Quiz
[3] “natural” unit in RBS (a) atoms/cm3
(b) atoms/cm2
(c) molecules/cm3
[2] typical depth resolution in RBS (a) 0.2 nm
(b) 2 nm
(c) 20 nm
[1] RBS is more sensitive for (a) heavy elements
(b) light elements
[4] with RBS it is easy to measure (a) an impurity with low atomic number in a matrix of high atomic number
(b) an impurity with high atomic number in a matrix of low atomic number
[5] RBS is more sensitive for (a) backscattering (180°)
(b) scattering at (90°)
4 Basic concepts (i) Energy transfer from a projectile to a target nucleus in an
elastic two-body collision (kinematic factor)
(ii) Likelihood of occurrence of such a two-body collision (scattering cross section)
(iii) Average energy loss of an high energy atom through a dense medium (stopping cross section)
(iv) Statistical fluctuations in energy loss of an atom moving through a dense medium (energy straggling)
Surface impurity
50 100 150 200 250 300 350 400
0
200
400
600
800
1000
1200
1400
1600
1800
ba
cksca
tte
r yie
ld, co
un
ts
channel
Surface impurity
50 100 150 200 250 300 350 400
0
200
400
600
800
1000
1200
1400
1600
1800
ba
ckscatte
r yie
ld, cou
nts
channel
Surface impurity
50 100 150 200 250 300 350 400
0
200
400
600
800
1000
1200
1400
1600
1800
0.0
0.2
0.4
0.6
0.8
1.0
b
acksca
tte
r yie
ld, co
un
ts
channel
0.92
0.56
0.36
K
5 keV/channel
0.25
Surface impurity
100 150 200 250 300 350 400
0.4
0.6
0.8
1.0
1.2
1.4
1.6
1.8
2.0
E =0.01327+0.00496·channelk·E
0 [M
eV
]
channel
Surface impurity
0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0
0
200
400
600
800
1000
1200
1400
1600
1800
b
ackscatte
r yie
ld, cou
nts
Energy [MeV]
C
OSi
Au
Surface impurity
0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0
0
200
400
600
800
1000
1200
1400
1600
1800
ba
cksca
tte
r yie
ld, co
un
ts
Energy [MeV]
C
OSi
Au
Element Channel K E1 σ C [MeV] [10-24 cm] [counts]
----------------------------------------------------------------------------------------- C 98 0.2526 0.5052 0.037 1100 O 145 0.3625 0.725 0.074 390 Si 225 0.5657 1.1314 0.248 460 Au 369 0.9225 1.845 8.2 1400
Θ=170°, Ω=4.11 msr, Q=10 μC = 6.25·1013 ions
Surface impurity
0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0
0
200
400
600
800
1000
1200
1400
1600
1800
ba
cksca
tte
r yie
ld, co
un
ts
Energy [MeV]
C
OSi
Au
Element Channel K E1 σ C (N·t) [MeV] [10-24 cm] [counts] [1015 atoms/cm2]
----------------------------------------------------------------------------------------------------------------- C 98 0.2526 0.5052 0.037 1100 O 145 0.3625 0.725 0.074 390 20.5 Si 225 0.5657 1.1314 0.248 460 7.2 Au 369 0.9225 1.845 8.200 1400 0.67
Θ=170°, Ω=4.11 msr, Q=10 μC = 6.25·1013 ions
Elemental film
1.4 1.5 1.6 1.7 1.8 1.9 2.0
0
2000
4000
6000
8000
10000
12000
E* = k
Pt·E
0- E
ba
ckscatte
r yie
ld [cou
nts
]
E1 [MeV]
E1 = k
Pt·E
0
Elemental film
1.4 1.5 1.6 1.7 1.8 1.9 2.0
0
2000
4000
6000
8000
10000
12000
E* = k
Pt·E
0- E
ba
cksca
tte
r yie
ld [co
un
ts]
E1 [MeV]
E1 = k
Pt·E
0
𝐸 = 𝜖Nt ≅ 𝜀0𝑁𝑡 E1 = 1.844 MeV E*= 1.524 MeV ΔE = 320 keV
Surface impurity
0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0
0
200
400
600
800
1000
1200
1400
1600
1800
ba
cksca
tte
r yie
ld, co
un
ts
Energy [MeV]
C
OSi
Au
Element Channel K E1 σ C (N·t) [MeV] [10-24 cm] [counts] [1015 atoms/cm2]
----------------------------------------------------------------------------------------------------------------- C 98 0.2526 0.5052 0.037 1100 O 145 0.3625 0.725 0.074 390 20.5 Si 225 0.5657 1.1314 0.248 460 7.2 Au 369 0.9225 1.845 8.200 1400 0.67
Θ=170°, Ω=4.11 msr, Q=10 μC = 6.25·1013 ions
Surface impurity
0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0
0
200
400
600
800
1000
1200
1400
1600
1800
ba
cksca
tte
r yie
ld, co
un
ts
Energy [MeV]
C
OSi
Au
Element Channel K E1 σ C (N·t) (N·t) [MeV] [10-24 cm] [counts] [1015 atoms/cm2] [1015 atoms/cm2]
----------------------------------------------------------------------------------------------------------------------------- C 98 0.2526 0.5052 0.037 1100 O 145 0.3625 0.725 0.074 390 20.5 20.9 Si 225 0.5657 1.1314 0.248 460 7.2 7.4 Au 369 0.9225 1.845 8.200 1400 0.67 0.68
Θ=170°, Ω=4.11 msr, Q=10 μC = 6.25·1013 ions
Example 2: Liquid Target PEG400 with trace of TEABr
Polyethylene glycol (PEG)
Tetraethylammonium bromide (TEABr)
Example 2: Liquid Target PEG400 with trace of TEABr
Lanford et al., Nucl. Instr. and Meth. in Phys. Res. B 161-163 ,202 (2000)
Example 2: Liquid Target PEG400 with trace of TEABr
Williams, NUCLEAR INSTRUMENTS AND METHODS 26, 205 (I975)
Summary: 4 Basic concepts (i) Energy transfer from a projectile to a target nucleus in an
elastic two-body collision (kinematic factor)
(ii) Likelihood of occurrence of such a two-body collision (scattering cross section)
(iii) Average energy loss of an high energy atom through a dense medium (stopping cross section)
(iv) Statistical fluctuations in energy loss of an atom moving through a dense medium (energy straggling)