krit.club logo

Physics: Nuclear Physics - Uses, Risks, Detection, and Background Radiation

Grade 8IB

Review the key concepts, formulae, and examples before starting your quiz.

🔑Concepts

•

Radioactivity is the spontaneous emission of particles or energy from an unstable atomic nucleus. The activity is measured in Becquerels (BqBq), where 1Bq=11 Bq = 1 decay per second.

•

Ionizing radiation (Alpha α\alpha, Beta β\beta, and Gamma γ\gamma) has enough energy to remove electrons from atoms. This can cause DNA mutations, cell death, or cancer in biological organisms.

•

Detection: Ionizing radiation is detected using devices like the Geiger-Müller (GM) tube, which produces an electrical pulse for each particle detected, or photographic film badges that darken upon exposure.

•

Background Radiation: This is the low-level ionizing radiation that is constantly present in the environment. Sources include natural (Radon gas from rocks, cosmic rays from space, Carbon-14 in food) and man-made (medical X-rays, nuclear accidents).

•

Uses of Radiation: Medical tracers (131I^{131}I), cancer treatment (Radiotherapy using 60Co^{60}Co), industrial thickness gauges, and Carbon-14 dating for archaeology.

•

Safety Precautions: Minimizing exposure time, increasing distance from the source, and using shielding (e.g., lead aprons for γ\gamma rays or concrete walls).

📐Formulae

Corrected Count Rate=Total Count Rate−Background Count Rate\text{Corrected Count Rate} = \text{Total Count Rate} - \text{Background Count Rate}

n=tT1/2n = \frac{t}{T_{1/2}}

N=N0×(12)nN = N_0 \times \left(\frac{1}{2}\right)^n

Activity(A)=Number of DecaysTime (s)\text{Activity} (A) = \frac{\text{Number of Decays}}{\text{Time (s)}}

💡Examples

Problem 1:

A student measures the count rate of a radioactive source as 185185 counts per minute (cpm). The background radiation in the lab is 2222 cpm. Calculate the corrected count rate of the source.

Solution:

185−22163\begin{array}{r} 185 \\ - 22 \\ \hline 163 \end{array} Corrected Count Rate = 163163 cpm.

Explanation:

To find the true activity of a source, you must subtract the background radiation that is present in the room from the total measurement taken by the Geiger-Müller counter.

Problem 2:

An isotope has a half-life (T1/2T_{1/2}) of 88 days. If the initial mass is 8080 g, how much remains after 2424 days?

Solution:

First, find the number of half-lives: n=248=3n = \frac{24}{8} = 3 Then calculate the remaining mass: N=80×(12)3=80×18=10 gN = 80 \times \left(\frac{1}{2}\right)^3 = 80 \times \frac{1}{8} = 10\text{ g}

Explanation:

The mass halves every 8 days. In 24 days, it halves three times (80→40→20→1080 \rightarrow 40 \rightarrow 20 \rightarrow 10).

Problem 3:

A radioactive sample has an activity of 640Bq640 Bq. After 22 hours, the activity drops to 40Bq40 Bq. Determine the half-life of the sample in minutes.

Solution:

Determine how many times the activity halved: 640→320→160→80→40640 \rightarrow 320 \rightarrow 160 \rightarrow 80 \rightarrow 40 (This is 44 half-lives). Total time = 22 hours = 120120 minutes. T1/2=120 min4=30 minutesT_{1/2} = \frac{120 \text{ min}}{4} = 30 \text{ minutes}

Explanation:

By counting the number of steps taken to reach the final activity, we find n=4n=4. Dividing the total duration by the number of half-lives gives the duration of a single half-life.