An electron collides with a helium in its ground state, causing an electron to transition from 1s to 2s. The electron initially has 45.0 eV of kinetic energy.
(b)
Calculate the electron’s kinetic energy after the collision.
Helium and neon coincidentally have very similar energy gaps for certain transitions, allowing one atom to cause an excitation in the other.
The excited helium atom from part (b) then collides with a ground state neon atom. The neon atom becomes excited and subsequently emits two photons in order to return to its ground state.
(d)
(i)
If the helium is left back in its ground state after the collision, determine the amount of energy transferred to the neon atom.
(ii)
If one photon has an energy of 1.96 eV, calculate the wavelength of the other.
A radioactive source is used to measure the thickness of paper. A Geiger counter is used to measure the count rate on the opposite side of the paper to the radioactive source. The radioactive source used must be chosen carefully.
(a)
(i)
State and explain the type of radioactive source that should be used for this process.
(ii)
A new type of paper is placed between the Geiger counter and the radioactive source. Explain how the equipment can be used to show if the new paper is thicker or thinner than the previous type.
The scientist wonders how the experiment in part (a) would have changed if the sample was twice the size.
(b)
Assuming the experiment from part (a) was repeated with a sample the exact same age but twice the mass, calculate the length of time it would have taken to reach a count rate of 22.5 cpm.
The scientist can measure the count rate of the source but is unable to directly measure the activity of the source using their detector. Activity is the total number of particles emitted from the sample per unit time.
An unstable isotope of mercury, Hg-203, is tested for its radioactive emissions in a laboratory that has a background rate of 0.3 s–1.
A source is placed a fixed distance from a Geiger-Muller tube. Various materials are placed in between the detector and the source while the count rate is recorded. The results are shown below.
Material
Count rate / s–1
None
68
0.5 mm thick paper
69
2.0 mm thick paper
65
5 cm thick aluminium foil
15
(c)
State and explain what types of radiation are being emitted by the Hg-203 source.
