JKSSB Junior/Senior Radiotherapy Technician 2025 Solved Question Paper

Question 1

A Beam of electrons is travelling in a straight line. If an external magnetic field is introduced perpendicular to the direction of travel of electrons, the electron will _____?

Accepted Answer

Option D: Be deflected to travel perpendicular to the magnetic field and perpendicular to their initial direction of motion. According to the Lorentz Force Law ($\vec{F} = -e(\vec{v} 	imes \vec{B})$), a magnetic field perpendicular to an electron's velocity exerts a magnetic deflecting force perpendicular to both the velocity vector and the magnetic field lines (causing circular or curved trajectory without changing speed).

Question 2

Rate of transfer of energy by radiation can be increased by:

Accepted Answer

Option A: increasing the surface temperature. According to the Stefan-Boltzmann Law ($E = \epsilon \sigma A T^4$), the radiant energy emission rate is directly proportional to the fourth power of the absolute surface temperature ($T^4$).

Question 3

A Muon is a sub atomic particle which has a mass 207 times that of the mass of electron. What is the approximate mass of the muon in units of MeV?

Accepted Answer

Option C: 106 MeV. Electron rest mass energy $m_e c^2 \approx 0.511	ext{ MeV}$.
$$	ext{Mass of Muon} = 207 	imes 0.511	ext{ MeV} \approx 105.78	ext{ MeV} \approx 106	ext{ MeV}.$$

Question 4

Directly ionizing radiation does not include:

Accepted Answer

Option C: Neutron. Directly ionizing radiation consists of charged particles (electrons, positrons, protons, alpha particles) that ionize atoms directly via Coulomb interactions. Neutrons and photons are uncharged and represent indirectly ionizing radiation.

Question 5

A phantom that simulate various body tissues is called:

Accepted Answer

Option B: Anthropomorphic phantoms. An anthropomorphic phantom (such as the Rando phantom) is anatomically modeled to simulate human body contours and contains tissue-equivalent materials mimicking bone, lung, muscle, and soft tissue inhomogeneities.

Question 6

Of the following isotope which one has shortest half life:

Accepted Answer

Option B: 198Au. Half-lives comparison:
- Gold-198 ($^{198}	ext{Au}$): $T_{1/2} = 2.7	ext{ days}$
- Radon-222 ($^{222}	ext{Rn}$): $T_{1/2} = 3.82	ext{ days}$
- Palladium-103 ($^{103}	ext{Pd}$): $T_{1/2} = 17.0	ext{ days}$
- Radium-226 ($^{226}	ext{Ra}$): $T_{1/2} = 1600	ext{ years}$.
$^{198}	ext{Au}$ has the shortest half-life.

Question 7

What Kind of radioactive equilibrium can occur when a very long live radionuclide decays to very short lived one?

Accepted Answer

Option B: Secular. Secular equilibrium occurs when the parent half-life is vastly greater than the daughter half-life ($T_{	ext{parent}} \gg T_{	ext{daughter}}$, e.g. ^{226}	ext{Ra} → {}^{222}	ext{Rn}), so the parent activity does not decrease noticeably over many daughter half-lives.

Question 8

How many mCi of a radioactive radioisotope (T1/2 = 2.7 days) are required so that the samples activity will be 10mCi 24 hrs later?

Accepted Answer

Option D: 12.93. Decay constant $\lambda = \frac{0.693}{T_{1/2}} = \frac{0.693}{2.7	ext{ days}} = 0.2567	ext{ day}^{-1}$.
Time elapsed $t = 24	ext{ hrs} = 1.0	ext{ day}$.
$$A(t) = A_0 e^{-\lambda t} \implies A_0 = \frac{A(t)}{e^{-\lambda t}} = \frac{10	ext{ mCi}}{e^{-0.2567}} = \frac{10}{0.7736} \approx 12.93	ext{ mCi}.$$

Question 9

Heavy radioactive nuclei decay most frequently with emission of which of the following:

Accepted Answer

Option C: Alpha. Heavy radioactive nuclei ($Z > 82$, $A > 200$) achieve nuclear stability most frequently by shedding 2 protons and 2 neutrons through Alpha particle ($\alpha$) decay.

Question 10

Find the correct statement for WBCs:

Accepted Answer

Option A: Can squeeze through blood capillaries. White blood cells (leukocytes) exhibit diapedesis (extravasation), enabling them to actively deform and squeeze through tiny gaps in capillary endothelial walls into tissue spaces.

Question 11

Protein synthesis is a function of?

Accepted Answer

Option B: Rough endoplasmic reticulum. The Rough Endoplasmic Reticulum (RER) is studded with ribosomes on its cytosolic surface, functioning as the primary site of cellular protein synthesis and translational folding.

Question 12

Visible light has a wavelength of approximately 6×10^-7 m. Co60 gamma rays have a wavelength of 1×10^-12 m and the energy of 1.25 MeV. What is the approximate energy of light photons?

Accepted Answer

Option B: 2eV. Energy of photon $E = \frac{hc}{\lambda} = \frac{1240	ext{ eV}\cdot	ext{nm}}{\lambda}$.
For visible light $\lambda = 600	ext{ nm}$ ($6 	imes 10^{-7}	ext{ m}$):
$$E = \frac{1240	ext{ eV}\cdot	ext{nm}}{600	ext{ nm}} \approx 2.06	ext{ eV} \approx 2	ext{ eV}.$$

Question 13

The ratio of Compton interaction in one gram of hydrogen to one gram of water is about:

Accepted Answer

Option C: 2.0. Compton mass attenuation depends directly on electron density ($N_e = N_A \cdot Z/A$).
- For Hydrogen ($Z/A = 1/1 = 1.0$): $N_e \approx 6.022 	imes 10^{23}	ext{ e}^-/	ext{g}$
- For Water ($Z/A = 10/18 \approx 0.555$): $N_e \approx 3.34 	imes 10^{23}	ext{ e}^-/	ext{g}$
$$	ext{Ratio} = \frac{1.0}{0.555} \approx 1.8 \approx 2.0.$$

Question 14

Leakage for Co60 in the off position is:

Accepted Answer

Option D: Average 2mR/hr at 1 meter. According to international radiation safety standards for teletherapy units in the OFF/shielded position, leakage radiation through the source housing must not exceed an average of 2 mR/hr (0.02 mSv/hr) at 1 meter, and a maximum of 10 mR/hr at 1 meter.

Question 15

A series of dosimeter are irradiated in water with Co-60 and then with 15MV x-rays. In both cases the dose to the water at the position of the dosimeter was 1Gy. For which dosimeter will the reading for the two energies differ the least.

Accepted Answer

Option A: Ionization chamber. An air-filled ionization chamber calibrated under cavity-gas Spencer-Attix theory has an energy response that is closest to water-equivalent tissue over megavoltage energy ranges (Co-60 to 15 MV), differing by less than 1-2% compared to diodes, films, or TLDs.

Question 16

An atomic mass unit (amu) is defined as _____.

Accepted Answer

Option D: 1/12 of the mass of a 6C12 atom. The unified atomic mass unit (1 u / amu) is standardly defined as exactly $1/12$ of the mass of an unbound neutral Carbon-12 ($^{12}	ext{C}$) atom at rest ($1	ext{ amu} \approx 1.66054 	imes 10^{-27}	ext{ kg} \approx 931.5	ext{ MeV}/c^2$).

Question 17

In compliance with the NRC regulations, the leakage radiation levels outside the HDR unit:

Accepted Answer

Option C: Should not exceed 1 mR/h at a distance of 10 cm with the source in the Shielded position. Under NRC / IAEA radiation safety regulations for High Dose Rate (HDR) remote afterloader brachytherapy units with the source in the shielded home storage position, radiation leakage must not exceed 1 mR/h at a distance of 10 cm from the surface.

Question 18

What is the difference between acceptance testing and commissioning of equipment?

Accepted Answer

Option A: Acceptance test runs a small portion of dataset of commissioning.. Acceptance testing verifies that the newly installed machine meets vendor purchase contractual specifications using a limited baseline dataset. Commissioning is the comprehensive clinical dataset acquisition (PDD, beam profiles, output factors) required for clinical treatment planning.

Question 19

If a dual-energy linear accelerator uses 6 and 18 MV:

Accepted Answer

Option B: The output of both photon energies must be checked daily.. According to AAPM TG-142 quality assurance guidelines for linear accelerators, daily QA requires checking the beam output constancy of ALL clinical photon and electron energies utilized for treatment.

Question 20

The accuracy of the mechanical isocenter can be checked by:

Accepted Answer

Option B: Using a front pointer positioned at the isocenter and a horizontal rod with a fine point held in a ring stand. The mechanical isocenter (gantry, collimator, and couch rotational intersection point) is traditionally verified mechanically using a mechanical front pointer positioned at the isocenter and a mechanical pointer/horizontal rod with a fine needle point mounted on a ring stand.

Question 21

The most common interstitial irradiation technique is:

Accepted Answer

Option A: Percutaneous afterloading with angiocatheters and iridium-192. Interstitial brachytherapy commonly utilizes flexible plastic tubes / angiocatheters inserted into the tumor bed under imaging guidance, through which radioactive Iridium-192 ($^{192}	ext{Ir}$) wire/seeds or HDR stepping sources are afterloaded.

Question 22

In interstitial therapy, the radioactive sources are fabricated in the form of:

Accepted Answer

Option A: Needles, Wires and Seeds. Radioactive sources for interstitial implants are engineered as rigid needles (e.g. Cesium-137, Radium), flexible wires/hairpins (Iridium-192), and tiny radioactive seeds (e.g. Iodine-125, Palladium-103).

Question 23

The most common method of intracavitary brachytherapy is:

Accepted Answer

Option C: Fletcher tandem and ovoid applicator. For cervical gynecological cancer intracavitary brachytherapy, the Fletcher-Suit-Delclos (FSD) tandem and ovoids (colpostats) applicator system is the global standard.

Question 24

In which treatment can be used for Intraluminal Catheter?

Accepted Answer

Option D: Used for treatment of endobronchial carcinoma. Intraluminal brachytherapy inserts a catheter directly into the lumen of tubular organs, standardly used for treating obstructive endobronchial carcinoma, esophagus, or bile duct tumors.

Question 25

Surface applicators can be used to treat:

Accepted Answer

Option A: skin cancer. Customized surface mold / plaque applicators (holding beta or low-energy gamma emitters like Sr-90, P-32, Ir-192) are applied directly to superficial lesions to treat skin cancer and keloids.

Question 26

Why are there no naturally occurring isotopes with an atomics number greater than 92?

Accepted Answer

Option D: They exist, but their half-lives are too short to exist naturally. Transuranic elements ($Z > 92$, beyond Uranium) have unstable nuclei with half-lives vastly shorter than the 4.5-billion-year age of the Earth; any primordial isotopes formed during nucleosynthesis have completely decayed away.

Question 27

What is Nonmaleficence?

Accepted Answer

Option A: Avoidance of Harm. In medical ethics, Nonmaleficence is the foundational duty to 'first, do no harm' (Primum non nocere), obligating practitioners to refrain from inflicting needless pain, injury, or toxic harm on patients.

Question 28

The belly board's main advantage is:

Accepted Answer

Option D: Minimize small bowel dose. In prone pelvic radiotherapy (e.g. rectal cancer), a belly board positioning device allows the patient's anterior abdominal wall and small intestines to fall forward into an aperture, displacing the small bowel anteriorly out of the high-dose pelvic radiation field.

Question 29

What is Beneficence?

Accepted Answer

Option B: Active promotion of good. Beneficence is the moral principle that guides healthcare providers to act positively for the benefit, welfare, and best interest of the patient (active promotion of good).

Question 30

Which one of the following radioisotopes is most commonly used in remote after loader units?

Accepted Answer

Option C: 192Ir. Iridium-192 ($^{192}	ext{Ir}$) is the standard radioisotope used in modern High Dose Rate (HDR) remote afterloaders due to its high specific activity, compact seed dimensions (0.6 mm diameter), and moderate gamma energy (~380 keV) allowing flexible catheter navigation.

Question 31

What is the main reason for the difference in biologic effects caused by neutrons and photons?

Accepted Answer

Option C: The density of ionization.. Fast neutrons produce recoil protons with high Linear Energy Transfer (LET), resulting in a much higher microscopic density of ionization per track length (dense clusters of DNA double-strand breaks) compared to sparsely ionizing low-LET photons.

Question 32

Irradiation with x-rays of HeLa and Chinese hamster cells harvested at mitosis has shown that the cells are most sensitive when they are:

Accepted Answer

Option A: in the M phase of the cell cycle.. Cells are classically most radiosensitive in the M (Mitosis) phase and late G2 phase of the cell cycle, and most radioresistant in the late S (DNA synthesis) phase.

Question 33

Mitotic cells under conditions of hypoxia are as radiosensitive as:

Accepted Answer

Option B: cells in the late S phase.. Mitotic (M-phase) cells are inherently hyper-radiosensitive; when deprived of oxygen (hypoxia with OER ~2.5-3), their radiosensitivity drops to an extent comparable to fully oxygenated cells in the radioresistant late S phase.

Question 34

The variation of cell radiosensitivity with cell age is important to radiotherapy because:

Accepted Answer

Option A: The first dose of radiation synchronizes the cell population.. In fractionated radiotherapy, the initial radiation fraction preferentially kills cells in the sensitive phases (M/G2), leaving surviving cells synchronized in resistant phases (late S), which subsequently reassort into sensitive phases prior to the next fraction.

Question 35

Which of the following statements is false?

Accepted Answer

Option D: All proliferating mammalian cells have cell cycle phases of equal length irrespective of their type.. Statement D is false: Different mammalian cell lineages have vastly different cell cycle durations ($T_c$ ranging from hours in crypt cells to months/years), with the greatest duration variation occurring in the G1 phase.

Question 36

The OER for alpha particles is equal to:

Accepted Answer

Option D: 1.0. For high-LET densely ionizing radiation like Alpha particles (~100-200 keV/μm), biological damage is produced by direct dense ionization independent of oxygen free radicals, yielding an Oxygen Enhancement Ratio (OER) of 1.0.

Question 37

Sensitization by oxygen takes place if oxygen is present:

Accepted Answer

Option A: During irradiation.. Under the oxygen fixation hypothesis, oxygen must be present during the brief irradiation pulse (or within microseconds) to react with radiation-induced transient DNA free radicals (R^\bullet + O_2 → RO_2^\bullet) and fix lethal damage.

Question 38

The distance to which oxygen can diffuse in tumour cells:

Accepted Answer

Option C: is approximately 70 micrometers at the venous end of a capillary and less at the arterial end.. Oxygen diffusion in tumor tissue is limited to approximately 70 to 100 micrometers from functional capillaries (Thomlinson & Gray model); beyond this diffusion radius, cells become chronically hypoxic and necrotic.

Question 39

The fraction of hypoxic cells in human tumors has been estimated to be:

Accepted Answer

Option B: 10-15%. Radiobiological tumor assays and microelectrode/PET measurements estimate the hypoxic fraction in solid human tumors to typically range between 10% and 15%.

Question 40

The most sensitive stage for the lethal effects of radiation is:

Accepted Answer

Option A: Preimplantation.. The preimplantation stage (0 to 9 days post-conception in humans) is the most sensitive period for radiation-induced lethality / embryonic death (the 'all-or-none' phenomenon).

Question 41

Radiation damage is divided into (a) lethal damage, (b) sublethal damage and (c) potentially lethal damage (PLD). Which of the following statements is true?

Accepted Answer

Option A: PLD will cause cell death under ordinary circumstances.. Potentially Lethal Damage (PLD) is component damage that ordinarily causes cell death under standard physiological post-irradiation conditions, but can be repaired if cells are incubated in suboptimal growth conditions (e.g. plateau phase / delayed plating).

Question 42

Sublethal damage repair is:

Accepted Answer

Option C: the reason for the increase in cell survival which is observed when a radiation dose is split into two fractions separated by a time interval.. Sublethal Damage (SLD) repair is the operational mechanism (Elkind repair) responsible for the increase in cell survival observed when a total radiation dose is divided/split into two fractions separated by a time interval of hours.

Question 43

The increase of cell survival because of sublethal damage repair:

Accepted Answer

Option B: Is hindered by the increase in radiosensitivity as the cells progress around the cell cycle ("reassortment").. As time increases between split doses, surviving synchronized cells progress around the cell cycle and enter more sensitive phases (M/G2 - reassortment), which produces a dip in survival that counteracts pure repair.

Question 44

The dose-rate effect:

Accepted Answer

Option C: consists in the reduction of the biologic effect of a given dose when the exposure time is increased.. The dose-rate effect states that lowering the dose rate (or extending exposure duration) reduces the biological effectiveness of a given dose of low-LET radiation because sublethal damage repair occurs during the prolonged irradiation period.

Question 45

The most radiosensitive cells are:

Accepted Answer

Option A: the bone-marrow cells.. Under the Law of Bergonié and Tribondeau, rapidly dividing, undifferentiated hematological stem cells in the bone marrow (erythroblasts, myeloblasts) are the most radiosensitive normal tissue cells in the adult body.

Question 46

The loss of Intensity on the anode side of the X-ray tube is called:

Accepted Answer

Option C: Heel Effect. The Anode Heel Effect describes the reduction in X-ray beam intensity toward the anode end of the field caused by self-absorption of photons within the anode target material itself.

Question 47

If the activity of a radioactive sample drops to 1/32 of its initial value after 7.5 hours its half life will be:

Accepted Answer

Option D: 1.5 Hours. Since $\frac{1}{32} = \left(\frac{1}{2}ight)^5$, exactly 5 half-lives have elapsed in 7.5 hours:
$$5 	imes T_{1/2} = 7.5	ext{ hours} \implies T_{1/2} = \frac{7.5}{5} = 1.5	ext{ Hours}.$$

Question 48

Half lives of two radioactive substances A and B respectively are 20 min. and 40 min. initially, the samples of A and B have an equal number of nuclei. After 80 min. the ratio of the remaining number of A and B nuclei is:

Accepted Answer

Option C: 1:4. After 80 minutes:
- For A ($T_{1/2} = 20	ext{ min}$): $\frac{80}{20} = 4	ext{ half-lives} \implies N_A = N_0 \left(\frac{1}{2}ight)^4 = \frac{N_0}{16}$
- For B ($T_{1/2} = 40	ext{ min}$): $\frac{80}{40} = 2	ext{ half-lives} \implies N_B = N_0 \left(\frac{1}{2}ight)^2 = \frac{N_0}{4}$
$$	ext{Ratio } \frac{N_A}{N_B} = \frac{N_0/16}{N_0/4} = \frac{4}{16} = 1:4.$$

Question 49

The half-life of radionuclide is 77 days, then its decay constant is:

Accepted Answer

Option C: 0.009/day. Decay constant:
$$\lambda = \frac{\ln 2}{T_{1/2}} = \frac{0.69315}{77	ext{ days}} \approx 0.009	ext{ day}^{-1}.$$

Question 50

The half life of radioactive substance is 20 minutes. The time between 20% and 80% decay will be:

Accepted Answer

Option B: 40 minutes. - At 20% decay, remaining fraction is $80\% = 0.80 N_0$.
- At 80% decay, remaining fraction is $20\% = 0.20 N_0$.
Ratio of remaining amounts $= \frac{0.80}{0.20} = 4 = 2^2$, which corresponds to exactly 2 half-lives.
$$	ext{Time} = 2 	imes 20	ext{ minutes} = 40	ext{ minutes}.$$

Question 51

What is the public annual dose limit for the lens of the eye?

Accepted Answer

Option D: 15 mSv/year. Under ICRP and AERB regulatory guidelines, the equivalent dose limit for the lens of the eye for members of the public is 15 mSv/year (occupational limit is 20 mSv/year).

Question 52

What is the occupational dose limit for extremity?

Accepted Answer

Option D: 50rem/year. The annual occupational equivalent dose limit for the hands, feet, and extremities (and skin) is 50 rem/year (500 mSv/year) under US NRC and ICRP standards.

Question 53

What is the annual whole body dose limit for the public?

Accepted Answer

Option A: 1 mSv/year. The annual effective whole body dose limit for individual members of the general public is 1 mSv/year (0.1 rem/year) under ICRP, NCRP, and AERB regulations.

Question 54

What is the maximum exposure that AERB allows to occupational workers per year?

Accepted Answer

Option B: 30 mSv. The Atomic Energy Regulatory Board (AERB, India) mandates an occupational effective dose limit of 20 mSv/year averaged over 5 consecutive years, with a maximum ceiling of 30 mSv in any single year.

Question 55

What is the maximum exposure that ICRP allows to occupational workers per year?

Accepted Answer

Option A: 50 mSv. ICRP Publication 103 allows an occupational effective dose limit of 20 mSv/year averaged over defined 5-year periods, subject to a maximum constraint of 50 mSv in any single year.

Question 56

The activity of radioactive substance decays from 8000 becquerel to 4000 becquerel in 5 days. The activity of the substance after the next 10 days will be:

Accepted Answer

Option D: 1000 becquerel. Halving from 8000 Bq to 4000 Bq in 5 days indicates $T_{1/2} = 5	ext{ days}$.
In the next 10 days ($2 	imes 5	ext{ days} = 2	ext{ half-lives}$):
$$A = 4000 	imes \left(\frac{1}{2}ight)^2 = 4000 	imes \frac{1}{4} = 1000	ext{ becquerel}.$$

Question 57

The maximum permissible dose of radiation to the operator of X-ray machine is:

Accepted Answer

Option C: 5 rem/year. The maximum permissible whole-body occupational radiation dose for X-ray operators and radiographers is 5 rem/year (50 mSv/year).

Question 58

The single most effective method of reducing patient somatic exposure when taking radiograph is to use:

Accepted Answer

Option B: Speed E film. Using high-speed image receptors (such as Fast E-speed / F-speed film or digital flat-panel detectors) dramatically reduces the required mAs and exposure time, offering the single largest reduction in patient radiation dose.

Question 59

Which of these factors has no effect on response of cells to irradiation?

Accepted Answer

Option C: Image receptor used. Biological cellular response depends on radiation quality (LET), oxygen tension ($pO_2$), and dose-rate. The image receptor (detector/film) captures transmitted photons outside the patient and has zero influence on biological cell damage.

Question 60

What fraction of radioactive material will get disintegrated in a period of two half-lives?

Accepted Answer

Option D: Three-fourth. After two half-lives, the remaining fraction is $\left(\frac{1}{2}\right)^2 = \frac{1}{4}$.
The fraction disintegrated $= 1 - \frac{1}{4} = \frac{3}{4}$ (Three-fourth).

Question 61

What is Veracity?

Accepted Answer

Option D: Duty to tell the truth and avoid deception. In medical ethics, Veracity is the moral obligation of healthcare professionals to communicate honestly, disclose complete clinical truths, and avoid deception with patients.

Question 62

What is the main concern addressed by GDPR (General Data Protection Regulation) in data privacy.

Accepted Answer

Option A: Ensuring data privacy. GDPR (General Data Protection Regulation) establishes comprehensive legal frameworks to ensure personal data privacy, consent, and protection for individuals.

Question 63

Speed of ultrasound depends upon:

Accepted Answer

Option A: Medium. The speed of ultrasound propagation ($c = \sqrt{B/\rho}$) is determined exclusively by the acoustic properties of the propagation medium (bulk modulus elasticity and density), independent of wave frequency or amplitude.

Question 64

Bones look white in x-ray photograph because:

Accepted Answer

Option B: They are good absorbers of X-rays. Bone has a high effective atomic number ($Z \approx 13.8$) and high physical density (calcium hydroxyapatite), strongly absorbing X-rays via photoelectric effect and leaving the detector unexposed (appearing white/radiopaque).

Junior/Senior Radiotherapy Technician2025

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JKSSB — Junior/Senior Radiotherapy Technician (2025)