Mechanics -- Problem Set #2

Q6: Pulse-height analysis

(a) Gamma-ray pulse-height analysis:

Figure: This is a pulse-height analyzer, showing the distribution of pulse-signals

from the gamma-ray detector in the foreground. The cylindrical tube contains a

photomultiplier tube, with a NaI scintillator built onto the front of it. In front of both

is a small sliding rack which holds a plastic disk the size of four stacked quarters.

Imbedded in the plastic disk is a small amount of Cs-137 gamma-emitting isotope,

which has produced the trace on the screen.

(b) falling droplets: finding distribution of sizes of raindrops from their terminal momentum

Figure: Time-exposure photograph of solid plastic balls of different sizes, dropped

into tall water tanks, with a stroboscope flashing ten times per second. You can

measure, from these photographs, the relative speeds with which the balls fall.

The largest ones have the most weight, but also the most drag force. Which one

of the two increases faster with diameter -- weight or drag force?