Unit 5: Radioactivity Flashcards
What was Rutherford’s experiment?
Directed a narrow beam of a-particles. All of the same kinetic energy. In an evacuated container. At a thin gold film.
Why did the a-particles in Rutherford’s experiment need to be of the same KE?
Slower alpha particles would be deflected more than faster ones on the same initial path
Why did the container need to be evacuated?
Such that the particles did not colide with air particles
What were the observations from rutherford’s experiment?
-Most a-particles passed through -A few a-particles deflected - some more than 90degrees
What were the interpretations from Rutherford’s experiment?
mass is concentrated in a small region, the nucleus. Nucleus positively charged because it repels a-particles. Nucleus itself is very small as few a-particles are deflected by a significant angle.
3 Type of radiation
Alpha, Beta, Gamma
Applications of radiation
a - fire alarms b - thickness of paper y - diagnosstic techniques in medicine
Describe alpha radiation
Atom loses 2 protons and 2 neutrons
Describe beta(-) radiation
Atom loses one electron, has a neutron turn to a proton and gives off an anti-electron neutrino
Describe beta(+) radiation
Atom loses one positron, has a proton turn into a neutron and gives off an electron neutrino
Describe electron capture
Atom takes in an electron and results in a proton turning into a neutron and gives off an electron neutrino
Why can radiation be damaging
it affects living cells as it can destroy cell membranes and damage DNA
States the 4 main properties of the inverse square law for y radiation
1 - Gamma source emits radiation in all directions 2 - Spreads out with distance 3 - Amount of radiation per unit area (Intensity) will decrease with distance 4 - Intensity decreases with the square of the distance
What is the equation for intensity and what are the variables
I = kI0/d2
where I = Intensity, k = constant, d = distance, I0 = Intensity at source
Describe the random nature of radioactive decay
- One can not know exactly when or which particles will decay
- Any sample of particular isotope has the same rate of decay
Define activity and the equation giving the variables and the unit used to measure it
- Activity of a sample is the number of atoms that decay each second
- Is proportional to the size of the sample
- A = Lambda*N
- A = Activity, Lambda = Decay constant, N = number of atoms
- Becquerels (Bq) = 1 decay per second
What is the half life of an isotope?
Average time taken for the mass of an isotope to decrease by half of its initial mass
Draw a diagram representing the principle of half life
standard exponential decay graph with radiative nuclei on the y and time on the x
What is the equation for half life and give the variables
- T1/2 = ln2/lambda
- T1/2 = Half life, ln2 = the natural log of 2, lambda = decay constant
What equation gives the amount of atoms/activity/mass/count rate after an isotope has decay for x amount of time, giving the variables
- N = N0 e-lamba*t
- Where N = number of atoms left, N0 = Inital number of atoms, e = 2.734, lambda = decay constant, t = time
Define the decay constant ( lambda) giving its unit
- The probability of an individual nucleus decaying per second.
- Unit is S-1
Explain carbon dating
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