B.G. Schmidt

Determination of the on-target polarization of an optically-pumped polarized lithium ion beam☆

Abstract An optically-pumped polarized lithium ion source has been built and is currently producing highly polarized 6 Li − beams with on-target 6 Li 3+ currents up to 150 nA. An absolute measurement of the on-target tensor polarization was made during a one week calibration run, which yielded t 20 = −0.938±0.013, averaged over the entire run. The on-target vector polarization is typically t 10 = 1.02±0.06. The nuclear polarization of the atomic beam at the source has been measured by laser-induced fluorescence to be typically t 10 = 1.14±0.06 and t 20 = −1.14±0.06. A 4 He gas polarimeter has been calibrated as a secondary standard for monitoring both vector and tensor polarizations.

An optically pumped polarized lithium ion source

Abstract A laser-optically-pumped polarized lithium ion source is being developed to provide beams of nuclear polarized 6,7Li− for injection into the FSU tandem Van de Graaff-linac. Electro-optically modulated, circularly polarized light optically pumps a lithium atomic beam into a single magnetic substate, M I = I, M J = 1 2 . No inhomogeneous magnetic field (sextupole or quadrupole Adiabatic rf transitions enable the polarization to be changed by transferring the population into different magnetic substates. Using a second electro-optic to modulate a second beam from the same laser, and Zeeman tuning, the polarization of the atomic beam is obtained by laser induced fluorescence. The polarized atomic beam is ionized to Li+ and then charge exchanged to Li−.

Target structure independent Li→7 elastic scattering at low momentum transfers

Abstract Analyzing powers and cross sections for the elastic scattering of polarized 7 Li by targets of 6 Li, 7 Li and 12 C are shown to depend only on the properties of the projectile for momentum transfers of less than 1.0 fm −1 . The result of a detailed analysis of the experimental data within the framework of the coupled channels model with ground state reorientation and transitions to the excited states of the projectile and targets included in the coupling schemes are presented. This work suggests that nuclear properties of weakly-bound nuclei can be tested by elastic scattering experiments, independent of the target used, if data are acquired for momentum transfers less than ∼ 1.0 fm −1 .

Operational experience with the FSU optically pumped polarized lithium ion source

Abstract The dye-laser optically pumped polarized 6,7 Li − ion source of the FSU tandem-linac heavy-ion accelerator has completed its first year of operation. The ion source has produced highly polarized beams of 6 Li for nuclear physics experiments with on-target currents of 6 Li 3+ greater than 150 nA. Absolute measurements of the on-target 6 Li polarization have yielded P yy = −1.33± 0.02 and P y > 0.74 ± 0.03 for the nuclear tensor and vector polarization, respectively. No loss of polarization due to acceleration by the linac booster was observed.

An absolute standard for 6Li vector analyzing powers

Abstract Reactions with the spin structure 1 + + 0 + → 0 + + 0 + have properties which allow an absolute determination of ∣ iT 11 ∣ via measurement of two of the tensor analyzing powers. Vector analyzing powers of the 12 C ( 6 L i , α 3 ) 14 N reaction are deduced to accuracies of about 6% from measurements of the tensor analyzing powers T 20 and T 21 at E Li = 33 MeV. The vector analyzing power in 6 L i + 4 He elastic scattering is measured at E c.m. = 6.2 MeV and θ c.m. = 150°, establishing a secondary standard convenient for fast monitoring of 6 Li vector polarization.

Transport of polarized ions through a tandem-superconducting-linac heavy-ion accelerator☆

Abstract Mechanisms for the loss of polarization of beams of nuclear spin polarized 6,7 Li accelerated by the FSU tandem Van de Graaff superconducting linac heavy-ion accelerator are considered. The linac uses superconducting solenoids for radial focusing. Estimates and detailed calculations show that for most experiments the depolarization due to the conventional beam line is negligible, while, provided account is taken of the precession produced by the solenoids, the depolarization due to the linac is negligible for 6 Li 3+ and small for 7 Li 3+ . An experiment was carried out to investigate the depolarization of a vector polarized 6 Li 3+ beam due to acceleration by the linac. No loss of polarization was observed.

Analyzing powers for 6L↘i+12C scattering at 30 and 50 MeV

Comparison between elastic analyzing powers at 30 and 50 MeV show no decrease in their magnitude at the higher energy. A combined optical model analysis of both energies shows T21 to arise from the tensor interaction, T20 to be an interference between tensor and J dependent interactions, and iT11 to be the most complicated, arising from an explicit spin‐orbit, tensor, and J dependent interactions. The inelastic 12C vector analyzing powers require an explicit spin‐orbit interaction to reproduce the magnitude of the oscillations.

Optically pumped polarized lithium source at FSU

The dye‐laser optically pumped polarized 6,7Li− ion source of the FSU tandem‐linac heavy‐ion accelerator has completed 11/2 years of operation. Highly polarized beams of 6Li have been accelerated with on target currents typically greater than 50 particle nA. The source uses electro‐optically modulated circularly polarized light to optically pump an atomic beam into a single magnetic substate. Adiabatic rf transitions to other substates enable the polarization to be changed. The polarization of the atomic beam is measured by laser induced fluorescence using a second electro‐optic to modulate the beam from the same laser, and Zeeman tuning. The polarized atomic beam is surface ionized to Li+ and undergoes charge exchange to Li−. The tandem‐linac can accelerate the beam up to 60 MeV.

Interactions obtained from precision polarized 6Li scattering experiments

Detailed analyzing power angular distribution measurements allow the contributions from the different interaction terms responsible for producing them to be isolated. The high quality data needed for these studies can now be taken because of the development of an intense laser pumped alkali ion source with close to maximum polarization and greatly improved reliability.

Operation of a radio-frequency ion source in a tandem electrostatic accelerator

Abstract A radio-frequency ion source using electrostatic inflection has been operated in the terminal of a model FN tandem Van de Graaff accelerator. This arrangement is useful for high resolution resonance experiments in atomic and low energy nuclear physics and for hydrogen profiling using the the 6.4 MeV 1 H( 15 N, αγ) 12 C reaction.