Topology of multifragmentation of light relativistic nuclei by P. I. Zarubin, JINR On behalf of the BECQUEREL Collaboration All this and more on the Web site

Since 1970 A.M. Baldin Relativistic Nuclear Physics Li

Mg-Si Dissociation into charge state  +proton

Advanced Composition Explorer Cosmic Ray Isotope Spectrometer Radioactive Clock isotopes Abundances of Iron, Cobalt, and Nickel Isotopes 1

Clustering building blocks: more than one nucleon bound, stable & no exited states below particle decay thresholds – deuteron, triton, 4 He, and 3 He nuclei

“Are you Boromean too?” A=6  =0.092 MeV

1. a limiting fragmentation regime is set in, 2. the reaction takes shortest time, 3. fragmentation collimated in a narrow cone – 3D images, 4. ionization losses of the reaction products are minimum, 5. detection threshold is close to zero. Advantages of relativistic fragmentation

4.5 A GeV/c 16 O Coherent Dissociation (PAVICOM image)

4.5A GeV/c 16 O Coherent Dissociation with 8 Be like fragmentation The reliable observation of charged relativistic fragments is a motivation to apply emulsion technique (0.5 micron resolution). Requirements of conservation of the electric charge and mass number of a projectile fragments are employed in the analysis. Measurements of multiple scattering angles make it possible to estimate the total momentum of hydrogen and helium projectile fragments and thereby to determine their mass.

4.5A GeV/c 20 Ne Peripheral Dissociation into charge state with 8 Be like fragments

4.5A GeV/c 24 Mg Peripheral Dissociation into charge state with 8 Be and 12 C * like fragments

4.5A GeV/c 28 Si Dissociation into charge state (narrow cone) with pair of 8 Be and triple 12 C * like fragments

The common topological feature for fragmentation of the Ne, Mg, and Si nuclei consists in a suppression of binary splitting to fragments with charges larger than 2. The growth of the fragmentation degree is revealed in an increase of the multiplicity of singly and doubly charged fragments up to complete dissociation with increasing of excitation. This circumstance shows in an obvious way on a domination of the multiple cluster states having high density over the binary states having lower energy thresholds.

dN/dT n  T n  =(M* n  - n  M  )/(4 n  ), MeV A GeV/c 12 C: =0.4 MeV 22 Ne  5  24 Mg  5  + 3 He

Alpha-particle condensation in nuclei P. Schuck, H. Horiuchi, G. Ropke, A. Tohsaki, C. R. Physique 4 (2003) At least light nα-nuclei may show around the threshold for nα disintegration, bound or resonant which are of the α-particle gas type, i. e., they can be characterized by a self-bound dilute gas of almost unperturbed α-particles, all in relative s-states with respect to their respective center of mass coordinates and thus forming a Bose condensed state. Such state is quite analogous to the recently discovered Bose condensates of bosonic atoms formed in magnetic traps. The only nucleus, which shows a well-developed α-particle structure in its ground state is 8 Be. Other nα-nuclei collapse in their ground states to much denser system where the α-particles strongly overlap and probably loose almost totally their identity. When these nα-nuclei are expanded, at some low densities α-particles reappear forming a Bose condensate. If energy is just right, the decompression may stall around the α-condensate density and the whole system may decay into α- particles via the coherent state. 12 C→3 α, …., 40 Ca→10 α, 48 Cr→3 16 O, 32 S→ 16 O+4 α

Deuteron-Alpha Clustering in Light Nuclei 10 B(19.9%) 6 Li(7.5%) 14 N(99.634%) 50 V(0.25%) d

+ 4.5A GeV/c 6 Li Coherent Dissociation (PAVICOM image)

1A GeV 10 B Coherent Dissociation Into In 65% of such peripheral interactions the 10 B nucleus is disintegrated to two double charged and a one single-charged particles. A single-charged particle is the deuteron in 40% of these events and (2He+d)/(2He+p)  1 like in case of 6 Li.

Fragment Charge Events with Q=5 No mesons % White Stars % Total B Fragmentation Topology

4.5A GeV/c 14 N Coherent Dissociation with 8 Be like fragmentation  d/p   14 N nucleus, like the deuteron, 6 Li and 10 B belong to a rare class of even-even stable nuclei. It is interesting to establish the presence of deuteron clustering in relativistic 14 N fragmentation.

14 N dissociation accompanied by 8 Be like pair by 8 Be like  pair 3  after proton

1.3A GeV 9 Be dissociation in B  9 Be, Nuclotron, “white” star with recoil proton with heavy fragment of target nucleus

1A GeV 10 B Fragmentation to 8 B (PAVICOM image)

Triton-Alpha Clustering in Light Nuclei 11 B 7Li7Li 7 Li clustering. About 7% of all inelastic interactions of 7 Li nuclei are peripheral interactions (80 events), which contain only the charged fragments of a relativistic nucleus. Half of these events are attributed to a decay of 7 Li nucleus to  - particle and a triton(40 events). The number of decays accompanied by deuterons makes up 30%, and by protons – 20%. The isotopic composition points to the fact that these events are related to the dissociating structure of  -particle and the triton clusters. 11 B clustering. Analysis is in progress now.

7 Li 92.5 % 7 Be 53.3 d 8 B s 10 B 19.8% 11 B 80.2 % 12 C % 11 C m 12 N 11.0 ms 9 Be 100% 9 C s 10 C 19.2 s 8 Be 6.8 eV 9 B 540 eV 6 Li 7.5 % Ground states – lowest excitations

7 Be, stable 8 B, 770 ms 9 C, ms 6 Be, MeV 7 B, 1.4 MeV 8 C, 0.23 MeV 6 Вe  pp 4 He MeV 8 С  pp 6 Be MeV 7 B  p 6 Вe MeV 6 Вe  3 He 3 He MeV Crossing proton stability frontier

1.2A GeV 7 Be dissociation in emulsion. Upper photo: splitting to two He fragments with production of two target- nucleus fragments. Below: “white” stars with splitting to 2 He, 1 He and 2 H, 1 Li and 1 H, and 4H fragments.

Fragment Charge White Stars % Total75 7 Be Fragmentation Topology

Relativistic 7 Be fragmentation: 2+2 The 7 Вe *  3 He decay is occured in 22 “white stars” with 2+2 topology. In the latter, 5 “white” stars are identified as the 7 Вe *  (n) 3 He 3 He decay. Thus, a 3 He clustering is clearly demonstrated in dissociation of the 7 Be nucleus.

“Triple He Process: pure isotope fusion” Triple 3 He process: 2 4 He & MeV at the output ++ 9 C s 9 B 540 eV 13 O 8.58 ms 12 O 0.4 MeV 6 Be & 3 He The fusion 3 He 3 He 3 He  6 Be 3 He  9 С is one more option of the “3He process”. In the 9 С  8 C fragmentation, a crossing of the boundary of proton stability takes place. In this case, there arises a possibility in studying nuclear resonances by means of multiple 8 C  pppp 4 He and 8 C  pp 3 He 3 He decay channels, which possess a striking signature. It is quite possible that the study of these resonances would promote further development of the physics of loosely bound nuclear systems. 12 C nuclei with momentum 2.0 GeV/c per nucleon and intensity of about 10 9 nuclei per cycle were accelerated at the JINR nuclotron and a beam of secondary nuclei with a magnetic rigidity corresponding to the ratio Z/A=6/9 was formed. The information obtained was used to analyze 9 C nucleus interactions in emulsion.

“3He Process: mixed isotope fusion” Energy release: MeV ++ 11 C m 13 O 8.58 ms 6 Be & 4 He 12 N 11.0 ms ++ 14 O 70.6 s 15 O 122 s ++ 11 B 80.2 % CNO cycle 12 C % 7 Be 53.3 d 10 C 19.2 s 10 B 19.8% 14 O 70.6 s Energy release: 9.13 MeV

11 N 1.58 MeV 12 O 0.4 MeV 15 F 1 MeV 13 N 10 min 20 Na 448 ms 20 Mg 95 ms Walking along proton stability line 12 N 11 ms 16 Ne MeV 14 N 99.6% 13 O 8.58 ms 14 O 70.6 s 15 O 122 s 16 O 99.8% 19 F 100% 20 Ne 90.48% 16 F 0.04 MeV 17 F 64.5 s 18 F 110 min 17 Ne 109 s 18 Ne 1.67 s 19 Ne 17.2 s

Secondary beams of light radioactive nuclei will be produced mostly via charge exchange reactions. 8 B and 9 Be beams will be formed via fragmentation reaction of 10 B.

Fragmentation of relativistic nuclei provides an excellent quantum “laboratory” to explore the transition of nuclei from the ground state to a gas-like phase composed of nucleons and few-nucleon clusters having no excited states, i. e. d, t, 3 He, and . The research challenge is to find indications for the formation of quasi-stable or loosely bound systems significantly exceeding the sizes of the fragments. Search for such states on the nuclear scale is of undoubted interest since they can play a role of intermediate states ("waiting stations") for a stellar nuclear fusion due to dramatically reduced Coulomb repulsion. The fragmentation features might assist one to disclose the scenarios of few-body fusions as processes inverse to fragmentation.