Gas-Filled Detectors

GM Detector

operated in pulse mode, type of gas-filled detector

Townsend Avalanche

dn/dx = alpha*n, exponential growth of secondary electrons

Recombination

no gain in ion saturation area (pulse height is the same)

Ion saturation

area where ions are saturated

Proportional region

proportional because electrons remain proportional

Limited proportional region

converging lines area

Geiger-Mueller region

no distinction of energy deposited

2pi windowless gas-flow proportional counter

2pi bc only on the top, only 50% chance you detect sample despite intrinsic efficiency being 100% (only true for alpha/beta)

Work function

energy lost by charged particle/# ion pairs formed

Dead time

the interval after an ionizing event during which the counter is insensitive and cannot register a new event

Proportional counter

operates in pulse mode, type of gas-filled detector

How is pulse height a function of of applied voltage?

height incs w voltage

Operation of gas-filled detector in GM region

each geiger discharge ends w same buildup of positive charges, for fixed conditions, each pulse is the same size

Quench gas

add gas with lower ionization potential to cause collisions and transfer the positive charge to the quench gas

Fill gases

P-10, noble gases, hydrocarbons; preserve free electron transport and promote 1 avalanche per OG ion pair