The experimental evidence of t+t configuration for 6 He School of Physics, Peking University G.L.Zhang Y.L.Ye

Report content 1.the experimental intention 2.the experimental setup 3.the experimental data and result 4.theoretical calculate 5.summary

Pepole have researched deeply what nucleus are, what it is made up of and its moving rule for a long time, so gave all kinds of models. these are mainly stable nucleus. The nucleus who are far from  stable line were researched at the end of twenties century. At the beginning of Rutherford  scattering experiment, nuclear reaction was used for nuclear model and reaction mechanism by accerlated electron beam, proton beam, deuteron beam and  beam bombard nucleus, but they are stable isotope ion.

At recent years, in order to research nucleus who are far from  stable line and recognize their frame and their character so Radioactive Ion Beam was produced, short time radioactive ion beam was used for secondary beam. In order to know deeply the exotic nuclear inner frame, the experiment technology was developed, for example, Coulomb excitation, elastic scattering, breakup, transfer reaction and  delay neutron emissiom, etc.

1.1 neutron-rich nuclei 6 He 1985, Tanihata found 11 Li has a very large RMS(mean-square-radius)[1] 6 He is also a neutron-rich nuclei Three kinds of configurations. Fig.1[2] [1] Tanihata. et al., Phys.Rev.Lett.55, 2676(1985). [2]Jurgen Wurzer and Hartmut M.Hofmann, Phys. Rev.C55,688(1997)

Fig.1 three kinds of configurations for 6 He

1.2 25MeV/u 6 He+P 反应 [3] two neutron transfer or t transfer is not clear in reaction [3] R. Wolski et al., Phys. Lett. B 467(1999) MeV 6 He+ 12 C 反应 [4] observe several two-body exit channel, 15,16,17 N+ 3,2,1 H,but didn ’ t give data [4] M. Milin et al., Nucl. Phys. A 730(2004)

In conclusion, from the experiment and theory research the 6 He configuration, especially t+t configuration, but no clear result, there is tt configuration or not for 6 He, what is its probability, it is not sure, so explore further the configuration

The experiment was carried out at the radioactive ion beam line RIPS at RIKEN (Fig.2). Primary beam of 13 C at 70A MeV was used to bombard the thick Be target to produce the 6 He secondary beam through the projectile fragmentation process. By the combination of magnetic rigidity and energy loss analysis the 6 He at 25A MeV were separated from other products. The particle identification was based on the B-

E-TOF technique. Two plastic scintillation counters (0.5mm thick at F2 and 0.3mm thick at F3) were used to measure the time-of-flight (TOF) The secondary target was 9 Be of 100m in thickness and tilted at 45 relative to the beam direction. The effective area of the target was 30mm  30 mm. Two parallel plate avalanche

counters (PPAC) were placed in front of the target to monitor beam intensity. A slit was placed in front of F3-PPAC1; with a hole of 20mm  20 mm, in order to limit the beam size. The outgoing charged particles produced from the Be target were detected by a set of 6 telescopes, each composed of a PSD (position sensitive silicon detector), a large area Si detector (SSD) and a CsI scintillation detector, as shown in Fig.1.

Fig.2 the experimental setup Fig.3 six sets of telescopes

PSD1E%SSD1E SSD1E%CsI1E PSD2E%SSD2E SSD2E%CsI2E

3 deal with the data hot nuclei evaporation model for No.1 and No.2 telescope

balance source is 15 C and 13 C [5] Cabrera J et al. Phys.Rev., 2003, C68: [6] Bhattacharya C, Basu S K et al. Phys.Rev., 1991,C44: 1049

Fig.4 15 C for No.1 telescope Fig.5 13 C for No.1 telescope

Tab.1 obtain the nuclear temoerature for 25MeV/u 6 He+ 9 Be reaction 15 C 13 C DetectorT (MeV)Mean data T=5.6  0.1 (MeV) DetectorT (MeV)Mean data T=5.2  0.1 (MeV) 1H1H107 o 5.6  0.3 1H1H  o 6.1  o 5.6  0.3 2H2H  0.2 2H2H  o 6.1  o 5.5  0.7 3H3H  0.3 3H3H  o 6.4  o 5.7  0.9

Fig.6 near the beam direction for No.4 telescope Fig.7 far from the beam direction for No.4 telescope

Fig.8 the differential cross section for breakup

4 theoretical calculation Serber model: diffraction dissocistion and stripping diffraction dissociation: stripping:

[7] R.Serber, Phys. Rev., 1947, (72)1008 [8] R.J.Glauber, Phys. Rev., 1955, (99)1515 [9] A.G..Sitenko et al., Nucl. Phys., 1985, A442:122 [10] P.Banerjee et al., Nucl. Phys., 1993, A561:112 [11] R.Anne et al., Phys. Lett., 1993, B304: 55 [12] R.Anne et al., Phys. Lett., 1990, B250: 19

Fig.9 Serber model

For diffraction:

The wave function of the cluster relative motion before and after the collision

E is the incident particle energy

Angular ditribution of outgoing fragment

Stripping:

(i)wide maximum are observed in the spectra for all target nuclei; (ii)the maximum peaks correspond to the energies E’(m’/m)E, where E’,E,m’,mare the energies and masses of outgoing and incident particles, respectively; (iii)the cross sections reach their highest values at small angles, rapidly decrease at greater angles, and increase as the target mass number increases

For this model, regard 6 He as t+t configuration, give its cross section compared with the experimental data, at the same time, regard 6 He as 4 He+2n configuration, also give its cross section, so obtain the internal information of 6 He. This work is going on.

5 summary i)observe the light particle emission for 25MeV/u 6 He+ 9 Be reaction at back angles, especially many numbers triton, as connected with the configuration and isospin of 6 He. This work still need to be explored deeply. ii) observe direct reaction t and obtain its angle distribution for the experiment at forward angles, give the experimental evidence for t+t configuraion of 6 He iii)obtain the experimental angle distribution of t+t configuration and the

Experimental angle distribution 4 He+2n for 6 He, give the detailed information for 6 He configuration, make a benefit for the theoretical development, give the ratio of two configurations for 6 He

Thank you !