Sem 2 exam Flashcards
exam (28 cards)
What force holds nucleons together, and what force holds protons and electrons together?
Attractive nuclear force (physics) and electrostatic force (chemistry)
What makes an isotope unstable?
An excess of nucleons. The atom will shed this excess in varying kinds of radiation.
On an N vs Z (no. of neutrons vs no. of protons) graph, what kind of relationship can be identified with the line?
Above the line is too many neutrons so beta minus decay, and below the line is too many protons so beta plus decay.
When does alpha decay occur and what happens?
In alpha decay, an unstable nucleus emits an alpha particle (helium nucleus). Alpha decay typically occurs for nuclei with 83 or more protons.
When does beta minus decay occur and what happens?
Beta minus decay occurs when a nucleus has an excess of neutrons, and involves the decay of a neutron into a proton, electron, and antineutrino.
When does beta plus decay occur and what happens?
Beta plus decay occurs when a nucleus has an excess of protons, and involves the decay of a proton into a neutron, positron, and neutrino.
When does gamma decay occur and what happens?
In gamma decay, an unstable nucleus emits high-energy gamma rays. Gamma decay occurs when a nucleus is left with excess energy after an alpha or beta decay.
What does n in the gamma decay equation represent?
The number of rays emitted.
Compare the ionising ability and penetration through matter of alpha, beta, and gamma radiations
Alpha is the most ionising but least penetrating, beta is less ionising but more penetrating, and gamma is the least ionising but most penetrating.
What is ionising radiation?
Radiation where the particles emitted have the ability to knock electrons from atoms and ‘ion’-ise them
What is a half-life?
The number of radioactive nuclei in a sample of a given isotope decreases exponentially with time.
A half-life is the time required for half of the radioactive nuclei in a sample to decay.
The half-life of radioactive nuclei is independent of both the physical state and the chemical state of the material.
The activity of a radioactive substance is the number of radioactive nuclei that decay per unit time
What is nuclear fission?
Nuclear fission can be induced in some heavy nuclei by the collision of a neutron. The nucleus splits into two nuclei and several neutrons.
Describe the calculated properties of nuclear fission
The total mass of the reactants in a fission reaction is greater than that of the products, releasing energy given by E =𝚫mc^2, where 𝚫m is the mass of the reactants minus the mass of the products.
How can nuclear fission result in a chain reaction?
On average, more than one neutron is emitted in nuclear fission. This leads to the possibility that these neutrons will induce further fissions, resulting in a chain reaction.
If 20 grams of a radioactive isotope is present at 1:00 PM and 5 grams remain at 2:00 PM, what is the half life of the isotope?
20 -> 10 -> 5, so 2 half lives have passed. 2 half lives in 60 minutes (60/2) 1 half life per 30 minutes. Therefore, the half life is 30 minutes.
Iodine-131 has a half life 8 days. What fraction/percentage of the sample would remain at the end of 32 days?
If the isotope sample had a mass of 500 grams, how much of it would remain at this time?
The half life is 8 days, so throughout 32 days (32/8=4) it would go through 4 half lives. This means (1/2)^4 = 0.0625% will remain after 32 days.
(1/2)^4 * 500 = 31.25 grams will remain. (3.1*10 grams)
When considering motion, what equations are use for horizontal and vertical components?
Horizontal - the 3 equations of motion
Vertical - basic equations like v = s / t
Acceleration CAN be given by:
the change in velocity divided by the change in time.
Is vertical motion symmetrical?
Yes. However long something takes to go up, is how long it will take to come down.
What does the area under a curve in a time (x) against velocity (y) graph represent?
Distance, because v = s / t and s = vt.
What is impulse?
Change in momentum (delta P) or force multiplied by time (Ft).
How do you find force from momentum?
Force is equal to delta P divided by time. The change in momentum with respect to time.
Elastic collisions vs inelastic collisions
An elastic collision is one in which the total initial kinetic energy equals the total final kinetic energy. In an inelastic collision, some kinetic energy is transformed.
The law of conservation of momentum is:
The law of conservation of momentum states that, in the absence of an external force, the momentum of a system remains unchanged.
Total momentum of the system before interaction = total momentum of the system after interaction
