Energy loss of alpha particles in gases with MCA

Principle

A study is made of the connection between the energy E of alpha-particles and the path x travelled by them in air at standard pressure. The measurements recorded enable the differencial energy loss dE/dx to be calculated as a function of x.

Tasks

1. The spectrum of a covered ²⁴¹Am source is measured at a fixed distance s as a function of the pressure p. The distance s is selected in such a way as to correspond to the maximum range at the highest pressure measurable with the manometer used. The energy corresponding to the central points of the individual spectra are determined (after calibration of the measurement layout with an open ²⁴¹Am-emitter, see 3.) and plotted as a function of the distance x converted to a 1013 hPa basis. Using this function, the differential energy loss (dE/dx) is then calculated as a function of x and again plotted on the graph.
2. The spectrum of the source used in 1 is measured initially under the same geometric conditions under vacuum and subsequently with the vessel filled with helium, nitrogen or carbon dioxide, in each case under identical pressures. The different energy loss values are compared with the electron concentration in the particular gas.
3. The mean energy with which the alpha-particles leave the covered americium source is determined by calibration against the open americium emitter (E = 5.485 MeV). (This value is required for the evaluation in 1.)

Learning objectives

• Range
• Range dispersion
• Mean free path length
• Mean ionization energy of gas atoms
• Mean energy loss of a-particles per collision
• Differencial energy loss
• Bethe formula
• Electron concentration in gases