- Email: [email protected]
The rediscovered J = 52 state of Li7
Volume 4, number 6
PHYSICS
cesses and the effects of Stark mixing. They caldate the time for the pion to go from n - 15 to nuclear capture as 2.3 X lo-12 sec. If Day’s figure of - 1.2 x 10-12 set to go from fi = 0.006 to n _ 15 is added, then the figure to be compared to the present experimental result is - 3.5 X lo-12 sec. The agreement is reasonable. We wish to thank the Nevis Cyclotron Laboratory of Columbia University for the loan of the bubble chamber film and for help in obtaining certain essential apparatus. We are indebted to Dr. N. P. Samios for helpful discussions. We thank Mr. J. Grauman for aid with the calculations.
LETTERS
15 May 1963
l) Day, Snow and Sucher, Phys. Rev. Letters 3 (1959) 61. 2) J.Russell and G.Shaw, Phys.Rev. Letters 4 (1960)369. 3) Day, Snow and Sucher, Phys.Rev. 118 (1960) 864.
4) T. B.Day, Bull. Am. Phys.Soc., Ser. II, 5 (1960) 225 and University of Maryland Physics Dept. Technical
Report No. 175 (1960) (unpublished). 5) M. Leon and H. Bethe, Phys. Rev. 127 (1962) 636. 6) Fields et al., Phys. Rev. Letters 5 (1960) 69. 7) Doede, Hildebrand, Israel and Pyka, to be published Phys. Rev. 8) Eisler et al., Nuovo Cimento 10 (1958) 468. 9) R. J. Piano, Phys. Rev. 119 (1960) 1400. 10) E . Bierman, Phys. Rev. 127 (1962) 599. 11) W. Barkas and A.Rosenfeld, University of California Radiation Laboratory Report UCRL 8030 (Rev.)(1961) (unpublished). 12) Alvarez et al., Phys.Rev. 105 (1957) 1127. 13) A.S.Wightman, Phys.Rev.77 (1950) 521, and thesis, Princeton University (1959) (unpublished).
*****
THE
REDISCOVERED
J = : STATE
OF
Li7
M. H. W;hCHTER General Electric Company, APED, San Jose, California Received 19 April 1963
In recent years the calculation of energy levels in light nuclei has received considerable attention. In particular, the Li7 nucleus has been studied within the framework of the intermediate coupling shell model l) and of the cluster model 2). These investigations lead to a J = z state of Li7 with an excitation energy between 5 and 6 MeV, a prediction shared by the unified model of Clegg 3). It has been asserted repeatedly 2-4) that no corresponding experimental evidence exists for such a Li7 level and this lack of agreement is generally considered to be rather disturbing. It is the sole purpose of this note to draw attention to an old experiment 5) on the Li7 (r,o)H3 reaction. In this work the energy spectrum of emitted tritons and o-particles has been measured (for a 31 MeV Bremsstrahlung y-ray spectrum) and a peak was observed corresponding to a Li7 state at 5.5 MeV *). Although the evidence for this level was not * The existence of that e eriment is also revealed by a careful reading of ref. ? ), p. 32, 33.
very strong it was nevertheless statistically significant. Furthermore, the assignment J = 2 for this level was not inconsistent with experimental data on the angular distribution of emitted tritons. It appears from this result that the observed level might represent the controversial state and that a more thorough study of the Li7(y,o)H3 reaction should rovide useful information. The reactions 2) H%(cu,cr)H3and 3, Li7(p,p’), the latter with high energy protons, have also been proposed to this end.
References 1) J. M.Soper, Phil.Mag.2 (1957) 1219. 2) Tang, Wildermuth and Pearlstein, Phys.Rev. 123 (1961) 548. 3) A. B. Clegg, Nuclear Physics 33 (1962) 194. 4) Proc. Internat. Conf. on Nuclear Structure, Kingston, ed. D.A. Bromley and E. W. Vogt (University of Toronto Press, 1960) p.417. 5) Erd&s et al., Nuovo Cim. 12 (1954) 639. 6) F. A jzenberg-Selove and T. Lauritsen, Nuclear Physics 11 (1959) 1.
353
PHYSICS
cesses and the effects of Stark mixing. They caldate the time for the pion to go from n - 15 to nuclear capture as 2.3 X lo-12 sec. If Day’s figure of - 1.2 x 10-12 set to go from fi = 0.006 to n _ 15 is added, then the figure to be compared to the present experimental result is - 3.5 X lo-12 sec. The agreement is reasonable. We wish to thank the Nevis Cyclotron Laboratory of Columbia University for the loan of the bubble chamber film and for help in obtaining certain essential apparatus. We are indebted to Dr. N. P. Samios for helpful discussions. We thank Mr. J. Grauman for aid with the calculations.
LETTERS
15 May 1963
l) Day, Snow and Sucher, Phys. Rev. Letters 3 (1959) 61. 2) J.Russell and G.Shaw, Phys.Rev. Letters 4 (1960)369. 3) Day, Snow and Sucher, Phys.Rev. 118 (1960) 864.
4) T. B.Day, Bull. Am. Phys.Soc., Ser. II, 5 (1960) 225 and University of Maryland Physics Dept. Technical
Report No. 175 (1960) (unpublished). 5) M. Leon and H. Bethe, Phys. Rev. 127 (1962) 636. 6) Fields et al., Phys. Rev. Letters 5 (1960) 69. 7) Doede, Hildebrand, Israel and Pyka, to be published Phys. Rev. 8) Eisler et al., Nuovo Cimento 10 (1958) 468. 9) R. J. Piano, Phys. Rev. 119 (1960) 1400. 10) E . Bierman, Phys. Rev. 127 (1962) 599. 11) W. Barkas and A.Rosenfeld, University of California Radiation Laboratory Report UCRL 8030 (Rev.)(1961) (unpublished). 12) Alvarez et al., Phys.Rev. 105 (1957) 1127. 13) A.S.Wightman, Phys.Rev.77 (1950) 521, and thesis, Princeton University (1959) (unpublished).
*****
THE
REDISCOVERED
J = : STATE
OF
Li7
M. H. W;hCHTER General Electric Company, APED, San Jose, California Received 19 April 1963
In recent years the calculation of energy levels in light nuclei has received considerable attention. In particular, the Li7 nucleus has been studied within the framework of the intermediate coupling shell model l) and of the cluster model 2). These investigations lead to a J = z state of Li7 with an excitation energy between 5 and 6 MeV, a prediction shared by the unified model of Clegg 3). It has been asserted repeatedly 2-4) that no corresponding experimental evidence exists for such a Li7 level and this lack of agreement is generally considered to be rather disturbing. It is the sole purpose of this note to draw attention to an old experiment 5) on the Li7 (r,o)H3 reaction. In this work the energy spectrum of emitted tritons and o-particles has been measured (for a 31 MeV Bremsstrahlung y-ray spectrum) and a peak was observed corresponding to a Li7 state at 5.5 MeV *). Although the evidence for this level was not * The existence of that e eriment is also revealed by a careful reading of ref. ? ), p. 32, 33.
very strong it was nevertheless statistically significant. Furthermore, the assignment J = 2 for this level was not inconsistent with experimental data on the angular distribution of emitted tritons. It appears from this result that the observed level might represent the controversial state and that a more thorough study of the Li7(y,o)H3 reaction should rovide useful information. The reactions 2) H%(cu,cr)H3and 3, Li7(p,p’), the latter with high energy protons, have also been proposed to this end.
References 1) J. M.Soper, Phil.Mag.2 (1957) 1219. 2) Tang, Wildermuth and Pearlstein, Phys.Rev. 123 (1961) 548. 3) A. B. Clegg, Nuclear Physics 33 (1962) 194. 4) Proc. Internat. Conf. on Nuclear Structure, Kingston, ed. D.A. Bromley and E. W. Vogt (University of Toronto Press, 1960) p.417. 5) Erd&s et al., Nuovo Cim. 12 (1954) 639. 6) F. A jzenberg-Selove and T. Lauritsen, Nuclear Physics 11 (1959) 1.
353