Nuclear Physics Flashcards
Nucleons
Protons & Neutrons
Isotopes
Atoms of the same element that have the same number of protons in the nucleus, but a different number of neutrons.
RAM (Relative atomic mass) = …
Relative isotopic mass (RIM) x abundance
i.e.
(0.67 x 20) + (0.33 x 21)
Mass spectroscopy
An analytical tool used for measuring the molecular mass of a sample. In order to measure the characteristics of individual molecules, a mass spectrometer converts them to ions so they can be moved about and manipulated by external electrical and magnetic fields.
- A small sample is ionized, usually to cations by loss of an electron
- The ions are sorted and separated according to their mass and charge.
- The separated ions are then measured, and the results displayed on a chart or spectrogram.
Mass spectrometer detector
The analyser and detector of the mass spectrometer, and often the ionisation source too, are maintained under high vacuum to give the ions a reasonable chance of travelling from one end of the instrument to the other without any hinderance from air molecules.
Vertical columns are called
Groups
Horizontal rows are called
Periods
Trends - atomic radius
- Atomic radius increases down the group
- There are more electron shells, so the outer electrons are further away from the nucleus.
- Valence electrons are at higher energy levels and are not attracted as strongly to the nucleus because they are screened or shielded (pushed away) by other electrons in inner levels.
- Atomic radius gets smaller across the period.
- The nuclei have more protons and (+) charge, so electrons are more strongly attached to the nucleus.
Trend - Valency
- Ions in the same group have the same valency. All group 1 have a +1 charge ion.
- Ions from the same period increase to +4 then decrease as you move across period 3.
Safety precautions
STD, Shield, time, distance
- wear led lined apron
- minimise time exposed - put isotope away when finished testing
- use tongs to increase distance
Ionising Power Alpha
alpha particles are slow-moving particles and have time to interact with nearly all atoms in their path. The particles’ positive 2+ charge attracts electrons from the atoms they come into contact with, causing them ionized. The high ionising power of alpha particles means that they lose their energy quickly and so they have a poor penetrating ability.
Ionising Power Beta
beta particles are repelled by the electrons in atoms. The repulsion causes the beta particles to bounce between atoms. The collisions with atoms may cause some electrons to be ejected from the atom, ionising the atom. Collisions between beta particles cause little loss of energy and are relatively rate, so the particles have higher penetrating ability than alpha particles, but less ionizing power.
Ionising Power Gamma
gamma rays may interact with electrons or nuclei they collide with as they move through a substance, but as gamma rays have no charge, collisions or interactions are infrequent. Collisions occur only when a nucleus or electron is directly in the path of the gamma ray, which is not likely to happen because of the large amount of empty space in an atom. So, gamma rays have very low ionising power and therefore very high penetrating ability.
Ionising Power Neutrons
Neutrons have no charge and only tend to interact with the nuclei of substances they move through, rather than the electrons. As collisions occur only rarely, and even more rarely with the energy to cause significant interaction, neutrons have extremely high penetrating ability.
Fission
Nuclear fission occurs when an atomic nucleus splits into two or more pieces. This is usually triggered or induced by the absorption of a neutron, as shown below. Nuclides that are capable of undergoing nuclear fission after absorbing a neutron are said to be fissile. Only a handful of fissile nuclides exist in nature.
Relative Atomic mass
A weighted average mass of an element, depends on the mass of isotopes and their abundance. It is based on 1/12 of the mass of carbon.
Atomic Radius Depends on
The strength of the attraction between the outer-shell electrons and the nucleus.
This attractions depends on:
- The positive charge that attracts the outer-shell electrons
- The distance of the electrons from the nucleus.
Nuclear Shielding
Electron Shells “block” some of the attraction between the nucleus and electrons. i.e. the inner electrons shield the attraction between the nucleus and the valence electrons.
Radioactivity
When nuclei of unstable isotopes gain stability by undergoing changes.
These Reactions Are:
- Always called nuclear reactions
- Are always accompanied large emissions of energy
- Are spontaneous
- Are not affected by changes in temperature, pressure of prescence of catalysts
- Cannot be slowed down, sped up or turned off
What Causes Radioactive Decay
Caused by unstable nucleus (may be due to overall size, having too many or too few neutrons), changing the repulsion within the nucleus (protons to protons).
- Unstable radioisotopes of one element are transformed into stable, non-radioactive isotopes of other elements.
- All elements with an atomic number greater than 83 will be unstable.
3 Types of Radiation
Alpha Particle: positive charge, consists of heloium nuclei (42He)
Beta particle: negative charge, consists of fast-moving electrons formed by the decomposition of a neutron in an atom.
Gamma Rays: no charge, is high energy electromagnetic radiation given off by a radioisotope. Have no mass.
What is a bequerel?
The amount of transformations per second (measuring the activity of a radioactive sample)
Nuclear Fusion
small nuclei combine
Fusion occurs where small particles such as neutrons, hydrogen or helium nuclei combine to form a heavier nucleus such as lithium
How does a Geiger Counter Work?
It works by using a Geiger-Müller tube filled with low-pressure gas; when radiation enters the tube, it ionises the gas, causing a short electrical pulse. These pulses are counted and often heard as clicks or displayed on a screen to show radiation levels.
