A counter chronometer is described which measures time intervals up to 12.75 microseconds by counting the oscillations of a 20 Mc/s free-running oscillator with a scaler. Provision is made for resetting the scaler by a fast pulse if the measurement is not to be recorded. The scaler is based on conventional pentodes and germanium diodes, the high counting speed being attained by limiting voltage changes.
A brief technical description of the Pretoria fixed frequency cyclotron is given. It is a 112 cm machine which at present accelerates internal deuteron beams of 200 microamperes to 15 MeV. Interesting features are a double ion source and automatic target removal and despatch mechanism.
A fast energy analyser using a scintillation detector has been made which is able to trace the spectrum in 20 μs. It is shown that the ion beam has r.f. modulation of about 50 eV. A demodulating r.f. field after the exit channel eliminates this modulation if the ions pass through it at right phase, and thus the energy spread of the beam is diminished below 10 eV. By determining the time of flight of ions from the r.f. modulation to the demodulating field the conclusion was drawn that the r.f. modulation occurs immediately near the cathode.
An apparatus is described which reproduces with a staircase voltage waveform a magnetic field rising between 0 and about 120 gauss. The device is well suited for the measurement of the instantaneous value of the magnetic field in the gap of an electron synchrotron. It consists of a peaking strip magnetic probe, and an electronic apparatus.
It is shown that the masses and momenta of charged particles can be determined from measurements of multiple scattering in a propane bubble chamber. To measure a mass of the order of a π-meson or μ-meson mass with an accuracy of 30% it is sufficient to have a 36 cm range in propane; to determine a mass of the order of the proton mass with the same accuracy a range of 72 cm in propane suffices. To measure a particle momentum of the order of 100 MeV with an accuracy, say, of 15%, it is sufficient to have a range of 25 cm in propane.
A description is given of the electronic circuits of a large hodoscope system which is being used in experiments on the scattering of μ-mesons. The principle of the method employed is to determine the direction of the trajectory of the particle before and after scattering by means of three systems of crossed counters. The counters through which the particle has passed are identified by means of neon lamps.
The performance of the hodoscope which is described in the previous publication, is analyzed in detail. Spurious scattering is shown to be about 0.1% of the total counting rate. This inefficiency arises almost entirely from casual coincidences.
A read-out system is described which by a substraction method gives recorded number of pulses in the different channels on a scaler. The arrangement is specially made for binary coded analyzers.
One of the important problems to be solved in the construction of hydrogen bubble chambers is the temperature control. A new device to overcome this difficulty is described. It is based on a closed circuit of pressurized hydrogen. A prototype has worked successfully. Its application to a liquid hydrogen bubble chamber has proved to be satisfactory.
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