Z. Phys. A - Hadrons and Nuclei 342, 245--246 (1992) Short note '~176 Hadrons ffir Physik A and Nuclei 9 Springer-Verlag 1992 Radiationless transition probabilities in muonic 2~ H. Paganetti 1, p. David 1, H. H~inscheid 1, ,, j. Konijn 2, C.T.A.M. de Laat 3, W. Lourens 3, F. Risse ~'**, Ch. RSsel ~, L.A. Schaller 4, and A. TaM 3 ISKP, University of Bonn, Nussallee 14-16, W-5300 Bonn 1, Federal Republic of Germany 2 NIKHEF-K, P.O. Box 4395, 1009 AJ Amsterdam, The Netherlands 3 Physics Laboratory, University of Utrecht, P.O. Box 80000, 3508 TA Utrecht, The Netherlands 4 Department of Physics, University of Fribourg, CH-1700 Fribourg, Switzerland Received October 10, 1991 Abstract: The probability for non-radiative (n.r.) ex- citations in muonic 2~ was determined from a (#-,72C)- measurement by comparing the intensities of muonic X-ray transitions in single and coincidence spectra. The values of P,.~.(3p--~ls)=(17.9• and P,.~.(3d-~ls)=(3.0• were measured for the first time. The strength of the n.r. decay of the 2p-level was found to be (4.2• The n.r. transition probabilities of two subcomplexes of the (2p--*ls)-transition leading to different mean excitation en- ergies are (3.2• and (5.0• respectively. PACS: 13.10.+q~ 23.20.-g~ 36.10.-k~ 36.10.Dr Non-radiative (n.r.) transitions in heavy muonic atoms, in 1949 already predicted by Wheeler [1], may excite the nucleus which then may decay via prompt processes like fission, neutron emission, or 2c-deexcitation. Several ex- perimental determinations concerning the phenomenon of n.r. transitions have been published [2-9]. The n.r. transi- tions in muonic 2~ were studied in continuation of the preceding experiments on zCSpb, 232Th, and 23su [9]. The experiment was performed using the/zE4 channel of the Paul-Scherrer-Institut (PSI). The experimental set- up is described in more detail in ref. 10, which contains the result of the simultaneously measured fission probabil- ity of muonic 2~ The beam intensity, measured with a scintillator telescope, was 2• muons per second. Two large volume Ge-detectors each with a BGO-Compton sup- pression system were used to detect the muonic X-rays. A large CsF-crystal (5"x5") was employed in addition to de- fine coincidences between muonic X-rays. Following the conventional nomenclature, the probabil- ities for a certain transition refer to the population of the initial level. The formalism to determine the fraction of n.r. transition strengths between the levels of the muonic cascade has been outlined by RSsel et al. [9]. * Present address: Klinik und Poliklinik fiir Nuklearmedizin tier Universit~it Wfirzburg, W-8700 Wiirzburg, Federal Republic of Germany ** Present address: Bayer AG, W-5090 Leverkusen, Federal Re- public of Germany The probability for a non-radiative (2p--~ls)-transition P~.~.(2p--ls) has been determined from the analysis of the X-ray spectra recorded by the CsF-crystal. In order to evaluate the probability P,.~.(3p-~ls) it is necessary to an- alyze muonic transitions which populate the 3p-level. tn muonic 2~ the (4d~3p)-transitions clearly identified in the Ge-detectors have been used for this purpose. By considering all radiative and n.r. decays of the 3d- level Pn.T.(3d~ls) has been obtained. The total transi- tion probability P(3d~2p) has been evaluated by compar- ing the muonic X-ray spectra measured as single events with those measured in coincidence with the (2p-*ls)- transition. For muonic 2~ the results for P(3d--*2p) show significant deviations for the different fine structure transitions. This effect has previously been observed for 2~ [9]. For 2~ it was possible to analyze the n.r. de- cay width F .... (3d-~2p). For this purpose the formalism described in ref. 9 has been extended accordingly: P,~.r.(3d--+ls) = 1 - P(3d~2p) - P,.,~a(3d---~ls) = 1 - P(3d--~2p) - P(3d~2p) r,aa(3d~ls) X rTo.(3d- 2p) + r....(3d-,2p) The ratio of the radiative decay widths Fr~d(3d---~ls)/ Fr,~d(3d---+2p) has been calculated by Lohs et al. [11]. Taking into account the non-radiative E3-transitions (3ds/2~2p3/~) and (3d~/z-~2pl/2) due to the E3-resonance in 2~ [12,13] the non-radiative decay width F .... (3d---~2p) has been estimated. This has been done here by the deter- mination of the intensities of the nuclear 2c-rays belonging to the decay of the resonance. We have neglected other n.r, (3d---+2p)-transition modes and a possible population of these isomer shifted nuclear levels, following energeti- cally higher nuclear excitations by other n.r. transitions. Therefore this gives only an approximation for the proba- bility of a n,r. (3d-+2p)-transition. In table 1 the results for the n.r. transition prob- abilities P,~.~.(2p----~ls) (with a distinction between the two subcomplexes (2pl--~ls) and (2ph--~ls)), P,~.~.(3d----~ls), P,.~.(3p---~ls), and P,,.~.(3d---*2p) are listed together with