The Particle Adventure | Particle decays and annihiliations

Eternal questions The search for the fundamental The atom Is the atom fundamental? Is the nucleus fundamental? Are protons and neutrons
fundamental? The modern atom model The scale of the atom What are we looking for? The standard model The standard model quiz

Quarks and leptons Matter & antimatter What is antimatter? Quarks The naming of quarks Hadrons, baryons and mesons Leptons Lepton decays Lepton type conservation Lepton decay quiz Neutrinos Quiz - What particles are made of

The four interactions How does matter interact? The unseen effect Electromagnetism Residual EM force What about the nucleus? Strong Color charge Quark confinement Quarks emit gluons Residual strong force Weak Electroweak Gravity Interaction summary Quantum mechanics The Pauli Exclusion Principle Fermions and bosons A lot to remember

What is decay? Radioactivity Radioactive particles Confusion about decays A look into the nucleus If it can happen, it will Half life Missing mass Particle decay mediators Virtual particles Different interactions Annhiliations Bubble chamber and decays Neutron beta decays Electron / positron annhiliation Top production

Beyond the standard model The standard model as a theory Three generations What about masses? Grand Unified Theory Forces and the Grand Unified Theory Supersymmetry String theory Extra dimensions Dark Matter

Testing a theory Searching for the atom's structure Rutherford's result Rutherford's analysis How physicists experiment Deflected probe

Detecting the world A better microscope Wavelength - The cave Wavelength - The moral Wavelength and resolution explained The physicists tool: The accelerator Waves and particles The world's meterstick Mass and energy Energy-mass conversion

Accelerators How to obtain particles to accelerate Accelerating particles Accelerating particles: Animation Accelerator design Fixed target experiments Colliding beam experiment A linear or circular accelerator What makes particles go in a circle? Advantages of accelerator design Major accelerators The event Detectors Detector shapes

Modern detectors Typical detector components Measuring charge and momentum Detector cross section Quiz - Particle tracks The computer reconstruction A quark/gluon event The end

The Standard Model - Particle decays and annihiliations - Confusion about decays

Many heavy elements decay into simpler things. But a close observation of these decays reveals several confusing problems.

Consider uranium-238 decay.

A lump of uranium-238 will decay at a constant rate such that in 4,460,000,000 years -- give or take a few days -- half the uranium will be gone. But there is no way to tell when a specific uranium atom will decay; it could decay five minutes from now, or in ten billion years. Why will an atom decay only according to some probability?

Uranium-238 has a mass of 238.0508 atomic mass units (u). It can decay into thorium (234.0436 u) and an alpha particle (4.0026 u). But uranium's mass minus the mass of its decay products is 0.0046 u. Why is there missing mass?