Radioactivity Questions and Answers

Consider the following statements a The operation of the reactor is said to be critical if multiplication factor is equal to zero b The reaction rate is controlled by control rods made out of neutron absorbing material like boron Choose the incorrect statements Only a Only b Both a and b None of a and b

Decay rate for a certain mass of a radioactive substance measured at diffrent times varies with time as shown in fig countrate at t 8 hr will be Decays sec 1 200 150 100 50 Question Type Single Correct Type 25 2 decays sec 2 50 decays sec t hr 3 500 decays sec

Two radioactive materials X and X have decay constants 5A and respectively If initially they have the same number of nuclei then the ratio of the number of nuclei of X to that X will be 1 e after a time Options 1 1 2 KA 3 A

View In English If difference between points of time is 10 minutes radioactive substance when is 50 disintegrated and 75 disintegrated then average life of radioactive substance will be 1 3 10 minute 144 minute 36 8 minute 24 5 minute

The reason for why the sun shines and produces so much energy for billions of years was finally explained by Einstein s theory of A Photo electric Effect B Special Relativity C General Relativity D Quantum Mechanics E Black body Radiation

O A bacteria culture doubles every 10 minutes Using an exponential model of the form t P 2 where d is a doubling period find the time that it takes the culture to grow to 25 times its initial population A 3

Q 66 A radioactive battery consists of No atoms of radioactive element with disintegration constant and emitting a rays Fraction f of the emitted a rays is captured by other plate and converted into current Determine charge on the capacitor as a function of time HP C

18 The rate of disintegration was observed to be 1017 disintegrations per sec when its half life period is 1445 years The original number of particles are 1 8 9 1027 2 6 6 1027 4 1 2 10 7 3 1 4 1016 X

5 In the following Column I lists some physical quantities and the Column II gives approximate energy values associated with some of them Choose the appropriate value of energy from Column II for each of the physical quantities in Column 1 A B C D Column I Energy of thermal neutrons P Energy of X rays Q Binding energy per R nucleon S Photoelectric threshold of a metal Column II 0 025 eV 8 MeV 3 eV 10 keV

an elect a of the ord s a pho 15 In a mean life of a radioactive sample 1 About 1 3 of substance disintegrates 2 About 2 3 of the substance disintegrates 3 About 90 of the substance disintegrates 4 Almost all the substance disintegrates

3 A sample contains 16 g of a radioactive material the half life of which is two days After 32 days the amount of radioactive material left in the sample is 1 1 Less than 1 mg 2 4 3 4 1 g 2

59 secs The activity of a radioactive sample moving with velocity V is given by A detector at a distance from the sample detects number of counts per second If the count number detected by the counter remains constan what is the speed of the sample

The radioactive isotope Pt 188 decays into a stable nuclide after a series of 4 separate decays The daughter nucleus of each decay becomes the parent nucleus of the next one until after 4 decays a stable nuclide is formed In order the series of decays that Eu 144 goes through is a a B B is the final stable nuclide that is created after all these decays have occurred Give your answer in the form Z X Y N

Living matter has 1 3 x10 12 of its carbon in the form of 14C which has a half life of 5730 yr The mass of carbon in an animal bone fragment found in an archeological site is 200 g If the bone registers an activity of 16 decays s what is its age The answer is t 9 400 years How do you find this answer

10 A wood artifact is known to have decayed and only 55 of the original artifact remains The age of the wood artifac dating What is the age of the artifact if the half life of C 14 is 5 730 years 6 600 years 5 270 years 4 942 years 1 659 years

At least 2 to up to 5 answers may be correct 1 Fusion and fission processes can often be viewed as the reverse process with respect to each other Examples are a light frequency transformation b beta decay is the inverse process of a proton flipping into a neutron during hydrogen fusion c helium capture reactions that form heavy elements inside massive stars are the reverse of a decay d fission of a very heavy element into two lighter elements is the inverse of fusion of two medium mass elements into heavy elements e conservation of photon charg

5 The activity of a radioactive sample is measured as No counts per minute at t 0 and N e counts per minute at t 5 minutes The time at which the activity reduces to half its value is mlog 2 min Find m

Consider the stellar atmosphere consisting of hydrogen atoms which is in thermal equilibrium Let the average kinetic energy of hydrogen atoms be 1 0 eV Find a the temperature of the atmosphere b the ratio of the number of atoms in the second excited state to those in the ground state

If mean life of a radioactive material is x more than half life then x A B C D 37 44 63 50

the decay constant of two radioactive substances a and b are 4 per year and 5 per year respectively which one of the following is true for these two substances O substance a will decay faster than b O substance b will decay faster than a O both substances will decay at same rate O both substances will take infinite time to decay

M sec b The reaction L M is started with 10 g of L After 30 and 90 minute 5 g and 1 25 g of L are left respectively The order of reaction is a 0 c 1 b 2 d 3

The answer given is 3 but I guess answer should be 1 as will be formed when x is decayed and x will decay with ti e as no 1 e lambda X t so y should increase with time 156 A radioactive nucleus x decays to a stable nucleus y Then the graph between rate of formation of y R and time t will be 1 R R 2

SolveLancer Test Which of the following pairs represents the isobars in which preceding is the p decay product of the succeeding SolveLancer Test a 4N 4C b 22Ne Na 10 c 32P 325 15 16 d None of these

Example 14 A neutron fission counter is lined with U 235 to detect slow neutrons by ionizing fission fragments that produce an average energy of 200 MeV Find the pulse height produced by a capacitor of capacitance 40 pF connected to the collecting electrode Assume that an average energy of 35 eV is needed to produce an ion pair

If the rate constant for a first order reaction is k then time t the completion of 87 5 of the reaction is given by log102 0 301 O t 2 303 k t 0 693 k t 2 079 k

then the dot product of two 1 7 5 2 6 5 3 8 4 4 7 9 Two slits saperated by 4 mm are illuminated by light 2 of wavelength 6000A What will be fringe width on screen placed 2m away from slits vectors will be 1 0 12 mm 2 0 3 mm 3 3 0 mm 4 4 0 mm P V diagram of an ideal gas is as shown Find work 3 affar 2 6 5 4 7 9 fferatenf6000 fenf 2 1 7 5 4 3 8 4 1 0 12 mm 2 0 3 mm 3 3 0 mm 4 4 0 mm f P V te fa

will take to reduce the initial concentration value If rate constant for a first order reaction is 60 s 1 then how much time of the reactant to its th 0 2 3 10 s 4 6 x 10 s 06 9 x 10 s 01 2 10 2 s

Example 15 In a Stern Gerlach type experiment the magnetic field varies with distance in z direction according to dB dz 1 4 T mm Silver atoms travel a distance x 3 5 cm through the magnet The speed of atoms emerging from oven is v 750 m s Find the separation of the two beams as they leave the magnet Mass of silver atom 1 8 x 10 25 kg and its magnetic moment is 1 Bohr magneton

92 If the energy released in the fission of one 44 nucleus is 200 MeV then the number of nuclei required per second in a power plant of 16 kW will be 1 0 5 x 10 4 3 5 10 2 2 0 5 10 2 4 5 x 10 4 9 afe ven anforen in farcu a 16 kW va Tarzana Buft 1 0 5 10 4 3 5 x 10 2 2 200 sfatus fanda 2 0 5 10 2 4 5 10 a

Example 14 An electron circles a nucleus of charge Ze Of the two orbits 1 and 2 of radii ri and r2 respectively its total energy is greater while in orbit 1 Prove that T r2 Also show that the velocity and acceleration in orbit 2 are greater than those in orbit 1

A certain radio nuclide starts getting produced at a constant rate 104 s 1 by some mechanism at a certain moment t 0 At this moment there are already 105 number of radio nuclides present in the sample The mean life of the radionuclide is 20 seconds At t 40 sec what will be dN dt rounded to the nearest whole number Given that e 7 4 A 375 s B 676 C 676 s D 762 s

11 The type of equation shown below is an example of a an CaO H O Ca OH 2 O synthesis decomposition O single replacement O exchange of ions 3 points 12 Which of the following best describes exothermic chemical reactions 3 points

Select one a a The number of kilograms y of a radioactive element that remains after t hours can be modeled by the equation y 0 23 0 91 What is the rate of decrease of this radioactive element a O23 per hour O 91 per hour O 77 per hour 1 O 9 per hour

suppose a sample of a radioactive substance weighs 40mg One year later the sample weighs 27 5 mg What is the half life of this substance round your answer to two decimal places

Problem 11 Certain radioactive material decays in such a way that the mass remaining after t years is given by the function m t 320e 0 025t where m t is measured in grams Round your answers to one decimal place if needed a Find the mass of the material at time t 0 b How much of the mass remains after 50 years c How long will it take for the sample to lose half of its mass

How does the theory of dramatic inflation when the universe was extremely young help astronomers understand why the cosmic microwave background radiation indicates very similar values for the temperature and density of regions that are on opposite sides of the observable universe The inflation hypothesis says the two regions were in contact with each other before the time inflation occurred The inflation hypothesis says that the two regions exchanged microwave energy after the inflation occured The inflation hypothesis claims that the microwave background data is faulty The inflation hypothesis says that the two regions exchanged material after the inflation occurred

The activity of a radioactive substance reduces to 8 initial value in 60 years The mean life of the substance will be 28 9 years 27 years 20 years of 32 years

Q 134 A radio isotope X with a half life 1 4 x 10 years decays to Y which is stable A sample of the rock from a cave was found to contain X and Y in the ratio 1 7 The age of the rock is 1 4 20 10 years 2 8 40 10 years 3 1 96 10 years 4 3 92 10 years Q 12

13 Radioactive material A has decay constant 8 and material B has decay constant A Initially they have same number of nuclei After what time the ratio of number of nuclei of material B to that A will be e a c 82 b R 18 d Josta 92 elould own 1

The radioactive nucleus can decay by two different processes The half life for the first process is t and that for the second process is t2 The effective half life of the nucleus is Ot 12 O 214 2 11 12 412

X The emission accompanied of electron in decay is by the emission of antineutrino The emission of electron in decay is accompanied by the emission of neutrino Free neutron unlike a free proton is unstable

A black body is at a temperature of 5760 K The energy of radiation emitted by the body at wavelength 250 nm is U at wavelength 500 nm is U and that at 1000 nm is U3 Wien s constant 2 88 x 10 nmK Which of the following is b correct 1 U 0 3 U U 2 U3 0 4 U U1

A radioactive sample decays by simultaneous emission of two particles with respective half lives E and 340 years The time in years after which 1 16 th of the material remains is 2 170 4 510 1 340 3 968

A point like radioactive sample of decay constant X initially at a distance ro from a radiation counter starts moving towards the counter If the count number recorded by the counter remains constant with time express speed of the radioactive sample as function of time A ro Initially A At timot

6 Hydrogen H deuterium 4 singly ionized helium He and doubly ionized lithium Li all have one electron around the nucleus Consider n 2 to n 1 transition The wavelengths of emitted radiations are 2 22 23 and 24 respectively Then approximately 1 2 2 423 924 2 42 22 223 24 3 2 2 2 2 3 224 4 2 2 22 3 22

Taking the mass of the muon to be 106 MeV c the mass of the pion to be 140 MeV c and the mass of the neutrino to be zero Determine the energy of a muon produced in the decay assuming the pion is at rest

The half life of a certain radioactive material 100 Z X is 6 93 x 106 seconds In order to have an initial activity of 6 x 108 Bq the amount of material needed is A 10 16 kg B 10 kg C 10 kg D 104 ko

A soap bubble having radius of 1 mm is blown from a detergent solution having a surface tension of 2 5 x 10 2 N m The pressure inside the bubble equals at a point Zo below the free surface of water in a container Taking g 10 m s2 density of water 10 kg m the value of Zo is 1 100 cm 2 10 cm 3 1 cm 4 0 5 cm 2

Uranus and Neptune have enormously long periods for each orbit approximately 84 and 165 years respectively This causes the two worlds to rarely be in opposition that is as close as their orbits allow on any given pass such that Sun is on one side of Uranus and Neptune is on the other Neptune will next be at opposition with Uranus in the year A at a distance of AU 210

of the emitting atom assuming lonization potential of hydrogen is 13 6 eV 20 A neutron of kinetic energy 65 eV collides inelastically with a single ionized helium atom at rest It is scattered at an angle of 90 with respect of its original direction i Find the allowed values of the energy of the neutron and that of the atom after the cvollision the atom get emitted radiation horn The excited aton