Alpha decay studies of translead nuclei at the proton drip line

This is a self-archived version of an original article. This version may differ from the original in pagination and typographic details. Author(s): Title: Year: Version: Copyright: Rights: Rights url: Please cite the original version: CC BY 4.0 https://creativecommons.org/licenses/by/4.0/ Alpha decay studies of translead nuclei at the proton drip line © 2001 Jagellonian University Published version Uusitalo, J.; Kettunen, H.; Andreyev, A.N.; Eskola, K.; Greenlees, P.T.; Helariutta, K.; Huyse, M.; Jones, P.; Julin, R.; Juutinen, S.; Kankaanpää, H.; Kuusiniemi, P.; Leino, M.; Muikku, M.; Nieminen, P.; Rahkila, P.; Van De Vel, K.; Van Duppen, P. Uusitalo, J., Kettunen, H., Andreyev, A.N., Eskola, K., Greenlees, P.T., Helariutta, K., Huyse, M., Jones, P., Julin, R., Juutinen, S., Kankaanpää, H., Kuusiniemi, P., Leino, M., Muikku, M., Nieminen, P., Rahkila, P., Van De Vel, K., & Van Duppen, P. (2001). Alpha decay studies of translead nuclei at the proton drip line. Acta Physica Polonica B, 32(3), 1015-1018. 2001 Vol. 32 (2001) ACTA PHYSICA POLONICA B No 3 ALPHA DECAY STUDIES OF TRANSLEAD NUCLEI AT THE PROTON DRIP LINE   J. Uusitalo a , H. Kettunen a , A.N. Andreyev b , K. Eskola  P.T. Greenlees a , K. Helariutta a , M. Huyse b , P. Jones a R. Julin a , S. Juutinen a , H. Kankaanpää a , P. Kuusiniemi a M. Leino a , M. Muikku a , P. Nieminen a , P. Rahkila a K. Van de Vel b and P. Van Duppen b a Department of Physis, University of Jyväskylä FIN-40351, Jyväskylä, Finland b Institut voor Kernen Stralingsfysia, K. U. Leuven Leuven, Belgium  Dept. of Physis, University of Helsinki FIN-00014 Helsinki, Finland (Reeived November 28, 2000) Extensive  -deay studies of the very neutron deient isotop es 191 Po, 195 Rn, and 196 Rn have b een p erformed at the RITU gas-lled reoil separator. The reoil-   (  ) orrelation tehnique and the    oinidene tehnique have b een utilized to unambiguously onnet the observed  - deays to prop er nulei. Illustrative examples on how the  -deay an yield sp etrosopi information on the nulei studied will b e presented. PACS numbers: 23.60.+e, 27.80.+w, 29.30.h 1. Intro dution In this work evap oration residues from the heavy ion indued fusion reations have b een separated from the b eam using the JYFL gas-lled reoil separator RITU. In addition to nulear mass information,  -deay in the Pb region an provide imp ortant sp etrosopi information on intruder states, shap e o existene and onset of deformation esp eially when ne struture is observed.  Presented at the XXXV Zakopane Sho ol of Physis Trends in Nulear Physis, Zakopane, Poland, September 513, 2000.  This work has b een supp orted by the Aademy of Finland under the Finnish Centre of Exellene Programme 2000-2005 (Pro jet No. 44875, Nulear and Condensed Matter Programme at JYFL). (1015) 1016 J. Uusitalo et al. 2. Alpha deay study of 191 Po In the work p erformed at JYFL [1 3℄ the neutron deient 191 Po isotop e was studied utilizing  -  oinidene tehnique. The rst exp eriment to study the ne struture in the  -deay of 191 Po was arried out using the fusion evap oration reation 160 Dy( 36 Ar, 5 n ) 191 Po [1, 2℄. Later on a omplementary exp eriment was p erformed using the reation 142 Nd( 52 Cr, 3 n ) 191 Po [3℄. In these exp eriments two  -deaying isomeri states were observed with E  = 7334(5) keV and T 1 = 2 = 22(1) ms ( I  = 77(3) %) assigned to 191 g Po and the other E  = 7376(5) keV and T 1 = 2 = 93(3) ms ( I  = 50(3) %) assigned to 191 m Po. In addition,  -deay lines with E  = 6888(5) keV ( I  = 46(4) %) and E  = 6966(10) keV ( I  = 8(3) %), feeding the  - deaying exited  i 13 = 2  [  (2 p  2 h )℄ 0 + and  p 3 = 2  [  (2 p  2 h )℄ 0 + states in 187 g Pb and 187 m Pb, resp etively, were observed. In fat it turned out that the 6888 keV  -deay is unhindered (HF = 0.63) and the 7376 keV  -deay is strongly hindered (HF = 26). The detailed  -deay sheme for 191 Po is shown in Fig. 1. An extensive disussion of the 191 Po part of the sheme is presented in the referenes [13℄. Fig. 1. Level sheme for 191 Po and 195 Rn and observed hindrane fators HF. 3. Alpha deay study of 196 Rn and 195 Rn Fusion evap oration reations of the typ e 142 Nd( 56 Fe ; xn ) 198  x Rn were used to synthesize neutron deient Rn isotop es [4℄. Altogether 19 ER   - deay hains assigned to the 196 Rn isotop e were observed. For nine of the hains a full energy daughter deay was also found. The measured deay prop erties for the daughter ativity E  = 7167(11) keV and T 1 = 2 = (29 +15  8 ) ms p oint to 192 Po for whih E  = 7167(7) keV and T 1 = 2 = 33 : 2(14) ms [5℄ have b een rep orted. The deay prop erties of E  = 7461(9) keV and Alpha Deay Studies of Translead Nulei at the Proton Drip Line 1017 T 1 = 2 = (4 : 4 +1 : 3  0 : 9 ) ms were determined for the isotop e 196 Rn. These values are ompatible with those rep orted in [6℄, where E  = 7492(30) keV and T 1 = 2 = (3 +7  2 ) ms are given for 196 Rn. Altogether seven ER   m   d deay hains, where the mother ativity E  = 7555(13) keV and T 1 = 2 = (3 +2  1 ) ms was followed by daughter ativity E  = 6878(12) keV and T 1 = 2 = (110 +70  30 ) ms, were observed. In addition eleven ER   m   d deay hains where the mother ativity E  = 7536(11) keV and T 1 = 2 = (6 +3  2 ) ms was followed by daughter ativity E  = 7331(11) keV and T 1 = 2 = (15 +7  3 ) ms, were found. Finally, three deay hains, where the mother ativity E  = 7555(20) keV and T 1 = 2 = (9 +12  4 ) ms was followed by an ativity with E  = 7364(20) keV and T 1 = 2 = (95 +130  60 ) ms, were identied. The measured deay prop erties for the daughter ativities are ompatible with those rep orted for 191 Po (see ab ove). Based on these the deay prop erties of E  = 7555(11) keV and T 1 = 2 = (5 +3  2 ) ms ( 195 m Rn) and E  = 7536(11) keV and T 1 = 2 = (6 +3  2 ) ms ( 195 g Rn) an b e prop osed to b elong to the new nulide 195 Rn. 4. Disussion Through systemati study of  -deay hindrane fators HF and redued widths Æ 2 some struture information on the deaying states an b e dedued. As an b e seen from the level sheme (Fig. 1) although the  -deay energy of the 13 = 2 + isomeri state in 191 Po is slightly higher than the deay energy of the 3 = 2  ground state, its half-life is nearly 5 times longer. On the other hand, the existene of the unhindered (HF = 0.63) deay to the exited oblate 13 = 2 + state in 187 g Pb p oints to a deformed 13 = 2 + isomeri state in 191 Po. This has b een interpreted as a weak oupling of the o dd neutron to an intruder deformed 0 + state in the eveneven ore. The situation is ompletely dierent from the  -deay of the 3 = 2  ground state in 191 Po, where the feeding of the 3 = 2  isomeri state and the exited 3 = 2  state have equal strengths. The hindrane fators determined for 195 m Rn and 195 g Rn lead to the onlusion that the  -deays o ur b etween states of equal spin, parity and onguration. Thus the  -deay with the energy 7536 keV originates from the 3 = 2  ground state of 195 Rn and the  -deay with the energy 7555 keV originates from the 13 = 2 + isomeri state of 195 Rn as illustrated in Fig. 1. The redued  -deay widths for neutron deient even-mass Po, Rn and Ra isotop es, inluding 196 Rn studied in this work, are shown in Fig. 2. The redued  -deay widths of even-mass Po isotop es with neutron numb ers 112  N  126 inrease smo othly with dereasing neutron numb er. The redued widths for the ground state to ground state transitions remain onstant for 190  196 Po and derease markedly for 188 Po. The reason for this 1018 J. Uusitalo et al. Fig. 2. Redued width values for Po, Rn and Ra nulides. is that the  -deays from the ground state to 0 + intruder states in Pb are getting more favorable. This feature an b e seen in Fig. 2 where also redued widths for deays b etween the ground state and two partile two hole  (2 p  2 h ) proton intruder states are shown. An interpretation has b een given that the ground states of neutron deient Po isotop es starting from 194 Po are mixed with dierent ongurations, spherial  (2 p  0 h ) , oblate  (4 p  2 h ) (and prolate  (6 p  4 h )) , and therefore the ground states of these nulei are deformed. The redued  -deay widths of even-mass Rn isotop es with neutron numb ers of 114  N  126 inrease smo othly with de- reasing neutron numb er. The redued  -deay width value for 198 Rn is slightly higher and the  -deay of 196 Rn is learly faster than the smo oth b ehavior predits. In the latter ase the  -deay ould b e onsidered to take plae b etween the mixed deformed 0 + ground state in 196 Rn and mixed deformed 0 + ground state in 192 Po. This is in go o d agreement with results from reent  -ray studies where the same kind of intruder strutures were exp osed in 198 Rn, 194 Po, and 192 Po [7, 8℄. REFERENCES [1℄ A.N. Andreyev et al. , Phys. Rev. Lett. 82 , 1819 (1999). [2℄ A.N. Andreyev et al. , ENPE, Sevilla, Spain, AIP Conf. Pro. 495 , 121 (1999). [3℄ A.N. Andreyev et al. , submitted for publiation. [4℄ H. Kettunen et al. , Phys. Rev. C , to b e submitted. [5℄ N. Bijnens et al. , Z. Phys. A356 , 3 (1996). [6℄ Y.H. Pu et al. , Z. Phys. A54 , 1 (1997). [7℄ K. Helariutta et al. , Eur. Phys. J. A6 , 289 (1999). [8℄ R.B. Taylor et al. , Phys. Rev. C59 , 673 (1999).