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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?