Ackermann, D.

Andel, B.

Antalic, S.

Droese, C.

Even, J.

Hessberger, F.

Kalaninova, Z.

Laatiaoui, M.

Piot, J.

Vostinar, M.

GSI Repository

Total kinetic energy release in spontaneous fission of 255,256,258Rf∗F.P. Heßberger†1,2, D. Ackermann1, B. Andel3, S. Antalic3, C. Droese2,4, J. Even2, Z. Kalaninova´3, M.Laatiaoui2, J. Piot5, and M. Vostinar51GSI, Darmstadt, Germany; 2HIM, Mainz, Germany; 3Comenius University, Bratislava, Slovakia; 4Ernst-Moritz-ArndtUniversita¨t, Greifswald, Germany; 5GANIL, Caen, FranceSpontaneous fission (sf) is a major radioactive decaymode in the region of transuranium elements. Its studyprovides valuable information on the stability of heaviestnuclei. Therefore understanding the sf process is decisivefor the quest of the upper end of the periodic table.Main experimental observables are the partial sf half-lives,the hindrance factors for nuclei with odd proton and/or neu-tron numbers, the total kinetic energy release (<TKE>) aswell as the A - and Z - distribution of the sf fragments, andthe neutron muliplicities.The commonly used technique for decay studies of heaviestnuclei, i.e. implantation of the evaporation residues (ER)into a Si detector arrangement (’stop detector’) after in-flight separation from the projectile beam, is not reallysuited for measuring <TKE> and/or mass distributions.Firstly, recombination of charge-carriers will occur due tothe high ionization density of the sf fragments. Thus, thereis no linear dependence between the energy and the regis-tered pulse-height. Specific calibration procedures (see e.g.[1]) have to be applied. Secondly, the implantation depthsof the ER is smaller than the range of the sf fragments.Thus, with some probability, one of them will escape thedetector, depositing only part of its energy in it. So, themeasured energy value will not represent the full energyrelease in the sf process, and consequently the peak of theenergy distribution does not represent the <TKE>. Onepossibility to solve that problem is to register the escap-ing fragment in a detector box sourrounding the implanta-tion detector [2]. Yet, it requires a correction of the energylosses of the escaping fragment in the deadlayers of the im-plantation detecor and the box detector, which introducessome uncertainty.Alternatively the peak value of the energy distributionrecorded in the stop detector can be used as a measure for<TKE>. This procedure requires a reference value and inaddition the same mean implantation depths for the nucleiunder investigation, as the energy release of the escapingfragment depends on the length of the flight-path throughthe detector, hence on the implantation depth [2].As a test case we measured energy distributions for sf prod-ucts of 255,256,258Rf. The nuclei were produced by thereactions 207Pb(50Ti,2n)255Rf, 208Pb(50Ti,2n)256Rf, and209Bi(50Ti,1n)258Db EC→ 258Rf; mean kinetic energies forthe ERs from these reactions were equal within ±2.5%,∗Work supported by GSI(UNILAC)/HI Mainz/European CommunityFP7 - Capacities, contract ENSAR contract No. 262010/French-GermanCollaboration agreement INP2 P3-DSM/CEA and GSI/Slovak GrantAgency VEGA, contract No. 1/0576/13† f.p.hessberger@gsi.deand therefore also, in first order, the implantation depths.The results are compared in fig. 1, where besides the mea-sured mean values (Emean) the widths of the energy distri-butions are given. For 258Rf a<TKE> value of 197.6±1.1MeV is reported [3]. Using it as a reference value one ob-tains <TKE>/Emean = 1.033 and hence <TKE>(256Rf)= 197.0±1.2 MeV, and<TKE>(255Rf) = 198.8±1.0 MeV.This (preliminary) value is comparable for 256Rf with thatgiven in [3] (198.9±4.4 MeV), but more precise; that for255Rf is somewhat higher than the value<TKE> = 194±2MeV [4], obtained using the method from [2]. An improve-ment of the results and also information on the influence ofthe little energy variations of the ER may be expected frommodelling the distributions by, e.g. GEANT simulations.0153045 256RfE = 190.7 7 MeVFWHM = 45.6  1.9 MeV258RfE = 191.3 5 MeVFWHM = 45.5  1.4 MeV counts / 4 MeV0306090 255RfE = 192.5 5 MeVFWHM = 44.3  1.9 MeV  counts / 4 MeV50 75 100 125 150 175 200 225 250 275 3000306090 counts / 4 MeVE / MeVFigure 1: Energy distributions of sf events of 255,256,258Rfmeasured with the stop detector of SHIP.References[1] S.B. Kaufman et al., NIM 115, 47 (1974)[2] S. Hofmann et al., Eur. Phys. J. A 32, 251 (2007)[3] J.F. Wild et al., J. of All. and Comp. 213/214, 86 (1994)[4] S. Antalic et al., subm. to Eur. Phys. J. A (2014)GSI SCIENTIFIC REPORT 2014 MU-NUSTAR-SHE-P-01DOI:10.15120/GR-2015-1-MU-NUSTAR-SHE-P-01 165

Total kinetic energy release in spontaneous fission of $^{255,256,258}$Rf

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Total kinetic energy release in spontaneous fission of $^{255,256,258}$ Rf

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Total kinetic energy release in spontaneous fission of 255,256,258^{255,256,258}255,256,258Rf

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Total kinetic energy release in spontaneous fission of $^{255,256,258}$ Rf