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

Cigar-like Other examples – 11 Li, 14 Be, 8 He 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 ( 11 Li, 6 He, 14 Be). Dineutron 6 He

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

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

QFS of proton by constituents ( -n-n) of 6 He Halo projectile 6 He is considered as a system - claster (C) and spectator (S) Then QFS may be denoted as S+C( 1 H, 1 H)C+S where C = 5 He 4 He 2 n 1 n S = 1 n 2 n 4 He 5 He QFS – assumption that incident particle is scattered by a claster while spectator is at rest QFS of proton (projectile p) by dineutron – spectator ( 4 He) is at rest Our case – inverse kinematics QFS of dineutron (projectile 6 He) by proton – spectator ( 4 He) conserves its direction and intrinsic momentum distribution in the projectile In the experiment such event looks like the three-pronged star ( 6 He, 4 He,p) with 4 He 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

Preliminary experimental data on QFS Experiment: E int =15-22 MeV; He =0±1º; p 10º p 2 n-scattering pn and p 2 n-scattering pn-scattering E He /E 0 E p /E 0

Comparison of experimental data and three-body kinematics with account for momentum of spectator in QFS Elastic limit pn-QFS p 2 n-QFS E p /E 0 E He /E 0 Spectator conserves its direction of motion and intrinsic momentum distribution in projectile

Conclusions Irradiation of PEs has been performed using 6 He beam at 60 MeV Systematic processing of irradiated PEs with goal of obtaining data on QFS of proton by the constituents of halo-nucleus 6 He is started Preliminary data on 6 He-p interaction at energy of 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 6 He

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 X i (z) and Y i (z) are determined by center-of-mass coordinates in consecutive layers of PE

Two-neutron transfer cross-section G.M.Ter-Akopian et al. 1998; Yu.Ts.Oganessian et al He beam with energy of 151 MeV; 4 He and 1 H targets..it is found that the dineutron configuration of the 6 He 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 He beam with energy of 240 MeV; 1 H target …non-observation of capture on a di-neutron This indicates… that 4 He-n-n (i.e., no compact dineutron component) is the dominant configuration present in 6 He gs. Structure of neutron halo of 6 He So, even for the most studied 6 He-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.

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 < E int

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

Determination of the trajectory parameters E int, E 1, E 2, 1, 2 E int =f(E 0,R 0 ) E 1 =f(R 1 ) E 2 =f(R 2 ) The characteristic trajectory corresponding to the given reaction consists of the track of primary particle ( 6 He), 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, angles of emission of secondary particles, and ranges (energies) of the secondary particles.

Calculation of QFS kinematics Three-body kinematics: E int =15-22 MeV; He =0±1º; p 10º pn-scattering p 2 n-scattering pn and p 2 n-scattering E p /E 0 E He /E 0

Elastic limit pn-QFS p 2 n-QFS p 4 He-QFS p 5 He- QFS Comparison of experimental data and three-body kinematics with account for momentum of spectator in QFS E p /E 0 E He /E 0

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

Interaction of 6 He with 1 H in Photoemulsion at energy of MeV

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

Information on the structure of neutron halo can be obtained from the analysis of transfer reaction, quasi-free scattering and quasi-free capture Two neutron transfer reaction as a probe of halo structure 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

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

E вз, E 1, E 2, 1, 2,,разл E вз =f(E 0,R 0 ) E 1 =f(R 1 ) E 2 =f(R 2 )

Реакция передачи двух нейтронов 6 He+ 1 H 4 He+ 3 H Энергия взаимодействия E 0 =37 МэВ

Зависимость пробегов вторичных частиц от угла разлета для реакций упругого рассеяния и 2n-передачи Энергия взаимодействия E 0 =37 МэВ Упругое рассеяние 2n-передача Соотношение пробегов Соотношение углов вылета Компланарность

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

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

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 1 H( 6 He, 4 He) 3 H в интервале энергий 6 He МэВ