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A chopped cw dye laser has been used to excite selected levels of the B 3Πg state of N2 in a molecular beam of A 3Σu+ state metastables. Laser‐induced fluorescence was observed from the vibrational levels v=5 through v=12, and a photomultiplier was used in conjunction with a microcomputer system to perform time‐resolved detection of the decay light. The lifetimes have been measured to an accuracy of about 3%. They show a smooth decline from 5.87 μs for v=5 to 4.11 μs for v=12. No dependence on rotational level was observed, and no contributions to the B state decay were found from intrasystem cascading of the form B→W 3Δu→B→A 3Σu+.

A blue cw dye laser has been used to excite 14 transitions from the metastable c(2p)3Πu state to a previously unknown electronic state of H2, believed to be the (4s)3Σ+g state. The observed transitions are all Q branches and are diagonal in vibrational quantum number. Levels with v=0 and v=1 are detected by their radiative decay, but all of the v=2 levels are predissociative with lifetimes on the order of 500 ps. Approximate molecular constants are derived from the spectra and found to be similar to those of the hydrogen molecular ion. The effective quantum number is n*=3.97, in agreement with the quantum defect found for lower triplet s states.

This paper describes an apparatus for cooling an iron foil containing a radioactive impurity to a temperature in the range of 0.012 to 0.026°K by thermal contact with an adiabatically demagnetized chromium potassium alum salt pill. The purpose of the demagnetization is to orient the nuclei of the radioactive impurity. A superconducting solenoid is used to produce the high magnetic field required to remove the entropy from the chrome alum. The apparatus uses two helium Dewars—a large one which contains the superconducting magnet and a small one which contains the salt pill, the 1°K helium bath, and the radioactive sample. The salt pill is formed by pressing a mixture of chrome alum and Octoil S around 5000 0.076‐mm‐diam copper wires. The salt is supported by a graphite cylinder and helium exchange gas is used to establish heat contact between the salt and the 1°K helium bath. In one form of the apparatus the chrome alum salt and the sample are surrounded by a copper can which is cooled to 0.1°K by contact ...

The theory, design, and construction of a magnetically shielded solenoid are described. Three correction coils are employed in addition to the main solenoid winding. The solenoid is enclosed in three concentric magnetic shields which serve to screen the inner region of the solenoid from external magnetic fields. First the theory and design of a solenoid with correction coils and no magnetic shielding are discussed. Then calculations of the magnetic field due to a solenoid inside a closed cylinder of infinite permeability are summarized. These calculations show that a properly constructed shield can improve the homogeneity of the field due to a single solenoid by an order of magnitude. Optical pumping measurements of the field homogeneity in the central region and of the field distribution along the axis of the solenoid are reported. The measurements of the field distribution agree with the calculations to within a few hundredths of a percent. The shields reduce the disturbance due to changing external fields by a factor of 100. The main solenoid is 91.44‐cm long and has an inner diameter of 32.41 cm. The solenoid field is 18.6 G/A and the solenoid dissipates approximately 320 W when producing a field of 60 G. The solenoid‐shield system has at 60 G a homogeneity of 1 part in 105 over an 8‐cm‐diam sphere at the center of the solenoid. Construction details of the shields and coils are given and the solenoid power supply is described.

The construction and design principles of a focusing atomic beam apparatus are reported. This apparatus, which is of the radio‐frequency magnetic resonance type and which has been used to measure the spins and hyperfine splittings of four radioactive nuclides as reported elsewhere, utilizes the six‐pole focusing magnet of Friedburg and Paul and of Korsunskii and Fogel but in a way which avoids velocity aberrations. From an analysis of the optimization of intensities in the conventional and the focusing types of atomic beam apparatus it is concluded that the latter has an advantage of a factor of roughly twenty‐five.

A large solid angle Lyman‐α (121.5 nm) detector designed for atomic beam experiments is described. The detector consists of 6 NO photoionization chambers which surround the beam and provide an average detection efficiency for Lyman‐α photons of approximately 20% over the 3.5 cm length of the detector.