MYP Physics · 17 · data analysis
Remove background before finding half-life
Atomic and nuclear physics · Original GioPhysics question with a detailed, mark-by-mark answer guide.
- Demand
- routine
- Marks
- 7
- Topics
- 2
- Answer
- Complete
Measured count rate over time
The plotted points reproduce the two columns of the question table, in the original units.
Vertical axis (y): Measured rate / counts min⁻¹
Horizontal axis (x): Time / min
Read the exact data as a table
| Time / min | Measured rate / counts min⁻¹ |
|---|---|
| 0 | 420 |
| 5 | 220 |
| 10 | 120 |
| 15 | 70 |
| 20 | 45 |
These are the supplied values, not a worked answer. No fitted trend is drawn.
A detector records a background count rate of 20 counts per minute. The table shows the measured rate from a source plus background.
| Time / min | Measured rate / counts min⁻¹ |
|---|---|
| 0 | 420 |
| 5 | 220 |
| 10 | 120 |
| 15 | 70 |
| 20 | 45 |
- a
Calculate Calculate the corrected source count rate at 0, 10, and 20 minutes.
3 marks - b
Determine Determine the half-life and support it with two intervals.
2 marks - c
Predict Predict the measured detector rate at 25 minutes.
2 marks
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a
Calculate Calculate the corrected source count rate at 0, 10, and 20 minutes.
Read the data before explaining it. Quote the relevant values or trend, show the comparison or calculation, and then connect that numerical evidence to the physical conclusion—including uncertainty or anomalies when they matter.
- 1
Calculates 420 − 20 = 400 counts min⁻¹ at 0 min.
- 2
Calculates 120 − 20 = 100 counts min⁻¹ at 10 min.
- 3
Calculates 45 − 20 = 25 counts min⁻¹ at 20 min.
b
Determine Determine the half-life and support it with two intervals.
Read the data before explaining it. Quote the relevant values or trend, show the comparison or calculation, and then connect that numerical evidence to the physical conclusion—including uncertainty or anomalies when they matter.
- 1
Determines a half-life of 5 min.
- 2
Supports it with two corrected halvings, for example 400 → 200 → 100 over successive 5 min intervals.
c
Predict Predict the measured detector rate at 25 minutes.
Read the data before explaining it. Quote the relevant values or trend, show the comparison or calculation, and then connect that numerical evidence to the physical conclusion—including uncertainty or anomalies when they matter.
- 1
Halves the corrected 20 min rate from 25 to 12.5 counts min⁻¹.
- 2
Adds background to predict about 32.5 counts min⁻¹, accepting 32 or 33 for a whole-count-rate estimate.
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