Clustering pattern of light nuclei in peripheral dissociation above 1 A GeV by P. I. Zarubin, JINR, Dubna, Russia On behalf of the BECQUEREL Collaboration Please, find more on the Web site http://becquerel.lhe.jinr.ru
The BECQUEREL project is destined to continue irradiation of emulsions in relativistic beams of Dubna Nuclotron with the purpose of studying in detail processes of fragmentation of light stable and radioactive nuclei. The expected results would make it possible to answer some topical questions concerning the cluster structure of light radioactive nuclei. Thanks to the best spatial resolution, the nuclear emulsions would enable one to obtain unique results. Fragmentation of stable and radioactive nuclei to cluster fragments might reveal some new particularities of their origin and their role in stellar nucleosynthesis.
Dubna Nuclotron Few GeV beams of Relativistic Nuclei
Clustering building blocks:more than one nucleon bound, stable & no exited states below particle decay thresholds – deuteron, triton, 4He, and 3He nuclei
Ground states – lowest excitations 12N 11.0 ms 9C 0.1265 s 10C 19.2 s 12C 98.89 % 11C 20.38 m 8B 0.769 s 11B 80.2 % 10B 19.8% 9B 540 eV 7Be 53.3 d 9Be 100% 8Be 6.8 eV 6Li 7.5 % 7Li 92.5 %
Crossing stability frontier =1.58 MeV 11N =0.23 MeV 8C =1.4 MeV 7B =0.092 MeV 6Be =1.5 MeV 5Li
Advantages of relativistic fragmentation 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.
4.5 A GeV/c 16O Coherent Dissociation (PAVICOM image)
4.5A GeV/c 16O Coherent Dissociation with 8Be 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.
Example of “white” star: 3.65A GeV 20Ne Peripheral Dissociation into charge state 2+2+2+2+2 with 8Be like fragments
4.1A GeV/c 22Ne Charge Distribution of Fragments in Projectile Fragmentation Cone (without target excitations). Events: 90 Charge (>2) Light Fragment Charge, Z Number of Events 5 4 3 2 1 9+ 8+ 1 13 51 1 8+ - 2 7 7+ - - 1 1 6 7+ - - - 3 2 6+ - - 2 - 5 6+ - - 1 2 1 0+ - - 5 - 3 1 event 5+3+2 and 1 event 4+3+31
4.5A GeV/c 24Mg Peripheral Dissociation into charge state 2+2+2+2+2+2 with 8Be and 12C* like fragments
Example of distribution of “white” stars with respect to the charge topology: case of 24Mg of the energy of 3.65 GeV per nucleon. Zf 11 10 10 9 9 8 8 8 7 7 NZ=1 1 2 - 3 1 4 2 - 3 1 NZ=2 - - 1 - 1 - 1 2 1 2 Events 10 14 8 5 9 1 7 4 4 2 Zf 6 5 5 5 4 4 3 - - - NZ=1 2 5 3 1 6 4 5 6 4 2 NZ=2 2 1 2 3 1 2 2 3 4 5 Events 4 2 1 1 2 1 3 1 2 2 A distinctive feature of the charge topology in the dissociation of the Ne, Mg, Si, and S nuclei is an almost total suppression of the binary splitting of nuclei to fragments with charges higher than 2.
Fragmentation of a 3.65A GeV 28Si in emulsion. Upper photo: interaction vertex, jet of fragments in a narrow cone, four accompanying single-charged particles in wide cone and three fragments of target nucleus. Lower photo: it is possible to distinguish 3 Z=1 fragments and 5 Z=2 fragments. An intensive track on the upper photograph (the third one from above) is identified as a very narrow pair of Z=2 fragments corresponding to the 8Be decay.
dN/dTn 4.5A GeV/c12C:<T3>=0.4 MeV 22Ne5 24Mg5 +3He 0 1.6 2.4 0.8 Tn=(M*n - n M )/(4 n), MeV
Secondary beams of light nuclei are produced via fragmentation and charge exchange reactions. 8B and 9Be beams are formed from 10B while 9C from 12C.
1A GeV 10B Coherent Dissociation Into 2+2+1 In 65% of such peripheral interactions the 10B 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 6Li.
4.5A GeV/c 14N Coherent Dissociation with 8Be like fragmentation d/p 14N nucleus, like the deuteron, 6Li and 10B belong to a rare class of even-even stable nuclei. It is interesting to establish the presence of deuteron clustering in relativistic 14N fragmentation.
Triton-Alpha Clustering in Light Nuclei 7Li 11B 15N 19F 7Li clustering.A total of 1274 inelastic interactions were found in a nuclear emulsion irradiated by a 7Li beam with a momentum 3A GeV/c. About 7% of all inelastic interactions of 7Li 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 7Li 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. 11B clustering. Analysis is in progress now.
1.2A GeV 7Be dissociation in emulsion. Upper photo: splitting to two He fragments with production of two target-nucleus fragments. Below: “white” stars with splitting to two He, one He and two H, one Li and one H, and four H fragments. The 7Вe*3He decay is occured in 22 “white stars” with 2+2 topology. In the latter, 5 “white” stars are identified as the 7Вe*(n) 3He3He decay. Thus, a 3He clustering is clearly demonstrated in dissociation of the 7Be nucleus.
1A GeV 10B Fragmentation to 8B (PAVICOM image)
“Triple H&He Process: mixed isotope fusion” One more path to 12C and 4He production Toward CNO cycle& burning 12C 98.89 % 8B 0.769 s 12N 11.0 ms + The 10B nuclei with a momentum of 2.0 GeV/c per nucleon and an intensity of about 108 nuclei per cycle were accelerated at the JINR nuclotron and a beam of secondary nuclei of a magnetic rigidity corresponding to Z/A = 5/8 (10В8B fragmentation) was formed. Information on the 8B interactions in emulsion had been obtained. We plan to determine the probabilities of forming “white” stars in 8B7Bер, 3Hep, 6Lipp, and dpp. In the 8В7В fragmentation, a crossing of the limits of proton stability also takes place. Thus, there arises a possibility of studying the decay channels 7B p3He3He (an analog to 9B) and ppp4He.
“Triple He Process: pure isotope fusion” The fusion 3He3He3He6Be3He9С is one more option of the “3He process”. In the 9С8C 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 8C pppp4He and 8C pp3He3He 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. 12C nuclei with momentum 2.0 GeV/c per nucleon and intensity of about 109nuclei 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 9C nucleus interactions in emulsion. + 9C 0.1265 s 9B 540 eV 13O 8.58 ms 6Be & 3He Triple 3He process: 2 4He & 15.88 MeV at the output 12O 0.4 MeV
Crossing proton stability frontier 6Be, 0.092 MeV 7Be, stable 6Вe pp4He -1.372 MeV 6Вe3He3He +11.48 MeV 8B, 770 ms 7B, 1.4 MeV 7B p6Вe -2.21 MeV 8C, 0.23 MeV 9C, 126.5 ms 8С pp6Be -2.14 MeV