Fragmentation measurements at NSCL

Betty TsangNSCL User Workshop

Sept 27-28, 2003

58Ni + 9Be

N-Z

charg

e

58Ni

58Ni+Be

50Ca

Projectile Fragmentation experiments

• Experimental objectives:

– To measure fragment cross-sections produced in projectile fragmentation.

– Understand rare isotope production by testing various fragmentation models

– extract systematics for charge distributions, momentum distributions, fragmentation measurements

• A1900 operations, R&D for RIA, HI radiation therapy, space exploration etc.

•Primary beams:

–58Ni27+, 40Ca20+, …

–140MeV/u and intensity 107-1010pps

•Targets:

–9Be (100.4mg/cm2) and 181Ta (219.4mg/cm2)

CCF @ the NSCL

Coupled Cyclotron Facility

A1900 - Overview

p/p= 5%

d = 8msr

Dispersion D = 59.5

mm/%

Bmax= 6Tm

Superconducting magnets (NSCL design)

• Four 45° dipoles• 24 quadrupoles• High degree of

symmetry

A1900 – detector setup used

FP

Stand alone mode(standard A1900 setup)

I2

PPAC

Charge States measurement

Measure 2 charge states

at one time, automatic

normalization

Charge State Distributions from 140MeV/u 58Ni & 86KrTarasov, Lise++

Global (developed

at GSI) reproduces

the charge

distributions quite

well.

A1900 – momentum slit position

Stand alone mode(standard A1900 setup)

I2

.2%

I3(58Ni)

.2%

Fragment Identification -- 58Ni27+E

nerg

y l

oss [

ch

an

nels

]

ToF [channels]

Raw

N-Z

Z

Calibrated

)]//([ cMeVmbdpnN

fY

dp

d

LIVETARGETBEAM

ONTRANSMISSIxx

Relative yields of fragments -- up to 200 fragments identified

N-Z

charg

e

58Ni+Be

58Ni

N-Z

charg

e 50Ca

51Sc

58Ni

58Ni+Be

Relative yields of fragments -- neutron rich isotopes

Z N58Ni 28 30. . . . . . . . .

51Sc 21 3050Ca 20 30

Systematics study of momentum distributions

>200

momentum

distributions

per target

Increase the

data base for

systematics

study

Cross section comparisonB.Blank et. al. Physical Review 50 (2398), 1994

Vanadium (Z=23):

Cross section comparisonB.Blank et. al. Physical Review 50 (2398), 1994

Be and Ta target comparison--Isotope distributions

Be and Ta target comparison--Isotope distributions ratios

Isotope distribution ratios

Enhanced productions in n-rich and n-deficient regions

Effects are much larger for n-rich projectile

?? Similar trends for n-rich target and n-rich projectile

Excitation Energy Distributions

Sx

(ablx)

Neutron separation energy 0 near drip lineFragment Cross-sections yield information about Sn

Abrasion-Ablation model

• One of the physical fragmentation models

– Has been quite successful

E*

P

T

b

Abrasion (Shear-off)

Abrasion geometrical overlap

Ablation excitation function integration

Ablation (Evaporation)

ablx=

*)*,1(**),1(

**),(

0

0

dEEfdEExf

dEExf

x

x

S

S

=

abrx determined geometrically

from probability

= (Z!/(Z-x)!)/((N+Z)!/(N+Z-x)!)

x= abrx· ablx

f(1,E*) : one proton removal probability – fitting parameter

(triangular or exponential functions)

Idea: Measure the p-removal chain

use nuclei with known Sx to fit f(1,E*)

use f(1,E*) to extract Sx for nuclei with x protons removed.

x-proton, 0-neutron removal cross-sections

ablx=

*)*,1(**),1(

**),(

0

0

dEEfdEExf

dEExf

x

x

S

S

=

p-removal cross sections

Good agreement suggests Sn maybe extracted from

p-removal chain for 48Ca – current status48Ca

p+47K

p+46Ar

p+45Cl*

p +44S**

p+43P**

p+42Si**

p+41Al**

Bevalac48Ca+Be

Riken48Ca+Ta

48Ca

p+47K

p+46Ar

p+45Cl*

p +44S**

p+43P**

p+42Si**

p+41Al**

Experiment scheduled on Oct 8 & 9

Better determination of Sn

for 44S, 43P, 42Si and 41Al

(Sn>.5 MeV)

(Sn>1 MeV)

(Sn>4 MeV)

Summary• One of the first fragmentation cross-section measurements

using the A1900 at the NSCL

• Systematically measured data with 58Ni, 40Ca, 86Kr

– to be compared with 64Ni, 48Ca

– prove the principle of determination of Sn using p-removal chain

• Improvements from running experience :

– Need better understanding of the transmission through the A1900

– Need better start time with thin foils

– Need better energy FP detectors to resolve charge states

– Reduce the overhead time (33%) in magnet settings, charge state measurements, beam intensity calibration measurements etc. for each targets

– Reduction of “radiation” background for high beam intensity

– …

Acknowledgement

Michal Mocko,

M. Andronenko, L. Andronenko, M. Famiano, T. Ginter, H. Hua, X.D. Liu, W.G. Lynch, D. Oostdy, M. Steiner, A. Stolz, M.B. Tsang, M-J. van Goethem,

O. Tarasov, G. Verde,

M. Wallace, A. Zalessov

W. Friedman

Method of measurement

acceptance Full

(5%)

Narrow

(.2%)

Charge states

Transmission

# settings

PID

Beam

Dead time

Full acceptance

measurements require

improvements in the

A1900 detection systems

Momentum distributions

• Proton removal

channel

fragments

• By integrating

momentum

distributions

total cross

section for a

given fragment

Convolution of excitation functions

*)*,1(**),1(**),(00

dEEfdEExfdEExfxx SS

f(1,E*)=1./<> exp(-E*/<>)