The time-of-flight (TOF) method for the determination of electron-diffusion coefficients D and drift velocities w described earlier could not be used to investigate a number of gases because a Gieger—Müller counter was used for an electron detector. A new experimental apparatus using differential pumping and an electron-multiplier detector was developed to remove this restriction. Using this new apparatus, D and w have been measured for He, Ar, H2, N2, CO, CO2, CH4, and C2H4. Considerable divergence of D values from published values by the Townsend method have been obtained, indicating a fundamental difference in the methods.

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The ionization of helium atoms by antiprotons is considered in an independent-particle model (IPM) with a model potential that accounts for polarization and binding effects of the electrons in the two-centre Coulomb potential. The model is designed to reproduce the exact ionization potential of the quasimolecular system and to allow for the existence of one bound state in the united-atom limit. We find a single-ionization cross section that is in good agreement with the results of various correlated two-electron calculations, and a double-ionization cross section that is considerably improved compared to a standard IPM calculation with a fixed atomic target potential.

It has been shown that a commercially available halogen type Geiger-Mueller counter when properly shielded with Sn and Pb provides a very practical and satisfactory device for measuring the dose due to y-radiation in the presence of neutrons. The device measures the dose in roentgens with nearly uniform response for effective X-ray energies above about 200 keV and up to at least 1.25 MeV y-energies. Calculations show that the fast neutron response is less than 0.15 per cent, and experiments indicate that it is less than 0.5 per cent.Experiments show that about 5 x lo9 thermal neutrons per om2 give a response equivalent to 1 r of y-radiation. When necessary, the thermal neutron response can be decreased by a factor of 300 by using a Li shield described in the text.

We have developed a photoionization method for complete conversion of a quantumselected population to ionization, making possible sensitive and absolute measurement of the selected populations in a gas. Each photoionization involves the absorption of two photons (from a pulsed dye laser), one of which is resonant with an intermediate state.In this demonstration we measured the absolute number of He(2 i S) states per ion pair following interaction of pulses of 2-MeV protons with He.

The proportional counter method for measuring fast neutron dose in the presence of gamma radiation has been considerably improved through (1) redesign of the proportional counter, (2) a study of the behavior of the counter for various filling gases, and (3) development of a more convenient form of the electronics necessary for pulse integration and dose indication. The instrument is suitable for radiobiological research, neutron physics, and shielding research, as well as radiation protection. It will be shown that the response of the instrument is within ±5% of tissue absorbed dose over the energy range of 0.5 Mev to 14 Mev.

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Transfer of electronic energy from the resonance states Ar(1P1) and Ar(3P1) to diatomic nitrogen, hydrogen, and nitric oxide has been studied with a time-resolved quenching technique. Rate constants for energy transfer were deduced from the changes of the rate of decay of excited states corresponding to known changes of the density of the diatomic molecules. For Ar*–N2 the rate constants were 5.4×10−11 and 0.8×10−11 molecule−1⋅cm3 sec−1 for Ar(1P1) and Ar(3P1), respectively. For Ar*–H2, the measured rate constants were 22×10−11 and 21×10−11 molecule−1 cm3 sec−1 for Ar(1P1) and Ar(3P1), repectively. The results for nitric oxide were 54×210−11 and 32×10−11 molecule−1 cm3 sec−1 for Ar(1P1) and Ar(3P1), respectively.