Tilted Foil Technique Research Articles

Spin-polarized radioactive isotope beam produced by tilted-foil technique

The tilted-foil method for producing spin-polarized radioactive isotope beams has been studied using the re-accelerated radioactive 8Li and 123In beams produced at Tokai Radioactive Ion Accelerator Complex (TRIAC) facility. We successfully produced polarization in a 8Li beam of 7.3(5)% using thin polystyrene foils (4.2μg/cm2). The systematic study of the nuclear polarization as a function of the number of foils and beam energy has been performed, confirming the features of the tilted-foil technique experimentally. After the study, a spin-polarized radioactive 123In beam, which is the heaviest ever polarized in its ground state by this method, has been successfully generated by the tilted-foil method, for the nuclear spectroscopy around the doubly magic nucleus 132Sn.

Tilted-foil technique for producing a spin-polarized radioactive isotope beam

The tilted-foil method for producing spin-polarized radioactive isotope beams has been studied for the application to nuclear physics and materials science, using the radioactive nucleus 8Li ( \(\ensuremath I^{\pi}=2^+\) , g = 0.82678(9) , \(\ensuremath T_{1/2}=0.838(6)\) s) produced at the Tokai Radioactive Ion Accelerator Complex (TRIAC). We successfully produced polarization in a 8Li beam of \(\ensuremath 7.3\pm0.5\) % using 15 thin polystyrene foils (4.2 \(\ensuremath \mu \mathrm{g/cm}^2\) fabricated especially for this purpose. A systematic study of the nuclear polarization as a function of the number of foils, beam energy, tilt angle and foil material has been performed, confirming the features of the tilted-foil technique experimentally. The contributions made to the nuclear polarization of 8Li nuclei by the atomic states was investigated.

Spin polarization of low-energy radioactive nuclear beams by tilted-foil technique

The tilted-foil technique has been tested for a few keV/amu 14N beam. Atomic polarization on the order of a few % was clearly observed. By inserting a second foil, which is perpendicular to the beam direction, downstream of the first tilted foil, nuclear polarization approximately 1.2% was confirmed. The tilted-foil method is applicable for radioactive nuclear beams at such low-energy region.

Mechanism of Polarization Production by Means of the Tilted-Foil Technique Studied Using Beta-Radioactive Nuclei

In order to disclose the polarization mechanism of the tilted-foil technique, systematic experimental studies were performed through direct observations of the nuclear polarization of short-lived beta-emitters. The present studies concentrated on the mechanisms of the following processes: (1) production of atomic polarization in the beam–tilted-foil interaction, (2) polarization transfer between an atom and a nucleus, and (3) enhancement of nuclear polarization by the beam multi-tilted-foil interaction. The present results have confirmed the plausibility of a previous model in which the atomic-polarization process in the tilted-foil technique is attributed to the right–left asymmetry of the electron-capture process at the final surface of a tilted foil. The enhancement effect of nuclear polarization by the multi-tilted-foil technique could be consistently explained by a model proposed by Goldring and Niv. Further information on atomic processes is required to make a definite statement on hyperfine interactions and atomic configurations, which contribute to polarization transfer.

Magnetic moments of mirror nuclei with tilted-foil polarization

We report here on an ongoing experimental program initiated at the ISOLDE facility at CERN for the measurement of magnetic moments of short-lived radionuclides, with the emphasis on magnetic moments of mirror nuclei in far-from-stability regions. The nuclei are polarized by the tilted foil technique and the resulting 0–180○ βasymmetry is monitored as a function of rf frequency applied in an NMR setup. In order to achieve sufficiently high energy for transmission through the foils, the experimental setup is mounted on a high voltage platform. The first experiment in this program was the measurement of the βasymmetry and the NMR resonance for the ground state of 23Mg (I=3/2, T1/2=11.3 s), yielding μ=−0.533(6) nm. Improvements to the experimental setup are presently being designed, to be used in conjunction with the new developments at ISOLDE for obtaining high charge-state ions from the EBIS (REX-ISOLDE) ion source. This will help pave the way for measurements of magnetic moments of T=3/2 nuclei in the s–d shell and of T=1/2 f-shell nuclei. The study of relaxation times and other solid-state phenomena in semiconductors and other materials of interest using this technique is also contemplated.

Measurement of the magnetic moment of 23Mg using the tilted foil polarization technique

We report here on the first measurement in an experimental program initiated at the ISOLDE facility at CERN for the measurement of magnetic moments of short-lived radionuclides. The nuclei are polarized by the tilted foil technique and the resulting 0°–180° β asymmetry is monitored as a function of the frequency of the rf applied in an NMR setup. In order to achieve sufficiently high energy for transmission through the foils the experiment was mounted on a high voltage platform. In this experiment, earlier asymmetry measurements were confirmed and an NMR resonance was observed, corresponding to a preliminary value of the magnetic moment of −0.533(6) n.m., in agreement with a previous measurement. During the experiment, problems were encountered with the buildup of contamination on the stopper surface. Improvements to the experimental setup are presently being designed, aiming at improved vacuum and possibly lower temperature. This will help pave the way for measurements of magnetic moments of T = 3 2 nuclei in the s-d shell and T = 1 2 f-shell nuclei. The study of relaxation times and other solid-state phenomena in semi-conductors and other materials of interest using this technique is also contemplated.

Tilted foil technique applied to beta-NMR studies

In this article, applications of the tilted foil technique to beta-NMR studies using polarized beta-emitters by the Osaka group are reviewed. Many efforts have been made to expand the applicability of the tilted foil technique to a much wider variety of nuclei. Various aspects of experimental studies have been carried out to disclose fundamental polarization mechanisms utilized in the tilted foil technique.

Condensed matter physics with radioactive ion beams

An overview of the present uses of radioactive ion beams from ISOLDE for condensed matter research is presented. As simple examples of such work, tracer studies of diffusion processes with radioisotopes and blocking/channeling measurements of emitted particles for lattice location are discussed. Especially the application of nuclear hyperfine interaction techniques such as PAC or Mössbauer spectroscopy has become a powerful tool to study local electronic and structural properties at impurities. Recently, interesting information on impurity properties in semiconductors has been obtained using all these methods. The extreme sensitivity of nuclear techniques makes them also well suited for investigations of surfaces, interfaces, and biomolecules. Some ideas for future uses of high energy radioactive ion beams beyond the scope of the present projects are outlined: the study of diffusion in highly immiscible systems by deep implantation, nuclear polarization with the tilted-foil technique, and transmutation doping of wide-bandgap semiconductors.

Hyperfine quantum beat of short-lived beta-emitter8Li polarized by the tilted foil technique

To disclose the basic mechanisms of nuclear polarization creation realized by the tilted foil technique, hyperfine quantum beats of the nuclear polarization of the short-lived beta-emitter8Li(Iπ=2+,T1/2=840 ms) were measured as a function of the distance between two tilted foils. From the observed beats of the8Li nuclear polarization, it was found that the Fermi-contact interaction of the8Li nucleus with the ground 1s-electron in LiIII plays a main role in the final stage of polarization transfer from polarized orbital electrons to the8Li nucleus.

A fragment separator at LBL for the beta-NMR experiment

The Beam 44 fragment separator was built at the Bevalac of LBL for NMR studies of beta emitting nuclei. 37K, 39Ca, and 43Ti fragments originating from 40Ca and 46Ti primary beams were separated by the separator for NMR studies on these nuclei. Nuclear spin polarization was created in 39 and 43Ti using the tilted foil technique (TFT), and the magnetic moment of 43Ti was deduced. Fragment polarization was measured for 37K and 39Ca emitted to finite deflection angles. The beam 44 fragment separator in combination with a proper polarization technique, such as TFT or fragment polarization, has been very effective for such NMR studies.

Beta-polarization measurements in solids

Experimental developments recently made in the beta-NMR measurements are reviewed. For production of polarized beta-emitters, the tilted foil technique has been successfully combined with the NMR. The low- and intermediate-energy heavy-ion reactions were recently found to be another sources of polarized beta-emitters. To achieve wide applicability of the NMR technique to nuclei far from stability, the tilted foil technique and the projectile fragmentation process in high-energy heavy-ion collisions were recently combined with the beta-NMR technique in the fragment separator built at the LBL.

Polymer foil applicable to the tilted foil technique

A polymer foil of polyethylene-terephthalate was successfully used for the tilted foil to create nuclear polarization of beta-emitters. The foil was carefully prepared to produce atomic flatness on the surfaces. The resultant smoothness was confirmed with beta-NMR measurements on12B and found to be as good as those of carbon foils used previously in the measurements.

Nuclear polarization of short-lived β emitters 8Li, 12B and 27Si created by the tilted foil technique

Nuclear polarization of short-lived β emitters 8Li, 12B, and 27Si were created by means of the tilted foil technique. Multiple tilted foils were effectively used to increase the nuclear polarization of these β emitters. The technique has proved to be quite effective for the in-beam NMR studies on hyperfine interactions of β-radioactive probes implanted in crystals.

NMR detection of8Li and27Si polarized by the tilted foil technique

Nuclear spin polarization created by use of the beam-tilted-foil interaction, was studied by use of asymmetric β decay and NMR detection.