If at least one neutron from U-235 fission strikes another nucleus and causes it to fission, then the chain reaction will continue. If the reaction will sustain itself, it is said to be critical, and the mass of U-235 required to produce the critical condition is said to be a critical mass. A critical chain reaction can be achieved at low concentrations of U-235 if the neutrons from fission are moderated to lower their speed, since the probability for fission with slow neutrons is greater. A fission chain reaction produces intermediate mass fragments which are highly radioactive and produce further energy by their radioactive decay. Some of them produce neutrons, called delayed neutrons, which contribute to the fission chain reaction. In nuclear reactors, the reaction is slowed down by the addition of control rods which are made of elements such as boron, cadmium, and hafnium which can absorb a large number of neutrons. In nuclear bombs, the reaction is uncontrolled and the large amount of energy released creates a nuclear explosion.Theory based question
114) The average number of neutrons released by the fission of one uranium atom is
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Related Atoms and Nuclei MCQ with Answers
the number of electrons orbiting around its nucleus
The chemical behavior of an atom depends upon the number of electrons orbiting around its nucleus
30 min
As the amount of radioactive isotope remaining after 2 hrs is 1/16 of the intial amount,the eauation N=(N)initial x (exp(-kt)), here k denote lambda, takes the form N)initial/16=N)initial x (exp(-kt)) i.e., exp(-kt)=1/16 => -kt= log(1/16) .....[taking log on both the sides] =>-kt=-4log2 now time taken is 2 hrs therfore, 2k=4log2 => k=2log2 now half life =log2/k=1/2hrs=30 mins ,hence the answer (ii) THIS WAS FOR NCERT TRADITIONAL WORMS NEXT SOLUTION IS A BETTER APPROACH the amount left after n-half lives=initial amount/(2 raised to power n),now as the final amount 1/16 ,i.e., 1/(2 raised to power 4) of the initial amount, 4 half lives have passed therefore, 4(half life)=2 hrs => half life=30 min
7/8 part of the mass of the substance disintegrates in 30 days
The half life of a radioactive substance is 10 days. This means that 7/8 part of the mass of the substance disintegrates in 30 days
the strength of the nuclear force between the nucleons of its atoms
The half-life of a radioactive substance depends upon the strength of the nuclear force between the nucleons of its atoms