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Gamma-Spectroscopic investigations in the radiative fusion reaction 90Zr + 90Zr
Volume 168B, number 1,2
PtlYSICS LETTERS
27 February 1986
GAMMA-SPECTROSCOPIC INVESTIGATIONS IN T H E R A D I A T I V E F U S I O N R E A C T I O N 9°Zr + 9 ° Z r K.-H. S C H M I D T , R.S. S I M O N , J.-G. K E L L E R , F.P. H E S S B E R G E R , G. M O N Z E N B E R G , B. Q U I N T Gesell.~chaft fUr Schwertonenforschung. D-6100 Darmstadt, Fed Rep. Germany
H.-G. CLERC, W. SCHWAB, U. G O L L E R T H A N and C.-C. S A H M Instttut fi~r KernptTvsik, Techntsche Ilochschule Darmstadt. D-610[) Darm.~tadt, Fed Rep. Germany
Received 3 July 1985
The y rays emitted in the radiative fusion reaction ~°Zr+ ~Zr --, lS°Hg+ xy were measured. No indication was found for a specific direct capture process associated with a high-energy -f ray. ]'he shape of the observed y spectrum is compatible with a statistical deexcitation of the compound nucleus.
Recently the radiative fusion of massive nuclei could be observed in 90Zr-induced reactions with 90Zr ' 89y, 92Zr and 94Mo [1,2] and for the system 208pb + 50Ti [3]. In these experiments the radiativefusion product (e.g. 180Hg) was identified by its ground-state a decay. In this letter we report on a spectroscopic investigation of the system 9°Zr + 90Zr which provides first insight into the dynamics of the radiative fusion process. Preliminary results of the present experiment can be found in refs. [4,5]. A 90Zr target of 20 gg/cm 2 was irradiated with a 358 MeV 90Zr beam from the UNILAC heavy-ion accelerator at GSI Darmstadt. The target material had been deposited on a 130/ag/cm 2 Au backing at the
Nal
SHIP
TOF
AE E,x
+
H 13
Beam stop
Fig. 1. Schematical drawing of the experimental set-up. The arrangement of the Nal detectors is shown in an additional cut vertical to the beam axis.
GSI off-line mass separator. The experimental set-up is shown schematically in fig. 1. The 7 rays from the target were observed in a combined arrangement o f a cylindrical NaI sum crystal [6] with one of the six segments removed, and a section of the DarmstadtHeidelberg crystal ball [7,8], consisting of 15 NaI detectors each covering about 0.6% of 47r. The 15 crystal-ball detectors served to measure the spectral composition and the angular distribution of the 3' rays. All NaI detectors together which covered about 90% of 47r were used to determine the 7 sum energy and the 7-ray multiplicity. •~.t the beam energy chosen, the cross section of the radiative fusion amounts to about 40/lb [2] and represents less than one percent of the total fusion cross section, evaporation of one neutron or one proton as well as fission being the most prominent decay modes of the compound system [9]. The separation of the tiny fraction of 7 radiation originating from the radiative fusion was performed with the help of a two-step delayed coincidence. The fusion products (radiative-fusion products and evaporation residues) were separated from the primary beam and transported to a detector telescope by the velocity f'dter SHIP [ 10]. The fusion products could be distinguished from scattered projectiles pass39
Volume 168B, number 1,2
PItYSICS LETTERS
ing through SHIP by analyzing their time-of-flight, their energy loss as obtained from the secondaryelectron detector [1 1], and their energy. A 50 ns time window on the time distances between the detection of a 3' ray in the NaI detector arrangement around the target and the registration of a heavy recoil behind SHIP ensured a pure spectrum of')' rays emitted by the fusion products. In a second step, the evaporation residues implanted into the position-sensitive detector array were individually identified by their subsequent c~ decay. Due to the position resolution of about 0.3 mm FWHM, time correlations even for the c~ decay o f 180Hg with its rather long halflife of 2.9 s could be established. A 8% portion o f random sequences originating from 179Hg was corrected for in the spectra. By means of the delayed coincidence with the 6.29 MeV a decay of 179Hg (TI/2 = 1.09 s), the 3' rays associated with the In channel could be separated as well with a purity of more than 99%. The response of the 3'-detector arrangement was determined with sources of 152Eu, 207Bi, 60Co and 24Na with 3, lines between 122 keV and 2754 keV while the known energy calibration of the crystal-ball segments with well-established points at 4.4, 12.7 and 15.1 MeV
>
..... lnt
10 2
1o' J
'°r I
o~ 10 2
,~i. ......
C.9 10'
" .:- .~.
10 0
. . . . ..
0
2
.
.
/.
E /
.
.
.
6 8 MeV
10
Fig. 2. Raw 3" transition-energy spectra of individual 3' rays for the ~ channel and for the In channel as observed in the 15 Nal detectors of the crystal-ball section in the reaction 9°Zr (358 MeV) + 9°Zr. The bin size varies from 20 keV (low energies) to 500 keV (high energies). The spectra are compared with the results of model calculations using two different El "r strength functions (dashed: giant dipole resonance, dotted: single-particle E1 strength of 0.05 WU). The calculated spectra are folded with the detector response. 40
27 February 1986
from (p, p') on 12C has been used for the higher energies. Fig. 2 shows the spectra o f the individual 3, rays observed in the 15 NaI detectors o f the crystal-ball section. If compared to the spectrum for the In channel the spectrum associated with the 3' channel has a much larger relative intensity at high energies. This spectrum extends to 10 MeV while the initial excitation energy of the compound system is 21 MeV. If all radiative fusion events would be due to a direct process with one high-energetic 3' ray leading to states near the yrast line, more than 40 events above 10 MeV should have been observed. The angular distributions of the 3' rays were registrated with the 15 crystal-ball segments. Neglecting possible P4 terms we have determined the A 2 coefficients in the expansion W(0) = 1 + A 2 P2(cosO).The corresponding ratio W(0°)/W(90 °) = 1.53-+ 0.13 for the In channel is similar to the values found for different systems emitting several neutrons [12]. It is dominated by the anisotropy of stretched E2 transitions. For the 7 channel, a more isotropic angular distribution [W(O°)/W(90 °) = 1.0 -+ 0.3] is observed. The average 3' multiplicity was determined from the number of 3' detectors firing simultaneously by use of the calibrated response of the detector arrangement. The values are 7.7 +- 1.0 for the In channel and 11.5 + 1.5 for the 3' channel, respectively. The value o f 7.7 may be explained by about 4 statistical E1 3' rays [12], which carry away only a small amount of angular momentum and an yrast cascade of about 3.7 E2 transitions. From systematics of lighter strongly-deformed N = 99 isotones the ground-state spin of 179Hg may be assumed to be 7/2. With this value, a mean angular momentum of about 11 fi- may be deduced. For the radiative-fusion process, the statistical 3' cascade is longer in order to carry away the additional excitation energy o f about 13 MeV while the yrast cascade reaches to the 0 + ground state of 180Hg. Therefore the excess of 3.8 3' rays cannot be attributed to a higher average angular momentum for the radiative fusion. For a comparison with the predictions of the statistical model, the estimated energy distribution of the 3, rays connected with the 3' channel and with the In channel were calculated with the Monte Carlo type evaporation code CODEX [13]. In this calculation the evaporation of neutrons, protons and ,v particles as well as fission were included. The fusion cross section
Volume 168B, number 1,2
PIIYSICS LETTERS
and the initial angular-momentum distribution were estimated from experiment [9]. Level densities derived from microscopic calculations [14] were used where pairing correlations are treated in a more realistic way than in our previous calculations [15] using the code HIVAP. The fission barriers were slightly adjusted to reproduce the measured total evaporation-residue cross section [ 15 ]. The E 1 3' strength function f of the giant dipole resonance with the following parametrization has been used: f = (3.31 × 10 - 6 MeV - I ) ( N Z / A )
x E~r/l(E20 -
F2"'2"-d+ E2-~r2l"
The values for the resonance energy (E 0 = 14 MeV) and the width (F = 5 MeV) of the giant resonance are taken from systematics [ 16] and would correspond to a spherical compound nucleus. The strength amounts to the total E1 sum rule. This new calculation does reproduce the measured radiative-fusion cross section [2] which was not the case previously [15]. Also the measured 3' spectra o f both channels agree well with this model calculation. In particular the different slopes o f the spectra above 3 MeV are well reproduced. Two other assumptions for the 3' strength function have been studied: The spectrum estimated with the single-particle E l strength [17] does not reproduce the slope of the measured spectrum (see fig. 2), even if the strength (0.05 Weisskopf units per MeV) is adjusted to reproduce the measured radiative-fusion cross section. As a second possibility we assumed that the 3,-emitting system is strongly deformed with an axis ratio of 2 to 1, corresponding to a splitting o f the resonance with components at 9 and 17 MeV and relative strengths o f 1/3 and 2/3, respectively. In this case the model calculation predicts a cross section for the 3' channel which is 4 times larger than observed while the shape o f the spectrum is nearly unchanged up to 9 MeV. However, similar changes in the calculated cross section could be introduced by e.g. the values of the ground-state masses o f the fusion products which are not known experimentally and therefore were taken from a semiempirical description [18]. Final conclusions about the shape of the 3'-emitting system cannot be drawn before the 3' spectrum has been measured up to higher energies. From our analysis it may be concluded that the high-energy part o f the observed 3, spectra can be ex-
27 February 1986
plained in the framework of the statistical model. The 3' spectrum o f the radiative fusion process clearly shows the enhancement due to the giant dipole resonance. The important role of the giant dipole resonance in the statistical deexcitation process was demonstrated in ref. [19] and discusssed e.g. in ref. [20]. The combination of the velocity filter SHIP with a large 7-ray sum spectrometer and 15 modules o f the Darmstadt-Heidelberg crystal ball made possible the first 7-spectroscopic investigation in a radiative-fusion reaction between massive nuclei. The present experiment did not yield any evidence for a direct process that is accompanied by the emission of one highenergetic 3, ray which immediately cools the compound system down to the vicinity o f the yrast line. The present data are compatible with the statistical model for the deexcitation of the compound nucleus if the E1 3' strength is determined by the giant dipole resonance. This work was supported by Deutsches Bundesministerium ftir Forschung und Technologie.
References [1 ] J.43. Keller, li.-G. Clerc, K.-ll. Schmidt, Y.K. Agarwal, F.P. llessberger, R. Hingmann, G. M/jnzenberg, W. Reisdorf and C.-C. Sahm, Z. Phys. A311 (1983) 243. [2] J.-G. Keller, K.-H. Schmidt, W. Reisdorf, F.P. Hessberger, G. M/inzenberg, H.-G. Clerc and C.-C. Sahm, Proc. Winter Meeting on Nuclear Physics (January 1984, Bormio, Italy) p. 147. [31 Yu.Ts. Oganessian, M. ttussonnois, A.G. Demin, Yu.P. Kharitonov, H. Bruchertseifer, P. Constantinescu, Yu.S. Korotkin, S.P. Tretyakova, V.K. Utyonkov, I.V. Shirokovsky and J. Estevez, Radiochemica Acta 37 (1984) 113. [4] I-1.43.Clerc, C.-C. Sahm, E. Tsch6p, W. Schwab, K.-tt. Schmidt, R.S. Simon, J.43. Keller, W. Reisdorf, F. llessberger, G. Miinzenberg and B. Quint, in: Capture gammaray spectroscopy and related topics - 1984, ed. S. Raman (AIP New York, 1985) p. 636. [5] K.-II. Sehmidt, R.S. Simon, J.43. Keller, F.P. Ilessberger, G. M/jnzenberg, H.-G. Clerc, C.-C. Sahm, U. Gollerthan and W. Schwab, Proc. Winter Meeting on Nuclear Physics (January 1985, Bormio, Italy) p. 321. [6] P. Oblozinsky and R.S. Simon, Nucl. Instrum. Methods 223 (1984) 52. [7] R.S. Simon, J. Phys. (Paris) Coll. 41C (1980) 10. [8] V. Metag, R.D. Fischer, W. K/Jim, R. M/Jhlhans, R. Novotny, D. Habs, U. v. Helmolt, H.W. Iteyng, R. Kroth, D. Pelte, D. Schwalm, W. tlennerici, II.J. Hennrich, G. 41
Volume 1688, number 1,2
[9]
[10]
[11] [12] [ 13 ] [14]
42
PHYSICS LETTERS
Himmele, E. Jaeschke, R. Repnow, W. Wahl, E. Adelberger, A. Lazzarini, R.S. Simon, R. Albracht and B. Kolb, Nucl. Phys. A409 (1983) 331C. J.G. Keller, K.-H. Schmidt, H. Stelzer, W. Reisdorf, Y.K. Agarwal, F.P. tlessberger, G. Miinzenberg, H.-G. Clerc and C.-C. Sahm, Phys. Rev. C29 (1984) 1569. G. Miinzenberg, W. Faust, S. Hofmann, P. Armbruster, K. Giittner and H. Ewaid, Nucl. Instrum. Methods 161 (1979) 65. H.-G. Clerc, H.J. Gehrhardt, L. Richter and K.-H. Schmidt, Nucl. lnstrum. Methods 113 (1973) 235. R.M. Diamond and F.S. Stephens, Annu. Rev. Nucl. Part. Sei. 30 (1980) 85. U. GoUerthan and K.-H. Schmidt, to be published. K.-H. Schmidt, H. Delagrange, J.P. Dufour, N. C~irjan and A. Fleury, Z. Phys. A308 (1982) 215.
27 February 1986
[15] J.-G. Keller, K.-H. Schmidt, F.P. Hessberger, G. Miinzenberg, W. Reisdorf, H.-G. Clerc and C.-C. Sahm, Nucl. Phys., to be published. [16] P. Axel, Phys. Rev. 126 (1962) 671. [17] J.M. Blatt and V.F. Weisskopf, Theoretical nuclear physics (Addison-Wesley, Cambridge, MA., 1953) p. 583. [ 18 ] S. Liran and N. Zeldes, At. Data Nucl. Data Tables 17 (1976) 431. [19] J.O. Newton, B. Herskind, R.M. Diamond, E.L. Dines, J.E. Draper, K.H. Lindenberger, C. Schuck, S. Shih and F.S. Stephens, Phys. Rev. Lett. 46 (1981) 1383. [20] K.A. Shover, Invited Paper, Fifth Intern. Symp. Capture gamma-ray spectroscopy (September 1984, Knoxville) AIP Conf. Proc. No. 125, ed. S. Raman (AIP, New York 1985) p. 660.
PtlYSICS LETTERS
27 February 1986
GAMMA-SPECTROSCOPIC INVESTIGATIONS IN T H E R A D I A T I V E F U S I O N R E A C T I O N 9°Zr + 9 ° Z r K.-H. S C H M I D T , R.S. S I M O N , J.-G. K E L L E R , F.P. H E S S B E R G E R , G. M O N Z E N B E R G , B. Q U I N T Gesell.~chaft fUr Schwertonenforschung. D-6100 Darmstadt, Fed Rep. Germany
H.-G. CLERC, W. SCHWAB, U. G O L L E R T H A N and C.-C. S A H M Instttut fi~r KernptTvsik, Techntsche Ilochschule Darmstadt. D-610[) Darm.~tadt, Fed Rep. Germany
Received 3 July 1985
The y rays emitted in the radiative fusion reaction ~°Zr+ ~Zr --, lS°Hg+ xy were measured. No indication was found for a specific direct capture process associated with a high-energy -f ray. ]'he shape of the observed y spectrum is compatible with a statistical deexcitation of the compound nucleus.
Recently the radiative fusion of massive nuclei could be observed in 90Zr-induced reactions with 90Zr ' 89y, 92Zr and 94Mo [1,2] and for the system 208pb + 50Ti [3]. In these experiments the radiativefusion product (e.g. 180Hg) was identified by its ground-state a decay. In this letter we report on a spectroscopic investigation of the system 9°Zr + 90Zr which provides first insight into the dynamics of the radiative fusion process. Preliminary results of the present experiment can be found in refs. [4,5]. A 90Zr target of 20 gg/cm 2 was irradiated with a 358 MeV 90Zr beam from the UNILAC heavy-ion accelerator at GSI Darmstadt. The target material had been deposited on a 130/ag/cm 2 Au backing at the
Nal
SHIP
TOF
AE E,x
+
H 13
Beam stop
Fig. 1. Schematical drawing of the experimental set-up. The arrangement of the Nal detectors is shown in an additional cut vertical to the beam axis.
GSI off-line mass separator. The experimental set-up is shown schematically in fig. 1. The 7 rays from the target were observed in a combined arrangement o f a cylindrical NaI sum crystal [6] with one of the six segments removed, and a section of the DarmstadtHeidelberg crystal ball [7,8], consisting of 15 NaI detectors each covering about 0.6% of 47r. The 15 crystal-ball detectors served to measure the spectral composition and the angular distribution of the 3' rays. All NaI detectors together which covered about 90% of 47r were used to determine the 7 sum energy and the 7-ray multiplicity. •~.t the beam energy chosen, the cross section of the radiative fusion amounts to about 40/lb [2] and represents less than one percent of the total fusion cross section, evaporation of one neutron or one proton as well as fission being the most prominent decay modes of the compound system [9]. The separation of the tiny fraction of 7 radiation originating from the radiative fusion was performed with the help of a two-step delayed coincidence. The fusion products (radiative-fusion products and evaporation residues) were separated from the primary beam and transported to a detector telescope by the velocity f'dter SHIP [ 10]. The fusion products could be distinguished from scattered projectiles pass39
Volume 168B, number 1,2
PItYSICS LETTERS
ing through SHIP by analyzing their time-of-flight, their energy loss as obtained from the secondaryelectron detector [1 1], and their energy. A 50 ns time window on the time distances between the detection of a 3' ray in the NaI detector arrangement around the target and the registration of a heavy recoil behind SHIP ensured a pure spectrum of')' rays emitted by the fusion products. In a second step, the evaporation residues implanted into the position-sensitive detector array were individually identified by their subsequent c~ decay. Due to the position resolution of about 0.3 mm FWHM, time correlations even for the c~ decay o f 180Hg with its rather long halflife of 2.9 s could be established. A 8% portion o f random sequences originating from 179Hg was corrected for in the spectra. By means of the delayed coincidence with the 6.29 MeV a decay of 179Hg (TI/2 = 1.09 s), the 3' rays associated with the In channel could be separated as well with a purity of more than 99%. The response of the 3'-detector arrangement was determined with sources of 152Eu, 207Bi, 60Co and 24Na with 3, lines between 122 keV and 2754 keV while the known energy calibration of the crystal-ball segments with well-established points at 4.4, 12.7 and 15.1 MeV
>
..... lnt
10 2
1o' J
'°r I
o~ 10 2
,~i. ......
C.9 10'
" .:- .~.
10 0
. . . . ..
0
2
.
.
/.
E /
.
.
.
6 8 MeV
10
Fig. 2. Raw 3" transition-energy spectra of individual 3' rays for the ~ channel and for the In channel as observed in the 15 Nal detectors of the crystal-ball section in the reaction 9°Zr (358 MeV) + 9°Zr. The bin size varies from 20 keV (low energies) to 500 keV (high energies). The spectra are compared with the results of model calculations using two different El "r strength functions (dashed: giant dipole resonance, dotted: single-particle E1 strength of 0.05 WU). The calculated spectra are folded with the detector response. 40
27 February 1986
from (p, p') on 12C has been used for the higher energies. Fig. 2 shows the spectra o f the individual 3, rays observed in the 15 NaI detectors o f the crystal-ball section. If compared to the spectrum for the In channel the spectrum associated with the 3' channel has a much larger relative intensity at high energies. This spectrum extends to 10 MeV while the initial excitation energy of the compound system is 21 MeV. If all radiative fusion events would be due to a direct process with one high-energetic 3' ray leading to states near the yrast line, more than 40 events above 10 MeV should have been observed. The angular distributions of the 3' rays were registrated with the 15 crystal-ball segments. Neglecting possible P4 terms we have determined the A 2 coefficients in the expansion W(0) = 1 + A 2 P2(cosO).The corresponding ratio W(0°)/W(90 °) = 1.53-+ 0.13 for the In channel is similar to the values found for different systems emitting several neutrons [12]. It is dominated by the anisotropy of stretched E2 transitions. For the 7 channel, a more isotropic angular distribution [W(O°)/W(90 °) = 1.0 -+ 0.3] is observed. The average 3' multiplicity was determined from the number of 3' detectors firing simultaneously by use of the calibrated response of the detector arrangement. The values are 7.7 +- 1.0 for the In channel and 11.5 + 1.5 for the 3' channel, respectively. The value o f 7.7 may be explained by about 4 statistical E1 3' rays [12], which carry away only a small amount of angular momentum and an yrast cascade of about 3.7 E2 transitions. From systematics of lighter strongly-deformed N = 99 isotones the ground-state spin of 179Hg may be assumed to be 7/2. With this value, a mean angular momentum of about 11 fi- may be deduced. For the radiative-fusion process, the statistical 3' cascade is longer in order to carry away the additional excitation energy o f about 13 MeV while the yrast cascade reaches to the 0 + ground state of 180Hg. Therefore the excess of 3.8 3' rays cannot be attributed to a higher average angular momentum for the radiative fusion. For a comparison with the predictions of the statistical model, the estimated energy distribution of the 3, rays connected with the 3' channel and with the In channel were calculated with the Monte Carlo type evaporation code CODEX [13]. In this calculation the evaporation of neutrons, protons and ,v particles as well as fission were included. The fusion cross section
Volume 168B, number 1,2
PIIYSICS LETTERS
and the initial angular-momentum distribution were estimated from experiment [9]. Level densities derived from microscopic calculations [14] were used where pairing correlations are treated in a more realistic way than in our previous calculations [15] using the code HIVAP. The fission barriers were slightly adjusted to reproduce the measured total evaporation-residue cross section [ 15 ]. The E 1 3' strength function f of the giant dipole resonance with the following parametrization has been used: f = (3.31 × 10 - 6 MeV - I ) ( N Z / A )
x E~r/l(E20 -
F2"'2"-d+ E2-~r2l"
The values for the resonance energy (E 0 = 14 MeV) and the width (F = 5 MeV) of the giant resonance are taken from systematics [ 16] and would correspond to a spherical compound nucleus. The strength amounts to the total E1 sum rule. This new calculation does reproduce the measured radiative-fusion cross section [2] which was not the case previously [15]. Also the measured 3' spectra o f both channels agree well with this model calculation. In particular the different slopes o f the spectra above 3 MeV are well reproduced. Two other assumptions for the 3' strength function have been studied: The spectrum estimated with the single-particle E l strength [17] does not reproduce the slope of the measured spectrum (see fig. 2), even if the strength (0.05 Weisskopf units per MeV) is adjusted to reproduce the measured radiative-fusion cross section. As a second possibility we assumed that the 3,-emitting system is strongly deformed with an axis ratio of 2 to 1, corresponding to a splitting o f the resonance with components at 9 and 17 MeV and relative strengths o f 1/3 and 2/3, respectively. In this case the model calculation predicts a cross section for the 3' channel which is 4 times larger than observed while the shape o f the spectrum is nearly unchanged up to 9 MeV. However, similar changes in the calculated cross section could be introduced by e.g. the values of the ground-state masses o f the fusion products which are not known experimentally and therefore were taken from a semiempirical description [18]. Final conclusions about the shape of the 3'-emitting system cannot be drawn before the 3' spectrum has been measured up to higher energies. From our analysis it may be concluded that the high-energy part o f the observed 3, spectra can be ex-
27 February 1986
plained in the framework of the statistical model. The 3' spectrum o f the radiative fusion process clearly shows the enhancement due to the giant dipole resonance. The important role of the giant dipole resonance in the statistical deexcitation process was demonstrated in ref. [19] and discusssed e.g. in ref. [20]. The combination of the velocity filter SHIP with a large 7-ray sum spectrometer and 15 modules o f the Darmstadt-Heidelberg crystal ball made possible the first 7-spectroscopic investigation in a radiative-fusion reaction between massive nuclei. The present experiment did not yield any evidence for a direct process that is accompanied by the emission of one highenergetic 3, ray which immediately cools the compound system down to the vicinity o f the yrast line. The present data are compatible with the statistical model for the deexcitation of the compound nucleus if the E1 3' strength is determined by the giant dipole resonance. This work was supported by Deutsches Bundesministerium ftir Forschung und Technologie.
References [1 ] J.43. Keller, li.-G. Clerc, K.-ll. Schmidt, Y.K. Agarwal, F.P. llessberger, R. Hingmann, G. M/jnzenberg, W. Reisdorf and C.-C. Sahm, Z. Phys. A311 (1983) 243. [2] J.-G. Keller, K.-H. Schmidt, W. Reisdorf, F.P. Hessberger, G. M/inzenberg, H.-G. Clerc and C.-C. Sahm, Proc. Winter Meeting on Nuclear Physics (January 1984, Bormio, Italy) p. 147. [31 Yu.Ts. Oganessian, M. ttussonnois, A.G. Demin, Yu.P. Kharitonov, H. Bruchertseifer, P. Constantinescu, Yu.S. Korotkin, S.P. Tretyakova, V.K. Utyonkov, I.V. Shirokovsky and J. Estevez, Radiochemica Acta 37 (1984) 113. [4] I-1.43.Clerc, C.-C. Sahm, E. Tsch6p, W. Schwab, K.-tt. Schmidt, R.S. Simon, J.43. Keller, W. Reisdorf, F. llessberger, G. Miinzenberg and B. Quint, in: Capture gammaray spectroscopy and related topics - 1984, ed. S. Raman (AIP New York, 1985) p. 636. [5] K.-II. Sehmidt, R.S. Simon, J.43. Keller, F.P. Ilessberger, G. M/jnzenberg, H.-G. Clerc, C.-C. Sahm, U. Gollerthan and W. Schwab, Proc. Winter Meeting on Nuclear Physics (January 1985, Bormio, Italy) p. 321. [6] P. Oblozinsky and R.S. Simon, Nucl. Instrum. Methods 223 (1984) 52. [7] R.S. Simon, J. Phys. (Paris) Coll. 41C (1980) 10. [8] V. Metag, R.D. Fischer, W. K/Jim, R. M/Jhlhans, R. Novotny, D. Habs, U. v. Helmolt, H.W. Iteyng, R. Kroth, D. Pelte, D. Schwalm, W. tlennerici, II.J. Hennrich, G. 41
Volume 1688, number 1,2
[9]
[10]
[11] [12] [ 13 ] [14]
42
PHYSICS LETTERS
Himmele, E. Jaeschke, R. Repnow, W. Wahl, E. Adelberger, A. Lazzarini, R.S. Simon, R. Albracht and B. Kolb, Nucl. Phys. A409 (1983) 331C. J.G. Keller, K.-H. Schmidt, H. Stelzer, W. Reisdorf, Y.K. Agarwal, F.P. tlessberger, G. Miinzenberg, H.-G. Clerc and C.-C. Sahm, Phys. Rev. C29 (1984) 1569. G. Miinzenberg, W. Faust, S. Hofmann, P. Armbruster, K. Giittner and H. Ewaid, Nucl. Instrum. Methods 161 (1979) 65. H.-G. Clerc, H.J. Gehrhardt, L. Richter and K.-H. Schmidt, Nucl. lnstrum. Methods 113 (1973) 235. R.M. Diamond and F.S. Stephens, Annu. Rev. Nucl. Part. Sei. 30 (1980) 85. U. GoUerthan and K.-H. Schmidt, to be published. K.-H. Schmidt, H. Delagrange, J.P. Dufour, N. C~irjan and A. Fleury, Z. Phys. A308 (1982) 215.
27 February 1986
[15] J.-G. Keller, K.-H. Schmidt, F.P. Hessberger, G. Miinzenberg, W. Reisdorf, H.-G. Clerc and C.-C. Sahm, Nucl. Phys., to be published. [16] P. Axel, Phys. Rev. 126 (1962) 671. [17] J.M. Blatt and V.F. Weisskopf, Theoretical nuclear physics (Addison-Wesley, Cambridge, MA., 1953) p. 583. [ 18 ] S. Liran and N. Zeldes, At. Data Nucl. Data Tables 17 (1976) 431. [19] J.O. Newton, B. Herskind, R.M. Diamond, E.L. Dines, J.E. Draper, K.H. Lindenberger, C. Schuck, S. Shih and F.S. Stephens, Phys. Rev. Lett. 46 (1981) 1383. [20] K.A. Shover, Invited Paper, Fifth Intern. Symp. Capture gamma-ray spectroscopy (September 1984, Knoxville) AIP Conf. Proc. No. 125, ed. S. Raman (AIP, New York 1985) p. 660.