Which statement about the structure of an atom is correct?
It contains positively charged particles only.
It contains negatively charged particles only.
It contains no charged particles.
It contains positively charged particles and negatively charged particles.
Leaks in underground water pipes are detected using radioactive tracers. Fig. 10.1 shows a radiation detector above a water pipe.
Fig. 10.1
Before the radioactive tracer is added to the water, the detector measures the background radiation above the pipe. The average background radiation is 26 counts/minute.
Define background radiation.
Suggest one source of radiation that may make a significant contribution to the background count rate.
A radioactive tracer is added to the water. The counter in Fig. 10.1 shows the count rate in counts/minute above the leak in the water pipe.
Determine the count rate due to the tracer.
Suggest which radioactive emission, alpha, beta or gamma, is suitable for detecting the leak in the water pipe.
Explain your answer.
emission
explanation
Explain why the radioactive isotope must not have a very short half-life.
Explain why the radioactive isotope must not have a very long half-life.
[Total: 9]
The chemical symbol of the element lithium is Li . The proton number of lithium is 3 .
Fig. 9.1 is a representation of a nucleus of a radioactive isotope of lithium that is about to decay.
Fig. 9.1
Write down, using nuclide notation, the symbol that represents this isotope of lithium.
This isotope of lithium decays by -particle emission to form another nucleus.
Complete Fig. 9.2 to represent this decay by:
- using the same representation as in Fig. 9.1 and in the space after the arrow, draw a diagram of the nucleus formed by the decay
- writing the name of the particle that is identical to a -particle on the answer line provided.
Fig. 9.2
A radiation detector is set up in a laboratory where there are no radioactive samples.
On six separate occasions, the detector is switched on for 1.0 minute and the background count is recorded. The counts are:
State why the readings are not all identical.
Suggest a possible source for this background radiation.
A sample containing only one radioactive isotope is brought into the laboratory. The half-life of the isotope is 15 hours.
The sample is placed near to the radiation detector in this laboratory. The detector is switched on and, after 1.0 minute, a count of 440 is recorded.
The sample is left next to the detector and the experiment is repeated 45 hours later.
The detector is switched on for 1.0 minute.
Predict the reading for the count obtained on this occasion.
reading
The nuclei of the atoms in a substance are changing randomly and emitting radiation.
What is happening to the substance?
It is undergoing electromagnetic induction.
It is undergoing magnetisation.
It is undergoing solidification.
It is undergoing radioactive decay.