Production of Hyperpolarized ${\mathrm{H}}_2$ Molecules from $\overrightarrow{\mathrm{H}}$ Atoms in Gas-Storage Cells

The preservation of the nuclear polarization of hydrogen atoms during the recombination to molecules was observed on different surface materials in the temperature range from 45 to 100 K and for magnetic fields up to 1 T. On a gold and a fused quartz surface, the expected molecular polarization of about 50% or lower of the atomic polarization was measured, while a surface layer of perfluoropolyether (Fomblin) shows a nearly complete preservation (at least 97%) of the atomic polarization during the recombination process. Further experiments have the possibility of storing polarized deuterium molecules and to use them in nuclear-fusion installations. Another application might be the production of polarized substances for enhanced NMR techniques.

Figure 1

Experimental setup: Exchangeable storage cell (length 40 cm, inner diameter 10 mm) inside a superconducting magnet and fed by the $\overrightarrow{\mathrm{H}}$ beam from the atomic beam source (ABS). Atoms and molecules from recombination are ionized by electron impact. The cell is set to a potential up to $+5\mathrm{keV}$ to accelerate the atomic and molecular ions into the Lamb-shift polarimeter (LSP), which allows one to measure the polarization of the atomic and molecular ions [12, 13].

Figure 2

Relative proton polarization $P_p/P_a$ according to Eq. (4) as a function of the magnetic field strength over the cells. Copper surface: measured by $p\text{−}p$ elastic scattering on ${\mathrm{H}}_2$ molecules and H atoms effusing from a copper-mesh recombiner cell at room temperature into a Teflon-coated storage cell [5]. Gold surface: measured with the LSP on ${\mathrm{H}}^{+}$ ions extracted from a gold-coated storage cell, kept at 100 K. The degree of recombination for both measurements is large and $P_{m_0}$ reaches about half of the initial $\overrightarrow{\mathrm{H}}$ polarization $P_a$.

Figure 3

Nuclear polarization $P_p$ of the recombined ${\mathrm{H}}_2$ molecules in storage cells according to Eq. (4) relative to the polarization $P_a$ of the feeding $\overrightarrow{\mathrm{H}}$ beam as a function of the wall temperature.

Figure 4

Molecular polarization of the gas in the Fomblin-oil coated storage cell, kept at $T=100\mathrm{K}$, measured with the LSP on the ${\mathrm{H}}^{+}$ (plus) and ${{\mathrm{H}}_2}^{+}$ ions (times) as a function of the magnetic field strength over the cell.