Recoil Separator TechniquesJ.C. Blackmon, Physics Division, ORNL

RMS - ORNL

WF

WF

QTQD

Q

D

Target

FPERNA - Bochum

WF

WF

Target

D

QT

QT

QTFP

DRSORNL

QDVF D

VAMOSGANIL

Recoil separator basicsDRAGON

ISAC How do recoil separators compete?

Why underground?

Combination of magnetic and and electrostatic elements that spatially disperse charged reaction products by m/q

What is a recoil separator?

Dipole magnet

B =pq

SPIRAL at GANIL

large acceptance rotatable 6 m

Wien filter

EB

=pm

+ dispersedqm

no p dispersion

An alternate approach

Dipole magnet

B =pq

+Electrostatic deflector

EqV =

12 dispersedq

m

no p dispersion

FMA at ATLAS

very high selectivity

78Kr64Zn

135Tb < nb

Some recoil separator properties

High selectivity

Good energy acceptance

Modest angular acceptance

Well-suited for inverse kinematics

precoil ~ pbeam

<1

Separator Facility Format max EacceptanceVAMOS SPIRAL -W D 7.7° 10%

DRS HRIBF - -W W D 2.5° 5%ERNA Bochum -W D-W 1.8° 6%RMS HRIBF DxDxExDxE 1.7°x6.3° 10%

DRAGON ISAC DxExDxE 1.1°* 6% *apertures only

Capture in Inverse Kinematics

Carbon foil MCP

e- e-

Compact Windowless H2 Target

What might be studied underground?

12C(,), 16O(,) Supernovae ~ He burning

20Ne, 24Mg, 28Si, 32S, 36Ar, 40Ca(,) Supernova nucleosynthesis

14N(,)18O(,)22Ne(,)

AGB stars ~ s process

14N(p,)17O(p,)17O(p,)

Red giants ~ CNO cycle

22Ne(p,)23Na(p,)24Mg(p,)

Globular clusters ~ Ne/Mg/Na cycles

(p,) reactions

17O(p,)18FOxygen ratios in presolar grains

Galactic production of 17O

Oxygen ratios in red giant atmostpheres

Gamma rays from 18F decay in novae

Search for180-keV resonance

p < 6 eV

Dominate uncertainty for 1x108 K < T < 3x108 K

Measure in inverse kinematics with a recoil separator?

17O H2

17O(p,)18F in inverse kinematics

Daresbury Recoil SeparatorE

E+E

= 0.8 eV

(4x10-8)*Incident

680-keV resonance

clean identification of reaction products much more difficult as beam energy decreases

Er (keV) (eV) Yield/day(100pμA)

max

680 1 3x109 0.6°180 10-6 5000 1.0°67 10-10 1 1.7°

Beam rejection at low energies

10-8 * 1 pμA 60 kHz

21Na(p, ) @ 220 keV/u (Bishop et al.)

recoil-gamma coincidence

High selectivity without Z identification

(p,) vs. inverse kinematics

Energies < 200 keV/u

gamma detection required in both cases

no Z identification of heavy ion

separator TOF can tag events of interest

large recoil angle - transmission difficult

poor beam suppression high FP count rate

μA of HI beam vs. mA of protons

It is difficult for inverse kinematics to compete with a high current proton accelerator underground.

12C()16OKunz et al. (01)

Plaga et al. (87)

Azuma et al. (94)

SE1(300 keV) ~ SE2(300 keV) ~ 80 keVb

limited by gamma backgrounds

mA 4He 4 fusions/month

Need (300 keV) ~ 0.1 fb

4He(12C,)16O with a recoil separator

3x10-10

Ecm = 3.2 MeV

How low in Ecm can this technique be pushed?

Ecm > 1.4 MeV recoil provides clear 16O tag

Ecm < 1.4 MeV

E-E identification of recoil Z is lost

Increasing recoil cone must be accepted

Beam suppression is more difficult

If 10-10 beam suppression & 1000 cosmics/day

10 recoil-gamma background events/day

12C() fusion rate underground probably 10 times > inverse kin.

12C()16O vs. inverse kinematicsEcm(MeV)

max

(°)SE2/Stotal Stotal

(keV•b)

(p )bRate

(100pμA•1018cm-2)(fusions/day)

2.4 1.2 0.038 68 49000 3x106

2.0 1.2 0.1 31 7500 4x105

1.4 1.4 0.25 29 590 3x104

1.0 1.6 0.34 31 36 20000.8 1.7 0.36 34 4 2000.7 1.8 0.38 40 1 500.6 1.9 0.40 50 0.3 160.5 2.1 0.60 60 0.03 2

12C()16O - My perspective Unique astrophysical importance

Measurements in inverse kinematics will clearly improve our understanding

Measurements in inverse kinematics will not measure the cross section near the Gamow window anytime soon

() measurements above ground are limited by ambient backgrounds

Measurements underground would clearly be a substantial improvement

Issues:

• Level of beam induced background

• Robustness of solid carbon targets

Would measuring 4He(12C)16O underground be more sensitive than 12C()16O? More robust/stable target, less background (13C)

() on N=Z nuclei Important for understanding supernova nucleosynthesis

-rich freeze-out, -ray production (44Ti, 56Ni)

Sparse experimental information, especially for heavier nuclei

Statistical model calculations somewhat more uncertain due to low energy N optical potentials.

Rauscher et al. (00)

Some of these reactions have significant target issues (stability under high beam currents)

Measurement with a heavy ion beam on an alpha target could be easier and cleaner

Conclusions It is difficult for recoil separator measurements of (p,) reactions to compete with high-intensity proton beams for stable targets due to the very low energies. A compelling case can clearly be made for measuring these reactions underground.

LUNA and other facilities have the capability to measure these reactions, but the list of interesting measurements is extensive, and the pace of measurements is slow.

Improvements in our understanding of 12C()16O will be made through measurements in inverse kinematics above ground. However, these measurements are exponentially more difficult at low energies. Measurements at an underground facility are compelling and should be vigorously pursued.

The capability to measure such () reactions at low energies currently does not exist anywhere. A strong case can be made for a new underground accelerator facility to address this important physics.

mA beam of 4He

High intensity heavy (A<40) ion beam & He jet target?