Some isotopes of sodium are radioactive.
The isotope sodium-24 (Na-24) has the symbol:
1124Na^{24}_{11}\text{Na}1124Na
The isotope sodium-22 (Na-22) has the symbol:
1122Na^{22}_{11}\text{Na}1122Na
State the number of protons in a nucleus of Na-24.
Give one similarity and one difference between the nucleus of Na-22 and the nucleus of Na-24.
A technician measures the radiation emitted by a sample of Na-24.
The technician's results are shown in Table 18.1.
| Count-rate (counts per minute) | |
|---|---|
| Measurement 1 | 305 |
| Measurement 2 | 288 |
| Measurement 3 | 292 |
Explain why the technician's three measurements are not the same.
Use the technician's results in Table 18.1 to calculate the mean count-rate for Na-24.
Na-24 emits gamma radiation. The technician puts a thin sheet of aluminium foil between the Na-24 sample and the detector. State what happens to the count-rate.
Explain what is meant by the half-life of a radioactive isotope.
The half-life of Na-24 is 15 hours. The count-rate of a sample of Na-24 is 320 counts per minute. Calculate the count-rate of the Na-24 after 45 hours.
A radioactive isotope can be used as a tracer in a patient's body. It is monitored by a radiation detector outside the body.
Four possible radioactive isotopes are shown in Table 18.2.
| Radioactive isotope | Type of radiation emitted | Half-life |
|---|---|---|
| Radon-219 | Alpha | 4 seconds |
| Technetium-99m | Gamma | 6 hours |
| Cesium-137 | Gamma | 30 years |
| Polonium-210 | Alpha | 138 days |
Doctors wear a lead apron when they use radioactive isotopes. Explain why.
Which radioactive isotope from Table 18.2 is best to use as a radioactive tracer in a patient's body? Explain your answer.