Align the scattering center so that one of the axes (for the
circle any diameter will do) is parallel to the projectile gun. Use
the long rod and the grooves in the scatterers to make
an approximate
alignment and then make fine adjustments by firing a few shots
to see if the B-B's strike the wall directly beneath the gun. Make a
fiducial mark on the tape below the center of the gun barrel. When
the tape is removed from the scattering chamber, measure
the distance from the mark
to each grouping of shots to detemine the scattering angle.
Please note that the arc length measured from the
fiducial mark will give you the supplement of the scattering angle
.
The value of the impact parameter b is determined by the pitch of the screw and the number of turns of the adjustment knob. The screw has eighteen threads per inch which means that the gun moves 0.141 cm per turn of the knob.
To load the gun, rotate the sleeve until the hole is on top, drop in a B-B and close the hole. Fire the ball with a firm, quick squeeze of the rubber bulb. Best results are obtained when the connecting hose is held straight and the balls are not fired too hard.
To take data attach a fresh strip of sensitive tape with the waxed side out to the chamber wall. Double-sided scotch tape is provided to hold the tape in place. This operation should be done with care and patience. Use a length sufficient to cover about 2/3 of the circumference of the wall. Because of the symmetries you only need to scatter from one side of the targets. Shoot projectiles for a series of values of the impact parameter, shooting several shots for each value of b. From the scatter of points on the tape you can estimate the uncertainty of the results. Take at least 8-10 shots at each value of b and be sure to correlate the impact parameter with its group of shots. Please be careful to see that the projectiles don't bounce onto the floor - use the plastic cover while shooting and pick up any errant B-B's.