False Asymmetries Research Articles

A balanced ionisation chamber for accurate beam location

A description is given of a balanced ionisation chamber for use as a sensitive and stable monitor of the position of a proton beam in polarisation experiments. It is noted that, when used with a solenoid producing spin reversal, this type of detector does not necessarily eliminate false asymmetries completely.

Measurement of the polarization of D-D neutrons by a solenoid

A solenoid is described which turns the polarization vector of D-D neutrons over + 90° or —90°, while the detectors remain in a fixed position. The method avoids the false asymmetries that may be introduced if one turns the detectors over 180° and it allows heavy shielding. This way a good accuracy was obtained. For a thick, golden “drive-in” target the relative left-right asymmetry was found to be | R 0 | = (4.6 ± 0.2)% at E D = 450 keVM and ϑ 1lab = 50°; ϑ 2 lab = 42°.

A new method of measuring asymmetries in neutron polarization experiments

A solenoid has been constructed 11 feet in length and with a maximum rating of 1.14·106 ampere turns which enables the plane of polarization of a neutron beam to be turned through 90‡ in either direction. This enables asymmetry measurements to be made in neutron polarization experiments without moving the detecting apparatus. This is a great advantage in experiments in which polarization effects are small and false asymmetries, which can be introduced when the detector is moved, correspondingly very difficult to eliminate with sufficient accuracy. The method has been tested by using the partially polarized neutron beam produced with a beryllium target in the Harwell cyclotron. Asymmetry measurements were made by counting neutrons scattered at an angle of 1/3o off a uranium scatterer. Four values of the solenoid current were used and the results obtained agree well with those expected theoretically.