NP-Test-3

• Neutrons are thought to be composed of quarks, which are fundamental particles.
• The most accepted theory posits that a neutron consists of one up quark and two down quarks.
• Hence, the correct answer is A, "One up and two down quarks".

• The half-life of a substance is the time taken for half of the substance to decay.
• In an hour (60 minutes), there are three half-lives of a substance with a half-life of 20 minutes.
• Thus, the remaining active amount of the substance will be (1/2)^3 = 1/8.

• The slope of a decay graph, which is an isothermal curve, represents the decay activity.
• The decay activity is calculated as the number of decayed atoms divided by the time (No/t).
• Hence, the correct answer is C, "Activity".

• According to Bohr's model of the atom, the angular momentum of the electron is quantized and is an integral multiple of Planck's constant divided by 2π.
• This makes the angular momentum a discrete quantity.
• Hence, the correct answer is C, "Angular momentum".

• Cobalt 60 is a radioactive isotope used in medical treatments.
• It is known for its intense emission of gamma rays, which are used for therapeutic purposes.
• Hence, the correct answer is C, "γ-rays".

• During nuclear fission, the parent nucleus splits into two or more daughter nuclei.
• The ratio of the radii of the new nuclei is proportional to the cube root of their mass numbers.
• Given that the mass numbers are in the ratio 1:2, the radii would be in the ratio 8:1.

• The half-life of a substance is the time taken for half of the substance to decay.
• To decay to 1/16th of the original amount, four half-lives are required.
• Since the half-life of the substance X is 100μs, four half-lives would constitute 400μs.

• One Curie is a unit of radioactivity that represents 3.7 × 10^10 decays per second.
• It is approximately equal to the activity of 1 gram of radium.
• Hence, the correct answer is A, "1 gm".

• Cobalt 60 is a radioactive isotope commonly used in radiation therapy for cancer treatment.
• It emits high-energy gamma rays which are able to destroy cancer cells.
• Hence, the correct answer is B, "Cobalt 60".

• The decay constant "λ" is related to the half-life T of a radioactive substance by the relation λT = ln2.
• This relation is derived from the definition of half-life, which is the time required for half of a substance to decay.
• Hence, the correct answer is D, "λT = ln2".

• When storing radioactive substances, safety is a critical concern. The storage medium should be capable of absorbing radiation without becoming unstable.
• Lead is a heavy, dense metal which is particularly effective at absorbing various forms of radiation.
• Therefore, the correct answer is A, "Lead".

• The Compton effect refers to the change in direction and energy of a photon when it collides with a free electron.
• This phenomenon is best explained by the photon theory of light, which postulates that light consists of discrete packets of energy called photons.
• Therefore, the correct answer is A, "Photon theory of light".

• Different types of radioactive decay result in different changes to the atomic mass and atomic number of an element.
• An alpha particle emission decreases the atomic number (Z) by 2 and the atomic mass (A) by 4. A beta negative particle emission increases the atomic number (Z) by 1 without affecting the atomic mass (A).
• Given that the atomic mass and number of element X after emission are A-8 and Z-2 respectively, it can be inferred that the element emitted 2 alpha particles and 2 beta negative particles.

• The type of radioactive ray affects its ability to ionize and penetrate materials.
• Gamma rays, having no charge, can penetrate further than alpha rays which have a positive charge.
• Alpha rays, due to their charge, are more ionizing than beta rays which have a lesser charge.

• The energy of an electron increases, rather than decreases, as it moves to a higher orbit, making statement 1 incorrect.
• The radius of an orbit is indeed proportional to the square of the number of orbits according to the Bohr model (statement 2), and the energy of an electron is directly proportional to the square of the atomic number (statement 3).
• Therefore, the correct answer is C, "Statements 2 and 3 are accurate".

• The decay constant, often represented by the Greek letter lambda (λ), is a fundamental concept in understanding radioactive decay.
• It is defined as the fraction of the number of atoms undergoing decay per unit time.
• This indicates how quickly an atom of a particular substance will decay, providing an essential tool for predicting the behavior of radioactive materials.
• Therefore, the correct answer is A, "The decay constant is equal to the fraction of atoms undergoing decay per unit time".

• The half-life of an element, which is the time it takes for half of the atoms in a sample to decay, is a fixed property of each radioactive isotope.
• It is independent of the initial number of atoms and the time period; instead, it relies solely on the decay constant.
• Thus, highly radioactive elements will have a higher decay constant and a shorter half-life, and vice versa.
• Therefore, the correct answer is C, "The decay constant".

• Bosons represent a class of particles which, unlike leptons, hydrons, and meuons, are characterized by having no rest mass.
• This absence of mass at rest is a key characteristic of bosons, setting them apart from other particles.
• Therefore, the correct answer is C, "Bosons".

• Radiation can cause damage to living organisms in several ways, but the most critical mechanism is through ionization.
• Ionizing radiation can disrupt molecular structures or break chemical bonds, leading to molecular damage and disruptions in cellular processes.
• Consequently, the correct answer is A, "Ionization".

• Among the fundamental forces existing in nature, the gravitational force, despite its long reach, is known to be the most feeble.
• All the other forces—electric, magnetic, and nuclear—are stronger in comparison.
• As a result, the accurate answer is A, "Gravitational force".

• Medical practitioners often use radioiodine—a radioactive isotope of iodine—for performing scans that can detect thyroid cancer.
• After you ingest a pill containing a safe dose of radioiodine, the thyroid gland absorbs the radioactive iodine over several hours.

Therefore, the correct answer is A, "Radio iodine".

• When a radioactive nucleus emits a β-particle (beta particle), the proton-neutron ratio within the nucleus increases.
• This is because a neutron in the nucleus is converted into a proton, resulting in an increase in the proton-neutron ratio.
• Consequently, the correct response is C, "Increases".

• The decay constant, represented by the Greek letter lambda (λ), signifies the probability per unit time that a nucleus will decay.
• It is calculated as the change in the number of atoms over the change in time, making its unit inverse seconds (s^-1).
• As such, the correct answer is B, "s^-1".

• In radioactive decay, the emission of different particles can lead to changes in the atomic number and mass number of the radioactive element.
• However, when a γ-particle (gamma particle) is emitted, the atomic and mass numbers remain the same. Only the energy state of the nucleus decreases.
• Therefore, the correct answer is B, "γ-particle".

• The energy possessed by γ-radiation (gamma radiation) is measured in electron volts (eV), a unit of energy.
• While the exact energy can vary, it generally falls in the order of Megaelectronvolts (MeV).
• Therefore, the correct answer is B, "Megaelectronvolt (MeV)".