# Presentation: 096012

## Probing Shell Structure in Neutron-Rich Nuclei above 48Ca:Using the Tools at HandDay 2

*Michael P. Carpenter*

***RIA Summer School  Seminar***
***July 2006***

## Outline of Lectures

***Day 1***
***Nuclear Structure***** – a brief perspective **
**Changing Shell Structure in the Neutron Rich world.**
******-decay studies and deep inelastic reactions to study excited states in ****54****Ti and ****56****Ti – looking for evidence of shell gaps at N=32 and N=34.**
**Day 2**
**Coulomb Excitation of ****52,54,56****Ti**
**2-proton knockout and ********-decay into ****52****Ca**
**56,58,60****Cr using Gammasphere and the FMA**
**Future plans.**

## N = 32 Gap: YES  N = 34 Gap: NO

- 32

- 28

- 34

- R.V.F. Janssens *et al.*, PLB 546, 22 (2002)
- B. Fornal *et al., *PRC **70**, 064304 (2004)

**  **

- 1129

## Beyond 2+ Energies

**E(2****+****) values are a strong indicator of shell structure, but..**
**Additional evidence for the presence or absence of shell effects is most welcome and very desirable!**
**  ******** ****Measure B(E2; 0****+**** ******** 2****+****) values**
**At present, this can only be done with Ti nuclei from fragmentation **
**  ******** ****Intermediate Energy Coulomb Excitation!**** **

## Coulex of 132,134Sn at HRIBF

** ********rays measured with BaF array for ****132,134****Sn**
** ****Surprise B(E2) increases for ****132****Sn.**

**R. Varner *****et al.*****, Eur. Phys. J. A25, s01 (2005) 391.**

## Beyond 2+ Energies: B(E2; 0+  2+) values

- Ti

- ETi ≈ 80 MeV/nucl.
-  ≈ 0.4,   ≈ 1.1
- bmin ≈ 20 fm
- “touching spheres”1.2(ATi1/3+AAu1/3) ≈ 11 fm

- SeGA array

- Primary Beam: 130 MeV/u 76Ge
- Yields:  24000 s-1 52Ti; 2400 s-1 54Ti; 75 s-1 56Ti

## SEGA Array @ NSCL 

- The 75% Ge Crystal has its outer electrode divided into 8 segments along the crystal axis and 4 segments perpendicular to the axis, resulting in 32 fold segmentation

**SEGA with 16 Ge**

**W. Mueller *****et al*****., NIMA 466, 492 (2001)**

- beam

## GRETINA (Segmented Ge-Shell) 

- Tapered hexagon shape.
- Highly segmented 6x6=36
- 7 modules with 4 crystals each – cover ≈ 1π solid angle (cover 4π will take 30 modules).

## SEGA and GRETINA

**Simulation SeGA**

**Simulation GRETINA**

**30****Mg (pn) ****→**** ****30****Na  (100 MeV/u)**
**  ****v/c=0.43**
**charge exchange reaction**
**Gamma-gamma coincidence**
**NSCL data SeGA**
** ****(****E.  Rodriguez-Vieitez et al.)**

## Particle Identification at the S800

## 76Ge and 197Au: the Test Cases

- Lab Frame

- Projectile Frame

- Primary beam:      76Ge @ 140 MeV/nucl.
- Secondary beam: 76Ge @   81 MeV/nucl.
- 		 = 0.392
- 197Au target thickness: 257.67 mg/cm2
- max = 3.06° (CM)
- Number of 76Ge particles detected: 26.1E6

- 76Ge
- E= 562.6(6)keV
- (<max) = 394(47) mb
- B(E2, ) = 2923(346) e2fm4
- Adopted values:
- E= 562.93(3)keV
- B(E2, ) = 2780(30) e2fm4

- 197Au
- E= 547.03(24) keV
- (<max) = 94(20) mb
- B(E2, ) = 4223(898) e2fm4
- Adopted values:
- E= 547.5(3) keV
- B(E2, ) = 4494(409) e2fm4

## 197Au check: Do we know what we are doing?

- D.-C. Dinca *et al., *PRC **71**, 041302(R) (2005)

## An accurate technique that allows for absolute B(E2) measurements

- J. Cook *et al.,* (NSCL/MSU)

## B(E2; 0+  2+) values

- 52Ti, 2+  0+ (g.s.)

- 54Ti, 2+  0+ (g.s.)

- 56Ti, 2+  0+ (g.s.)

- 56Ti
- E= 1129(7) keV
- (<max) = 155(51) mb
- B(E2, ) = 599(197) e2fm4

- 54Ti
- E= 1497(4) keV
- (<max) = 83(15) mb
- B(E2, ) = 357(63) e2fm4

- 52Ti
- E= 1050(2) keV
- (<max) = 119(16) mb
- B(E2, ) = 593(81) e2fm4

- D.-C. Dinca *et al., *PRC **71**, 041302(R) (2005)

## Shell Effects in Ti isotopes: What do we know?

- From an experimentalist’s point of view:  N = 28 and N=32 gaps are quite visible
- in BOTH the E(2+) energies and in the B(E2;0+  2+) values
- and there is no experimental evidence for a N=34 gap

- D.-C. Dinca *et al., *PRC **71**, 041302(R) (2005)

## Comparison with GXPF1

- The Shell Model with the GXPF1 interaction has problems with
- N=34 and with
-  the B(E2) values for ALL Ti

*e**p **= 1.5, e**n ** = 0.5*

- D.-C. Dinca *et al., *PRC **71**, 041302(R) (2005)

## Possible Interpretation

## FPD6 and GXPF1 

- The data may be telling us that the gap between p3/2 and p1/2 is
- at least as large as GXPF1 says, but that p1/2 and f5/2 are at least
- as close together as FPD6 indicates

## Recent Theory Development: GXPF1A

**32**

**34**

**(6****+****)**

**(4****+****)**

***Recent Theory Development: GXPF1A***

_***GXPF1A vs GXPF1:***_
**T=1 matrix elements**
**involving  *********p******1/2 ******and **********f******5/2***
***modified***** **
****
*******p******1/2 ******- **********f******5/2******) gap****** ***
***reduced by ~0.5 MeV***

**M. Honma *****et al.,***** Proc. ENAM (2004)**

## Recent Theory Development: GXPF1A

***Recent Theory Development: GXPF1A***

**B. Fornal *****et al., PRC in press***

## Comparison with GXPF1A

- 48Ti

- 50Ti

- 52Ti

- 54Ti

- 56Ti

- 0

- 500

- 1000

- 1500

- 2000

-     E(2

- +

- )

- GXPF1

- 26

- E(2

- +

- ) Energy (keV)

- 28

- 30

- 32

- 34

- N

**GXPF1A**

**GXPF1A**

**M. Honma *****et al.,***** Proc. ENAM (2004)**

## Value of effective charges?

- B(E2) = (Apep + Anen)2

**A    Ap    An **
**48   8.8   15.4**
**50  10.7    9.5**
**52    9.0   14.4**
**54   10.7  10.6**
**56   10.3  11.4**

## Value of effective charges?

- B(E2) = (Apep + Anen)2

**A     A****p ****   A****n **
**48   8.8   15.4**
**50  10.7    9.5**
**52    9.0   14.4**
**54   10.7  10.6**
**56   10.3  11.4**

- With**  **ep= 1.15       en= 0.8 according to R. du Rietz *et al*., PRL 93,  222501 (2004)** **

## Experimental Evidence for N=32 Gap: 52Ca

- J.I.  Prisciandaro et al., PLB **501**, 17 (2001)

- E(2+) in 52Ca comes from a
- 1983 ISOLDE -decay study
- (A.Huck *et al*., PRC 31, 2226 (1985))
- where the separation between
-  decay and n-delayed decay was
- a problem
- At NSCL  52Ca intensity is too small for a
- Coulex experiment
**                      **
**                       ******** ****2p knockout!!**

- GXPF1

**28**

**34**

**32**

## 2p knockout into 52Ca

**Direct process**
- Knock-out of 2* f**7/2** *protons from 54Ti

**Cross section is small (~ 0.32 mb)**
****** **52Ca is magic

**No direct feeding of 2****+**** state:**
****** **Consistent with a Neutron excitation

**A. Gade *****et al*****., PRC in press.**

## 2p knockout into 52Ca

**2p knockout provides a way to study proton cross-shell excitations in n-rich nuclei**

**3****- ****is ********(d****3/2**** or  s****1/2****)-1 ****(*****f*****7/2****)) excitation**** **

**A. Gade *****et al*****., PRC in press****.**

## 2p-knockout “by-products”

- First Transitions in 55Ti from 2p-knockout with 57Cr

## Pushing towards n-rich Cr: 59,60Cr 

- 59Cr from 48Ca(13C,2p)59Cr at 130 MeV
- 60Cr from 48Ca(14C,2p)60Cr at 130 MeV
**s(2p)  < 1 mb   ********  s(3n/4n) ~ 100 mb**

- S.J. Freeman *et al*., PR C 69,  064301 (2004)

## 14C(48Ca,2p)60Cr @ 130 MeV

- E

- E

- ET2

- M/Q

***Pushing towards n-rich Cr: ******60******Cr***

- Ni

- Fe

- Mn

- Cr

- Ca scattered beam

- Ti

- Ni

- Fe

- Mn

- Cr

- Ca scattered beam

- Ti

## M=60 data

- M=60 Z=24 data

- with subtractions

***Pushing towards n-rich Cr: ******60******Cr***

- S. Zhu  *et al.,* to be published

## Pushing towards n-rich Cr: 60Cr (N=36)

- M=60Z=24 data

***Pushing towards n-rich Cr: ******60******Cr (N=36)***

- S. Zhu *et al*., to be published

## Pushing towards n-rich Cr: 57Cr (N=33)

- A. N. Deacon *et al.*, PLB **622**, 151 (2005)** **.

- 14C(48Ca,n)57Cr @ 130 MeV

## 57Cr: signs of collectivity

- A. N. Deacon *et al.*, PLB **622**, 151 (2005)** **.

**g****9/2  ****prolate structure**
**     ****also seen in ****55****Cr**

**Good agreement with GXPF1**

## Interpretation: 59Cr (N=35) and the Shell Model

- 9/2+ @ only 503 keVOblate deformation?Weak coupling?

- Honma, Otsuka, Brown and Mizusaki: full fp basis, GXPF1 interaction

***Interpretation: ******59******Cr (N=35) and the Shell Model***

- S.J. Freeman et al., PR C **69**,  064301 (2004)

- 13C(48Ca,2*p*)59Cr @ 130 MeV

## Deformation Forms Shell Gaps Too!

## 57,59Cr:  Shape Driving by the g9/2 orbital

***57,59******Cr:  Shape Driving by the g******9/2 ******orbital***

**S. Freeman *****et al.***** PRC 69,  064301 (2004)**
**A. Deacon *****et al.***** PLB 622, 151 (2005)**

## More from the Deep Inelastic

- E(2+0+) decreases with A
-  Level sequence not  regular just yet!
- ? Small oblate deformation ?

- 48Ca + 238U and 48Ca + 208Pb

**Zhu *****et al.*****, to be published**

## Conclusions & Outlook

**Neutron-rich nuclei continue to surprise us!**
**        ****- **there is a N=32 shell gap just above 48Ca
-              in Ti (and Cr) confirmed by level structure and B(E2; )
-         - first indications for the onset of oblate(?) deformation
-           (and the shape driving influence of the *g**9/2  *orbital) seen
-           in 59,60Cr
- 	   - 54Ca is an important measurement (N=34 gap)
**Theory needs work**
**        **- the GXPF1 interaction is not the complete answer
-         - the location of the p1/2 and f5/2 orbitals in n-rich nuclei
-           above 48Ca needs further study
-         - the g9/2 intruder needs to be included

## Where did we go and what did we do

** ****Approach:**   -decay spectroscopy of fragments
-                                   with (*A,Z*) selections  NSCL, ISAC
-                       prompt -ray spectroscopy following
-                           deep inelastic reactions  (thick & thin targets) ATLAS
-                       Coulomb excitation NSCL, (HRIBF)
-                       fusion-evap. reactions @ radioactive targets  ATLAS
-                       knockout reactions from fast fragments NSCL
***Data obtained with each of these techniques and facilities complement each other!***

**Where did we go and what did we do**

## Don’t Forget your Collaborators!

**ANL: ****	****	****R.V.F. Janssens, S Zhu, M.P. Carpenter ****	****	****	****F.G. Kondev *****et al.,***
**NSCL: ****	****	****P. Mantica, S. Liddick, *****et al.,***
**	****            ****	****	****A. Gade, D.-C. Dinca, D. Bazin, *****et al.,***
**Cracow: ****	****	****B. Fornal, R. Broda *****et al.***
**Manchester: ****	****S. Freeman, A. Deacon, et al.**
**Lowell:****	****	****P. Chowdury**
**FSU: ****	****	****S. Tabor *****et al.***
**TRIUMF: ****	****	****G. Hackman, C. Morton *****et al.***
**Theory: ****	****	****M. Honma, T. Otsuka, B.A. Brown, **
**	****	****	****	****T. Mizusaki**