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Submitted on 1 Jan 1971
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EXCITED LEVELS IN N = 126 ISOTONES STUDIED BY (HI, xnγ)-REACTIONS
K. Maier, J. Leigh, F. Pühlhofer, R. Diamond
To cite this version:
K. Maier, J. Leigh, F. Pühlhofer, R. Diamond. EXCITED LEVELS IN N = 126 ISOTONES STUD- IED BY (HI, xnγ)-REACTIONS. Journal de Physique Colloques, 1971, 32 (C6), pp.C6-221-C6-222.
�10.1051/jphyscol:1971648�. �jpa-00214866�
JOURNAL DE PHYSIQUE Colloque C6, supplkment au no 11-12, Tome 32, Novembre-Dicembre 1971, page C6-221
EXCITED LEVELS IN N = 126 ISOTONES STUDIED BY (HI, xnr)-REACTIONS (*)
K. H. MAIER (**), J. R. LEIGH, F. PUHLHOFER (***), and R. M. DIAMOND Lawrence Radiation Laboratory, University of California, USA
R6sum6. - Les niveaux excites des noyaux a N = 126 : 211At, 212R11, 213Fr et 214Ra ont 6tC etudies par reactions (ion lourd, xny) par spectroscopie y dans le faisceau. Des etats ayant deux a cinq particules excitkes et avec des spins jusqu'a 3912 ont kt6 observes. Les moments nlagnktiques et les valeurs de B(E 2) et B(E 3) ont kt15 mesures pour une partie de ces niveaux. Les propriCt6s electromagn6tiques sont discutkes.
Abstract. - Excited levels in the N = 126 nuclei zllAt, 212Rn, 213Fr, and 214Ra have been studied by in-beam y-spectroscopy with (HI, my)-reactions, and spins up to 3912 have been observ- ed. Magnetic moments, B(E 2) and B(E 3) values have been measured for some of these levels.
The electromagnetic properties will be discussed.
Excited levels in the N = 126 isotones "'At, '12Rn, 213Fr, and '14Ra have been studied by means of in-beam y-spectroscopy with (HI, xny) reactions [I].
A variety of ion beams between 4He and 1 6 0 from the Berkeley Hilac were used, and targets of separated Hg, TI, Pb, and Bi isotopes. The level schemes have been established by measuring excitation functions, y-y-coincidences, y-ray angular distributions, and conversion electron spectra. The half lives that are given have been determined by pulsed beam experiments and delayed y-y-coincidences. The two g-factors were measured by a time differential observation of the
l h g I 2 i n levels in N=126 nuclei
FIG. 1. - Experimental results on the levels of the (h9,z)n-
configuration in the N = 126 isotones with 2-6 protons beyond Z = 82. The scheme of 2loPo is taken from ref. [2].
(*) Work performed under the auspices of the U. S. Ato- mic Energy Commission.
(**) Present address : Hahn-Meitner-Institut, Berlin.
(***) On leave from Physikalisches Institut der Universitat, Marburg, Germany.
perturbed angular distribution in an external field following pulsed beam excitation. The results are summarized in figures 1 and 2.
FIG. 2. - The experimental level schemes of 211At and 213Fr.
For the shell model calculation of 211At see ref. [5]. The half lives of the 21-12 and 29+/2 levels are taken from Bergstrh et al.,
Physica Scripta 1970, 1 , 243.
It is expected that the low-lying levels of these nuclei with a closed neutron shell and 3 to 6 protons beyond Z = 82 should have predominantly (h,,,)" shell- model configurations. For the doubly-even nuclei this configuration gives just the observed spins O + , 2+, 4+, 6 + , 8" for seniority 0 and 2 ; for '''At
Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1971648
and '13Frthe four lowest levels observed in the isomer have the spins expected for (hg12)3 or (hg12)5. Between levels belonging to a jn-configuration M1-transitions are forbidden, and indeed we see none. Furthermore the g-factors of all jn-levels are predicted to be equal, and our value for the (hg12)4 8+ level in '12Rn agrees perfectly with that of the previously known (hg,2)2 8 + level in "OPo [2] and that of the hg12 groundstate in '09Bi. Similarly the E 2-properties of all (hg12)"- levels can be calculated from a single effective charge.
As discussed in ref. [3] this agrees with the experimental findings in '09Bi, 210Po, and '''At. We now find in addition that the B(E 2) values in '12Rn agree with the predicted value of 119 of the analogous transitions in210Po. For the half-filled shell ('I3Fr) E2-transitions are theoretically forbidden and experimentally the strength of the 21-12 -, 17-12 transition in '13Fr is 1 % of the strength of the corresponding transition in 211At. Thus all data so far mentioned agree very well with the assumption of pure configurations. However, the lifetimes found in 214Ra, particularly that of the 8+ level, are much too long. We have no explanation for this at present. A strikingly similar low B(E 2)
value is observed [4] in 9 4 R ~ which is 6 g9/, proton holes from doubly magic loOSn compared to 6 hg12 protons in '14Ra.
In '''At and '13Fr we have also observed the highest spin members of the (hg12)2 f,,, and (hg12)2 i13/, configurations. The energies of all levels below 3 MeV in '''At agree remarkably with a shell model calculation [5] and the level scheme of '13Fr is very similar. In 211At, three still higher levels have been found. From the arguments presented in [5] their structure most likely consists of 3 protons coupled t o a 5- neutron-particle-hole state as indicated in figure 2. The B(E 3) values of the 29'12 + 23-12 transitions in '''At and '13Fr are 40 000 $. 10000 and (35 000 + 12 000) e2 fm6 respectively. This is 8 times larger than the theoretical estimate for a single particle i1312 + f7I2 transition and reveals admixtures of the 3- octupole state in '08Pb to these levels. If the description of the 4 816 and 4 381 keV levels in '"At is correct, the 435 keV E 3 transition also is i,,,, + f,/,. Here we find even higher enhance- ment of the B(E 3) value (83 000 rt 9 000 e2 fm6) which equals that of the 3- + 0' transition in '08Pb.
References
11 ] MAIER (K. H.), LEIGH (J. R.), DIAMOND (R. M.), to be THIEBERGER (P.), and WIKSTROM (K.), Phys. Let-
published. ters, 1970, 32B, 476.
121 YAMAZAKI (T.), NOMURA (T.), KATOU (T.), INA- [4] JAKLEVIC (J. M.), LEDERER (C. M.), HOLLANDER (J. M.),
MURA (T.), HASHIZUME (A.), and, TENDOU (Y.) Phys. Letters, 1969, 29B, 179.
Phys. Rev. Letters, 1970, 24, 317. [S] MAIER (K. H.), LEIGH (J. R.), PUHLHOFER (F.), DIA- [3] BERGSTROM ((I.), FANT (B.), HERRLANDER (C. J.), MOND (R. M.), P h p . Letters, 1971, 35B, 401.
