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7/31/2019 Anirbit Pound and Rebka
1/74
The Pound and
Rebka experiment.
Anirbit
Dreams and
Reality
Removing sources
of extranneous
frequency shifts
The mechanics
and the electronics
of the experiment
It begins where it
ends
The Pound and Rebka experiment.
Anirbit
October 21, 2008
http://find/7/31/2019 Anirbit Pound and Rebka
2/74
The Pound and
Rebka experiment.
Anirbit
Dreams and
Reality
Removing sources
of extranneous
frequency shifts
The mechanics
and the electronics
of the experiment
It begins where it
ends
Miles to go before you sleep...
Dreams and Reality
Removing sources of extranneous frequency shifts
The mechanics and the electronics of the experiment
It begins where it ends
http://find/http://goback/7/31/2019 Anirbit Pound and Rebka
3/74
The Pound and
Rebka experiment.
Anirbit
Dreams and
Reality
Removing sources
of extranneous
frequency shifts
The mechanics
and the electronics
of the experiment
It begins where it
ends
The aim of the experiment
For various reasons (NOT necessarily coming from GeneralRelativity) theoretical physicists had started believing thatgravitational force affects energy of the photon and hencethere was a pressing need to experimentally test thisapparently non-intuitive prediction.
http://find/7/31/2019 Anirbit Pound and Rebka
4/74
The Pound and
Rebka experiment.
Anirbit
Dreams and
Reality
Removing sources
of extranneous
frequency shifts
The mechanics
and the electronics
of the experiment
It begins where it
ends
The aim of the experiment
For various reasons (NOT necessarily coming from GeneralRelativity) theoretical physicists had started believing thatgravitational force affects energy of the photon and hencethere was a pressing need to experimentally test thisapparently non-intuitive prediction.
Thats what Pound and Rebka tested in their famous 1960experiment published on 1st April 1960 in Physical ReviewLetters.
http://find/http://goback/7/31/2019 Anirbit Pound and Rebka
5/74
The Pound and
Rebka experiment.
Anirbit
Dreams and
Reality
Removing sources
of extranneous
frequency shifts
The mechanics
and the electronics
of the experiment
It begins where it
ends
The aim of the experiment
For various reasons (NOT necessarily coming from GeneralRelativity) theoretical physicists had started believing thatgravitational force affects energy of the photon and hencethere was a pressing need to experimentally test thisapparently non-intuitive prediction.
Thats what Pound and Rebka tested in their famous 1960experiment published on 1st April 1960 in Physical ReviewLetters.
Rebka was a graduate student under Pound at the HarvardUniversity.
http://find/7/31/2019 Anirbit Pound and Rebka
6/74
The Pound and
Rebka experiment.
Anirbit
Dreams and
Reality
Removing sources
of extranneous
frequency shifts
The mechanics
and the electronics
of the experiment
It begins where it
ends
References
Apparent Weight of Photons by Pound and Rebka on1stApril 1960PRL
Lectures by Mester Experimental Tests of GeneralRelativity
The Mossbauer Effect review paper by A.F.Boyle andH.E.Hoyle
Weighing Photons, I by R. V. Pound, Physics in
Perspective 2, 224 (2000) Weighing Photons, IIR. V. Pound, Physics in
Perspective 3, 4 (2001)
http://find/7/31/2019 Anirbit Pound and Rebka
7/74
The Pound and
Rebka experiment.
Anirbit
Dreams and
Reality
Removing sources
of extranneous
frequency shifts
The mechanics
and the electronics
of the experiment
It begins where it
ends
Thanks
I would also thank Prof.Arnab for the references and
Arnab Sen (senior DTP student) and Prof.Vikram forhelpful disucssions
http://find/http://goback/7/31/2019 Anirbit Pound and Rebka
8/74
The Pound and
Rebka experiment.
Anirbit
Dreams and
Reality
Removing sources
of extranneous
frequency shifts
The mechanics
and the electronics
of the experiment
It begins where it
ends
A rough idea of the magnitude of the effect
The Jefferson Physical Laboratory at Harvard has anenclosed and isolated tower that is 22.5m high. Thisgravitational force over this height difference can produce a
fractional frequency shift of 2.5 10
15 (gh
c2 ).
http://find/7/31/2019 Anirbit Pound and Rebka
9/74
The Pound and
Rebka experiment.
Anirbit
Dreams and
Reality
Removing sources
of extranneous
frequency shifts
The mechanics
and the electronics
of the experiment
It begins where it
ends
A rough idea of the magnitude of the effect
The Jefferson Physical Laboratory at Harvard has anenclosed and isolated tower that is 22.5m high. Thisgravitational force over this height difference can produce a
fractional frequency shift of 2.5 10
15 (gh
c2 ).
So that kind of number that they were trying tomeasure is of the order of 1015!
http://find/http://goback/7/31/2019 Anirbit Pound and Rebka
10/74
The Pound and
Rebka experiment.
Anirbit
Dreams and
Reality
Removing sources
of extranneous
frequency shifts
The mechanics
and the electronics
of the experiment
It begins where it
ends
A rough idea of the magnitude of the probe
Any source of photons has a Natural Linewidth which is a
completely quantum phenomemon coming from theuncertainity principle.
http://find/7/31/2019 Anirbit Pound and Rebka
11/74
The Pound and
Rebka experiment.
Anirbit
Dreams and
Reality
Removing sources
of extranneous
frequency shifts
The mechanics
and the electronics
of the experiment
It begins where it
ends
A rough idea of the magnitude of the probe
Any source of photons has a Natural Linewidth which is a
completely quantum phenomemon coming from theuncertainity principle.
The gamma photon source they had was 14Kev transition of
Fe57 and that has a Natural Lifetime of the order of = 107sec.
http://find/7/31/2019 Anirbit Pound and Rebka
12/74
The Pound and
Rebka experiment.
Anirbit
Dreams and
Reality
Removing sources
of extranneous
frequency shifts
The mechanics
and the electronics
of the experiment
It begins where it
ends
A rough idea of the magnitude of the probe
Any source of photons has a Natural Linewidth which is a
completely quantum phenomemon coming from theuncertainity principle.
The gamma photon source they had was 14Kev transition of
Fe57 and that has a Natural Lifetime of the order of = 107sec.
Hence a Natural Linewidth of = h
= 108eV.
http://find/7/31/2019 Anirbit Pound and Rebka
13/74
The Pound and
Rebka experiment.
Anirbit
Dreams and
Reality
Removing sources
of extranneous
frequency shifts
The mechanics
and the electronics
of the experiment
It begins where it
ends
A rough idea of the magnitude of the probe
Any source of photons has a Natural Linewidth which is a
completely quantum phenomemon coming from theuncertainity principle.
The gamma photon source they had was 14Kev transition of
Fe57 and that has a Natural Lifetime of the order of = 107sec.
Hence a Natural Linewidth of = h
= 108eV.
So the probe has a natural spread that is a fractionalFWHM of
E= 1012
http://find/7/31/2019 Anirbit Pound and Rebka
14/74
The Pound and
Rebka experiment.
Anirbit
Dreams and
Reality
Removing sources
of extranneous
frequency shifts
The mechanics
and the electronics
of the experiment
It begins where it
ends
The constraints
So far the probe sounds precise enough for the purpose but avariety of phenomenomenon can ruin this precision. Twomost important of these are:
http://find/7/31/2019 Anirbit Pound and Rebka
15/74
The Pound and
Rebka experiment.
Anirbit
Dreams and
Reality
Removing sources
of extranneous
frequency shifts
The mechanics
and the electronics
of the experiment
It begins where it
ends
The constraints
So far the probe sounds precise enough for the purpose but avariety of phenomenomenon can ruin this precision. Twomost important of these are:
Doppler broadening due to thermal motion of theemitter.
Th P d d
http://find/7/31/2019 Anirbit Pound and Rebka
16/74
The Pound and
Rebka experiment.
Anirbit
Dreams and
Reality
Removing sources
of extranneous
frequency shifts
The mechanics
and the electronics
of the experiment
It begins where it
ends
The constraints
So far the probe sounds precise enough for the purpose but avariety of phenomenomenon can ruin this precision. Twomost important of these are:
Doppler broadening due to thermal motion of theemitter.
A difference of 0.6C between the emitter and theabsorber can swamp out the gravitational effect.
Th P d d
http://find/7/31/2019 Anirbit Pound and Rebka
17/74
The Pound and
Rebka experiment.
Anirbit
Dreams and
Reality
Removing sources
of extranneous
frequency shifts
The mechanics
and the electronics
of the experiment
It begins where it
ends
The constraints
So far the probe sounds precise enough for the purpose but avariety of phenomenomenon can ruin this precision. Twomost important of these are:
Doppler broadening due to thermal motion of theemitter.
A difference of 0.6C between the emitter and theabsorber can swamp out the gravitational effect.
The recoil of the emitting nuleus broadens the emissionspectra.
The Pound and
h
http://find/http://goback/7/31/2019 Anirbit Pound and Rebka
18/74
The Pound and
Rebka experiment.
Anirbit
Dreams and
Reality
Removing sources
of extranneous
frequency shifts
The mechanics
and the electronics
of the experiment
It begins where it
ends
The constraints
So far the probe sounds precise enough for the purpose but avariety of phenomenomenon can ruin this precision. Twomost important of these are:
Doppler broadening due to thermal motion of theemitter.
A difference of 0.6C between the emitter and theabsorber can swamp out the gravitational effect.
The recoil of the emitting nuleus broadens the emissionspectra.
A free recoil will cause a spread of about 105 timesthe natural width
The Pound and
http://find/http://goback/7/31/2019 Anirbit Pound and Rebka
19/74
The Pound and
Rebka experiment.
Anirbit
Dreams and
Reality
Removing sources
of extranneous
frequency shifts
The mechanics
and the electronics
of the experiment
It begins where it
endsFrom these numbers it is obvious that Pound andRebka have to do everything they can to reduce theeffect of the recoil and thermal motion.
The Pound and
F i i i
http://find/http://goback/7/31/2019 Anirbit Pound and Rebka
20/74
The Pound and
Rebka experiment.
Anirbit
Dreams and
Reality
Removing sources
of extranneous
frequency shifts
The mechanics
and the electronics
of the experiment
It begins where it
ends
From constraints to creativity...
The Pound and
O i /R i d f th b i t
http://find/http://goback/7/31/2019 Anirbit Pound and Rebka
21/74
The Pound and
Rebka experiment.
Anirbit
Dreams and
Reality
Removing sources
of extranneous
frequency shifts
The mechanics
and the electronics
of the experiment
It begins where it
ends
Overview/Reminder of the basic concepts
As explained earlier we need a precise source of gammaphotons (of high energy (10 100Kev) so that thenatural line width
is very small of the order of 1012)
The Pound and
O i /R i d f th b i t
http://find/http://goback/7/31/2019 Anirbit Pound and Rebka
22/74
u
Rebka experiment.
Anirbit
Dreams and
Reality
Removing sources
of extranneous
frequency shifts
The mechanics
and the electronics
of the experiment
It begins where it
ends
Overview/Reminder of the basic concepts
As explained earlier we need a precise source of gammaphotons (of high energy (10 100Kev) so that thenatural line width
is very small of the order of 1012)
Thats where the then recent, 1958 discovery ofMossbauer effect (the so calledrecoilless photons)
comes in to achive this.
The Pound and
O e ie /Re i de of the basic co ce ts
http://find/7/31/2019 Anirbit Pound and Rebka
23/74
Rebka experiment.
Anirbit
Dreams and
Reality
Removing sourcesof extranneous
frequency shifts
The mechanics
and the electronics
of the experiment
It begins where it
ends
Overview/Reminder of the basic concepts
As explained earlier we need a precise source of gamma
photons (of high energy (10 100Kev) so that thenatural line width
is very small of the order of 1012)
Thats where the then recent, 1958 discovery ofMossbauer effect (the so calledrecoilless photons)
comes in to achive this. Once we have a precise source of photons the idea is to
measure the frequency shift of it due to gravitation
The Pound and
Overview/Reminder of the basic concepts
http://find/7/31/2019 Anirbit Pound and Rebka
24/74
Rebka experiment.
Anirbit
Dreams and
Reality
Removing sourcesof extranneous
frequency shifts
The mechanics
and the electronics
of the experiment
It begins where it
ends
Overview/Reminder of the basic concepts
As explained earlier we need a precise source of gamma
photons (of high energy (10 100Kev) so that thenatural line width
is very small of the order of 1012)
Thats where the then recent, 1958 discovery ofMossbauer effect (the so calledrecoilless photons)
comes in to achive this. Once we have a precise source of photons the idea is to
measure the frequency shift of it due to gravitation
NOT directly
The Pound and
Overview/Reminder of the basic concepts
http://find/http://goback/7/31/2019 Anirbit Pound and Rebka
25/74
Rebka experiment.
Anirbit
Dreams and
Reality
Removing sourcesof extranneous
frequency shifts
The mechanics
and the electronics
of the experiment
It begins where it
ends
Overview/Reminder of the basic concepts
As explained earlier we need a precise source of gamma
photons (of high energy (10 100Kev) so that thenatural line width
is very small of the order of 1012)
Thats where the then recent, 1958 discovery ofMossbauer effect (the so calledrecoilless photons)
comes in to achive this. Once we have a precise source of photons the idea is to
measure the frequency shift of it due to gravitation
NOT directly
but by determining the velocity of the source whichcancels this shift by the doppler shift.
The Pound and
R bkOverview/Reminder of the basic concepts
http://find/7/31/2019 Anirbit Pound and Rebka
26/74
Rebka experiment.
Anirbit
Dreams and
Reality
Removing sourcesof extranneous
frequency shifts
The mechanics
and the electronics
of the experiment
It begins where it
ends
Overview/Reminder of the basic concepts
As explained earlier we need a precise source of gamma
photons (of high energy (10 100Kev) so that thenatural line width
is very small of the order of 1012)
Thats where the then recent, 1958 discovery ofMossbauer effect (the so calledrecoilless photons)
comes in to achive this. Once we have a precise source of photons the idea is to
measure the frequency shift of it due to gravitation
NOT directly
but by determining the velocity of the source whichcancels this shift by the doppler shift.
The Pound and
R bk iWhat is Mossbauser Effect?
http://find/7/31/2019 Anirbit Pound and Rebka
27/74
Rebka experiment.
Anirbit
Dreams and
Reality
Removing sourcesof extranneous
frequency shifts
The mechanics
and the electronics
of the experiment
It begins where it
ends
What is Mossbauser Effect?
The crude picture:
The Pound and
Rebk e e i e tWhat is Mossbauser Effect?
http://find/7/31/2019 Anirbit Pound and Rebka
28/74
Rebka experiment.
Anirbit
Dreams and
Reality
Removing sourcesof extranneous
frequency shifts
The mechanics
and the electronics
of the experiment
It begins where it
ends
What is Mossbauser Effect?
The crude picture:
A nucleus inside a crystal lattice undergoes a quantumtransition and emits a gamma photon.
The Pound and
Rebka experimentWhat is Mossbauser Effect?
http://find/7/31/2019 Anirbit Pound and Rebka
29/74
Rebka experiment.
Anirbit
Dreams and
Reality
Removing sourcesof extranneous
frequency shifts
The mechanics
and the electronics
of the experiment
It begins where it
ends
What is Mossbauser Effect?
The crude picture:
A nucleus inside a crystal lattice undergoes a quantumtransition and emits a gamma photon.
But classically because of the various possible latticevibration modes the emitted photons will have a considerablespread in energy.
The Pound and
Rebka experimentWhat is Mossbauser Effect?
http://find/7/31/2019 Anirbit Pound and Rebka
30/74
Rebka experiment.
Anirbit
Dreams and
Reality
Removing sourcesof extranneous
frequency shifts
The mechanics
and the electronics
of the experiment
It begins where it
ends
What is Mossbauser Effect?
The crude picture:
A nucleus inside a crystal lattice undergoes a quantumtransition and emits a gamma photon.
But classically because of the various possible latticevibration modes the emitted photons will have a considerablespread in energy.
Fortunately the world is quantum theoretic!
The Pound and
Rebka experimentWhat is Mossbauser Effect?
http://find/7/31/2019 Anirbit Pound and Rebka
31/74
Rebka experiment.
Anirbit
Dreams and
Reality
Removing sourcesof extranneous
frequency shifts
The mechanics
and the electronics
of the experiment
It begins where it
ends
What is Mossbauser Effect?
The crude picture:
A nucleus inside a crystal lattice undergoes a quantumtransition and emits a gamma photon.
But classically because of the various possible latticevibration modes the emitted photons will have a considerablespread in energy.
Fortunately the world is quantum theoretic!
Energy is trivially conserved in the process but momentumconservation is the subtlety.
The Pound and
Rebka experiment.
http://find/7/31/2019 Anirbit Pound and Rebka
32/74
Rebka experiment.
Anirbit
Dreams and
Reality
Removing sourcesof extranneous
frequency shifts
The mechanics
and the electronics
of the experiment
It begins where it
ends
If the crystal lattice is very close packed the sound wavesin the lattice, Phonons, can propagate very fast at timescales comparable to nuclear transition times (or
life-time of the excited nucleus) and hence take away themomentum without needing the nucleus to recoil.
The Pound and
Rebka experiment.
http://find/7/31/2019 Anirbit Pound and Rebka
33/74
p
Anirbit
Dreams and
Reality
Removing sourcesof extranneous
frequency shifts
The mechanics
and the electronics
of the experiment
It begins where it
ends
If the crystal lattice is very close packed the sound wavesin the lattice, Phonons, can propagate very fast at timescales comparable to nuclear transition times (or
life-time of the excited nucleus) and hence take away themomentum without needing the nucleus to recoil.
Hence giving a sharp emission frequency limitedpredominantly by the energy uncertainity and the thermalvibration.
The Pound and
Rebka experiment.
http://find/7/31/2019 Anirbit Pound and Rebka
34/74
Anirbit
Dreams and
Reality
Removing sourcesof extranneous
frequency shifts
The mechanics
and the electronics
of the experiment
It begins where it
ends
If the crystal lattice is very close packed the sound wavesin the lattice, Phonons, can propagate very fast at timescales comparable to nuclear transition times (or
life-time of the excited nucleus) and hence take away themomentum without needing the nucleus to recoil.
Hence giving a sharp emission frequency limitedpredominantly by the energy uncertainity and the thermalvibration.
Further the stiffness of the crystal causes the energylevels of the emitter to be far spaced and that alsoreduces the broadening by suppressing the transitionprobabilities.
The Pound and
Rebka experiment.
http://find/7/31/2019 Anirbit Pound and Rebka
35/74
Anirbit
Dreams and
Reality
Removing sourcesof extranneous
frequency shifts
The mechanics
and the electronics
of the experiment
It begins where it
ends
There are more precise arguments using uncertainityprinciple and these can also be justified by elaborateperturbation theory.
The Pound and
Rebka experiment.
http://find/7/31/2019 Anirbit Pound and Rebka
36/74
Anirbit
Dreams and
Reality
Removing sourcesof extranneous
frequency shifts
The mechanics
and the electronics
of the experiment
It begins where it
ends
There are more precise arguments using uncertainityprinciple and these can also be justified by elaborateperturbation theory.
These arguments shows that we have an upper bound oforder of 100Kev for the gamma photons to show MossbauerEffect.
The Pound and
Rebka experiment.Miles to go before you sleep...
http://find/7/31/2019 Anirbit Pound and Rebka
37/74
Anirbit
Dreams and
Reality
Removing sourcesof extranneous
frequency shifts
The mechanics
and the electronics
of the experiment
It begins where it
ends
Dreams and Reality
Removing sources of extranneous frequency shifts
The mechanics and the electronics of the experiment
It begins where it ends
http://find/7/31/2019 Anirbit Pound and Rebka
38/74
The Pound and
Rebka experiment.
7/31/2019 Anirbit Pound and Rebka
39/74
Anirbit
Dreams and
Reality
Removing sourcesof extranneous
frequency shifts
The mechanics
and the electronics
of the experiment
It begins where it
ends
Note the following important things:
Mossbauer Effect is a purely quantum phenomenon.
If the emitter de-excites to the same atoms as thelattice then phonon propagation is facilitated and theemission line sharpens.
The Pound and
Rebka experiment.
http://find/7/31/2019 Anirbit Pound and Rebka
40/74
Anirbit
Dreams and
Reality
Removing sourcesof extranneous
frequency shifts
The mechanics
and the electronics
of the experiment
It begins where it
ends
Note the following important things:
Mossbauer Effect is a purely quantum phenomenon.
If the emitter de-excites to the same atoms as thelattice then phonon propagation is facilitated and theemission line sharpens.
The Pound and
Rebka experiment.
http://find/7/31/2019 Anirbit Pound and Rebka
41/74
Anirbit
Dreams and
Reality
Removing sourcesof extranneous
frequency shifts
The mechanics
and the electronics
of the experiment
It begins where it
endsGetting a great Mossbauer Effect was an important
aspect where Pound and Rebka won over theircompetitors by carefully annealing the source so thatthe emitter (0.4 curie of 270 day Co57) diffuses to adistance of 3 105 cm into a 0.005 inch of iron disk.
The Pound and
Rebka experiment.The two important aspects of the experiment
http://find/7/31/2019 Anirbit Pound and Rebka
42/74
Anirbit
Dreams and
Reality
Removing sourcesof extranneous
frequency shifts
The mechanics
and the electronics
of the experiment
It begins where it
ends
What is required to get the Mossbauser effect?
The Pound and
Rebka experiment.The two important aspects of the experiment
http://find/7/31/2019 Anirbit Pound and Rebka
43/74
Anirbit
Dreams and
Reality
Removing sourcesof extranneous
frequency shifts
The mechanics
and the electronics
of the experiment
It begins where it
ends
What is required to get the Mossbauser effect?which was discussed in the previous slide
The Pound and
Rebka experiment.The two important aspects of the experiment
http://find/7/31/2019 Anirbit Pound and Rebka
44/74
Anirbit
Dreams and
Reality
Removing sourcesof extranneous
frequency shifts
The mechanics
and the electronics
of the experiment
It begins where it
ends
What is required to get the Mossbauser effect?which was discussed in the previous slide
What are the other sources of frequency shifts thathave to be eliminated?
The Pound and
Rebka experiment.The two important aspects of the experiment
http://find/7/31/2019 Anirbit Pound and Rebka
45/74
Anirbit
Dreams and
Reality
Removing sourcesof extranneous
frequency shifts
The mechanics
and the electronics
of the experiment
It begins where it
ends
What is required to get the Mossbauser effect?which was discussed in the previous slide
What are the other sources of frequency shifts thathave to be eliminated?
The Pound and
Rebka experiment.
A i bi
Other sources of frequency shiftsd h i l
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46/74
Anirbit
Dreams and
Reality
Removing sourcesof extranneous
frequency shifts
The mechanics
and the electronics
of the experiment
It begins where it
ends
and their removal
The Pound and
Rebka experiment.
A i bit
Other sources of frequency shiftsd th i l
http://find/7/31/2019 Anirbit Pound and Rebka
47/74
Anirbit
Dreams and
Reality
Removing sourcesof extranneous
frequency shifts
The mechanics
and the electronics
of the experiment
It begins where it
ends
and their removal
The energy of the emitted gamma photons is sensitiveto temperature. A difference of 0.6C can swamp outthe gravitational effect.
The Pound and
Rebka experiment.
Anirbit
Other sources of frequency shiftsd th i l
http://find/7/31/2019 Anirbit Pound and Rebka
48/74
Anirbit
Dreams and
Reality
Removing sourcesof extranneous
frequency shifts
The mechanics
and the electronics
of the experiment
It begins where it
ends
and their removal
The energy of the emitted gamma photons is sensitiveto temperature. A difference of 0.6C can swamp outthe gravitational effect.
Hence the source and the absorber were kept at thesame temperature maintained by a thermocouple.
The Pound and
Rebka experiment.
Anirbit
Other sources of frequency shiftsa d thei e o al
http://find/7/31/2019 Anirbit Pound and Rebka
49/74
Anirbit
Dreams and
Reality
Removing sourcesof extranneous
frequency shifts
The mechanics
and the electronics
of the experiment
It begins where it
ends
and their removal
The energy of the emitted gamma photons is sensitiveto temperature. A difference of 0.6C can swamp outthe gravitational effect.
Hence the source and the absorber were kept at thesame temperature maintained by a thermocouple.
There were very high intrinsic frequncy shifts between
the source and the emitter.
The Pound and
Rebka experiment.
Anirbit
Other sources of frequency shiftsand their removal
http://find/7/31/2019 Anirbit Pound and Rebka
50/74
Anirbit
Dreams and
Reality
Removing sourcesof extranneous
frequency shifts
The mechanics
and the electronics
of the experiment
It begins where it
ends
and their removal
The energy of the emitted gamma photons is sensitiveto temperature. A difference of 0.6C can swamp outthe gravitational effect.
Hence the source and the absorber were kept at thesame temperature maintained by a thermocouple.
There were very high intrinsic frequncy shifts between
the source and the emitter.
This effect was elimated by exchanging the sourceand the absorber many times during the experiment.
The Pound and
Rebka experiment.
Anirbit
http://find/7/31/2019 Anirbit Pound and Rebka
51/74
Anirbit
Dreams and
Reality
Removing sourcesof extranneous
frequency shifts
The mechanics
and the electronics
of the experiment
It begins where it
ends
The Pound and
Rebka experiment.
Anirbit
http://find/7/31/2019 Anirbit Pound and Rebka
52/74
Dreams and
Reality
Removing sourcesof extranneous
frequency shifts
The mechanics
and the electronics
of the experiment
It begins where it
endsThese two effects were not considered by the previous
experimenters like Cranshaw and hence through theydid similar experiments their data was not convincingthat the shift was coming completely due togravitational effect.
The Pound and
Rebka experiment.
Anirbit
Reduction of the absorption
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Dreams and
Reality
Removing sourcesof extranneous
frequency shifts
The mechanics
and the electronics
of the experiment
It begins where it
ends
Pound and Rebka used the 14Kev transition and these giveabout 70% recoilless gamma photons at room temperature.
The Pound and
Rebka experiment.
Anirbit
Reduction of the absorption
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Dreams and
Reality
Removing sourcesof extranneous
frequency shifts
The mechanics
and the electronics
of the experiment
It begins where it
ends
Pound and Rebka used the 14Kev transition and these giveabout 70% recoilless gamma photons at room temperature.
These gamma photons can be absorbed by air.
The Pound and
Rebka experiment.
Anirbit
Reduction of the absorption
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Dreams and
Reality
Removing sourcesof extranneous
frequency shifts
The mechanics
and the electronics
of the experiment
It begins where it
ends
Pound and Rebka used the 14Kev transition and these giveabout 70% recoilless gamma photons at room temperature.
These gamma photons can be absorbed by air.
So they kept a constant flow ofHe through the Mylar Bagat the rate of 30liters/hr.
The Pound and
Rebka experiment.
Anirbit
Miles to go before you sleep...
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Dreams and
Reality
Removing sources
of extranneous
frequency shifts
The mechanics
and the electronics
of the experiment
It begins where it
ends
Dreams and Reality
Removing sources of extranneous frequency shifts
The mechanics and the electronics of the experiment
It begins where it ends
The Pound and
Rebka experiment.
Anirbit
Some idea of the instrumentation Mechanics
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Dreams and
Reality
Removing sources
of extranneous
frequency shifts
The mechanics
and the electronics
of the experiment
It begins where it
ends
Mechanics
The Pound and
Rebka experiment.
Anirbit
Some idea of the instrumentation Mechanics
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Dreams and
Reality
Removing sources
of extranneous
frequency shifts
The mechanics
and the electronics
of the experiment
It begins where it
ends
Mechanics
The source of gamma photons was sinosoidally moved usinga loudspeaker kind of apparatus oscillating at a frequency of10 15 Htz.(intentionally kept much higher than the shiftthat gravity would cause).
The Pound and
Rebka experiment.
Anirbit
Some idea of the instrumentation Mechanics
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Dreams and
Reality
Removing sources
of extranneous
frequency shifts
The mechanics
and the electronics
of the experiment
It begins where it
ends
The source of gamma photons was sinosoidally moved usinga loudspeaker kind of apparatus oscillating at a frequency of10 15 Htz.(intentionally kept much higher than the shiftthat gravity would cause).
The frequency shift between the emission point and theabsorption point was measured during both the cycles andthe difference between then gave information about the
frequency shift due to gravitation.
The Pound and
Rebka experiment.
Anirbit
Some idea of the instrumentation Mechanics
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Dreams and
Reality
Removing sources
of extranneous
frequency shifts
The mechanics
and the electronics
of the experiment
It begins where it
ends
The source of gamma photons was sinosoidally moved usinga loudspeaker kind of apparatus oscillating at a frequency of10 15 Htz.(intentionally kept much higher than the shiftthat gravity would cause).
The frequency shift between the emission point and theabsorption point was measured during both the cycles andthe difference between then gave information about the
frequency shift due to gravitation.
This method of measurement increased the sensitivity and
removed errors due to background shifts of the modulation. The Pound and
Rebka experiment.
Anirbit
Some idea of the instrumentation Electronics
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Dreams and
Reality
Removing sources
of extranneous
frequency shifts
The mechanics
and the electronics
of the experiment
It begins where it
ends
The Pound andRebka experiment.
Anirbit
Some idea of the instrumentation Electronics
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Dreams and
Reality
Removing sources
of extranneous
frequency shifts
The mechanics
and the electronics
of the experiment
It begins where it
ends
There is an elaborate electronic circuit which essentiallyamplifies the signals from the photomultiplier connected to
the absorber which is a scintillation crystal.
The Pound andRebka experiment.
Anirbit
Some idea of the instrumentation Electronics
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63/74
Dreams and
Reality
Removing sources
of extranneous
frequency shifts
The mechanics
and the electronics
of the experiment
It begins where it
ends
There is an elaborate electronic circuit which essentiallyamplifies the signals from the photomultiplier connected to
the absorber which is a scintillation crystal.
There were 2 such circuits and alternately in each quatercyle of the source the signal was fed into it. The difference
in counts was a measure of the assymmetry and hence of thefrequency shift due to gravitation.
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The Pound andRebka experiment.
Anirbit
Their Results
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Dreams and
Reality
Removing sources
of extranneous
frequency shifts
The mechanics
and the electronics
of the experiment
It begins where it
ends
Pound and Rebka found the frequency shift as12
(5.13 0.51) 1015 good to 10%.
The Pound andRebka experiment.
Anirbit
Their Results
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Dreams and
Reality
Removing sources
of extranneousfrequency shifts
The mechanics
and the electronics
of the experiment
It begins where it
ends
Pound and Rebka found the frequency shift as12
(5.13 0.51) 1015 good to 10%.
Pound and Snider later improved this to an uncertainity of1% (PRL 13 539(1964))
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7/31/2019 Anirbit Pound and Rebka
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The Pound andRebka experiment.
Anirbit
Final reflections
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Dreams and
Reality
Removing sources
of extranneousfrequency shifts
The mechanics
and the electronics
of the experiment
It begins where it
ends
We must keep in mind that this experiment is NOT atest of General Relativity.
This was a truly a path-breaking experiment which forthe first time showed that gravity-photon interaction
can be measured on laboratory length scales.
The Pound andRebka experiment.
Anirbit
Final reflections
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Dreams and
Reality
Removing sources
of extranneousfrequency shifts
The mechanics
and the electronics
of the experiment
It begins where it
ends
We must keep in mind that this experiment is NOT atest of General Relativity.
This was a truly a path-breaking experiment which forthe first time showed that gravity-photon interaction
can be measured on laboratory length scales.I would like to draw a parallel of this experiment withthe Michelson-Morley Experiment.
The Pound andRebka experiment.
Anirbit
D d
Final reflections
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Dreams and
Reality
Removing sources
of extranneousfrequency shifts
The mechanics
and the electronics
of the experiment
It begins where it
ends
We must keep in mind that this experiment is NOT atest of General Relativity.
This was a truly a path-breaking experiment which forthe first time showed that gravity-photon interaction
can be measured on laboratory length scales.I would like to draw a parallel of this experiment withthe Michelson-Morley Experiment.Both of these experiments pushed the limits of precisionand resolution of measurement of length and time.
The Pound andRebka experiment.
Anirbit
D d
Final reflections
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72/74
Dreams and
Reality
Removing sources
of extranneousfrequency shifts
The mechanics
and the electronics
of the experiment
It begins where it
ends
We must keep in mind that this experiment is NOT atest of General Relativity.
This was a truly a path-breaking experiment which forthe first time showed that gravity-photon interaction
can be measured on laboratory length scales.I would like to draw a parallel of this experiment withthe Michelson-Morley Experiment.Both of these experiments pushed the limits of precisionand resolution of measurement of length and time.
We should note that the time difference between thediscovery of Mossbauer Effect and its miraculous use totest gravity-photon interaction is only 2-years!
The Pound andRebka experiment.
Anirbit
Dreams and
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Dreams and
Reality
Removing sources
of extranneousfrequency shifts
The mechanics
and the electronics
of the experiment
It begins where it
ends
I see here a lesson to learn in terms of research that we mustalways be aware of the current frontiers and...
The Pound andRebka experiment.
Anirbit
Dreams and
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Dreams and
Reality
Removing sources
of extranneousfrequency shifts
The mechanics
and the electronics
of the experiment
It begins where it
endsThe chief enemy of creativity is good sense. Picasso
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