Chair of theoretical and nuclear physics

Al-Farabi KAZAKH NATIONAL UNIVERSITY

N. Takibayev, V. Kurmangaliyeva

Selected Chapter of Nuclear Physics and Nuclear Astrophysics

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Four fundamental interactions are conventionally recognized: gravitational, electromagnetic, strong nuclear, and weak nuclear.

Everyday phenomena of human experience are mediated via gravitation and electromagnetism.

Fundamental interactions, also called fundamental forces or interactive forces, are modeled in fundamental physics as patterns of relations in physical systems, evolving over time, that appear not reducible to relations among entities to a more basic relation.

Lectures 1 and 2

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Gravitational Field

Lectures Focus

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Gravitational Field - Historical facts

Lectures Focus

Heliocentric Theory

Nicholas Copernicus (1473 – 1543)All planets, including Earth, move in orbits around the sun

The gravitational force is given by:

where G is a constant called the Universal Gravitational Constant

221

r

mGmF

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Lectures Focus - Gravitational field strength

• It is also called the field intensity• The gravitational field strength at a point is the

gravitational force acting on a unit mass placing at the point

mass

nalgravitatiog

strength

nalGravitatio force ,

field

Unit: N kg-1 On the earth’s surface, g 10 N kg-1 On the moon’s surface, g 1.7 N kg-1

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Lectures Focus : Gravitational potential

• Due to the existence of the field, a net amount of work has to be done to move a unit mass from one point to another. We say that different points in the field have different gravitational potential

• It represents the work done in taking a unit mass from one point in a g-field to another

• Unit: J kg-1

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Lectures Focus - Equipotential surfaces

• Surfaces containing points having the same gravitational potential

• The spacing of the equipotential surface is an indication of the field strength

• The g-field is pointing in the direction of decreasing gravitational potential

• Mathematical form:F G

Mm

r 2

In modern physics, gravitation is the only fundamental interaction still modeled as classical/continuous (versus quantum/discrete).

Acting over potentially infinite distance, traversing the known universe, gravitation is conventionally explained by physicists as a consequence of space-time's dynamic geometry, "curved" in the vicinity of mass or energy, via Einstein's general theory of relativity (GR).

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In general relativity, the effects of gravitation are ascribed to spacetime curvature instead of a force. The starting point for general relativity is the equivalence principle, which equates free fall with inertial motion, and describes free-falling inertial objects as being accelerated relative to non-inertial observers on the ground. In Newtonian physics, however, no such acceleration can occur unless at least one of the objects is being operated on by a force.

Lectures Focus – Gravitation

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The strong interaction, synthesizing chemical elements via nuclear fusion within stars, holds together the atom's nucleus, and is released during an atomic bomb's detonation.

Strong nuclear force

• Strong nuclear• Electromagnetic• Weak nuclear• Gravitational

Strongest

Weakest

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Electromagnetic force

• Causes electric and magnetic effects– Like charges repel each other– Opposite charges attract each other– Interactions between magnets

• Weaker than the strong nuclear force• Acts over a much longer distance range

than the strong nuclear force

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Weak nuclear force

• Responsible for nuclear decay• Weak and has a very short distance range• The weak interaction is involved in radioactive decay. Note:• The weak nuclear force is NOT the weakest of the

fundamental forces.• GRAVITY is the weakest force, but most important in

understanding how objects in the universe interact.

The smallest pieces of matter…• Nuclear physics and

particle physics study the smallest known building blocks of the physical universe -- and the interactions between them.

• The focus is on single particles or small groups of particles, not the billions of atoms or molecules making up an entire planet or star.

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… and their large effects …

… affect us all.

– History: alchemy, atomic weapons

– Astronomy: sunshine, “metals”, cosmology

– Medicine: PET, MRI, chemotherapy

– Household: smoke detectors, radon

– Computers: the World-Wide Web

– Archaeology & Earth Sciences: dating

Atoms, Periodic table

The periodic table lists about 114 atoms with distinct properties: mass, crystal structure, melting point…

The range and pattern of properties reflects theinternal structure of the atoms themselves.

Inside Atoms: neutrons, protons, electrons

Carbon (C )

Atomic number Z=6 (number of protons)

Mass number A=12 (number of protons + neutrons)

# electrons = # protons (count them!)

(atom is electrically neutral)

Gold (Au)Atomic number Z = 79

Mass number A = 197

# electrons = # protons

Properties of nucleons

Name Spin Mass Electric Charge

Proton 1/2 ~ 1 GeV +1

Neutron 1/2 ~ 1 GeVbut >

0

• Units: – The electric charge of an electron is -1 in these units.– Mass units are “billion electron volts” where 1 eV is a typical

energy spacing of atomic electron energy levels.

• Question: Why are the masses nearly the same but the electric charges so different?

Further layers of substructure:

u quark: electric charge = 2/3

d quark: electric charge = -1/3

Proton = uud electric charge = 1

Neutron = udd electric charge = 0

Международная сеть центров ядерных реакций (NRDC)Introducing the neutrino

Another subatomic particle, the neutrino, plays a crucial role in radioactive decays like n -> p+ + e- + ve

The ve (electron-neutrino) is closely related to the electron but has strikingly different properties.

Name Spin Mass Electric Charge

electron 1/2 0.0005 GeV -1

electron-neutrino

1/2 < 0.00000001 GeV 0

Exotic Matter Particles

Other subatomic matter particles are heavier copies of those which make up ordinary atoms (u, d, e, ve)

Sub-atomic interactions

• Two familiar kinds of interactions are – gravity (masses attract one another)– electromagnetism (same-sign charges repel, opposite-

sign charges attract)

More exotic phenomena hint at new interactions peculiar to the subatomic world:

• What binds protons together into nuclei ?– Must be a force strong enough to overcome repulsion

due to protons’ electric charge• What causes radioactive decays of nuclei ?– Must be a force weak enough to allow most atoms to

be stable.

Subatomic particles interact by exchanging integer-spin “boson” particles. The varied interactions correspond to exchange of bosons with different characteristics.

Force Strength Carrier Physical effect

Strong nuclear 1 Gluons Binds nuclei

Electromagnetic .001 Photon Light, electricity

Weak nuclear .00001 Z0,W+,W- Radioactivity

Gravity 10-38 Graviton? Gravitation

Mass MysteriesOtherwise similar particles are seen experimentally to

have very different masses (e.g. muon & electron). Plotting masses in units of the proton mass (1 GeV):

Two "symmetry breaking" mysteries emerge:• Flavor Whence the diverse fermion masses ?• Electroweak Why are the W & Z heavy while the g is massless?

Higgs MechanismThe Standard Model of particle physics postulates a

particle called the Higgs boson, whose interactions give rise to all mass:

• During an earlier epoch of our universe, all the known elementary particles were massless.

• The Higgs boson triggered a phase transition (as when water freezes into ice) which caused all particles interacting with the Higgs boson to become massive.

• The W and Z bosons and the fermions are massive because they interact with the Higgs boson.

• The photon and gluon remain massless because they do not interact directly with the Higgs boson.

A variety of masses:

The Higgs field would form a uniform background within the universe. Each particle would interact with the Higgs boson to a different degree.

The more strongly a particle interacted with the Higgs, the more mass it would gain and the more inertia it would display

Acceleration & SteeringProtons will be accelerated

and collided in LHC. Two beams will travel in opposite directions.

Electric fields produce acceleration because like charges repel and unlike charges attract each other.

Magnetic fields steer the beams of protons because charged particles move in circles when exposed to magnetic fields.

magnets

Detection

The collision energy condenses into particles (e-, p, p…)

Detectors surrounding the collision point are sensitive to the passage of energetic particles.

At four places around the LHC ring, protons from the two counter-rotating beams will collide. ATLAS

Higgs Detection: H -> gg A Higgs decaying to 2 energetic

photons would be a striking event in the LHC detectors.

events

energy

background

Higgs signal

The combined energies of the signal photons would cluster at the mass of the Higgs boson. In contrast, background events include photon pairs with a variety of energies.

ATLAS

References

• Lectures 1 and 2 (*.pdf)• http://en.wikipedia.org/wiki/Standard_Model• http://www2.slac.stanford.edu/vvc/theory/fundamental.html• Google images• http://en.wikipedia.org/wiki/Gravitation