FISSION VAMOS

Transcription

1 FISSION VAMOS 239 Np E x ~ 7.5 MeV F. Farget, O. Delaune, X. Derkx, C. Golabek, T. Roger, A. Navin, M. Rejmund, C. Rodriguez-Tajes, C. Schmitt GANIL, France K.-H. Schmidt, B. Jurado CENBG, France D. Doré, M. Delphine de Salsac SPhN, France J. Benlliure, M. Caamaño, E. Casarejos, D. Cortina, B. Fernandez-Dominguez, D. Ramos USC, Spain L. Audouin, C.-O. Bacri, IPNO, France A. Heinz Chalmers U., Sweden F. Farget Fission 2017 Chamrousse

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3 FISSION VAMOS Surrogate reactions : a powerful tool for fission investigation 1974 : fission probabilities (talk of P. Marini) 1996 : Coulomb fission in inverse kinematics with radioactive beams (K.-H. Schmidt et al.) 2008 : multi-nucleon transfer induced fission in inverse kinematics 2010 : multi-nucleon transfer induced JAEA (talk of N. Katsuhisa) SOFIA experiments (talk of L. Audouin, ) + Access to actinides that are not possible via irradiation technique + Broad range of excitation energy + Inverse kinematics : improved resolution in the fission fragment ID

4 multi-nucleon transfer using inverse kinematics transfer recoil Θ g lab ~30 carbon target light fission fragment uranium beam heavy fission fragment fissioning system VAMOS SPIDER ΔE-E,θ Bρ-ToF-ΔE-E

5 Multi-nucleon transfer SPIDER C. Rodriguez-Tajes et al., PRC (2014)

6 Identification of fission fragments Bρ ~ A/qV ToF ~ V ΔE ~ Z 2 /V 2 E ~ AV 2

7 Identification of fission fragments Bρ ~ A/qV ToF ~ V ΔE ~ Z2/V2 E ~ AV2

8 Isotopic distribution of fission fragments 238 U E x ~ 7.4 MeV 239 Np E x ~ 7.5 MeV 240 Pu E x ~ 10.7 MeV 244 Cm E x ~ 23 MeV 250 Cf E x = 46 D. Ramos PhD thesis, USC Spain

9 Mass distributions 238U 238U 240Pu 239Np D. Ramos PhD thesis, USC Spain 244Cm 250Cf

10 Neutron excess 240 Pu

11 Neutron excess Y(Z) U 238 U 1.65 <N>/Z Y(Z) Pu 240 Pu 1.65 <N>/Z Z Z Y(Z) Np 1.65 <N>/Z Y(Z) Cm Np 250 Cf 1.65 <N>/Z Z Z

12 Total Neutron multiplicity h i(z) =N fiss (hni Z + hni Zfiss Z) D. Ramos PhD thesis, USC Spain

13 average mass 1.3 is restricted 1.2 to mass 0.8 units, considering locity was estimated better than 2%. The resulting the first small 1.5 possible variations on angular1 momentum and 35 and second momentum of the fission velocity distribution The fission velocity Scission thereflecting limited fragment excitation important energy. Z=45 properties characterization It is then possible FIG. 4. (Color online) Upper pane V (A, Z) and V (A, Z) are displayed for each fragment Z=52 Z=59 to associate to both fission-fragment atomic number the average 0.9 of the scission configuration, such as deformation and <V >(Z) as a function of the fr isotopicaly identified, in figures 1 and 2, for 240 Pu and Z=38 FIG. 5. (Color masses of the nascent fragments. fission velocities Due <V to the momentum produced in the fission of Cf. It > and <V 1 2 > from equation 1, and 0.8 the fragments p Cf fissioning systems, respectively prescription of the fission kinematic The average velocity conservation, <V >(Z) for the eachratio deduce atomicof number Z and its average equal standard to thefrom deviation reverse are defined ratio the the two 1.5 average fragment 1.3initial velocities masses 1.1 is <A 1 > and <A 2 > their atomic nu average standard deviation of the fi velocity using the momentum as: of the initial measurement andz=46 mass conservation: masses: : blue open and equation 1 and text for to the details. estimat P Y (A,Z)V (Z,A) V 1 = A Z=39 Z=53 2 A <V >(Z) = P V 2 A 1.3 <A <V >= A 2 > open and full t 0.9 FS (4) P Y (A,Z) <V > Z= A 1.5 <A1.3 (1) 2 >= A FS 1.1 <A (5) fragments. The 1 > of the liquid-dr A < V > (Z) = Y (A,Z) Z=47 V (Z,A) P Z=40 Z=54 The resulting Y (A,Z) 1.4 average 1.2 neutron 1 excess of the scission A fragments is displayed in blue open circles in figures 5 These exper They are displayed in figure 3 and 4 for both and sys-tems. The average velocity <V >(Z) is compared defined to as <A>(Z) Z culations [14], for both fissioning systems The neutron excess Z =< Neutron N>/Z, number Nor charge polarisation triangles, for t the liquid-drop model prediction of the fission kinematics [11], with constant deformation and neck parameters. emphasized structure compared to the simple < A > tron excess of of the fission fragments, is chosen, as it shows a more ments, respect FIG. 1. Mean values of the fission velocity spectra as a function of the neutron number of the isotopes produced the Following this prescription, the total kinetic energy(z) TKEmass information, which increasing steadily with well reproduce at scission is given by: Z. The error bars displayed comprise the uncertainty on fission of 240 viations with the fission velocity Pu, for measurement each atomic number. and The on error the bars fissioningnucleus mass, as the statistical source of uncertainty. It pound nucleu show TKE =1.44 Z the second momentum of the velocity spectra. for the calcula 1Z 2 (2) D is compared to the post-evaporation neutron-excess of 45 MeV, and the fragments, displayed in black full circles, deduced tions of the si where D is the distance between the charged centroids from the average post-evaporation mass measured in the disapeared [16 of both fragments A 1 and A 2, and may be written experiment: as a to previous work [5], a better agreement with the theoretical expectation is reached, as the correction for the number of the lar steady incr function of the fragment deformation parameters 1 and 2 and d the distance between them: P energy loss in the target is now taken into account. In D = r 0 (A 11/3 ( )+A 21/3 (1 + 2 figure 3, <A>(Z) some deviations = around PA AY (A, Z) slope that will Z 52 and Z 42 with A 3 2 )) + d, (3) respect to the liquid-drop model can Y (A, be observed. Z) (6) calculations ca They value of the n The neutron excess of the scission fragments of 240 Pu function of th are the FISSION signature 2017 of Chamrousse the presence of shell e ects in the

14 Evolution with Excitation energy D. Ramos PhD thesis, USC Spain E x (MeV)

15 Conclusions A powerful experiment : -Several fissioning systems in one experiment -Complete isotopic distribution -Neutron multiplicity as a function of split -Kinematic reconstruction : TKE and scission properties -A challenge for theoretical description!! Perspectives : -multi-nucleon transfer and fusion is the only possibility to study actinides beyond U -HiE-ISOLDE, GANIL (S3, SPIRAL1) are good candidates to pursue exciting programmes based on inverse kinematics -High-Energy laboratories (FAIR, RIKEN,..) equipped with powerful spectrometers present promising possibilities

16 Results: Fission Channels Super Long : Symmetric channel, large deformation Standard I : Asymmetric channel, Z~52, spherical heavy fragment, compact scission configuration Standard II : Asymmetric channel, Z~55, deformed heavy fragment Ych (%) A fiss σ(z)ch Zch A fiss SL decreases up to A~240 SI dominates over SII SI : Z~52, SII: Z~55 (A<244) Larger width of SII than SI (random neck rupture) A fiss C. Böckstiegel et al. NPA 802 (2008) 12 27

17 Average neutron scission Average neutron scission 17

18 Moment angulaire induit dans les réactions de transfert Expérience E653, décembre 2014 C. Rodriguez, GANIL Ampleur et nature du moment angulaire 44

19 Y(Z) Cf <N>/Z Z 1.4