Isotopic distribution of fission fragments in multi-nucleon transfer reactions in inverse kinematics with VAMOS F. Rejmund, M. Caamaño, X. Derkx, O. Delaune,

Présentation au sujet: "Isotopic distribution of fission fragments in multi-nucleon transfer reactions in inverse kinematics with VAMOS F. Rejmund, M. Caamaño, X. Derkx, O. Delaune,"— Transcription de la présentation:

1 Isotopic distribution of fission fragments in multi-nucleon transfer reactions in inverse kinematics with VAMOS F. Rejmund, M. Caamaño, X. Derkx, O. Delaune, C. Golabek, T. Roger, A. Navin, M. Rejmund, C. Schmitt, A. Shrivastava GANIL, France G. Barreau, B. Jurado CENBG, France K.-H. Schmidt GSI, Germany B. Fernandez Liverpool Univ., UK D. Doré, S. Panebianco SPhN, France J. Benlliure, E. Casarejos, USC, Spain L. Audouin, C.-O. Bacri, IPNO, France L. Gaudefroy, J. Taieb CEA DIF, France Ministère De l’Enseignement et de la Recherche 2 actions 2 ans post-doc 9 mois post-doc 1/2 thèse 1 thèse flêchée

2 Principle of the experiment
Multi-nucleon transfer induced fission: systematic of fissioning systems Inverse kinematics: complete distribution of the fission fragments Spectrometer: isotopic identification of the fission fragments 238U MeV/u transfer recoil glab~30° fissioning system U beam heavy fission fragment light fission fragment C target transfer - fission ~ 100 mbarn Angle de grazing ~35° fusion - fission ~ 1000 mbarn transfer • U, Np, Pu, Am, Cm • different E* fission • A: • Z: • q: • E: MeV/u D.C. Biswas et al. PRC 56 (1997) 1926 inverse kinematics - restricted angular distribution<25°

3 • β, γ •KE •Z •M •M/q Experimental set-up at VAMOS • Path • Bρ
acceptance: • 14 deg Θ • ~ 3 deg Φ • 10 % Bρ ionization chamber 21 Si detectors drift chamber SeD drift chamber Eres at 20 deg dE X,Y ToF X,Y reconstruction • Path • Bρ • Θlab, Φlab VAMOS spectrometer at GANIL. very large acceptance of ~14 deg, and 10% in momentum. be rotated in a specific angular region. description VAMOS rotated 20 deg to allow the detection either of the light or the heavy fragment. whole fragment momentum distribution. different settings scan this region of the fission kinematics. M. Rejmund • β, γ 20 deg Aside E, dE, recoil angle SPIDER •KE •Z •M •M/q EXOGAM 238U beam

4 Identification of the fissioning system with SPIDER
65 µm Si dE 1 mm Si E target-like recoil ∆Θ ~ 1deg ∆E* ~ 2 MeV Wide systematic of actinides High population of the 2p channel No isotopic identification The reconstruction of the events split between the transfer reaction and the fission two annular silicon detectors measure the energy loss and total energy as close to each other as it was possible allowed the fission fragments to pass through their inner hole reconstruction of the binary transfer reaction deduced the fissioning system and E* figure Different channels can be estimated from the Qreac 238U (inelastic) and few % 237U (1n) 239Np (1p) and few % of 240Np (1p1n) ~ 70% of 240Pu (2p) and ~ 30% of 241Pu (2p1n) ~ 60% 243Am (3p2n) and ~ 40% of 244Am (3p3n) Eje Rec Q(MeV) (mb) 13C 237U 11B 239Np 10B 240Np 10Be 240Pu 9Be Pu 6Li 244Am

5 fission after n emission
Fission probability 2nd fission : fission after n emission (*) 238U(α,α’)f Burke et al., Phys. Rev. C 73, (*) ENDF Below fission barrier ! ! ! Preliminary results ! ! ! 1st chance 2nd chance

6 Fragments range from Z ≈ 30 to Z ≈ 60 in an energy range of 600 MeV
Identification of fission fragments: Z dE ∝ (qeff)2/β2 f(β) qeff ∝ βZ^1/3 + qshift We can have a clearer idea with these figures. As we saw before, the fragment Z is obtained with the measured E and dE. Here we see the relation between both, and how clear the different lines, corresponding to different Z appear. At low energies we can observe the effect of the Bragg peak, and the signal of particles that stop before reaching the last detector. A dedicated formula can be found to deduced Z with a precision enough to identified charges from 36 to 59. ∆Z/Z ≈ 1.5 ·10-2 Fragments range from Z ≈ 30 to Z ≈ 60 in an energy range of 600 MeV

7 Fragment distribution from A ≈ 90 à A ≈ 150
Isotopic resolution of fission fragments with VAMOS: A, A/q A = E/(γ-1) A/q = Bρ/(βγ) Here we see the mass versus mass over charge calculated as we saw previously. The blops correspond to different masses and different charge states. Each line correspond to a fixed charge state, so if we select one of this lines, we project on M/Q and multiply by the Q as integer, we obtained a mass identification with such accuracy between mass 90 to 140. The Z and mass identification revealed more than 300 fission fragments detected in VAMOS. Fragment distribution from A ≈ 90 à A ≈ 150 ∆A/A ≈ 0.6·10-2

8 Identification non ambigue en A, Q et Z
Calibration of the identification with EXOGAM EXOGAM Z=44 Ru M= Ru Identification non ambigue en A, Q et Z

9 Velocity of fission fragments

10 Fusion-inudced and transfer-induced fission
E*~ 45 MeV Minor shell effect E*~ few MeV Shell effects dominants

11 Isotopic yields for different transfer channel
Isotopic identification (mass and charge) and kinetic energy of fission fragments over the entire fragment production is done for the first time.

12 Perspectives  : Repeat the experiment  identification isotopique des actinides  neutrons en coïncidence – SPhN  Longer term: 1. Enlarge stematic  other targets (more complex processes)  Other beams Th beam  Radioactive actinide beams produced in SPIRAL2 target, HIE Isolde 2. FAIR This is so far the status of the analysis. - The isotopic identification and kinematics reconstruction will be done in Spider to finish with the complete characterizatio of the fissioning system - In Vamos we will perform the normalization of the data ensamble to calculate systematic fission cross sections for the different systems. But what is already very important: We already proved for the first time that the whole identification of fission fragments, this is mass and charge, along with their energy and angular distribution is experimentally possible. And it is done.

13 HiE ISOLDE: an opportunity for fissionists
10 MeV/u actinide beams Already available: Rn, 10^3-10^8 pps Fr, 10^5-10^9 pps Ra 10^4-10^8 pps Possibility to extend to other actinides (Th,U,…) Simple set-up to measure precisely element yields as a function of excitation energy IC,E,ToF D Ac p telescope

14 Additional diapositives

15 Single particle and vibrational states in 133Sn A. Navin, M
Single particle and vibrational states in 133Sn A. Navin, M. Rejmund et al.,

16 RDDS lifetime measurement after fusion fission A. Goergen et al.,
7 x 90° 4 x 135° focus on nuclei “in the valley” near Z  46 (where data is scarce) obtain lifetimes in >50 isotopes cover a wide range of lifetimes 134Te 18° Q 12C Q 238U, 6.15 MeV/u v2 D v1 116Pd Mg nuclear shapes in the transitional region are very complex transition from deformed (Zr) to spherical (Sn) transition from prolate to oblate along isotopic chain triaxial shapes: rigid or gamma soft ? sensitive test for configuration mixing calculations suitable for approximations, e.g. E(5), IBM B(E2) values are key observables 62Fe RDDS spectra @VAMOS after multi-nucleon transfer in 238U+64Ni obtain consistent data over wide range of isotopes and lifetimes in one experiment extend lifetime data to: higer spin non-yrast states (gamma bands !) more neutron-rich isotopes odd-A nuclei: absolute B(M1) and B(E2) Cologne Plunger at VAMOS (E553)

17 Distributions de masse expérimentales
Mass distribution n Fission: phénomène macroscopique Distribution des fragments fortement influencée par les effets de couche Stabilisation des fragments lourds par les effets de couche dans les nombres de neutron PF1 E,ToF =>M dM/M ~2 A~140

18 Description de la distribution des fragments de fission
Goutte liquide : Fission symmétrique en fragments également déformés Effets de couches: Minima des courbes de potentiel sont modifiés Deformed shell Spherical shell Shell gap à N=86,88,92 ?? Toujours controversé! Taux de fragments de fission impossibles à prédire (AIEA a abandonné l’évaluation des Y(Z,A)

19 Distributions isotopiques (Z,A) expérimentales
Spectromètre (Lohengrin, ILL) Mesure précise de A Mesure de Z avec une chambre à ionisation -Energie cinétique des fragments très basse =>méthode limitée aux fragments légers (pas d’information sur les effets de couche dans les fragments lourds) Spectroscopie  Rapports de branchement, isomères inconnus… Distribution isotopique complète difficile à mesurer Conclusions sur le rôle des neutrons restent incomplètes 238U(n,F) EXFOR Data tables

20 Cinématique inverse: Fission électromagnétique de faisceaux secondaires
distribution E* <E*> ~12 MeV pour tous les pré-actinides K.-H. Schmidt et al., NPA665(2000)221

21 Cinématique inverse : distribution en Z complète
Z distribution TKE distribution Z, N moyen 233U Standard I : Z ~ 52.5 Standard II : Z ~ 55 232Pa AH=ZH+NH ZH/NH=ZC/Ac 228Pa 229Th Charge constante moyenne: Shell gap mouvant ? Influence d’un nombre magique en protons ? Contradiction avec la compréhension générale de la distribution des fragments de fission So what can we learn from this observables? The charge and TKE proved to be very useful. e.m. induced-fission at GSI in inverse kinematics. we will come to this later. three different modes of fission: two assymetric and one symmetric mode. influence of particular neutron and proton shells. recent analisys doubts about this interpretation, importance to the role of the protons, than to the mass. 226Th 220Th Besoin de données en Z,A ! C. Böckstiegel et al. NPA 802 (2008) 12

22 Multi-nucleon transfer reaction
High resolution of the fissioning system Large range of transfer Channels 238U+12C Eje Rec Q(MeV) (mb) 13C 237U 14C 236U 11B 239Np 12B 238Np 13B 237Np 10Be 240Pu 9Be Pu 8Be Pu 11Be 239Pu 7Li 243Am 6Li 244Am 4He 246Cm 6He 244Cm 232Th(12C,8Be) 236U 234U(t,pf) 235U(n,f) 236U(12C,8Be) 240Pu 238Pu(t,pf) 239U(n,f) Cheifetz et al,,1981

23 Transfer-induced fission reactions: wide range of fissioning systems
Neutron-rich actinides : 238U beam, 12C Target Energy range 0-40 MeV

24 Even-odd staggering in odd-Z nuclei
Zero staggering at symmetry: Unpaired nucleon chooses both fragments with equal probability Negative staggering at asymmetry: unpaired nucleon chooses the heaviest fragment S. Steinhaüser, Nucl. Phys. A 634(1998)89 Evidence for the influence of the fission-fragment phase space

25 Seeking for information..
We propose to use multi-nucleon transfer induced fission in inverse kinematics in order to Identify isotopic fission yields in complete fragment distribution Define the fissioning system in excitation energy, mass, charge Over a broad range of neutron-rich actinides Study the structure effects as a function of excitation energy and fissioning nucleus These data would complement GSI data Important results on shell effects and pairing effects are expected !!

26 Advantage of inverse kinematics
High radioactivity : the production of samples for irradiation is difficult (=>systematics in direct kinematics is limited) Combined with a spectrometer isotopic resolution of the full isotopic distribution (light and heavy fragments) in-flight measure of the isotopic distribution (before beta decay) Using transfer reaction to induce fission precise knowledge of the excitation energy

27 It is not a question of Q value Q=M(F1)+M(F2)-M(CN)
Statistical consideration: P(Z1,Z2)  (Z1)(Z2) E (Ze)= (Zo)  Ze Zo Ze Dependence with E* : e-o effect disappears very fast when pairing is still present in binding energy (Ecrit>11MeV)

28 if the nucleus would be a simple liquid drop
Fission process: if the nucleus would be a simple liquid drop Liquid drop model: nucleus described as a drop of charged liquid E = Ev ES Ecb Esym = - A + r02A2/3(1+2) + Z2/(r0A1/3(1+)) + (N-Z)2/A Bohr and Wheeler 1939 Fission barriers at 10% of the Evaluated up-to-date values J.-F. Berger, Ecole Joliot Curie 2006

29 Transfer-induced fission in inverse kinematics@GANIL
recoil 238U 12C heavy FF light FF FF

30 Experimental isotopic distribution (Z,A)
Spectrometer (Lohengrin, ILL) Precise measure of A - Ionisation Chamber ∆E=Z2/v2 -low kinetic energy of fission fragments =>limited to light fragments (no information on shell effects in heavy fragments) Element yield ZH=ZCN-ZL=54 Average proton number constant AH=ZH+NH=140 Average mass constant Theory Influence of neutron number =>Influence of moving neutron shell gap? =>Existence of proton shell gap? J.P. Bocquet, R. Brissot Nucl. Phys. A

31 Fluctuations paire-impaires dans les fragments de fission: une observable de la dissipation
Effet pair-impair global z = Yze- Yzo/(Yze+Yzo) z =40% J.P. Bocquet, R. Brissot Nucl. Phys. A

32 Explication qualtitative des effets pair-imapirs
Fission de noyaux pair: pas de fragment impair sans dissipation MeV Pairing gap 229Th+n 5 Eintr +Ecoll ? saddle scission 23090Th Effet pair-impair : une conséquence de la dissipation dans la descente -25 L’amplitude des effets pair-impairs reflète la probabilité qu’aucune paire soit brisée à la scission

33 Les effets pair-impairs dépendent de la fissilité du système
Global even-odd effect z = Yze- Yzo Comme la répulsion Coulombienne au sein du noyau augmente, la forme au point selle devient de plus en plus compacte Saddle Th Saddle Cm Z2/ A1/3 La descente du point selle au point de scission augmente, comme Ediss, avec la fissilité

34 Les effets pair-impair dépendent de la symétrie
Effets pair-imapirs locaux: déviation d’une distribution Gaussienne Bilan energétique: Q = TKE + TXE TXE = Q - TKE = Edef(Z1) + Edef(Z2) + Eintr Notions de: Fission froide asymétrique, <=>déformation extrême Fission symétrique chaude Pourtant associée à de grandes déformations (modèle de la goutte liquide) Effets pair-impairs non mesurés à la symétrie

35 Systématique sur les effets pair-impair
S. Steinhaüser, PhD Thesis, TU Darmstadt, 1998 Effets pair-impairs constants pour les distributions symétriques Pourtant énergie d’excitation similaire, et fissilité basse =>Effet de l’asymétrie ?

36 Systématique sur l’effet pair-imapirs local
 Yields Z Pour la première fois l’effet pair-impair est observé sur la distribution complète en Z, sur une large systématique de systèmes fissionants Symmetry: Z = 0.5 ZCN Asymmetry: Z = 54

37 Effets pair-impair à la symétrie et à l’asymétrie
Fission e-m en cinématique inverse Accès aux effets pair-impair à la symétrie pour la première fois Effet pair-impair constant à la symétrie forte influence de l’asymétrie sur l’amplitude de l’effet pair-impair p global p local asymmetry p local reachable sym Fission induite par n en cinématique directe -chute du  est provoquée par la chute de  local à l’asymétrie -chute de  avec la fissilité correspond à une perte progressive de l’asymétrie quand le noyau fissionant devient plus lourd F. Rejmund, Seminar on Fission, Corsendonk 2007, Wagemans M. Caamano, Proc. Int. Conf. Fission and Fission Fragment Spectroscopy, Sanibel, Florida, 2008

38 La fission : modèle de la goutte liquide
saddle point energy E* Bf Q scission point deformation brief description of the fission process most extreme scenarios: deformed, heated, and torn appart. evolution through deformation nucleus with a certain E* deform passes over the fission barrier. more and more deformed, energetically more favourable energy is used in collective and intrinsic degrees of freedom, friction and dissipation nucleons are continuously rearranged in two groups, guided by their nuclar structure nuclei are separated with a certain amount of energy, mainly from Coulomb repulsion. experimental: access mainly to the first and last stage Quantities as the fragment mass, charge and the TKE (and also evporated particles) what happened in between. A1,Z1 A2,Z2 TKE, evaporation Afiss, Zfiss,E* E = EV ES ECb Esym = - aA br02A2/3(1+2) cZ2/(r0A1/3(1+)) d(N-Z)2/A

39 Influence de la structure en couche des nucléons
L’état fondamental n’est pas sphérique (si couche in complète) Second minimum dans la PES à grande déformation(fission isomers) Fission asymétrique es favorisée

40 Distribution isotopique avec VAMOS : Z
dE ∝ (qeff)2/β2 f(β) qeff ∝ βZ^1/3 + qshift We can have a clearer idea with these figures. As we saw before, the fragment Z is obtained with the measured E and dE. Here we see the relation between both, and how clear the different lines, corresponding to different Z appear. At low energies we can observe the effect of the Bragg peak, and the signal of particles that stop before reaching the last detector. A dedicated formula can be found to deduced Z with a precision enough to identified charges from 36 to 59. ∆Z/Z ≈ 1.5 ·10-2 fragments identifiés de Z ≈ 36 à Z ≈ 60 dans une gamme d’énergie de 600 MeV

41 Faisceaux secondaires: grande systématique
K.-H. Schmidt et al., NPA665(2000)221

42 Description de la distribution des fragments de fission
La théorie prédit -une barrière double et des isomères de fission -une fission asymétrique Standard I (N=82) et II (N~90) (asymétrie) Standard Superlong (symetrie) Une description précise manque car: -description complexe des paramètres de déformation -interaction nucléon nucléon à déformation extrême inconnue (shell gaps) Wilkins et al. PRC 14 (1976) 1832

43 identification isotopique (masse et charge) et mesure de l’énergie
238U+12C fission induite par transfert: perspectives -distributions en masse, charge et energie des fragments de fission en fonction of E* Systématique des sections efficaces de fission du Pa au Cm Identification isotopique dépend d’une stabilisation du signal fusion-fission transfer-fission This is so far the status of the analysis. - The isotopic identification and kinematics reconstruction will be done in Spider to finish with the complete characterizatio of the fissioning system - In Vamos we will perform the normalization of the data ensamble to calculate systematic fission cross sections for the different systems. But what is already very important: We already proved for the first time that the whole identification of fission fragments, this is mass and charge, along with their energy and angular distribution is experimentally possible. And it is done. identification isotopique (masse et charge) et mesure de l’énergie Sur la production entière des fragments est faite pour la première fois