Modern Studies of the Atom

Hideki Yukawa- 1935- Theorized that a particle passes back and forth between protons and neutrons to hold the nucleus together.Predicted the existence of a particle called a meson (also known as pions). The meson was observed in 1947.

Enrico Fermi-1934- Theorized that a neutral particle is emitted during beta decay which he called the neutrino.

Cs → Ba + e− + ν (beta decay)

neutrinoelectron

Neutrino- tiny neutron – Observed in 1956

Radioactive Decay

Alpha

Beta

Gamma

_________

_______

_____

Antiparticles-Mirror image of each particle. Particle have the same mass but the opposite charge.(ie: electron and positron)

Paul Dirac -late 1920s Theorized that electrons should be expected in two energy states, one positive and one negative. He called these antiparticles.

hfee 2

When Matter meets antimatter annihilation occurs. Energy and radiation is given off.

Depends on frequency

ee rays

When gamma rays pass close to nucleus, a particle and antiparticle are formed.(requires 1.02MeV or more of energy)

The Standard Model

Matter

Hadrons

Baryons

3 Quarks

Mesons

2 quarks

LeptonsParticles made of quarks

Protons and neutron

electrons

QUARKSFundamental particle of the

standard model.6 types or flavors.Have charge.Can’t exist on their own.Make up Baryons and Mesons.

TERMSHadrons- anything composed of quarksMesons-subatomic particles composed of a quark and antiquark. Baryons- particles formed by three quarks. Includes protons and neutrons.Leptons- Doesn’t have quarks. Includes electrons, muons, Tau, neutrino and antiparticles.

QUARKS

Up (u) +2/3

Down(d) -1/3

Charm (c) +2/3

Strange(s) -1/3

Top (t) +2/3

Bottom (b) -1/3

DATES OBSERVED up- 1964

Down- 1964Strange- 1964Charm-1975

Bottom- 1977Top- 1995

Neutrons are made of 2 down quarks and one up quark. (udd)

(+2/3) + (-1/3) + (-1/3) = 0

Protons are made of 2 up quarks and one down quark.(uud)

(+2/3)+(+2/3)+(-1/3) = +1

Strong Force-Short range force that holds quarks together to form protons and neutrons in the nucleus.

Electromagnetic force- Attractive and repulsive force between charges. Binds the electrons to the nucleus.

Gravitational force-Weakest of four forces. Force due to the mass of the atom.

Weak Force- Responsible for formation of elements and release of nuclear energy and beta decay.

Gluon- the exchange particle between quarks

Higgs Boson Higgs Boson- subatomic particle

with zero electric charge and mass greater than zero. Its thought to interact with other particles to give them mass.

Observed at CERN on July 4th, 2012.

The Higgs boson would help explain the origin of mass in the universe. The Higgs boson completes the standard model.

PARTICLE ACCELERATORS

Cyclotron- E.O. Lawrence accelerated protons to a very high speed and projected them into a stationary target.

Synchrotron

Fermi National Accelerator Lab- Batavia Illinois-Tevatron- 4miles wide- Accelerates protons to 99.9% speed of light. Uncovered the top quark

Similar to a Cyclotron. Particle experience a higher magnetic field therefore moves at a higher speed.

Linear Accelerator

Longest is in Palo Alto California. Its 3.3 km long and buried 7.6m underground.

Particles are accelerated as they pass through a series of conductors.

Particle Colliders

CERN- French-Swiss collider that is sponsored by 19 European countries in hopes of locating the Higgs-Boson particle. (17miles wide and 574ft deep)

Instead of a stationary target, this aims two high speed particles at each other and detects particles that are emitted.

Standard Model Limitations

• The standard model doesn’t predict the mass of the fundamental particles that make up luminous matter.

• Doesn’t predict the existence of dark matter• Key particles have not been directly observed.

Their existence is inferred by experimental observations.

• 1% discrepancy in how the neutrino behaves. Due to results, they feel there may be an unknown force or particle influencing it.

Dark Matter • Dark matter is matter that

doesn’t emit or scatter light or other electromagnetic radiation. It cannot be directly detected. Dark matter is believed to make up 83% of the matter in the universe and 23% of the mass-energy.

• Regular Matter makes up only 17% of all matter.

Dark Matter is not….• Is not in the form of mass that we see. • is not made up of baryons. We know this

because we would be able to detect baryonic clouds by their absorption of radiation passing through them.

• dark matter is not antimatter, because we do not see the unique gamma rays that are produced when antimatter annihilates with matter.

Unanswered questions• Is there only one type of Higgs Boson?• Are protons absolutely stable? If not, then

what is the proton‘s half-life?• Why is there now more detectable matter

than antimatter in the universe?• What governs the transition of quarks and

gluons into mesons and baryons?

• What is the nature of the nuclear force that binds protons and neutrons into stable nuclei or rare isotopes?