Atomic Structure Flashcards
how can an electron change energy levels? (2)
- if the atom absorbs electromagnetic radiation, an electron can move from a lower energy level to a higher energy level
- the atom can now emit that electromagnetic radiation and return back to the lower energy level
define radioactive decay
- some isotopes have an unstable nucleus and to become stable, the nucleus gives out radiation
define radioactive activity
the rate at which a source of unstable nuclei decay
how do we measure the activity of a radioactive source?
using a geiger-muller tube
what is an alpha particle?
- the same as a helium nucleus
- has two protons and two neutrons
what is a beta particle? (2)
- an electron that is ejected from the nucleus at a very high speed
- formed inside the nucleus when a neutron changes into a proton and an electron
what is the range in air for the three types of particles?
ALPHA PARTICLES
- travel 5cm
BETA PARTICLES
- travel around 15cm
GAMMA RADIATION
- travel several metres in air
what is the penetrating power for he three types of radiation?
ALPHA PARTICLES
- stopped by a thin sheet of paper
BETA PARTICLES
- stopped by a few mhm of aluminium
GAMMA RADIATION
- stopped by lead or concrete
what is the ionising power of the three types of radiation?
ALPHA PARTICLES
- strongly ionising
BETA PARTICLES
- quite strongly ionising
GAMMA RADIATION
- weakly ionising
what is alpha decay?
atomic mass decreases by 4
atomic number decreases by 2
what is beta decay?
atomic mass does not change
atomic number increases by 1
define half-life
the time it takes for the number of nuclei of the isotope in a sample to halve
define irradiation
exposing an object to nuclear radiation
what are the three precautions for people who work with radioactive isotopes?
- gloves protect against alpha radiation
- lead apron protects against beta and gamma radiation
- lead walls
define contamination
when unwanted radioactive isotopes end up on other materials
