Radiation Physics and Protection Practice Questions

Q: The following diagram shows production of X-rays. This is known as: (Recent NEET Pattern 2016-17)

Bremsstrahlung effect. ***Bremsstrahlung effect*** - The diagram shows an **incoming electron** being decelerated as it passes near the nucleus of an atom, causing it to lose energy and emit an **X-ray photon**. - This process, where an electron is slowed down ("braked") by the electric field of the nucleus, resulting in the emission of radiation (X-rays), is precisely what is known as **Bremsstrahlung**, or "braking radiation." *Bragg effect* - The **Bragg effect** describes the phenomenon where X-rays are diffracted by the atoms in a **crystal lattice** at specific angles. - It is used in **X-ray crystallography** to determine the atomic and molecular structure of a crystal, and not the primary production of X-rays itself. *Compton effect* - The **Compton effect** involves the **scattering of a photon** (like an X-ray) by a charged particle, typically an electron, resulting in a decrease in the photon's energy and an increase in its wavelength. - This describes the **interaction of existing X-rays with matter**, not the mechanism of X-ray generation as depicted in the diagram. *Thomson scattering* - **Thomson scattering** is the elastic scattering of **electromagnetic radiation** by a free charged particle, usually an electron, producing radiation of the **same wavelength** (no energy loss). - It is a classical explanation for the scattering of light and does not account for the production of X-rays or the change in electron energy.

Q: Which of the following typically results in the maximum radiation exposure?

PET CT. ***PET CT*** - **PET CT (Positron Emission Tomography-Computed Tomography)** combines the radiation from both a PET scan (using radiotracers like FDG) and a CT scan, resulting in the highest typical radiation exposure among the listed options. - The integration of functional (PET) and anatomical (CT) imaging, while providing comprehensive diagnostic information, significantly increases the total absorbed dose (~20-30 mSv). *Chest X-ray* - A **chest X-ray** involves a very low dose of radiation (~0.1 mSv), making it one of the imaging modalities with the least radiation exposure. - Due to its low dose and widespread use, the benefits of chest X-rays in diagnosing pulmonary and cardiac conditions far outweigh the minimal radiation risk. *IV pyelography* - **Intravenous pyelography (IVP)**, or intravenous urography, uses X-rays and contrast dye to visualize the urinary tract, delivering a moderate radiation dose (~3-5 mSv). - While higher than a standard X-ray, its dose is significantly lower than that of complex combined imaging like PET-CT. *Barium Enema* - A **barium enema** involves multiple X-ray images of the large intestine after administering barium contrast, leading to a moderate to high radiation dose (~8-15 mSv). - The series of exposures required to adequately visualize the entire colon contributes to a higher cumulative dose compared to single-shot X-rays.

Q: Which of the following investigations work on the same principle?

CT and X-ray. ***CT and X-ray*** - Both **Computed Tomography (CT)** and **X-ray** imaging utilize **ionizing radiation** to generate images of the body's internal structures. - They work by passing X-ray beams through the patient, with different tissues absorbing the radiation to varying degrees, which is then detected to create an image. *MRI and PET Scan* - **Magnetic Resonance Imaging (MRI)** uses **strong magnetic fields and radio waves** to create detailed images of soft tissues, based on water content. - **Positron Emission Tomography (PET) scans** use **radioactive tracers** to visualize metabolic activity and blood flow, detecting gamma rays emitted from the patient. *CT and MRI* - **CT scans** use **ionizing radiation** (X-rays) to produce cross-sectional images. - **MRI scans** use **magnetic fields and radio waves** and do not involve ionizing radiation. *USG and HIDA Scan* - **Ultrasound (USG)** uses **high-frequency sound waves** to create real-time images of organs and structures. - **Hepatobiliary Iminodiacetic Acid (HIDA) scans** are a type of nuclear medicine study that uses a **radioactive tracer** to evaluate liver and gallbladder function.

Q: Which of the following statements about the half-life of radioisotopes is false?

I-131: 60 years. ***I-131: 60 years*** - The half-life of **Iodine-131 (I-131)** is approximately **8 days**, not 60 years. This makes the statement false. - I-131 is commonly used in nuclear medicine for thyroid imaging and treatment, and its relatively short half-life is advantageous for patient safety. *Co-60: 5.26 years* - The half-life of **Cobalt-60 (Co-60)** is indeed approximately **5.26 years**. - Co-60 is a significant radioisotope used in **radiotherapy** and for sterilization of medical equipment. *Ra-226: 1626 years* - The half-life of **Radium-226 (Ra-226)** is approximately **1626 years**, making this statement correct. - Ra-226 is a naturally occurring radioisotope with a very long half-life, historically used in medicine and still present in some environmental contexts. *Ir-192 : 74 days* - The half-life of **Iridium-192 (Ir-192)** is approximately **73.8 days (often rounded to 74 days)**, making this statement correct. - Ir-192 is commonly used in **brachytherapy** for cancer treatment and **industrial radiography**.

Q: A developer at high temperature will cause:

Very dark image. ***Very dark image*** - A developer solution at a **high temperature** accelerates the chemical reactions involved in reducing exposed silver halide crystals. - This over-development leads to an excessive amount of metallic silver being generated, resulting in an **overly dense** and thus very dark image. *Clear white spots on the film* - **White spots** on film typically indicate areas where the silver halide crystals were either not exposed to radiation or were not developed, often due to a **fixer spot** or **air bubble**. - High developer temperature causes over-development, not under-development or lack of development in specific areas. *Very light image* - A **very light image** suggests under-development, which can occur due to **low developer temperature**, insufficient developing time, or an exhausted developing solution. - Conversely, high developer temperature causes over-development, leading to a dark image. *Yellow stains* - **Yellow stains** on film are usually a sign of **insufficient rinsing** after fixing, allowing residual thiosulfate compounds to react with silver, or using an **exhausted fixer solution**. - While processing errors can occur, yellow stains are not a direct consequence of high developer temperature.

Q: Which of the following reduces the development of unexposed Ag halide crystals, and also acts as an antifog agent?

Sodium bromide. ***Sodium bromide*** - As a **restrainer**, sodium bromide **reduces the development of unexposed silver halide crystals** by competing with the developing agents for adsorption onto the crystal surface. - It also acts as an **antifogging agent** by increasing the threshold potential required for the reduction of silver ions, thereby preventing the reduction of unexposed crystals that might otherwise be reduced due to minor defects or chemical fog. *Potassium hydroxide* - **Potassium hydroxide** is a **strong alkali** used as an **activator** in photographic developers to maintain a high pH. - It does not reduce the development of unexposed crystals or act as an antifogging agent; rather, its role is to **accelerate the development process**. *Sodium sulfite* - **Sodium sulfite** is primarily used as a **preservative** in photographic developers to prevent the oxidation of developing agents by atmospheric oxygen. - While it can help maintain the stability of the developer, it does not directly act as a restrainer or antifogging agent to control fog due to unexposed crystals. *Phenidone* - **Phenidone** is a **developing agent**, known for its high activity and super-additive effect when combined with hydroquinone. - Its function is to **reduce exposed silver halide crystals** to metallic silver, not to reduce the development of unexposed crystals or act as an antifogging agent.

Q: Half-life of Cobalt-60:

5.3 years. ***5.3 years*** - The **half-life of Cobalt-60** is approximately 5.27 years, often rounded to 5.3 years. - This specific half-life is crucial for its applications in **radiotherapy** and **sterilization**, as it determines the rate of decay and activity. *4.3 years* - This value is not the correct half-life for **Cobalt-60**. - A slightly different half-life would significantly impact calculations in medical physics and nuclear applications. *3.3 years* - This value is not accurate for the **half-life of Cobalt-60**. - Such a shorter half-life would mean a faster decay rate, affecting its utility in continuous radiation sources. *6.3 years* - This value is not the correct half-life for **Cobalt-60**. - A longer half-life would imply a slower decay, altering its radioactive properties and safe handling protocols.

Q: At t = 0 there are 6 x 10^23 radioactive atoms of a substance, which decay with a disintegration constant (λ) equal to 0.01/sec. What would be the initial decay rate?

6 x 10^21. ***6 x 10^21*** - The **initial decay rate** (A) is calculated using the formula **A = λN**, where **λ** is the disintegration constant and **N** is the initial number of radioactive atoms. - Given **λ = 0.01/sec** and **N = 6 x 10^23** atoms, the decay rate is **0.01 x 6 x 10^23 = 6 x 10^21 decays/sec**. *6 x 10^19* - This value is significantly lower than the calculated initial decay rate, suggesting an error in calculation or an incorrect application of the decay rate formula. - It does not account for the product of the disintegration constant and the total number of atoms. *6 x 10^23* - This value represents the **initial number of radioactive atoms** (N), not the initial decay rate. - The decay rate is a measure of how many atoms decay per unit of time, which requires multiplying N by the disintegration constant λ. *6 x 10^22* - This value is an order of magnitude higher than the correct decay rate. - An error in multiplying by 0.01 (which is 10^-2) would lead to this incorrect result.

Q: The longest half life is that of:

Uranium. ***Uranium*** - **Uranium-238**, a common isotope, has an incredibly long half-life of approximately **4.468 billion years**, which is comparable to the age of the Earth. - This extremely long half-life is due to its slow **alpha decay**, making it a very stable radioactive element. *Radon* - **Radon-222** has a relatively short half-life of about **3.8 days**. - Its short half-life makes it a significant indoor air pollutant as it rapidly decays into other radioactive isotopes. *Cesium* - **Cesium-137**, a product of nuclear fission, has a half-life of approximately **30 years**. - While longer than radon, its half-life is much shorter compared to uranium, meaning it decays significantly faster. *Radium* - **Radium-226**, a decay product of uranium, has a half-life of approximately **1,600 years**. - Although much longer than radon and cesium, it is still orders of magnitude shorter than the half-life of uranium-238.

Q: Hounsfield units are used in CT density scale to measure attenuation value of different materials compared to water. The value of fat in HU would be around:

-100. ***-100*** - **Fat** has a lower density than water, causing less X-ray attenuation. This results in negative Hounsfield Unit (HU) values. - A value of **-100 HU** is characteristic for fat, indicating its low density compared to the reference point of water (0 HU). *100* - A value of **100 HU** typically represents soft tissues that are denser than water but less dense than bone, such as muscle or early stages of hemorrhage. - This value indicates a higher X-ray attenuation than fat, which is contrary to the properties of fat. *1000* - A value of **1000 HU** is characteristic of **dense bone** or calcifications, which strongly attenuate X-rays due to their high density and atomic number. - This significant positive value is far from the negative values associated with fat. *-1000* - A value of **-1000 HU** represents **air**, which has the lowest density and therefore the lowest X-ray attenuation, appearing black on CT images. - While negative, this value is much lower than that of fat, indicating a significantly less dense material.

Question 1

The following diagram shows production of X-rays. This is known as: (Recent NEET Pattern 2016-17)

Accepted Answer

Bremsstrahlung effect

Answer

Bragg effect

Answer

Compton effect

Answer

Thomson scattering

Question 2

Which of the following typically results in the maximum radiation exposure?

Accepted Answer

PET CT

Answer

Chest X ray

Answer

IV pyelography

Answer

Barium Enema

Answer

X-ray abdomen

Question 3

Which of the following investigations work on the same principle?

Accepted Answer

CT and X-ray

Answer

MRI and PET Scan

Answer

CT and MRI

Answer

USG and HIDA Scan

Question 4

Which of the following statements about the half-life of radioisotopes is false?

Accepted Answer

I-131: 60 years

Answer

Co-60: 5.26 years

Answer

Ra-226: 1626 years

Answer

Ir-192 : 74 days

Question 5

A developer at high temperature will cause:

Accepted Answer

Very dark image

Answer

Clear white spots on the film

Answer

Very light image

Answer

Yellow stains

Question 6

Which of the following reduces the development of unexposed Ag halide crystals, and also acts as an antifog agent?

Accepted Answer

Sodium bromide

Answer

Potassium hydroxide

Answer

Sodium sulfite

Answer

Phenidone

Question 7

Half-life of Cobalt-60:

Accepted Answer

5.3 years

Answer

4.3 years

Answer

3.3 years

Answer

6.3 years

Question 8

At t = 0 there are 6 x 10^23 radioactive atoms of a substance, which decay with a disintegration constant (λ) equal to 0.01/sec. What would be the initial decay rate?

Accepted Answer

6 x 10^21

Answer

6 x 10^19

Answer

6 x 10^23

Answer

6 x 10^22

Question 9

The longest half life is that of:

Accepted Answer

Uranium

Answer

Radon

Answer

Cesium

Answer

Radium

Question 10

Hounsfield units are used in CT density scale to measure attenuation value of different materials compared to water. The value of fat in HU would be around:

Accepted Answer

-100

Answer

100

Answer

1000

Answer

-1000

Radiation Physics and Protection — MCQs

Radiation Physics and Protection — MCQs

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