Introduction to Nuclear physics; The nucleus a complex system
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Héloïse Goutte CERN Summer student program 2010
Introduction to Nuclear physics;
The nucleus a complex system
Héloïse GoutteGANIL
Caen, France
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Héloïse Goutte CERN Summer student program 2010
• What is the heaviest nucleus ?
• How many nuclei do exist ?
• What about the shapes of the nuclei ?
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Héloïse Goutte CERN Summer student program 2010
Terra ingognita
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Héloïse Goutte CERN Summer student program 2010
Ground –state nuclear deformation predicted with theHartree-Fock-Bogoliubov approach with the Gogny force
Nuclei are predicted to be either: spherical prolate or oblate
http://www-phynu.cea.fr
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The nucleus : a complex system
I) Some features about the nucleusdiscoveryradiusbinding energynucleon-nucleon interactionlife timeapplications
II) Modeling of the nucleusliquid dropshell modelmean field
III) Examples of recent studies exotic nucleiisomersshape coexistencesuper heavy
IV) Toward a microscopic description of the fission process
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Héloïse Goutte CERN Summer student program 2010
I) Some features of the nucleus
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Héloïse Goutte CERN Summer student program 2010
The discovery of the nucleus
The structure of the atom was first probed by the Rutherford experiment in 1909.A beam of particles generated by the radioactive decay of radium was directed onto a sheet of a very thin gold foil.
particles
Target Au
source
screen
The unexpected results demonstrated the existence of the atomic nuclei.
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Héloïse Goutte CERN Summer student program 2010
Before this exp. people thought that particles should all be deflected by at mosta few degrees. But some ‘s were deflected through angles much larger than 90 degrees !!
The results suggest that the greater part of the mass of the atom was concentrated into a very small region.Atoms are almost empty except a hard scattering center: the atomic nuclei
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Héloïse Goutte CERN Summer student program 2010
Some questions about the Rutherford experiment
Why a thin target ?
What about electrons ?
Why in the vacuum ?
How can we determine the size of the atomic nucleus from this experiment ?
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Héloïse Goutte CERN Summer student program 2010
Some tracks about the Rutherford experiment
Why a thin target ?
To be sure that the projectile do interact with only one nucleus
What about electrons ?
Electrons do not affect the trajectory of the projectile which is much heavier
Why in the vacuum ?
In the air, the slowing down of the beam and of the scattered make the analysis more complicated and can even stop the particles before detection.
How can we determine the size of the atomic nucleus from this experiment ?
At the distance « a0 » from the center of the nucleus, when the particle go back :Coulomb repulsion = kinetic energy of the particle
The size of the gold nucleus is 2.8 10-14 m
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Héloïse Goutte CERN Summer student program 2010
A nucleus is made of Z protons and N neutrons (the nucleons).
A nucleus is characterized by its mass number A = N + Z and its atomic number Z.
It is written AX.
ATOM NUCLEUS NUCLEON(10-9 m) (10-14 m) (10-15 m)
A nucleus is almost 100000 times smaller than an atom
Do all the nuclei have the same radius ?
The scale of a nucleus
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R = 1.25 x AR = 1.25 x A1/3 1/3 (fm)(fm)
Nuclear radius
The radius increases with A1/3
The volume increases with the number of particles
Radii are extracted from elastic scattering of particles on different targets.
R(f
m)
A1/3 1fm = 10-15 m
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From infinitely small to infinitely large
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Proton and neutrons are: hadron particles (particles governed by the strong
interaction)
They are baryons (made of 3 quarks)Proton uud (charge +e)Neutron udd (charge 0)
Proton and neutron have almost the same mass
Nuclear masses
Mpc2 = 938.272 MeVMnc2 = 939.565 MeV
Mec2 = 0.511 MeV
1 MeV = 106 eVMp= 1.7 10-27 kg
2000 times the mass of the e- :
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Héloïse Goutte CERN Summer student program 2010
The nucleon-nucleon interaction
Proton and neutron interact through the strong interaction.
The strong interaction isvery intenseof short range
Proton –neutron interaction : Vpn > Vnn Vpp Vnn
V (MeV)
r(fm)
What about gravitation in a nucleus ?
The nuclear interaction is stabilizing the nucleus
PLUS
Coulomb interaction between protons (repulsive)
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The four elementary interactions
Name Intensity bosons range
strong 1 Gluons 1 fm =10-
15m
Electromagnetic
10-2 Photons infinity
faible 10-5, 10-6 Leptons contact
gravitation
10-34 Gravitons ? long
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The Nucleon-Nucleon potentialThe Nucleon-Nucleon potential
Distance betweenthe nucleons (fm)
VNN
1 GeV
-50 MeV
1 2 3
«hard core» attractive part«hard core» attractive part
The nucleon-nucleon interaction is still unknown nowadays !!!
Phenomenological parameterization of the interaction ;
THIS IS ONE OF THE MOST IMPORTANT PROBLEM NOWADAYS
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Binding energy
M(A,Z) = N Mn + Z Mp – B(A,Z)
Binding energy per nucleon: B(A,Z)/A ≈ 8 MeV
A stable nucleus is a bound system i.e. its mass is lower than the mass of its components.
(if not the nucleus would release its excess of energy by spontaneously evolving to a state of lower energy composed of free particles)
B(A,Z) : binding energy
Stable bound system for B > 0
Mass of a given nucleus :
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Héloïse Goutte CERN Summer student program 2010
Binding energy per nucleon
Which nuclei could fission spontaneously ?
Mass number A
B/A
(M
eV p
er n
ucle
on)
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Héloïse Goutte CERN Summer student program 2010
The most stable nuclei
Nuclear powerplant
ITER project
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FISSIONFISSION A B + C + A B + C + EE
FUSION FUSION A + B C + A + B C + EE
Energy balance : A MN- BA = B MN- BB + C MN- BC + ∆E
Energy difference : ∆E = BB+ BC- BA
Energy balance : A MN- BA+ B MN- BB = C MN - BC + ∆E
Energy difference : ∆E = BC- BB - BA
Energetic features : Exoenergetic fission only for elements heavier than Fe.Exoenergetic fusion for elements lower than Fe;
(Mp=Mn=MN)
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Some results on stellar nucleosynthesis
Correlation between B/A and abundance
•The abundance of the elements in the Univers depends on their stability
•The abundance of the elements in the Univers reflects the nuclear interaction.
• The most abundant element (hydrogen) is also the lighter one
• Fe (the most stable and abundant) is the nucleus at the limit between : * the burning by fusion for the elements lighter than Fe * the radiative capture of neutrons by elements heavier than Fe.
From E. Gallichet
Atomic number (Z)
Abundance
(%)
B/A
(MeV
)
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Nuclear Life times
A few nuclei are stable : their lifetimes are infinite (comparable to the lifetime of the proton 1033 years.)
The others are unstable : they transform into more stable nuclei
Exponential decay
Half –life T defined as the time for which the number of remaining nucleiis half of its the initial value.
)(tNdt
dN
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Héloïse Goutte CERN Summer student program 2010
Z
A
NX
Z
A
NX
1
1
Z
A
NX
1
1
Z
A
NX 1 1
Z
A
NX 1 1
Z
A
NX
2
4
2
--
++,,
pp
nn
NeutronsNeutrons
Pro
tons
Pro
tons
Different types of radioactivity
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Héloïse Goutte CERN Summer student program 2010
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(170 h)(170 h) (35 h)(35 h)
(55 y)(55 y)
226226Ac (29 h)Ac (29 h)
226226Ra Ra
222222FrFr
226226ThTh
1
29 h
1
35 h
1
170 h
1
55 y
Total versus partial life times
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Life times span many orders of magnitude:
Nitrogen 16 T1/2 = 7.13 s
Oxygen 15 = 2.037 mn
Radium 224 = 3.62 d
Carbon 14 = 5730 y
Molybdenum 100 = 1019 y
Tellurium 124 = 2.2 1028 y
Examples : half lives
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Why do the stable nuclei do not follow the N= Z line ?
Why do we search for new nuclei ?
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How do we experimentally study a nucleus ?
ee- - ,e,e++ ppnnHeavy ions Heavy ions ................
I ) Elastic and inelastic scattering
II ) Transfer ex : (p,n), (d,p) … …
Excitation energy (MeV)
Momentum transferred
R(fm)
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III) Gamma spectroscopy
1) To excite the nucleus
2) To observe its decay
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Num
ber
of
dete
cted p
hoto
ns
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Example of a level scheme
The barcode of a nucleus
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148Sm 160Gd
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Some applications of Nuclear Science
Nuclear physics makes indeed many essential contributions to
Energy production* Electricity generation
* fission : research on * new generations of power plants, new fuel cycles * reduction by transmutation of the long – term impact of the nuclear wastes produced (ADS or GEN IV reactors)
* fusion for the far future : (ITER project) Medicine
* diagnostic * detection of the decay of radioactive isotopes SPECT Single Photon Emission Computer Tomography PET Positron Emission Tomography* IRM Imaging by Magnetic Resonance
* therapy (proton-, hadron-therapy …)
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Héloïse Goutte CERN Summer student program 2010
Some applications of Nuclear Science (2)
From NuPECC long Range Plan 2004
Art and archaeology* datation* identification of constituent materials
(ex : AGLAE Accélérateur Grand Louvre pour l’Analyse Elémentaire)
Environmental studies* ex : observation of modification of ocean circulation patterns(measurement of 129I /127I in seawater as a function of depth and distance to the coast)
…
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Some features of the nuclei :Summary
• The existence of the atomic nuclei : the Rutherford experiment in 1909
• The nucleon-nucleon interaction is not precisely known.
• Many nuclei are predicted but not observed up to now
• Most of them are neutron rich, and are supposed to have played a role during the nucleosynthesis.
• Nuclei are characterized by their level scheme : their barecode.
• Many applications of the nuclear physics