Amounts Of He Research Articles

Studies of Phase Changes in Argon

The influence of the geometry of the sample chamber on the melting behaviour of Ar samples is discussed. Melting curves of Ar samples doped with various small amounts of He, H2, Ne, N2, CO, O2, CH4 and Kr impurities were determined relative to "pure" samples. It was found that He, H2 and Ne did not alter the melting curve; N2, CO, O2 and CH4 lowered the liquidus point of Ar by 2.4, 2.4, 1.8 and 3.0 mK for 100 vppm of these impurities, respectively; Kr increased the scatter of points along the melting curve without noticeably altering the liquidus point. – Values for the triple point temperature and pressure and the boiling point were found to be 83.7976 K and 516.730 ± 0.010 mmHg (68891.6 N/m2) and 87.2946 K, respectively. – The vapour pressure of solid and liquid Ar can be described by ln P = AS + (BS/T) and ln P = AL + (BL/T) + CLT for 81 K ≲ T ≲ 83.8 K and 83.8 K ≲ T ≲ 87.3 K respectively. Numerical values of these constants are compared with some previous determinations. Latent heats of sublimation, vaporization and fusion are calculated to be 7751.6, 6562.0 and 1189.6 joules/mole respectively.

The reaction of nitric oxide with vibrationally excited ozone

The reaction between nitric oxide and vibrationally excited ozone was studied in a fast flow reactor by monitoring the visible emission from electronically excited NO 2 ∗. The antisymmetric mode ( ν 3) of O 3 was excited with a Q-switched 9.6 μm CO 2 laser, and a laser-induced signal was detected, with a rise rate constant of (4.0 ± 0.5) × 10 11 cm 3/mole sec and a decay rate constant of (1.1 ± 0.1) × 10 11 cm 3/mole sec for an NO-rich mixture. The latter was unaffected by addition of large amounts of He or Ar, indicating that the signal was not a thermal effect. Most of the measurements were made at 350°K; however, the He and Ar dilution results suggest that the enhanced reaction rate is not very sensitive to temperature. In order to explain the observed rise times, it was necessary to postulate an intermediate step prior to the chemical reaction. A model which is consistent with our data has energy transferred from ν 3 to ν 2 (the bending mode) at a rate of (2.9 ± 0.5) × 10 11 cm 3/mole sec for NO and a rate of (1.1 ± 0.2) × 10 11 cm 3/mole sec for He. According to this model, the rate constant for the reaction of NO with O 3 ( ν 2= 1) producing vibrationally excited ground state NO 2 †, NO + O 3 † (010) 3 NO 2 † + O 2 is (1.5 ± 0.2) × 10 11 cm 3/mole sec, and the relative rate for the reaction of O 3 ( ν 2 = 1) and O 3(ν 2 = 0) with NO was estimated to be k 3(1) k 3(0) ≈ 22 .

Collisional deactivation of vibrationally excited singlet molecular oxygen

Measurements of the collisional deactivation time of the ν′ = 1 vibrational level of the 1Δg electronic state have been made using a high pressure gas cell equipped with an acoustic detector. To separate relaxation effects from effects due to viscosity, thermal conductivity, cell geometry, and nonuniform irradiation by the laser beam a detailed theoretical treatment of the acoustical behavior of the cell was required. Application of these results to the existing system was carried out and used to determine the appropriate relaxation times from the experimental data. Accordingly it was determined that for pure oxygen p τ = 0.05 sec · atm. Addition of increasingly large amounts of He caused this value to fall steadily to a limiting value p τ = 0.016 sec · atm which agrees well with the data obtained by previous investigators for the ν′ = 0 vibrational level.

Interpretation of XUV spectroheliograms

Some parameters of chromospheric structure are drawn from recently published XUV spectroheliograms. The HeII emission above the limb arises from the small amount of He+ still existing at 106°. The larger amounts of He+ in the cooler corona at the poles explain the polar cap absorption in λ 304. The flat distribution of emission in Oiv and Ov, with a sharp spike at the limb, is caused by the rough structure of the chromosphere and the variable excitation in the emitting spicules. The intensity of the Nevii lines shows that the transition zone between chromosphere and corona is very sharp.

Thermal Conductivity of Isotopic Mixtures of Solid Helium

Comments are given concerning the work carried out by Walker and Fairbank on the thermal conductivity of He/sup 4/ containing small amounts of He/ sup 3/ and its comparison to the Klemens theory and results calculated from the variational treatment of Berman et al. It is pointed out that the Klemens formula is in error by a factor of 55. An increase of 55 in the Walker and Fairbank's theoretical curve causes this curve to rest almost in the middle of the observed data. It is concluded that there seems to be no need to invoke lines of He/sup 3/ atoms to explain the observations made during the investigations. (B.O.G.)

The transition temperature in liquid helium. II

The Feynman–Kikuchi theory of the λ -transition, discussed in a previous paper, is improved in various respects. A more general formulation of the approximate path integral for two-atom permutations gives the result that these permutations should be unimportant except below about 1°K, where they may become more important than the other kinds of permutations. The lattice model is generalized by allowing vacant lattice sites (holes) so that there is a gas-liquid transition as well as a λ -transition. If one assumes that the lattice spacing is fixed and the only effect of pressure is to change the number of holes, then one finds that the transition temperature decreases with pressure if the ‘effective mass’ for many-sided polygons is taken to be more than twice the real mass. On the other hand, with such a large effective mass the transition temperature itself comes out too low. If one allowed the lattice spacing and effective mass to vary with pressure, one could obtain better numerical agreement with experiment, but with so many adjustable parameters such agreement would not be significant. The effect of lattice structure on the transition is also discussed, and it is found that the product of effective mass, square of lattice spacing, and transition temperature should increase with the co-ordination number of the lattice. The treatment can also be extended to mixtures of helium isotopes; the effect of small amounts of 3 He or 6 He is similar to that predicted by other theories.

Cosmic-ray evidence on the origin of meteorites

The birth of a meteorite coincides with the breakup of its parent body and also with the beginning of the meteorite’s exposure to cosmic rays. This continued exposure creates through nuclear evaporations definitely calculable amounts of3He, about 2/3 of it by way of tritium. Hence the date of breakup can be obtained from the3He content; or better still, from the3He and tritium content measured in the. same sample. However, the latter method has only limited applicability. The two methods give good accord; of six meteorites dated, all are found to be about 300 million years old. This agreement establishes confidence in the calculations of the3He production rate and leads to some considerations concerning the process of nuclear excitation. The age is also in good accord with Opik’s calculation of the mean lifetime of meteoritelike bodies against capture by the inner planets. From this agreement conclusions can be drawn concerning the mechanism of meteorite creation and concerning the relative constancy of cosmic-ray intensity as far back as 300 million years.

Simplified Radio-Frequency Ion Source

The quartz or glass sheathed cylindrical cathode probe of the conventional rf ion source has been eliminated. The conventional glass pad electron beam ``back stop'' has been replaced by nonfracturing porcelain. Commerical Pyrex pipe has been used in the construction of the glass thimble in which the plasma is formed, and the thimble sealed to the base with O-ring pressure seals. The anode probe is removable for ease in cleaning. The source produces 300 μa of H+; it also produces 200 μa of He+, and at low operating gas pressures, usable amounts of He++, as large as a few tenths of a percent of the He+ output.

XLIX. Isolation and measurement of the helium-i, helium-3 and tritium produced in steel by 340mevproton bombardment

Summary The small amounts of 4He, 3He, and 3H, produced in a block of steel bombarded with 340 mev protons have been isolated. Measurements have been made of the total helium by a gas-volumetric method, of the tritium by counting of the associated β-particles, and of the 3He: 4He ratioby mass-spectrometry. The ratio 4He: 3He: 3H has been found to be 1·00 : 0·048 : 0·078; this result is discussed in the light of Le Couteur's theory of nuclear evaporation.