Hyperfine Interactions 61 (1990) 1383-1386 1383

POLYMER FOIL APPLICABLE TO THE TILTED FOIL TECHNIQUE

A. OZAWA, S. MOMOTA, A. KITAGAWA, Y. MATSUO, Y. TAKAHASHI, M. SAKAMOTO, K. MATSUTA, Y. NOJIRI, T MINAMISONO and Z NAGASAWA* Deparlnlenl of Physics, Osaka Uni~, Toyonaka, Osaka 56~ Japan *Unitika, C&itt, Uj~ Kl,olo 611, Japan

A polymer loll 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 on 12B and found to be as good as those of carbon foils used previously in the measurements.

i. INTRODUCTION

Short-lived beta-radioactive nuclei have been effectively used in our laboratory at Osaka for experimental researches on various fields of fundamental physics/I/, .e.g., nuclear electro-magnetic structures, weak processes of beta-decays, reaction mechanisms of heavy-ion collisions, hyperfine interactions of impurities in crystals, and atomic processes in solids. For these experiments, an NMR technique applicable to short-lived' beta-emitters has been developed and effectively used at Osaka/2/.

For the NMR technique applied to beta-emitters, preparation of polarized beta-emitters of interest is quite crucial in the first step of the measurements. To polarize the beta-emitters, the tilted foil technique/3/ has been introduced in thebeta-NMRmeasurements since 1983/4/.

For good creation of the nuclear polarization, surfaces of the tilted foils should be smooth in the range of atomic distances. The foils so far used in the previous experiments were mainly thin foils of evaporated carbon ( a few ~g/c~ ). However, thin carbon foils in a large area ( e.g., 10 cm 2 of 2 ~g/c~ thick ) are usually difficult to prepare. From the viewpoint of the tensile strength of the foil to be used, polymer foils are considered more suitable than carbon foils, especially when those with such large effective areas as 25 cm 2 are required.

2. EXPERIMENTAL

As one of the new polymer foils, a foll of s ( PET ) 0.25 ~m thick was prepared and tested for the use in the NMR measurements/5/. In order to prepare smooth surfaces of PET, a foil was tightly pasted on a metallic frame. After both surfaces were rinsed with methyl-alcohol, the foil was annealed by irradiating with strong infrared light.

To confirm the smoothness of the PET surfaces obtained with the present procedures, the degrees of nuclear polarization of beta-emitter 12B created by these PET foils were observed with the beta-NMR method. The experimental setup used in the present measurements is illustrated in Fig.l. The 12B nuclei were produced through the llB(d,p)12B reaction at deuteron energy E 4 - 3.85 MeV. The

ejected 12B nuclei were collected in the recoil angle 30 o relative to the incident beam. The nuclear polarization produced in the reaction was found to be very small, ( 0.30 • 0.09 ) %. A PET foil of 0.25 ~m thick was set at a

tilt angle of 60 o at the entrance of an electrostatic lens. The 12B kinetic nuclei were focused and collected in a catcher placed behind the lens. The catcher for 12B implantation was a Pt foil 5 ~m thick in this case.

t�9 J.C. Ballzer A.G.. Scientific Publishing Company

3~4 / I . ()~uwcl r l ul.. Po/rn ler f o i l Ul,lfficid~lc' 11, l i l lcd f i , i l lcchmque

The polarization of 12B was detected through the beta-NMR measurements; .e., beta-decay asymmetry of 12B was compared with that of 12B of which spin

)olarization was inverted by the adiabatic fast passage ( AFP ) method of NMR. The nuclear polarization induced with one sheet of the PET foil which was p r e p a r e d with the method mentioned above was ( 1.57 i 0.12 ) %. This degree of polarization was found as large as that with a carbon foi].

These PET foils are particularly helpful for the use in the beta-NMR measurements on nuclear moments of mirror nuclei in the f-shell. These measurements are now going on by use of high energy projectile fragments at the Bevalac of the LBL/6/. In these measurements, ten sheets of large size foils ( - 500 mm 2 ) are used for the multi-foil technique. For the effective application of the tilted foil technique to such swift ions as the projectile fragments produced in the relativistic heavy-ion collisions, charge states of the ions should be reduced enough to be atomically polarized in the final collisions between the outgoing ions and lattice atoms. To realize the reduction in the charge states, the surfaces of the PET foils were covered with thin layers of Au, in which the ions have the relatively higher electron capture cross section than with lighter materials. The PET foils covered with Au metal ( - 50 A thick ) were also tested by detecting the induced nuclear polarization of 12B with the same beta-NMR technique. The surface smoothness of the Au covered foils was found to be strongly dependent on production conditions of the methods applied. Among various methods of the productions, the ion plating method was found the best from the viewpoint of the surface smoothness of PET. These foils were successfully used in the recent beta-NMR measurements on one of the mirror nuclei in the f-shell, 43Ti, performed at the Bevalac of the LBL/')/.

3. CONCLUSION

In conclusion, the polyethylene-terephthalate (PET) foil can be used as a tilted foil to create the nuclear polarization of beta-emitters. Especially, the foil covered with Au metal was proven suitable for the use of swift ions in the relatively high charge states, which are produced through projectile fragmentation processes in high-energy heavy-ion collisions.

ACKNOWLEDGEMENTS

We thank Prof. K. Kasiwagi of Toyo Univ. for performing evaporations of Au metal onto the PET films with the ion plating method. The present work was supported in part by the Grant in Aid for Scientific Research, the International Scientific Collaborative Research given from the Ministry of Education, Culture and Science, Japan. Also the partial support was given by the U.S.A.-Japan collaborative Research given by both the Japan Sclentlfic Foundation, and the National Scientific Foundation, U.S.A.. Finally, but not least, the work was also partially supported by the Yamada Science Foundation.

REFERENCES

/i/ T. Minamisono, Hyp. Int. 21 (1985) 103, K. Nakai, Hyp. Int. 21 (1985) i.

/2/ K. Sugimoto, et al., Phys. Left. 18 (1965) 38, and J. Phys. Soc. Japan 21 ( 1966 ) 213. T. Minamisono, J. Phys. Soc Japan 34 suppl. (1973) 324.

/3/ li.G. Berry and M. Hass, Ann. Rev. Nucl. Part. Sci.32 ( 1982 ) R e f e r e n c e s t h e r e i n .

I.

..I. ( ) :un 'u dt ~d., Po /wndr . /b i l Ul*t~hcuh/d ns n/ Icd /011 lc'chnlquv 13,~5

/4/ Y. No j i r i and B.I. Deutch, Phys.Rev. Let t . , 51 (1983) ]80. u Nojir] et al., J. Phys. Soc. Japan 55Suppl.(lgB6) 39].

/5/ A. Ozawa et al., Annual Report, OULNS Osaka Univ. 1987, p.80. /6 / T. Hinamisono et al., Bevalac experiment E732H. /7/ K. ~atsuta et al., Contribution to this Conference.

P

Fig.l. Experimental setup for tests of tilted foil surfaces by means of production of polarized beta-emitter 12B.