

\"stopping_power_formula_2\"<\/a><\/p>\n

In this expression, m is the rest mass of the electron, \u03b2 equals v\/c, which expresses the particle’s velocity relative to the speed of light, \u03b3 is the Lorentz factor of the particle, Q equals to its charge, Z is the atomic number of the medium and n is the density of the atoms in the volume. For non-relativistic particles (heavy charged particles are mostly non-relativistic), dT\/dx is dependent on 1\/v2<\/sup><\/strong>. This can be explained by the greater time the charged particle spends in the negative field of the electron when the velocity is low.<\/p>\n

The stopping power<\/strong> of most materials is very high for heavy-charged particles, and these particles have very short ranges. For example, the range of a 5 MeV alpha particle is approximately only 0.002 cm in aluminium alloy. Most alpha particles can be stopped by an ordinary sheet of paper or living tissue. Therefore the shielding of alpha particles does not pose a difficult problem. On the other hand, alpha radioactive nuclides can lead to serious health hazards when ingested or inhaled (internal contamination).<\/p>\n

Specifics of Fission Fragments<\/strong><\/p>\n

The fission fragments have two key features (somewhat different from alpha particles or protons), which influence their energy loss during travel through matter.<\/p>\n