Fast Beams, Production and Detection

Nuclear Spin Symmetry Conservation in 1H216O Investigated by Direct Absorption FTIR Spectroscopy of Water Vapor Cooled Down in Supersonic Expansion

“…In a free-jet, the gas reaches its limit velocity v ∞ very rapidly downstream from the nozzle, i.e., after covering a distance equivalent to only a few slit widths. The limit velocity corresponds to a complete conversion of the enthalpy of the gas into kinetic energy (Mach number M → ∞; flow temperature T → 0 K), and it is then easily retrieved from the conservation of energy equation, v ∞ = (2 c p T 0 ) 1/2 , where c p is the heat capacity at constant pressure of the carrier gas and T 0 is the stagnation temperature, fixed at 313 K in the present study. The value obtained for a flow of argon is 570 m/s, which is remarkably close to the value of 558 m/s calculated from the Mach number and the temperature extracted from the Pitot probe measurement ( v = aM , where is the speed of sound, γ is the specific heat ratio, and r is the specific gas constant), thus validating the T → 0 K approximation.…”

Two Dimensional Imaging of the Virtual Source of a Supersonic Beam: Helium at 125 K

“…This estimation does not represent satisfactorily the data as shown in Section 4. In the second way, the estimation of the perpendicular temperature is calculated approximating the gas expansion by a continuum expansion in which the temperature scales with the distance r from the source as T normalC ( r ) = 0.287 · T normalo r − 4 / 3 where T o is the source temperature. Assuming the same distance for the quitting surface as in the first way, the final temperature at the quitting surface can be calculated as T C * = T C ( D QS ).…”

“…Low (thermal) energy, neutral atom and molecule beams are important in several fields of science and applied research. − They are employed for example in high energy physics for jet target experiments, in experiments on molecular interaction, in spectroscopic studies of fragile species, , and in the investigation of matter wave properties and quantum coherence. − …”

“…In a supersonic expansion, also referred to as a free jet expansion, , gas at a stagnation pressure p o and temperature T o expands from a high pressure reservoir through a small nozzle into a low pressure ambient background chamber. The mean free path λ o of the atoms or molecules in the reservoir must be small compared to the nozzle diameter d N ( d N ≫ λ o ).…”

“…The mean free path λ o of the atoms or molecules in the reservoir must be small compared to the nozzle diameter d N ( d N ≫ λ o ). Such an expansion generates a high intensity beam with a very small velocity spread . The beam can be characterized by the following two velocity distributions: The so-called parallel velocity distribution that can be measured in time-of-flight experiments along the beam axis and the perpendicular velocity distribution that can be measured with additional intensity scans across the beam.…”