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Study of the decay out of a superdeformed band in 143Eu
Frog. Part. Nucl. Phys., Vol.28, pp. 279-280,1992. Printedin CheatBritain.Allrightsreserved.
0146-6410/92$15.00 @1992PergamonPressLtd
Study of the Decay out of a Superdeformed Band in
143Eu
A. ATA(~1, B. HERSKIND 1, J. NYBERG 1, M. PIIPARINEN1, G. DE ANGELIS2, S. FORBES3, N. GJ~RUP 1, G. HAGEMANN 1, F. INGEBRETSEN4, H. JENSEN 1, D. JERRESTAI~, H. KUSAKARI1, R. LIEDER 1, G. NL MARTI6, S. MULLINS3, D. SANTONOCrro I , H. SCHNARE6, G. SLETrEN 1, K. STRAHLE6, M. SUGAWARA1, P. O. TJ~M 4, A. VIRTANEN1 and R. WADSWORTH7 1 The Niels Bohr Institute, University of Copenhagen, Denmark 2 Laboratori Nazionali di Legnaro, Legnaro, Italy 30liverLodge Laboratory, University of Liverpool, U.K. 4 Department of Physics, University of Oslo, Norway 5 The Studsvik Science Laboratory, NykObing, Sweden 6 Institfllr Kernphysik, Jltlich, Germany 7Department of Physics, University of York, York, U.K.
The connection between the super-deformed (SD) and the normal-deformed (ND) states has not been observed yet owing its difficulty to a statistical, highly fragmented decay path out of the SD bands. This leaves both the spin and the excitation energy of the SD bands undetermined. In the present contribution we are presenting results of a new experimental approach where we take advantage of triple and higher fold coincidences to study the decay out of a SD band. It is well known from previous works 1) that the decay out of a SD band starts from one or two of the lowest lying known states of the band. After a few consecutive transitions all the decay routes end in a few ND yrast states. We assume that cascades of only two transitions de-excite the SD band through many different intermediate states and they sum up to well defined energies. In events of triple coincidence we sum the energies of two -y rays which are in coincidence with a transition in the SD band to produce a sum spectrum where we would like to identify discrete transitions related to the decay out of the SD band. In order to test this method, we carried out an experiment at the Niels Bohr Institute Tandem Accelerator Laboratory where we used the (160 MeV) sTC1 + 11°Pd ---*14SEu + 4n reaction. The NORDBALL detector array with 19 Compton-suppressed Ge detectors and 1 LEP detector together with the BaF2 ball for multiplicity and sum energy selection were employed. About 109 triple and higher fold coincidence events were collected during the experiment, 10% of them being 4-fold Ge-coincidences. Fig.1 shows a spectrum which is double gated on the transitions of the SD band. The transitions between the known 2) low lying states in l ~ E u which are populated by the SD band are indicated by an open diamond in the figure. The intensity of the band is about 1% relative to the total population of 143Eu. This SD band has previously been reported s) and assigned to 142Eu. In order to clear up the assignment problem, we put one gate on the SD band and another gate on a lower lying transition in 142Eu and in 14SEu, respectively. The SD band can be seen in the latter case, but not in the former one, leaving little doubt that the SD band belongs to 143Eu. The insert of fig.1 marks two transitions which are assigned to be the next higher transitions in the band. The sum spectrum that is the sum of 2 "y-ray energies which are in coincidence with one of the SD transitions is shown in fig. 2. In the energy region between 1.5 MeV to about 3 MeV, all the prominent peaks are identified as being the sum of 2 transitions in the SD band which has a very constant j(2). The transitions which connect the SD band with the ND states are expected to be seen above 3 MeV. The peaks marked by arrows in the figure are candidates which may be assigned to be the linking transitions. The energy separation between these peaks agree with a decay into two (25/2-) states at energies of 3343 keV and 3364 keV in the level scheme of 143Eu. Further data analysis is in progress. 279
A. Ata~ et al.
280 450 m 350
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o 150
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O v O
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450 .
350
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°
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I 'L
.
.
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800
.
,.,
.
.
,
250 o 150 C.9 5o -50 800
900
1000 1100 1200 1300 1400 1500 1600 1700 1800 E~, ( k e V )
Fig.l : Gamma-ray spectrum coincident with two SD band members. It is a sum of a few clean gates. The band members with energies 484, 547, 809, 672, 733, 794, 854, 914, 973, 1032, 1091, 1150, 1208, 1286, 1325, 1385, 1444, 1503, 1564, 1623, 1586, 1744 keV are marked by (V) and known low-lying states in 1~Eu are denoted by (@). The spectrum is shown with a background subtraction and it is corrected for the detector efficiencies.
2000 1700
3186 keV
'
1400 "~ l l O 0
3210 keY
200 -100 1500
.
. . 2000
. 2500
3000
3500
4000
E~(keV) Fig.2 : S u m spectrum, sum of 2 7-ray energies which are in coincidence with one of the SD band members.
References : 1. J.F. Sharpey-Schafer, New Aspects of Nuclear Dynamics, Edited by J.H. Koch and P.K.A.de Witt Ruberts (Plenum Publ. 1989), p. 147 and references therein. 2. M. Mfiller-Veggian et al., Z.Phys. A330(1988)343 and M. Piiparinen et al., to be published. 3. S.M. MuUins et al., Phys.Rev.Lett. 86(1991)1677.
0146-6410/92$15.00 @1992PergamonPressLtd
Study of the Decay out of a Superdeformed Band in
143Eu
A. ATA(~1, B. HERSKIND 1, J. NYBERG 1, M. PIIPARINEN1, G. DE ANGELIS2, S. FORBES3, N. GJ~RUP 1, G. HAGEMANN 1, F. INGEBRETSEN4, H. JENSEN 1, D. JERRESTAI~, H. KUSAKARI1, R. LIEDER 1, G. NL MARTI6, S. MULLINS3, D. SANTONOCrro I , H. SCHNARE6, G. SLETrEN 1, K. STRAHLE6, M. SUGAWARA1, P. O. TJ~M 4, A. VIRTANEN1 and R. WADSWORTH7 1 The Niels Bohr Institute, University of Copenhagen, Denmark 2 Laboratori Nazionali di Legnaro, Legnaro, Italy 30liverLodge Laboratory, University of Liverpool, U.K. 4 Department of Physics, University of Oslo, Norway 5 The Studsvik Science Laboratory, NykObing, Sweden 6 Institfllr Kernphysik, Jltlich, Germany 7Department of Physics, University of York, York, U.K.
The connection between the super-deformed (SD) and the normal-deformed (ND) states has not been observed yet owing its difficulty to a statistical, highly fragmented decay path out of the SD bands. This leaves both the spin and the excitation energy of the SD bands undetermined. In the present contribution we are presenting results of a new experimental approach where we take advantage of triple and higher fold coincidences to study the decay out of a SD band. It is well known from previous works 1) that the decay out of a SD band starts from one or two of the lowest lying known states of the band. After a few consecutive transitions all the decay routes end in a few ND yrast states. We assume that cascades of only two transitions de-excite the SD band through many different intermediate states and they sum up to well defined energies. In events of triple coincidence we sum the energies of two -y rays which are in coincidence with a transition in the SD band to produce a sum spectrum where we would like to identify discrete transitions related to the decay out of the SD band. In order to test this method, we carried out an experiment at the Niels Bohr Institute Tandem Accelerator Laboratory where we used the (160 MeV) sTC1 + 11°Pd ---*14SEu + 4n reaction. The NORDBALL detector array with 19 Compton-suppressed Ge detectors and 1 LEP detector together with the BaF2 ball for multiplicity and sum energy selection were employed. About 109 triple and higher fold coincidence events were collected during the experiment, 10% of them being 4-fold Ge-coincidences. Fig.1 shows a spectrum which is double gated on the transitions of the SD band. The transitions between the known 2) low lying states in l ~ E u which are populated by the SD band are indicated by an open diamond in the figure. The intensity of the band is about 1% relative to the total population of 143Eu. This SD band has previously been reported s) and assigned to 142Eu. In order to clear up the assignment problem, we put one gate on the SD band and another gate on a lower lying transition in 142Eu and in 14SEu, respectively. The SD band can be seen in the latter case, but not in the former one, leaving little doubt that the SD band belongs to 143Eu. The insert of fig.1 marks two transitions which are assigned to be the next higher transitions in the band. The sum spectrum that is the sum of 2 "y-ray energies which are in coincidence with one of the SD transitions is shown in fig. 2. In the energy region between 1.5 MeV to about 3 MeV, all the prominent peaks are identified as being the sum of 2 transitions in the SD band which has a very constant j(2). The transitions which connect the SD band with the ND states are expected to be seen above 3 MeV. The peaks marked by arrows in the figure are candidates which may be assigned to be the linking transitions. The energy separation between these peaks agree with a decay into two (25/2-) states at energies of 3343 keV and 3364 keV in the level scheme of 143Eu. Further data analysis is in progress. 279
A. Ata~ et al.
280 450 m 350
0
250
•
O
o 150
O
I
I
|
•
O v O
50 -50 100
200
300
400
500
450 .
350
.
.
.
.
I
.
.
.
.
.
°
600
700
I 'L
.
.
.
800
.
,.,
.
.
,
250 o 150 C.9 5o -50 800
900
1000 1100 1200 1300 1400 1500 1600 1700 1800 E~, ( k e V )
Fig.l : Gamma-ray spectrum coincident with two SD band members. It is a sum of a few clean gates. The band members with energies 484, 547, 809, 672, 733, 794, 854, 914, 973, 1032, 1091, 1150, 1208, 1286, 1325, 1385, 1444, 1503, 1564, 1623, 1586, 1744 keV are marked by (V) and known low-lying states in 1~Eu are denoted by (@). The spectrum is shown with a background subtraction and it is corrected for the detector efficiencies.
2000 1700
3186 keV
'
1400 "~ l l O 0
3210 keY
200 -100 1500
.
. . 2000
. 2500
3000
3500
4000
E~(keV) Fig.2 : S u m spectrum, sum of 2 7-ray energies which are in coincidence with one of the SD band members.
References : 1. J.F. Sharpey-Schafer, New Aspects of Nuclear Dynamics, Edited by J.H. Koch and P.K.A.de Witt Ruberts (Plenum Publ. 1989), p. 147 and references therein. 2. M. Mfiller-Veggian et al., Z.Phys. A330(1988)343 and M. Piiparinen et al., to be published. 3. S.M. MuUins et al., Phys.Rev.Lett. 86(1991)1677.