Isospin effect in the projectile fragmentation of calcium isotopesand a possible experimental observable?

Chun-Wang Ma Department of Physics, Henan Normal University

Email: machunwang@126.com

Outlook:

1. Backgrounds 2. The SAA Model 3. PF of calcium isotopes 4. Results and Discussion 5. Conclusions

1. Backgrounds Projectile fragmentation is one of the basic

experimental method in RIB era.NSCL experiment: 40,48Ca+9Be/181Ta, 58,64Ni+9Be/181Ta, 86Kr+9Be

New generation or updated RIB facilities expand the nuclear chart to more neutron-rich and proton-rich sides.

Increasing interests in EOS of asymmetric nuclear matter: n-rich nuclei

Hotter in the research of ISOSPIN physics. Neutron density distribution of neutron-rich

nucleus hard to be extracted or measured. Neutron skin thickness important in nuclear phys.

etc.

1. backgrounds– neutron skin thickness and EOS

1. Backgrounds Neutron density distribution or neutron skin

thickness of asymmetric nuclear matter: not easy to know but important in nuclear physics.

Isospin phenomena are strongly related to the different proton and neutron density distribution of asymmetric nucleus.

Can the isospin phenomena be used to extract neutron density distribution of neutron skin thickness directly? The observable!

D.Q.Fang, et al., PhysRevC61(2000)044610;Ma Chun-Wang, et al., Chin.Phys.B,17(2008)1216;Ma Chun-Wang, et al., Phys.Rev.C79(2009)034606,Chin. Phys. B18(11)(2009), to be published

Chin. Phys. B 17(04)(2008)1674

1. Backgrounds Isospin dependence of PF

140A MeV 40,48Ca/ 58,64Ni+9Be

Ma Chun-Wang, et al., Chin. Phys. B18(11)(2009), to be published

Isospin effect in fragments production and it’s decreaseObvious in the productions of peripheral reactions. (big difference of proton and neutron density distribution in the surface of nucleus)Decrease and disappear in the productions of central collisions. (similar proton and neutron density distributions in the core of nucleus)

1. Backgrounds How do the peak position of the

fragments distributions change in the PF of a series of isotopes?

If there are some parameters or observables that are related to neutron skin thickness? Find the correlation between neutron skin thickness and some observables.

2. The statistical abrasion-ablation (SAA) model

Brohm & Schmidt, Fang, Zhong, etc, Simple and useful; 2-steps reactions:

Collisions—participant and spectator

De-excitation

Refs:NPA569(1994)821, PRC61(2000)044610, CPC 27(2003)39, EPJA10(2001)381,PRC79(2009)034606

2. The statistical abrasion-ablation (SAA) modelThe colliding nuclei: parallel tubes.

transmission probabilities for neutrons (protons) at b:

the average absorbed mass in an infinitesimal tubes at b Density distributions: Fermi-type

Isotope production

De-excitation

Y.Eisenberg, PhysRev 52(1954)1378

Key for frag production

3. PF of odd odd 36-5236-52CaCa isotopes Fragments productions of 80A MeV 36-52Ca+12C reactions

Plateau and its drop

Disappearance of the isospin effect: the overlap of the fragment cross section distributions

4. Results and discussion Fit these isotopic distributions by Gaussian function Peak positions Widths

Good linear correlation: pk Vs. Zfrag

Fit the linear correlations between pk position and Zfrag

Slope (b)Intercept (a)

preliminary

4. Results and discussion correlations between slope b and binding energy, b and Nproj

1441.0

44485.2)6169.14/exp(4037.12

xy

8299.0:.

3833.20205.0

squareRadj

xy

preliminary

4. Results and discussion Correlation between b and Sn-Sp:

96431.0:.

1536.21016.0

squareRadj

xy

preliminary

4. Results and discussion Correlation between b and neutron skin thickness

99194.0:

)0483.0(5179.1:

)0017.0(1639.2:

squareAR

a

b

abxy

Good linear correlation:

preliminary

4. Results and discussion

prelim

inary

5. Conclusion The cross sections of fragments produced in 80 A

MeV even 36-52Ca PF on 12C were calculated by the SAA model.

The fragments isotopic cross section distributions were fitted by Gaussian function, peak positions were obtained.

The Apk have good linear correlation to the Zfrag. The linear correlation were fitted and slopes b were obtained.

The correlation between b and Nproj., Sn, Sn-Sp, δnp were analyzed.

Good linear correlation between b and δnp are found.

Still a question: b possible to serve as an observable for neutron skin thickness?