Radiation

Question	Answer
What is a radioactive substance?	Radioactive substances are substances that emit radioactivity.
Why are some nuclei unstable?	In unstable nuclei, the strong nuclear forces do not generate enough binding energy to overcome the repulsion force inside the nucleus. Or, substances could be radioactive if the proton:neutron ratio is too big or small.
An unstable nucleus becomes stable by. . .	. . . emitting alpha, beta, or gamma radiation- decays. Decaying is a random event that happens with nothing being done to the nucleus
What is decaying?	emitting radiation.
Give two properties of radioactive subtsances.	1) Decaying is completely random. 2) The probability of decay is the same for each nucleus
What is a geiger counter and how does it work	A Geiger counter is a machine used to detect radioactivity. The counter clicks each time a particle of radiation enters the tube.
What was Rutherford's alpha particle scattering experiment?	Rutherford's experiment involved a vacuum chamber, to prevent air molecules absorbing the alpha particles. Each time an alpha particle was shot, a small dot of light was observed.
What were the results of this experiment?	--> Most of the particles went straight through --> some were partly deflected --> very, very few were deflected at angles over 90 degrees.
What did the results show	1) atoms are mostly empty space 2) a positive, concentrated, central, small nucleus 3) electrons are very light
Why was it accepted	1) Rutherford + co were respected 2) it predicted the existence of the neutron 3) explained radioativity
what determines if a nucleus is unstable	- too many protons or neutrons disturb the balance, disrupting the binding energy from the strong nuclear forces causing the nucleus to be unstable.
Nuclei with atomic no above __ are radioactive	83.
ALPHA	- same as a helium atom - proton no goes down by 2 - mass no goes down by 4 - travels a few cms in air - stopped by paper - most ionizing, least penetrating - slightly deflected in field
BETA	- a high speed, energy electron - mass no. of 0, atomic no. -1 - mass no doesn't change, atomic no goes up by one - medium penetration/ionization highly deflected in field travels ms stopped by aluminum
GAMMA	- electromagnetic ray - unlimited range of air stopped by lead (thick) - isn't deflected in field
What is background radiation?	radiation from unstable nuclei in materials around us and in the atmosphere
how to take background radiation into account	1) measure count rate without source 2) measure count rate with source ans to step 2) minus ans to step 1
how to test different materials	place material between Geiger Counter and source add more layers till the count rate is 0 the radiation had been stopped
How to test the range	move the source away from the tube. when the source is beyond the range of radiation, the count rate will be 0.
Define ionization.	when electrons are knocked out of atoms, making them have a charge, because of radiation.
define irradiated	when an object is exposed to ionising radiation
define contamination	unwanted presence of materials containing radioactive atoms on other materials
how to avoid radiation	keep as far away as possible spending little time at at-risk areas shielding yourself with concrete barriers long tools, special handles
Define peer review	when findings are published and shared with other scientists so they can check them
define activity	The number of unstable atoms emitted per second or the decay of a substance per second
half life	the period of time it takes for the number of radioactive nuclui of isotops in a sample to halve.
count rate	number of counts per second
count rate after N half lives	Initial count rate / 2^n

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	Created by Aaishah Din almost 7 years ago