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due to the oscillating charge in the antenna
Along this line onedoes not observeany acceleration
Radiation from a dipole-antenna
R
charge ; ( , ) ( / )rad radE q E R t observed acceleration t R c
20
1 1( , ) ( / ) ;
4rad
eE R t acc t R c
R c
To get the dimension right !
Electromagnetic radiation( / )
0
( / )0
mass acceleration force=charge field
[ ] ( / ) [ ]
[ ]
[ ] ( )
i t R cin
i t i c R
i kRin
m acc e E t R c e E e
e E e e
e E t e
0
25
0 20
( ) ;
( )
1 2.82 10
4
i kRrad
in
E t er
E t R
er Ang
mc
Here one observes the full acceleration,but delayed in time by R/c !
1( )radE R
R
Guess that
2 22 2
1 14radE energy density radiated energy R
R R
20
2
2
m/sec Force = Energy
1( , )
4
OK(m/sec)
rad
e acce E R t
R c
2
Polarisation
P=cos2(ψ)
P=1
Interference (mathematical)
z
r
rk zkz
in
2
k’ Q
rk ' outrQrkk )' ( res
0. . (1 )isc ampl r e Q r
0. . ( ) isc ampl r e d Q rr r
Number density
0. . ji
j
sc ampl r e Q r
many
wavecrest
k1
2
as drawn #2 is behind #1 for ”in”
but ahead for ”out” , therefore ” – ”
Phase
0 .
1,2 … many
The dream experiment
2 *2 1 2 2 2 2;i iA f e f e I A A 1Q r Q r
2 2
1 2 1 2
2 1 2 1 2
( ) ( )2 21 2 1 2 1 2
{ } { }
i i i i
i i
I f e f e f e f e
f f f f e f f e
1 1Q r Q r Q r Q r
Q r r Q r r
2 2 122 1 2 1 2.
12
sin( )2
orient average
Q rI f f f f
Q r
2
.
sin( )2 i j
i i jorient averagei i j i j
Q rI f f f
Q r
1,2 … many
DetectorViewingField
Detector
X-ray beam
Kr
Gas cell
sin2
)(2sin
1 2
kQ
QfIntensity
Measuring atomic and molecular formfactors from gas scattering
j
ijmol
ielatom
jeff
def
rQ
rQ rr)(
a=[15.2354 6.70060 4.35910 2.96230]; b=[3.0669 0.241200 10.7805 61.4135];c=1.71890; % Ga
a=[16.6723 6.0710 3.4313 4.27790];b=[2.63450 0.2647 12.9479 47.7972];c=2.531; % As
24( / 4 )0
1
( ) jb Q
j jj
f Q a e c
1cos 2 ( )
sin sin( )
2 2sin
Qri x
i Q r
x Qriorientationalaverage
Qr e dxe d d Qr
eQrd d
Q r
Unit sphere
d
d
r
Q
iorientationalaverage
e Q r
r
sinsind
sind d d
Fourier transform of a Gaussian
Fourier transform : ( ) ( ) i q xF q f x e dx
2 2
( ) a xf x Ae
2 2/(4 )( ) q aAF q e
a
2 2 2 2/ 2 / 21or with ( ) ; ( )
2x qf x e F q e
( ) ( ) when 0Gaussian x x
( ) ( ) (0) f x x dx f
F.T. 1 (delocalize( ) ( )
localized
d in )
in
Gaussi qan x x
x
Convolution of 2 Gaussians
2 2 2 2( ) / 211 1 2/ 2
1( )x xx
h x e e dx
2 2 2 2 2 2
1 2/ 2 / 2 / 2( ) q q qH q e e e
i.e. h(x) is also Gaussian with 2 2 21 2
Side View
Top ViewRing wave (2D) orSpherical wave (3D)
2 23D : 4 independent of i k re
A r rr
Energy density Surface area
locally a plane wave iAe k r
Aperture d Almost planewave when
d
Perfect planewave
k’
k
A point scatterer in the beam
i kReA
R
Spherical wave
2Flux : c Intensity Flux Area scattered in
thru
dI
d
22
2
2
2
i kR i kR Ac e e R
R
c A
dA
d
Defines thescatteringcross section1c
Area is
2R
scattering length
scattI i k x
in e
2LL=(N+1)(
2LL=NNo real beam is perfectly monochromatic
From the 2 equations, derive
21
2LL
the longitudinal coherence length
P(
wavelength band
No real beam is perfectly collimated
P(
D
2 TL
LT
Hereand B beams in phase
A and B out-of-phase
show from the figure that
2T
RL
D
With R being the distance from to
source observation point
A
B The transversecoherence length
Absorption
zeIzI
dzzIdI
0)(
)(
) ,number atomic( Z
34 1
) ,(
ZZ
The experimental setup
X-rays
Sample
Rotation
Scintillator
20m
CCD
< 2 mdeg
E = 8-27 keV
0.7 x 0.7 mm
Tomography
• Study the bulk structures, 3D
• Nondestructive• Small
lengthscales (350 nm)
Fra http://www.unge-forskere.dk/
Galathea III
Single slice
100 microns
Compton Scattering
3
'1 (1 cos )
'
3.86 10
C
C
k
Åmc
Energy and momentum conservation