In nuclear reactions we are concerned with the transition

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In nuclear reactions we are concerned with the
transition
?i gt ? ?f gt
In photo-nuclear reactions we are concerned with
the transition
? ?i gt ? ?f gt
The hamiltionian for the system involves the
nuclear hamiltonian and the EM one
H Hnucl Hem
The transition amplitude for this reaction is
Mfi ltf? Hem?Igt
Hnucl is generally written as
Hnucl HSM R
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Photons are mighty
proton
nucleus
But photons are gentle
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Total absorption cross section
E? (MeV)
?7 fm
Interaction with a few nucleons
Interaction with whole nucleus
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The Giant Dipole region The wavelength of the
photon is much bigger than the size of the
nucleus.
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The Giant Dipole region The nucleus is forced
into collective vibrations, and at the right
frequency, resonance
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The Giant Dipole region The nucleus is forced
into collective vibrations, and at the right
frequency, resonance
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The Giant Dipole region The nucleus is forced
into collective vibrations, and at the right
frequency, resonance
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The Giant Dipole region The nucleus is forced
into collective vibrations, and at the right
frequency, resonance
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The Giant Dipole region The nucleus is forced
into collective vibrations, and at the right
frequency, resonance
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The Giant Dipole region The nucleus is forced
into collective vibrations, and at the right
frequency, resonance
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The Giant Dipole region The nucleus is forced
into collective vibrations, and at the right
frequency, resonance
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The Giant Dipole region The nucleus is forced
into collective vibrations, and at the right
frequency, resonance
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The resonance energy
Em const A-1/3
E (hc/?)varies as 1/R
Nucleus models as liquid drop
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For Light nuclei.16O
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E1 (electric dipole) absorption
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E (electric dipole) absorption
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E (electric dipole) absorption
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E (electric dipole) absorption
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The resonance width
Narrow near closed shell nuclei why?
Deformed nuclei
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Photoproton reaction
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Direct knockout mechanism
Fine (not quite) for protons!
Neutrons have no charge? Expect (?,n) small.
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12C(?,n) 12C(?,p)
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Photoneutron reaction
? ? ?
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Why does a photon knock out a neutron as often as
a proton?
1. The photon interacts with the proton, then
the proton knocks out the neutron
The direct knock-on model, with final state
interactions. (DKO)
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Knock-on mechanism
Still predicts (?,n) cross section as too small.
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Why does a photon knock out a neutron as often as
a proton?
2. The photon interacts with proton - neutron
pairs that look like deuterons
The Quasi-deuteron model (QDM)
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Quasi-deuteron interaction
Works pretty well, but is it true?
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Two-nucleon emission
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Why does a photon knock out a neutron as often as
a proton?
3. The nucleus is really more complicated, and
the photon interacts with any charge in the
nucleus, including p mesons. The detailed
interactions must be considered
The microscopic calculation model
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How to find the true interaction
Measure the states that are left following the
(g,pn) reaction.
Perfect! Predictions are different and we can
discriminate. Problem The measurements are hard
to do.
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16O(?.pn)14NGS
2.3.MeV GS I1
14Nnp
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16O(?.pn)14N2.3
2.3.MeV I0 GS
14Nnp
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Tagging the photons
How to determine te energy of a photon that
interacts with the target when the photon
spectrum is continuous.
E? Ee - Etag
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A New State in 6He following the 7Li(?,p)6He
Reaction Mark Bolands PhD
The fascinating nucleus 6He, with twice as many
neutrons as protons. On the neutron drip line
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6He is modelled as an ? core with a halo of 2
weakly-coupled neutrons
Collective oscillations of the neutrons against
the core give soft-dipole state
Other interactions of the 3 bodies give a range
of unbound resonances with different J?
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6He
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• 6He has a ß-decay halflife of 800 ms
• Not suitable as a target
• Could be projectile
• radio-active beam experiments

How to test the predictions?
Charge-exchange 6Li ? 6He Heavy-ion
experiments e.g. 6Li(7Li,7Be)6He
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Heavy Ions
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6He!
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Photonuclear measurement 7Li(?.p)6He is the
elegant solution
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50 to 70 MeV
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Mark Boland setting up the GLUE Chamber
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Set up for 7Li(g,p) Experiment
Solid-state proton detector (Proton energy)
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Energy lost in thin detector
Total energy of particle
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6He p
7Li
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MAX LABORATORY Lund Sweden.
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Upgrade of accelerator 2003
Leading to a new regime of photonuclear
experiments in 2004
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Unitarity of Cabibbo-Kobayashi-Maskawa matrix A
check on the standard model
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26Al
26Mg
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In such super allowed decays, what has happened
is that one of the up quarks in the proton has
changed to a down quark.
and can be determined from the halflife value for
super allowed ?-decay.
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?-ray detector
27Al
26Mg
?-ray detector
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Photons and Nucleon Structure

• above the ?-meson threshold.

• will begin to probe the inter-nucleon meson cloud
  and the quark structure.

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Examining the sub-structure of the proton
A measurement of the of the photo-absorption of
the proton at 2 GeV Seeking the source of the
proton spin
Sophisticated experiment to use the 8-GeV
electron synchrotron near Osaka in Japan
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A move into studying the composition of the
proton and neutron.
With wavelengths much less than the size of the
nucleons we can probe their substructure..the
effects of the quarks and gluons.
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Only part of the proton spin (1/2) results from
quarks. The rest involves the gluons. To
resolve this, a massless probe (the photon) is
needed. The measurement will be to measure the
total absorption of photons at about 2
GeV. Sophisticated experiment
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SPring-8 (Super Photon ring-8 GeV). One line is
devoted to producing monochratic photons by LASER
scattering.
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Producing high-energy photons by Compton
backscattering
8 GeV electrons
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Producing high-energy photons by Compton
backscattering
Argon Laser
8 GeV electrons
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Producing high-energy photons by Compton
backscattering
Argon Laser
8 GeV electrons
3 GeV ?-ray