Topic 7 & 12 - Atomic + Nuclear + Quantum

Isotopes

Atoms with the same number of protons, but a different number of neutrons.

Radioactive decay

The random and spontaneous transformation of an unstable nucleus into a lighter one, followed by the emission of a particular type of particle (e.g. an alpha particle, a beta particle, a gamma photon, etc.)

Decay constant

The probability that an unstable nucleus will decay per unit time.

Half-life

The time it takes for the activity of a radioactive sample to halve = The time it takes for the number of radioactive nuclei to halve in size.

Nuclear fission

A nuclear reaction in which a slow moving neutron bombards heavy atomic nuclei, splitting it up into lighter nuclei and releasing energy and more neutrons.

Nuclear fusion

A nuclear reaction in which atomic nuclei of low atomic number fuse to form heavier nuclei with the release of energy.

Transmutation

The changing of one chemical element to another by changing the number of protons in a nucleus through bombarding it with particles.

Activity (often measured in Bq = s-1)

The number of decays per unit time (in other words, the rate of decay).

Photoelectric Effect

* Light consists of particles of light with energy:


* A certain amount of energy is required to release an electron from a metal surface (= work function)
* When the frequency is low, the photon energy is low
* If photon energy < work function, no electrons will be emitted and current = 0.

Work Function

The minimum amount of energy required to release an electron from the surface of a metal. (Typically measured in eV)

Photon

A “particle of light” with energy = Planck's constantfrequency of light ()

Binding energy

(Minimum) energy required to separate a nucleus into free nucleons. (OR the energy released when a nucleus is assembled out of free nucleons.)

Mass defect

Difference between the mass of the nucleus and the mass of its constituent particles

Exchange particle

A virtual particle that mediates the interaction between two other particles.

Wavefunction

A mathematical description of a system (e.g. a particle) that determines the **probability** of outcomes when a measurement is performed (e.g. its position). It’s absolute value squared times volume gives us the probability of finding a particle in the volume surrounding a given point (this is called the Born postulate).

Rutherford atomic model

* most of the atom is empty space;
* most of the mass/(protonic) charge of the atom is concentrated in the nucleus/ nucleus is dense;
* nucleus is positively charged;
* (most) alphas are not close enough to nuclei to be deflected;
* (very few) alphas (are) close enough to nuclei to be deflected;

Outline how emission spectrum of atomic hydrogen may be obtained in the laboratory 

* light from a hydrogen discharge tube/hot hydrogen gas/ hydrogen tube with potential difference across it;
* is passed onto a prism/diffraction grating;


* and then is observed on a screen/through a telescope;

Explain how such spectra give evidence for the existence of discrete atomic energy levels

* each wavelength corresponds to the energy of the photon emitted;


* when an electron makes a transition from a higher to lower energy level;
* since only discrete wavelengths/finite number of wavelengths are present,
* then only discrete energy levels are present / OWTTE;

Describe how the existence of the antineutrino accounts for the continuous nature of beta spectra

* the total emitted energy is shared between the electron and the antineutrino;


* the energy/velocity can be shared/distributed in an infinite number of ways 

How particles can be used in scattering experiments to estimate nuclear sizes

* «high energy particles incident on» thin sample 


* detect angle/position of deflected particles
* reference to interference/ diffraction/ minimum/ maximum/ numbers of particles

Decay characteristics

Random: cannot be predicted which/when nucleus will decay 

Spontaneous: cannot be modified/influenced in any way

Outline why wave model of light cannot account for photoelectric effect