Post on 20-Jan-2016
transcript
Depth Profiling
with Low-Energy Nuclear Resonances
H.-W. Becker, IAEA May 2011CRP: Reference Database for Particle Induced Gamma-ray Emission (PIGE)
Ruhr-University of Bochum
first some information about:
Experimental background – the lab in Bochum
Scientific background – Ion Beam Analysis and Nuclear Astrophysics
The Lab in Bochum
Ruhr-Uni-Bochum4 MV Dynamitron Tandem
500 keV – open air – single ended
100 kV – Implanter (not shown)
The NRRA set-up in BochumP = 2x10-9 mbar
The 4 summing crystal12x12 inch NaI(TL) with borehole
high efficiency( 50% photopeak efficiency at 2 MeV)
integrating over angular distributions
summing cascades into one peak
Ion Beam Analysis and Nuclear Astrophysics
Nuclear Resonance Reaction Analysis example 15p12C
6.2 6.3 6.4 6.5 6.6 6.7 6.8 6.9 710-1
100
101
102
103
104
105
E = ER
0 2 4 6 8 10 12
0
100
200
300
400
500
600
700
Beam Energy = 6.446 MeV
Co
un
ts
Gamma Ray Energy (MeV)
E > ER
samplee
Detektor
E = ERE > ER
sample 100.28
0
1000
2000
3000
4000
5000
6000
6.300 6.350 6.400 6.450 6.500 6.550 6.600 6.650 6.700 6.750 6.800 6.850
energy [MeV]
co
un
ts
Strahlenergie [MeV]
Wirk
un
gsq
ue
rsch
nitt
[re
l.]
detector resolution for identifing the -ray only
6.2 6.3 6.4 6.5 6.6 6.7 6.8 6.9 710-1
100
101
102
103
104
105
What determines the depth resolution in NRRA ?
samplebeam
sample 100.28
0
1000
2000
3000
4000
5000
6000
6.300 6.350 6.400 6.450 6.500 6.550 6.600 6.650 6.700 6.750 6.800 6.850
energy [MeV]
co
un
ts
1.) resonance width Γ2.) beam energy resolution ΔEbeam
3.) Doppler broadening ΔED
stopping powerandtotal energy resolution:
to get a feeling: 1nm requires 70 eV resolution at 400 keV
total energy resolution:
1.) resonance width Γ2.) beam energy resolution ΔEbeam
3.) Doppler broadening ΔED
by tilting the sample sub-nm resolution possible
t
ppD m
FTkEm2ln4E
e.g. for Si ~ 70 eV at room temperature
stopping power for protons
0
20
40
60
80
100
120
140
160
180
1 10 100 1000 10000 100000
proton energy [keV]
keV
/ µ
m Silicon
Carbon
stopping power:
The 500 kV machine in Bochum:
0
500
1000
1500
2000
2500
3000
3500
4000
4500
415.8 416 416.2 416.4 416.6 416.8 417 417.2
proton energy
yiel
d
Lewis-peak
total resolution eV(mainly Doppler broadening)HV – ripple 30-40 eV
1 nm
Ep = 417 keVResonanz in 29Si
stability test
50
100
150
200
250
300
0 10 20 30 40 50 60 70
time [min]
gam
ma y
ield
at
50
% p
oin
t
20 eVstability:
The ultimate resolution:
Phys. Rev. B 58 1103 (1998)
21Ne(p,)22Na, Ep = 272 keV Resonance
21Ne solid target (at 8 K !)
resonance width 1 eVbeam resolution 10 eVDopplerbroadening 17 eV
normal thick target yield
Lewis peak
Nuclear Resonance Reaction Analysiswith Proton Induced Low Energy Resonances
0,0001 0,001 0,01 0,1 1 10 100
18O(p,a)11B(p,3a)24Mg(p,g)27Al(p,g)
21Ne(p,g)14N(p,g)
26Mg(p,g)27Al(p,g)
23Na(p,g)25Mg(p,g)29Si(p,g)27Al(p,g)
26Mg(p,g)19F(p,ag)28Si(p,g)
25Mg(p,g)27Al(p,g)29Si(p,g)
24Mg(p,g)15N(p,ag)25Mg(p,g)27Al(p,g)13C(p,g)
26Mg(p,g)
resonance strength ( *abundance)
some proton induced resonances between 150 keV and 500 keV:
One example – Diffusion studies in Olivin(making use of the isotope sensitivity of NRRA)
There is a correlationbetween diffusionand plastic flow
mechanical properties
microscopic properties
Knowledge of the diffusion parameters necessary !
pinning down temperature, pressure and time-scales from observation
Motivation:
100 m
100000 years
BA AB
ExperimentNatur
BA AB
e.g.: A + B -> AB
~ 8 days 10 nm
Measurement of diffusion processes in the laboratory:
kT
QDD exp0
time scale
temperature scale
Chemical potentialproduction of layerswith well defined stoichiometry
, Q = activation energy
Investigation of Si diffusion in Olivin
nativesample
artificial Olivin layerenriched in 29Si(PLD)
Olivin(Fe,Mg)2SiO4
Testfall: Si Diffusion in Olivin
(Diffusionskonstanten aus SIMS Messungen bekannt)
R. Dohmen, S. Chakraborty, H.-W. Becker Geophys. Res. Lett. 29 (2002) 261-264
results:
-50
50
150
250
350
450
550
650
750
850
950
410 415 420 425 430 435 440
proton energy [keV]
gam
ma
yiel
d
diffusion constant in good agreementwith our earlier data
reference layer, ~ 35 nm dick
first temperature process
second temperature process
40 20 0 20 40 60 80 100 120 140
0
0.2
0.4
0.6
0.8
1
1.2
dis tanc e from the surface (nm )
norm
aliz
ed c
once
ntar
tion
1 .15442
0.05
B j
ampi 0 83
650 83
initialj 0 83
750 83
Dliter
150hr 20
0
xj ampi 1 hr 15 initialj 1 hr y liter
depth [nm]
conc
entr
atio
n
Handbook of Modern Ion Beam Material Analysis (1995)
information appears to be poor ….
but lot of data are available from Nuclear Astrophysicsand increasingly from Material sciencea first attempt to collect the data (~ 1995)
… but a lot of data available and still coming
It would be nice to evaluate, extract and bring in a comprehensive form for material analysis:
• The reaction and the abundance of the isotope
• Resonance energy ER
• Q-value or excitation energy• Resonance strength or cross section • Resonance width • Non resonant cross section, next resonance - ray energies, plots of spectra would be useful• Meaning of the values for practical purposes
summary:
• Nuclear Reaction Analysis with low energy resonances can be a powerfull tool for depth profiling in the nm range
• There are quite a few reonances between 150 kV und 500 kV offering various opportunities for applications
• Sensitivity for isotopes offers special applications
• Probably most if not all necessary data are available
• Data evaluation collection and translation into material science lenguage desirable …