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Exam 30: Nuclear Physics

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Question 21

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Two radioactive nuclides X and Y both decay to stable products.The half-life of X is about a day,while that of Y is about a week.Suppose a radioactive sample consists of a mixture of these two nuclides.If the mixture is such that the activities arising from X and Y are initially equal,then a few days later the activity of the sample will be due

A) predominantly to nuclide Y.
B) predominantly to nuclide X.
C) entirely to nuclide Y.
D) to nuclides X and Y equally.

E) C) and D)
F) None of the above

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Question 22

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In a head-on collision,an alpha particle (Z = 2) of energy 8.20 MeV bounces straight back from a nucleus of charge 80.0 e.How close were the centers of the objects at closest approach?

A) 2.81 × 10^-14 m
B) 3.39 × 10^-12 m
C) 6.56 × 10^-15 m
D) 2.17 × 10^-14 m

E) A) and C)
F) B) and D)

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Question 23

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A positron (or antielectron) is made to stop in a sample of matter.Soon after,how many gamma rays are observed with what energy each?

Suppose the half-life of some element is 2 days.If you purchase 10 grams of the element (which was produced in a laboratory 4 days ago) ,how much of this element would you have 3 days after you purchased it?

A radioactive nuclide of atomic number Z emits an alpha particle and the daughter nucleus then emits a beta particle.What is the atomic number of the resulting nuclide?

An archaeologist finds the ¹⁴C in a sample of 3.10 g of material to be decaying at 107 counts per second.A modern 1.00-g sample of the same material decays at 151 counts per second.The half-life of ¹⁴C is 5730 years.How old is the sample?

The material used in nuclear bombs is ²³⁹Pu,with a half-life of about 20,000 years.How long must we wait for a buried stockpile of this substance to decay to 4% of its original ²³⁹Pu mass?

Stable nuclei have equal numbers of protons and neutrons.

The primary reason very large nuclei are unstable is due to

Today,uranium contains 0.72% ²³⁵U (half-life = 0.70 billion years) and 99.28% ²³⁸U (half-life = 4.5 billion years) .At a time 1.9 billion years ago,what was the fraction of ²³⁵U in uranium?

If a 20 kg brick is made entirely of radioactive atoms of half-life 5 days,at the end of 5 days this brick will have a mass of 10 kg.

Which of the following is not true of the nuclear force?

The maximum permissible workday dose for occupational exposure to radiation is 11 mrem.A 77 kg laboratory technician absorbs 2.3 mJ of 0.5 MeV gamma rays in a work day.The relative biological efficiency (RBE) for gamma rays is 1.00.The number of gamma-ray photons absorbed by the technician in a workday is closest to:

The binding energy per nucleon increases steadily with the mass number of the nucleus.

A stable nucleus contains many protons very close to each other,all positively charged.Why do the protons not fly apart due to mutual Coulomb repulsion?

What mass of ¹⁴C (half-life = 5730 years) do you need to provide a decay rate of 280.0 Bq?

If half of a radioactive substance decays in the first 10 s,the other half will decay in the next 10 s.

The following masses are known: 1.008665 u 1.007825 u 226.025403 u The binding energy of ,in MeV,is closest to:

A nuclear bomb explosion results in a mass decrease of about 2.10 g between the initial and the final ingredients.How much energy is released?

A hospital patient has been given ¹³¹I (half-life = 8.04 days) ,which decays at 4.2 times the acceptable level for exposure to the general public.How long must the patient wait to reach the acceptable level? Assume that the material merely decays and is not excreted.