P7-radioactivity Flashcards
What are the 3 types of radiation
Alpha radiation
Beta radiation
Gamma radiation
Radiation:
release pf energy in the form of moving waves or streams of particles
Radioactivity:
A substance that contains stable nuclei that become stable by emitting radiation
Geiger counter
Device that lets you measure the number of radioactive elements around you.
(A geiger counter clicks even when it’s NOT near a radioactive source, this effect is due to background radiation, this radiation is from radioactive substances:
In the environment(such as the air)
From space (cosmic rays)
From devices such as x-ray tubes)
How did we realise about the structure of a atom the experiments
The plum pudding model(this is the model scientists felt represented the structure of the atom)->Rutherford used positively charged alpha (a) particles to probe atoms in a thin gold metal foil->if the plum pudding model was correct-this is what should have happened, it should have passed through->but some particles deflected back->Rutherford deduced that this must be because there was a positively charged mass in the middle of the atom->Rutherford called this positively charged mass in the middle of the atom-the nucleus
What did Rutherford’s experiment show about the structure of an atom and explain how it supports the nuclear model of the atom
Alpha particles are positively charged
The nucleus of an atom is also positively charged
These charges can repel each other changing the direction of the alpha particle
Most of the atom is made of space and so some alpha particles just pass straight through
Rarely some alpha particles hit the nucleus and repel back
A “radioisotope” is
Simply an isotope that is radioactive e.g. carbon 14
Alpha (a)
An atom decays into a new atom and emits an alpha particle (2protons and neutrons). Alpha radiation is the nucleus of a helium atom travelling at extremely high speed.(the decayed atom has changed into a new element as the number of protons and neutrons has changed into a new element)
Beta (B)
An atom decays into atom by changing a neutron into a proton and electron is called a beta particle and high energy fast moving electron is only emitted as the proton stays in the nucleus. (The decayed atom has gained a proton and so has changed into a new element)
Gamma radiation (Y)
After alpha or beta particle decay the surplus energy is something emitted. The atom itself is not changed. Gamma radiation is part of the EM spectrum, a wave with a very high frequency, very short wavelength. It emits gamma radiation,it releases energy in the form of electromagnetic radiation
When the number of protons and electrons in the atom are equal, scientists say the atom is balanced. Most atoms are stable.
However radioactive atoms
Aren’t they are unbalanced and unstable. They ‘want’ to become stable (balanced). So they try to achieve this state, they emit(give out) energy in the form of radiation
Ionising power
Different types of radiations ability to cause other atoms to lose electrons and therefore form ions
Alpha has the most ionising power
Has the largest charge so ionises atoms easily as it passes them
Beta has less ionising power than alpha but more than beta
Smaller charge, moderately ionises atoms as it passes them
Gamma least ionising power
As it doesn’t interact with atoms as much when it passes them
Alpha is also the most
Dangerous as it has the greatest ionising power
Ionisation
When the radiation from a radioactive substance can knock electrons out of atoms which become charged because they lose electrons
Irradiated
When an object is exposed to ionising radiation, but it doesn’t become radioactive
Radioactive contamination
Unwanted presence of materials containing radioactive atoms or other materials
The hazard from contamination is due
To the decay of the nuclei of the contaminating atoms, the type of radiation emitted affects the level of hazard
Workers who use ionising radiation reduce their exposure by
Keeping as far away as possible from the source of radiation (e.g.by using special handling tools with long handles)
Spend as little time as possible in at-risk areas
Shielding themselves by staying behind thick concrete barrier and/or using thick lead plates
Radioactive decay is also
Random
The activity of a radioactive source=
Number of unstable atoms in the source that decay/sec
Count rate=
Number of counts/sec-using a geiger counter
Radioactive decay =
Spontaneous process that can’t be controlled and is not affected by temperature. However each radioactive element has its own particular decay rate, which is called the half-life
Half life of a radioactive element
The time that it takes half the atoms in a sample to decay-average time taken for the count rate (and so the number of parents atoms) to fall by half is always the same
The number of sixes rolled with a fair dice is a
Gd model show random nature of radioactive decay coz can’t predict which dice/atom will ‘decay’ or when. Active sample=less time for the sample to decay (shorter half life).
Count rate (number of unstable nuclei)after n half lives=
Initial count rate(number of unstable nuclei)/2^n
n=number of half lives
Resolution of an instrument=
Smallest non-zero reading that can be measured
Systematic errors
When a measuring instrument consistently reads changes in the quantity to be a scale factor greater or less than the actual change
Zero errors
Specific systematic error were the instrument doesn’t read zero when the quantity should be zero
Random errors:
An error in a measurement caused by unknown and unpredictable changes in an experiment
