Radioactivity Flashcards
(29 cards)
What is an isotope?
An isotope is when there are two or more atoms of the same element with different numbers of neutrons, this means they have different atomic masses.
How is an ion formed?
An ion is formed when an atom gains or loses an electron. If it gains an electron it becomes negatively charged and if it loses an electron it becomes positively charged.
Why do scientists look for new evidence?
New experimental evidence may lead to a scientific model being changed or replaced.
What did we first believe about atoms?
Before we discovered electrons we thought that atoms were small, undividable spheres.
What was the plum pudding model?
After J.J thompson discovered electrons he came up with the plum pudding model which was a ball of positive charge with negative electrons scattered throughout it.
What was the alpha particle scattering experiment?
This was an experiment carried out by Rutherford in which he fired alpha particles at a gold sheet and while most alpha particles went through the sheet some scattered in varying directions meaning there was a positive mass was focused in the centre of the atom.
What did the alpha particle scattering experiment lead to?
The alpha particle scattering experiment lead to the development of a new model called the nuclear model in which there was a positive mass in the centre of the atom with electrons orbiting it.
How did Niels Bohr adapt the nuclear model of the atom?
Niels Bohr theorised that the electrons orbited the nucleus at specific distances.
Who discovered electrons?
J.J thompson discovered electrons.
Who discovered protons?
Ernest rutherford discovered protons after further testing after he created the nuclear model.
Who discovered neutrons?
James chadwick discovered neutrons 20 years after the idea of the nucleus was accepted.
What is radioactive decay?
Some atomic nuclei are unstable and so they give out radiation to become more stable. This is a random process called radioactive decay. The rate at which a nuclei decays is called activity which is measured in bequerels (Bq).
What is count rate?
Count rate is the number of decays recorded each second by a detector (e.g a geiger-muller tube). Count rate is proportional to activity (they are not identical as count rate is in a single direction whilst activity is the radiation in all directions.
What are the three main types of radiation?
An alpha particle - this consists of 2 protons and 2 neutrons, it is the same as a helium nucleus.
A beta particle - a high speed electron ejected from the nucleus after a neutron turns into a proton.
A gamma ray - electromagnetic radiation release from the nucleus.
What are the penetrative properties of each type of radiation?
Alpha particles are highly ionising meaning they are weakly penetrating and can be stopped by thin sheets of paper.
Beta particles a less ionising and can travel greater distances through the air and can be stopped by a few mm of aluminium.
Gamma rays are weakly ionising and so are highly penetrative and can only be stopped by a thick concrete/lead or else they travel through the air nearly endlessly.
How are alpha particles used?
Alpha particles are used in smoke detectors as they can ionise the air well and so can conduct electricity. When smoke enters the detector less ionisation can occur as the smoke blocks the alpha particles. This means the current becomes lower which triggers the alarm.
How are beta particles used?
Beta particles can be used to measure the thickness or paper or metal. Beta particles are emitted on one side of the material and a detector is on the other which measures how many beta particles are getting through. If too many get through the thickness of the material is increases and if too few get through the thickness of the material is decreased.
How are gamma rays used?
Gamma rays have various uses with most of them involving destroying cells in the sterilisation of food or medical equipment. They can also be used to find leaks in underground pipes.
What is a substance’s half life?
Radioactive decay is a random process and so we measure a substance decay by it’s half life which is the amount of time for the number of nuclei or count rates in a sample to halve.
What is contamination?
Contamination is the unwanted presence of materials containing radioactive atoms on other materials. The more ionising the radiation the higher the hazard.
What is irradiation?
Irradiation is the process of exposing an object to nuclear radiation, an irradiated object is not radioactive.
What is the danger of being contaminated?
If you are contaminated you might transport radioactive substances and irradiate or contaminate others. This can be managed by wearing protective clothing like gloves or hazmat suits.
Why is peer review important?
Findings of studies can be published and shared with other scientists so the findings can be checked and verified.
How is radiation used in medicine?
Radiation tracers can be used to find blocks or tumours inside your body. Tracer have a half-life short enough to be gone after a reasonable amount of time and prevent harm. Tracers are gamma as they need to be highly penetrating to work.
Gamma rays are used in concentrated beams to destroy cancerous tumours. This can also be done via radioactive implants.
