Nuclear Physics Flashcards
(45 cards)
-what did the Rutherford scattering prove?
- what did it contradict?
-the existence of a nucleus
-contradicted Thomson’s plum pudding model, which stated the atom was made up of a sea of positive charge and small areas of electrons embedded
What equipment did Rutherford use?
- alpha source
-gold foil - chamber covered in fluorescent coating
what would the Rutherford experiment show if the plum pudding model was true?
positively charged alpha particles would be deflected by a very small amount when passing through the foil
What were the actual results for the Rutherford experiment and what did they mean?
-most alpha particles passed straight through the foil with no deflection
= atom is mostly empty space
-A small amount of particles were deflected by a large angle
= centre of atom is positively charged
-Very few particles were deflected by more than 90°
=centre of atom is vert dense and small
What are the 3 types of radiation?
-Alpha
-Beta
-Gamma
What is the: (Alpha)
1. Range in Air?
2. Ionising power
3. Deflected by electric and magnetic fields?
4. What is it Absorbed by?
- 2-10cm
- Highly
- Yes
- Paper
What is the: (Beta)
1. Range in Air?
2. Ionising power
3. Deflected by electric and magnetic fields?
4. What is it Absorbed by?
- around 1m
- Weakly
- Yes
- Aluminium foil
What is the: (Gamma)
1. Range in Air?
2. Ionising power
3. Deflected by electric and magnetic fields?
4. What is it Absorbed by?
1.Infinte range
2. Very weak
3. No
4. Several metres of concrete or inches of lead
How would you identify which type of radiation is emitted?
- use Geiger counter to find background radiation
- place source of radiation close to Geiger counter and measure count rate
- Place sheet of paper between the source and the Geiger counter and measure count rate agin, if count rate decreases significantly then the source is alpha radiation
- Repeat with aluminium foil and several inches of lead, if a significant decrease for aluminium foil, then it is beta. if a significant decrease for several inches of lead, then it is gamma
How can these types of radiation be used to monitor the thickness of certain materials while they are being produced?
e.g for the production of aluminium foil, a beta source is placed on one side of the material, while a detector is placed on the other. If the material becomes too thick, less beta radiation will pass through the foil, therefore the reading on the detector decreases causing the roller to move closer; opposite for the material becoming too thin. Same method for alpha and paper, and gamma and steel
what are the applications of gamma radiation?
-sterilise surgical equipment
- radiotherapy
what is the equation for the intensity of radiation? (inverse square law)
I= k / x²
how would you verify the inverse square law?
measure the count rate of a gamma source at different distances from the GM tube, making sure to adjust to the background radiation. then plot graph of corrected count rate to 1/x² which will form a straight line
How can radioactive sources be handled safely?
-use of tongs
-storing in lead-lined container when not in use
-limit exposure
what are examples for sources of background radiation?
-Radon gas
-Cosmics rays
-Rocks
what does random mean?
you can’t predict when the next decay will happen
what is the decay constant, λ?
the probability of a nucleus decaying per unit time
what is the exponential equation for the number of nuclei?
N= N₀e^(-λt)
-what is half-life?
- what is the equation for half life?
-the time taken for the number of nuclei to halve
- T₀.₅=ln2/λ
-what is activity?
-what is the equation for activity?
-the number of nuclei that decay per second
-A=λN
what is the exponential equation for activity?
A=A ₀e^(-λt)
what are the applications of half life?
-dating of objects
-medical diagnosis
why might a nucleus become unstable?
-too many neutrons
-too many protons
-too many nucleons
-too much energy
why, on a Graph of N against Z for stable nuclei, do the number of neutrons and protons not increase uniformly?
because beyond a certain point, the electromagnetic force of repulsion becomes larger than the strong nuclear force keeping the nucleus together, so more neutrons are needed to increase the distance between the protons in order to decrease the magnitude of the electromagnetic force keep the nucleus stable
