Physics
Cloud chamber
A line of droplets, and every answer comes out of its shape: how long, how thick, how straight, and which way it bends.
What happens
A chamber measures nothing. It draws a line of droplets and lets you read it. Length comes from the stopping power - an alpha of five MeV dies in four centimetres of air, a ten MeV proton runs a metre. Thickness carries the Bragg peak: ionisation is heaviest at the END of a heavy track, so an alpha is a blunt stub with a fat tip. Straightness is mass: a one MeV electron wanders two degrees a centimetre, a fast muon eighteen thousandths. And the bend in a field gives the momentum and the SIGN of the charge - which is how the positron was found, in a photograph, with a lead plate.
Equations used in the module
Equations −dE/dx = K z² (Z/A) (1/β²)·[½ ln(2m_e c²β²γ²T_max/I²) − β²] R = ∫ dE / (−dE/dx) θ₀ = (13.6 MeV / βpc)·z·√(x/X₀)·(1 + 0.038 ln(x/X₀)) r_perp = p_perp / (|q|B)
