Clustering pattern oflight nuclei in peripheral dissociation above 1 A GeVby 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 Dubna Nuclotron Few GeV beams of Few GeV beams of Relativistic NucleiRelativistic Nuclei

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

7Li 92.5 %

7Be 53.3 d

8B 0.769 s

10B 19.8%

11B 80.2 %

12C 98.89 %11C 20.38 m

12N 11.0 ms

9Be 100%

9C 0.1265 s 10C 19.2 s

8Be 6.8 eV

9B 540 eV

6Li 7.5 %

Ground states – lowest excitations

=1.5 MeV

=0.092 MeV

=0.23 MeV

=1.4 MeV

=1.58 MeV

5Li

6Be

7B

8C

11N

Crossing stability frontier

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 4.5 A GeV/c 1616O O

Coherent DissociationCoherent Dissociation

(PAVICOM image)(PAVICOM image)

4.5A GeV/c 4.5A GeV/c 1616O Coherent O Coherent Dissociation with Dissociation with 88Be like Be like fragmentationfragmentation

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:Example of “white” star: 3.65A GeV 3.65A GeV 2020Ne Peripheral Dissociation Ne Peripheral Dissociation into charge state 2+2+2+2+2 with into charge state 2+2+2+2+2 with 88Be like fragmentsBe like fragments

Charge (>2) Light Fragment Charge, Z Number of Events

  5 4 3 2 1  

9+8+

1 1351  1

8+ - 2 7

7+   - - 1 1 6

7+   - - - 3 2

6+   - - 2 - 5 6+   - - 1 2 1

0+ - - 5 - 3

4.1A GeV/c 4.1A GeV/c 2222NeNe Charge Distribution of Fragments in Projectile Fragmentation Cone (without target excitations). Events: 90

1 event 5+3+2 and 1 event 4+3+31

4.5A GeV/c 4.5A GeV/c 2424Mg Peripheral Dissociation into charge stateMg Peripheral Dissociation into charge state

2+2+2+2+2+2 with 2+2+2+2+2+2 with 88Be and Be and 1212CC** like fragments 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

Tn=(M*n - n M )/(4 n ), MeV

0

0.8 1.6 2.4

4.5A GeV/c12C:<T3>=0.4 MeV

22Ne5 24Mg5 +3He

CClluusstteerriinngg iinn LLiigghhtt NNuucclleeiitt

33HHee

66LLii

77LLii

66HHee

77BBee

88BB

1122CC

1100BB

1122NN

1111BB

1111CC

99BBee

1100CC

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.

++4.5A GeV/c 4.5A GeV/c 66Li Coherent Li Coherent Dissociation (PAVICOM image)Dissociation (PAVICOM image)

66LLii

1A GeV 1A GeV 1010B Coherent B Coherent Dissociation Into 2+2+1Dissociation 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.

Fragment Charge Events with Q=5

No mesons

% White Stars

%

5 4 3 2 1

1 - - - - 4 4 0 0

- 1 - - 1 2 2 1 3

- - 1 1 - 10 11 5 12

- - - 2 1 60 65 30 73

- - - 1 3 15 16 5 12

- - - - 5 2 2 0 0

Total 93 41

10B Fragmentation Topology

4.5A GeV/c 4.5A GeV/c 1414N Coherent Dissociation with N Coherent Dissociation with 88Be like fragmentationBe 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.

Fragment Charge White Stars

%

6 5 4 2 1

- - - 3 1 12

1 - - - 1 6

- 1 - - 2 3

- - - 2 3 2

- - 1 1 1 1

- - - 3 1 1

14N Fragmentation Topology

Triton-Alpha Clustering in Light Nuclei11B7Li 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.

Relativistic 7Be fragmentation: 2+2

Fragment Charge White Stars

%

3 2 1

- 1 2 38 51

- 2 - 28 37

1 - 1 7 9

- - 4 2 3

Total 75

7Be Fragmentation Topology

1A GeV 1A GeV 1010B B Fragmentation to Fragmentation to 88BB

(PAVICOM image)(PAVICOM image)

“Triple H&He Process: mixed isotope fusion”

+

12C 98.89 %

One more path to 12C and 4He production

8B 0.769 s 12N 11.0 ms

Toward CNO cycle& burning

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”

Triple 3He process: 2 4He & 15.88 MeV at the output

+ 9C 0.1265 s

9B 540 eV

13O 8.58 ms

12O 0.4 MeV

6Be & 3He

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.

7Be, stable

8B, 770 ms

9C, 126.5 ms

6Be, 0.092 MeV

7B, 1.4 MeV

8C, 0.23 MeV

6Вe pp4He-1.372 MeV

8С pp6Be-2.14 MeV

7B p6Вe-2.21 MeV

6Вe 3He3He+11.48 MeV

Crossing proton stability frontier