Experimental approaches towards the

1
Experimental approaches towards the measurement
of a-induced reactions
Joachim Görres, University of Notre Dame JINA
http//www.nd.edu/nsl
http//www.jinaweb.org
2
Present Techniques
Active Shielding with detector arrays (LENA -
UNC, Notre Dame) Passive shielding underground
(LUNA, SUSEL) Inverse kinematics with recoil
separator (BOCHUM, TRIUMF, Notre
Dame) Indirect techniques ANC, Trojan Horse,
etc (FSU, Texas AM, ANL, Catania,)
3
Yield Of Narrow Resonances
(Number of Reactions Per Incoming Projectile)
Gltlt?
?2
??

2e
?
Y(a)/Y(p) 1/10 for same ?? and E
?2 1/µ
e(a,E) (2-4) e(p,E/4)
4
Targets (a-beam)
Better Than Protons
Larger Coulomb Barrier
Less beam induced background than protons at same
energy
Use of lower Z target material is possible e.g
TiN, Cu backing
Worse Than Protons
Y?2/e (factor 10)
Blistering (in many metals)
Sputtering
Blisters after a-bombardment
21Ne implanted in Au
Before
After
Surface Damage ? Thicker Target
5
Direct Method (a,n)- Reactions
NERO (JINA)
e.g.22Ne(a,n)
present upper limit lt 50 neV
Stuttgart
Reaction rate uncertain within factor 10
(P.Koehler)
6
Karlsruhe BaF Array
Background
13C(a,n)
Converter (d20 cm)Paraffin/80g Cd Cd-Sheets
Between Crystals
e.g.13C(a,n)
7
Coincidence Method 24Mg(a,?)28Si
8
O(Ge) 30 O(NaI) 40
Background Run
Ge
photopeak
Gammasphere 10 at 1.33 MeV
total eff. gt 3 MeV
E(NaI)gt3MeV
NaI
photopeak
Suppression Factor gt 30000
9
E(NaI)gt3MeV
??part 35 µeV
Compilation 1, 100-gt gs
10
Results
Possible Low Energy 24Mg(a,?)28Si Resonances
estimated from a systematic examination of
nearby levels
11
Reaction Rate
Elisabeth Lizzie Strandberg, PhD Notre Dame,
2007
To be published
12
Underground Laboratory
background reduction by 3 orders of magnitude
13
(No Transcript)
14
(No Transcript)
15
(No Transcript)
16
Final resting place for the defense
generated transuranic waste
17
Mixture of Table Salt NaCl (white) Polyhalite
K2Ca2Mg(SO4) (Pink)
18
40K Activity
Polyhalite
KCl 100 pink 20 white lt6
No excess RaTh observed
Hallstadt
1461 keV
p.s. most of the counts you see are room
back- ground from concrete walls of lab
19
Near Future
On-site background test (?/n-detectors) Renovate
230 keV accelerator (funded) Test
measurements Install at WIPP
St. Barbara
Far Future
2 MeV Accelerator Neutron detector (a,n) reactions
20
Recoil separator Principle
Reduced background for ? spectroscopy
? detector
target
separation
projectiles
Detection Identification
projectiles
recoils
(heavy)
recoils
(light)
projectiles
Ionization chamber PSD Time of flight
Velocity/energy selection
Drawings from D. Schürmann
21
The Design Goal
Alpha and Proton Capture Reactions on sd-Shell
Nuclei
Realistic Evaluation of Eight Reactions
Existing Recoil Separators
Stable Beam
Assumptions 100 microA Beam Intensity 1/h
Minimum Count Rate 33 Efficiency
Erna Dragon Ares DRS
22
Yield Estimate (for (a,?) reactions)
Not including background count rates
Assume count rate of 1 /hour efficiency 33
Number of reactions 3/h
nonresonant reactions
resonant reactions
NT3 1017/cm2
s 10 pb
?? 5 neV
need ?-recoil coinc. to clean up
place device underground to reduce count rate in
?-detector
23
24Mg(a,?)28Si at Ea 600 keV
24
Wien filter electrostatic fringe field
Velocity filter vE x B
E-field of optimized WF
Clamped magnetic field
E-field of standard WF electrodes
25
layout of St.George
St.George
24Mg(a,?)28Si
26
Georg Berg Manoël Couder Larry Lamm Daniel
Schürmann Ed Stech Joachim Görres Michael
Wiescher
The Team
St. Georg in Gelsenkirchen
27
Epilogue
Sir Arthur Eddington
28
(No Transcript)