basics to radioactivity Flashcards
1
Q
Radioactivity
A
- Spontaneous emission of small particles and or radiation (energy) by unstable atomic nuclei to attain more stable nuclear state
look at ppt
2
Q
1896- Henry Becquerel-
A
studied phosphorescence with uranylsulfate, discovered the uranium radioactivity.
Nobel prize in physics- 1903 for discovery of radioactivity
3
Q
Becquerel
A
- Investigated connection between x-rays and naturally occurring phosphorescence
- When uranium salts were placed by a photographic plate covered with opaque paper the plate was discovered to be fogged
- This was a property of the uranium atom
- He showed that the rays emitted uranium caused gases to ionize and that they differed from x-rays in that they could be deflected by electric or magnetic fields
4
Q
1896
A
- Marie curie pursued the study of becquerel rays
- Studied radioactive material
- The pitchblende contained traces of some unknown radioactive component which was far more radioactive than uranium
- In 1898 she announced the existence of this new substance
- After several years they isolated 2 new chemical elements, radium and polonium
- Radioactivity was found to be unaffected by chemical and physical testing showing that the radiation came from the atom itself- specifically from the disintegration or decay of an unstable nucleus
5
Q
Discovery of radioactivity
A
- 1898- ernest Rutherford began studying the nature of the rays that were emitted
- Classified into three distinct types according to their penetrating power
- Alpha decay- positively charged can barely penetrate a piece of paper
- Beta decay- negatively charged pass through as much as 3mm of aluminium
- Gamma decay- neutral; extremely penetrating
6
Q
Types of radiation
A
- Alpha rays- nuclei of helium atoms )2 protons and 2 neutrons)
- Beta rays- electrons (created within the nucleus)
- Gamma rays- high energy photons (packets of energy)
7
Q
Alpha decay
A
- The loss of 2 neutrons and 2 pr0tons changes the atom
look at ppt
8
Q
Alpha decay smoke detector
A
- Americium 241 has a half life of 432.6 years.
- Emitted α particle ionises the air molecules which conduct current between two terminals
- Smoke clings to ionised air molecules and slows them down
- Current decreases and a transistor switch activates the alarm
- Contains 0.3µg of the isotope or 37Bq or 1 Ci of radioactivity.
- Radiation risk much smaller than background radiation.
- Sensitive to flaming stage of fire
- Optical smoke detectors sensitive to smouldering stage of fire
9
Q
Beta decay (negatron decay)
A
- The electron emitted in beta decay is NOT an orbital electron; the electron is created in the nucleus itself
- One of the neutrons changes to a proton and in the process (to conserve charge) throws off an electron
- These particles are referred to as beta particles so as not to confuse them with orbital electrons
10
Q
Beta decay and the neutrino
A
- Scientists found that some of the fundamental principles in physics did not hold true (law conservation of energy and law of conservation of momentum- both linear and angular)
- 1930- wolfgang pauli proposed there was a new particle that was very difficult to detect was emitted in beta decay, as well as the electron
- Neutrino- symbol is ‘nu’ (v)
- So the equation becomes: (bar denotes anti neutrino)
look at ppt
11
Q
Positron decay
A
- Occurs when there are too few neutrons compared to protons
- These isotope lies between the stable isotope line
- This beta decay, the particle that is emittied is called positron but has a charge of +1 but same mass as an electron
- The positron is called the antiparticle to the electron
- Many different radioisotopes are positron emitters, such as Fluorine18, Oxygen15, and Carbon11.
look at ppt
12
Q
Positron emission tomography (PET)
A
- nuclear medicine functional imaging technique that is used to observe metabolic processes in the body.
- The system detects pairs of gamma rays emitted indirectly by a positron-emitting radionuclide (tracer), which is introduced into the body on a biologically active molecule. 3-D images of tracer concentration within the body are then constructed by computer analysis.
- Biological molecule e.g. fludeoxyglucose (FDG), an analogue of glucose, shows tissue metabolic activity corresponding to glucose uptake. Indicates cancer metastastis (90% of use)
look at ppt
- 20min scan. Red areas show more accumulated tracer substance (18F-FDG) and blue areas are regions where low to no tracer have been accumulated. Used to detect cancers.
13
Q
Electron capture
A
- Occurs when a nucleus absorbs one of the orbiting electrons
- Usually the innermost electrons
- The electron disappears and a proton becomes a neutron in the process
- A neutrino is emitted in electron capture decay
- This has been detected by the emission of x-rays due to other orbital electrons jumping down to fill in the lower energy levels and releasing energy of that energy
look at ppt
14
Q
Source of instabilities
A
- Too big
- Too many neutrons for the protons
- Not enough neutrons for the protons
- Too many excess energy
15
Q
Nuclear stability- Determined by the number of neutrons to protons
A
Atomic number (Z) less than 20 (Calcium):
- Ratio close to 1 fall in zone of stability
Atomic number (Z) going from 21( Scandium)- 83( Bismuth):
- Number of neutrons always greater than the number of protons
- Neutrons help to stabilise the nucleus and overcome repulsive electric forces of the protons
- Ratio increases from 1 to 1.5 as Z increases from 21 to 83
Atomic number (Z) greater than 83 (Bismuth):
- Ratio greater than 1.5 ( proportionately more neutrons needed to stabilise larger number of protons)
- All unstable and decay and are radioactive
- Outside zone of stability
