Сессия-конференция Секции ядерной физики ОФН РАН «Физика фундаментальных взаимодействий»

1. Сессия-конференция Секции ядерной физики ОФН РАН «Физика фундаментальных взаимодействий» ИССЛЕДОВАНИЕ СТРУКТУРЫ НЕЙТРОННОГО ГАЛО В РЕАКЦИИ КВАЗИСВОБОДНОГО РАССЕЯНИЯ ПРОТОНА НА ГАЛО-ЯДРЕ 6He Г.Е. Беловицкий, В.П.Заварзина, С.В.Зуев, Е.С.Конобеевский, А.В.Степанов Институт ядерных исследований РАН, Москва

2. Object of investigation – structure of neutron halo Investigation of reactions using beams of radioactive nuclei have extended the area of nuclear physics on nuclei far from the stability line. Many new phenomena characteristic for unstable nuclei, for example nuclei with neutron halo were discovered. Especially interesting are so-called Borromean nuclei - nuclei with two-neutron halo (11Li, 6He, 14Be). Cigar-like 6He Dineutron Other examples – 11Li, 14Be, 8He

3. Irradiation of nuclear photoemulsions by 6He beam Flerov Laboratory of Nuclear Reaction (JINR, Dubna) 6He-beam with energy of 60 MeV Width of PE stack ~ 1600 m Interaction energy - 15-60 MeV Target nuclei– H, C, N, 0, Br, Ag Angular resolution ~ 1º Energy resolution ~ 2-5%

4. Interaction of 6He with 1H in photoemulsion at energy of 15-22 MeV X Reactions – one- and two-neutron transfer; QFS Secondary particles: 4He,1H,2H,3H Comparable ranges Trajectory - three-pronged star 1H - =9º; E=3.8 MeV Eint=21 MeV 4He - =0.5º; E=15.6 MeV Z Y Restriction – E4He > 3 MeV E1-3H > 1 MeV Z

5. QFS of proton by constituents (-n-n) of 6He Halo projectile 6He is considered as a system - claster (C) and spectator (S) Then QFS may be denoted as S+C(1H,1H)C+S where C = 5He4He2n1n S = 1n2n 4He5He QFS – assumption that incident particle is scattered by a claster while spectator is at rest QFS of proton (projectile p) by dineutron – spectator (4He) is at rest Our case – inverse kinematics QFS of dineutron (projectile 6He) by proton – spectator (4He) conserves its direction and intrinsic momentum distribution in the projectile In the experiment such event looks like the three-pronged star (6He,4He,p) with 4He track emitting from the interaction point at close to zero angle and with momentum close to 4/6 of momentum of projectile at energy of interaction

6. Preliminary experimental data on QFS Experiment: Eint=15-22 MeV;He=0±1º;p≤ 10º pn and p2n-scattering p2n-scattering pn-scattering Ep/E0 EHe/E0

7. Comparison of experimental data and three-body kinematics with account for momentum of spectator in QFS Spectator conserves its direction of motion and intrinsic momentum distribution in projectile Ep/E0 Elastic limit p2n-QFS pn-QFS EHe/E0

8. Conclusions • Irradiation ofPEshas been performed using 6He beam at 60 MeV • Systematic processing of irradiated PEs with goal of obtaining data on QFS of proton by the constituents of halo-nucleus 6He is started • Preliminary data on 6He-p interaction at energy of 15-22 MeV are compared with three-body kinematical calculations for QFS • A part of data does not contradict with simplified kinematical calculations of QFS of proton by dineutron claster of 6He

9. Thank you!

10. Determination of particle trajectories Three-dimensional scanning of PE is performed at automated setup PAVIKOM at P.N. Lebedev Physical Institute The images of consecutive (with step of several m) PE layers are obtained and transferred to the computer In each layer we select darkening areas (globes) with characteristics inherent for tracks of given charged particle Coordinates (x, y) of centers of mass of all globes in each layer (z-coordinate) are determined and stored Then, the particle trajectories Xi(z) and Yi(z) are determined by center-of-mass coordinates in consecutive layers of PE

11. Structure of neutron halo of 6He Two-neutron transfer cross-section G.M.Ter-Akopian et al. 1998; Yu.Ts.Oganessian et al. 1999 6He beam with energy of 151 MeV; 4He and 1H targets “..it is found that the “dineutron “ configuration of the 6He nucleus gives the dominant contribution to the two-neutron transfer cross-section.” Quasi-free capture E.Sauvan, F.M.Marques et al. 2001; N.A.Orr, F.M.Marques 2003 6He beam with energy of 240 MeV; 1H target “…non-observation of capture on a di-neutron” “This indicates… that 4He-n-n (i.e., no compact dineutron component) is the dominant configuration present in 6Hegs.” So, even for the most studied 6He-nucleus it is impossible to draw a final conclusion on the structure of neutron halo. New experiments for various reactions and at various energies are needed.

12. Study of reactions induced by halo-nuclei in nuclear photoemulsion REACTIONS – NEUTRON TRANSFER, QUASI-FREE SCATTERING BEAM – HALO-NUCLEI (6,8He,11Li,14Be) ENERGY – 3 < Eint <15 Mev/nucleon TARGET – PHOTOMULSION (H,C,O,N,Br,Ag)

13. Reactions used for halo structure determination 6He Two neutron transfer reaction Quasi-free scattering Quasi-free capture

15. Determination of the trajectory parameters Eint, E1, E2,1,2 Eint=f(E0,R0) E1=f(R1) E2=f(R2) The characteristic trajectory corresponding to the given reaction consists of the track of primary particle (6He), interaction point (IP), and trajectories of secondary particles emitting from the interaction point. Then the program determines range (energy) of the primary particle at the interaction point, anglesof emission of secondary particles, and ranges (energies) of the secondary particles.

16. Calculation of QFS kinematics Three-body kinematics: Eint=15-22 MeV;He=0±1º;p≤ 10º pn-scattering pn and p2n-scattering p2n-scattering Ep/E0 EHe/E0

17. Comparison of experimental data and three-body kinematics with account for momentum of spectator in QFS Ep/E0 p4He-QFS p5He-QFS Elastic limit p2n-QFS pn-QFS EHe/E0

18. Separation of events of two-neutron transfer reactioninduced by 6He in different target nuclei By the ratio of ranges By the opening angle

19. Interaction of 6He with 1H in Photoemulsion at energy of 15-22 MeV

20. Single frame 80*60 micron at fixed depth Frames at all depths at fixed (X,Y) form Set of frames

21. Information on the structure of neutron halo can be obtained from the analysis of transfer reaction, quasi-free scattering and quasi-free capture Thus the information on the structure of neutron halo can be directly obtained from the analysis of differential cross section of two-neutron transfer reaction Two neutron transfer reaction as a probe of halo structure

23. Тестовое облучение ФЭ в Лаборатории Ядерных Реакций, ОИЯИРеакция передачи двух нейтронов 6He+A4He+B Пучок 6He – энергия 60 МэВ Толщина стопки ФЭ ~1600 мкм Энергия взаимодействия 20-60 МэВ Ядра-мишени – H, C, N, 0, Br, Ag

25. Eвз, E1, E2,1,2,,разл Eвз=f(E0,R0) E1=f(R1) E2=f(R2)

27. Реакция передачи двух нейтронов 6He+1H4He+3HЭнергия взаимодействия E0=37 МэВ

28. Зависимость пробегов вторичных частиц от угла разлета для реакций упругого рассеяния и 2n-передачиЭнергия взаимодействия E0=37 МэВ Упругое рассеяние Соотношение пробегов Соотношение углов вылета Компланарность 2n-передача

29. Траектория события упругого рассеяния 6He+1H6He+1HEвз=32 МэВ УПРУГОЕ РАССЕЯНИЕ Угол разлета - 2,8º Угол вылета 6He – 0,8º, Угол вылета 1H – 2º, Пробег 6He – > 200 мкм Пробег 1H – > 200 мкм 1/2=2,5 ПЕРЕДАЧА 2n Угол разлета - 2,8º Угол вылета 4He – 0,6º, Угол вылета 3H – 2,4º, Пробег 4He > 200 мкм Пробег 3H = 50 мкм 1/2=4

30. Траектория события передачи 2n6He+1H4He+3HEвз=40 МэВ ПЕРЕДАЧА 2n Угол разлета - 63º Угол вылета 4He – 17º, Угол вылета 3H – 46º, Пробег 4He > 340 мкм Пробег 3H = 230 мкм 1/2=2,7 УПРУГОЕ РАССЕЯНИЕ Угол разлета - 63º Угол вылета 6He – 8º, Угол вылета 1H – 55º, Пробег 6He > 340 мкм Пробег 1H = 140 мкм 1/2=6,8

31. Заключение • Проведены тестовые облучения ФЭ на пучке 6He • Проведена фотосъемка части облученных ФЭ на установке ПАВИКОМ • Разработаны программы определения траекторий заряженных частиц в ФЭ • Разработаны программы поиска трехлучевых звезд и определения всех параметров реакций, приводящих к их образованию • Начата систематическая обработка экспериментальных данных с целью получения угловых и энергетических распределений реакции 1H(6He,4He)3H в интервале энергий 6He 20-60 МэВ