Revision Questions 2

Revision Questions 2

1. / Technetium-99, which has a long half-life, is produced as a radioactive waste product in nuclear reactors. One way of reducing the danger of this isotope is to change it into technetium-100 by bombardment with particles, as shown by the nuclear equation.

(a) / Identify particle X. / 1
(b) / Technetium-100 decays by beta-emission.
Write a balanced equation for this reaction. / 1
(c) / Technetium-100 has a half-life of 16s.
If a sample of technetium-100 is left for 48s, what fraction of the sample would remain? / 1
(3)
2. / Carbon dating can be used to estimate the age of charcoal found in archaeological sites.
The graph shows how the count rate of a sample of radioactive carbon-14 changes over a period of time.

(a) / Use the graph to find the half-life of carbon-14. / 1
(b) / Carbon-14 decays by beta-emission.
Write a balanced nuclear equation for this decay. / 1
(c) / Why can carbon dating not be used to estimate the age of fossil fuels? / 1
(3)
3. / Polonium-210 is a radioisotope that decays by alpha-emission.
The half-life of polonium-210 is 140 days.

(a) / Draw a graph to show how the mass of 200g of the radioisotope would change with time.
(Additional graph paper, if required, can be found on page 32). / 1
(b) / Write a balanced nuclear equation for the alpha-decay of polonium-210 / 1
(2)
4. / Phosphorus-32 us a radioisotope that decays by beta-emission.
(a) / Write the nuclear equation for the decay of phosphorus-32 / 1
(b) / The half-life of phosphorus-32 is 14.3 days.
Calculate the time it would take for the mass of phosphorus-32 in the 8g sample to fall to 1g. / 1
(2)
5. / Americium-241 is an alpha-emitting radioisotope that is used in a popular type of smoke detector.
(a) / (i) / Write a balanced nuclear equation for the alpha decay of americium-241 (atomic number 95) / 1
(ii) / Suggest a reason why this type of smoke detector is not regarded as a health hazard, even though it contains a radioactive source. / 1
(2)
6. / Tritium , is an isotope of hydrogen. It is formed in the upper atmosphere when neutrons from cosmic rays are captured by nitrogen atoms.

Tritium atoms then decay by beta-emission.

(a) / Complete the nuclear equation above for the beta-decay of tritium atoms. / 1
(b) / In the upper atmosphere, tritium atoms are present in some water molecules. Over the years, the concentration of tritium atoms in rain has remained fairly constant.
(i) / Why does the concentration of tritium in rain remain fairly constant? / 1
(ii) / The concentration of tritium atoms in fallen rainwater is found to decrease over time. The age of any product made with water can be estimated by measuring the concentration of tritium atoms.
In a bottle of wine, the concentration of tritium atoms was found to be 1/8 of the concentration found in rain.
Given that the half-life of tritium is 12.3 years, how old is the wine? / 1
(3)
7. / All the isotopes of technetium are radioactive.
(a) / Technetium-99 is produced as shown.

Identify X. / 1
(b) / The graph shows the decay curve for a 1.0g sample of technetium-99.

(i) / Draw a curve on the graph to show the variation of mass with time for a 0.5g sample of technetium-99.
(An additional graph, if required, can be found on page twenty-eight) / 1
(ii) / Technetium-99 is widely used in medicine to detect damage to heart tissue. It is a gamma-emitting radioisotope and is injected into the body.
Suggest one reason why technetium-99 can be safely used in this way. / 1
(3)
8. / Thorium-227 decays by alpha emission.
(a) / Complete the nuclear equation for the alpha decay of thorium-210.
/ 1
(b) / A sample of thorium-227 was placed in a wooden box. A radiation detector was held 10cm away from the box.
Why was alpha radiation not detected? / 1
(2)
9. / Positron emission tomography, PET, is a technique that provides information about biochemical processes in the body.
Carbon-11, 11C, is a positron emitting radioisotope that is injected into the bloodstream.
A positron can be represented as
(a) / Complete the nuclear equation for the decay of 11C by positron emission.
/ 1
(b) / A sample of 11C had an initial count rate of 640 counts min-1. After 1 hour the count rate had fallen to 80 counts min-1.
Calculate the half-life, in minutes of 11C. / 1
(c) / 11C is injected into the bloodstream as glucose molecules (C6H12O6). Some of the carbon atoms in these glucose molecules are 11C atoms.
The intensity of radiation in a sample of 11C is compared with the intensity of radiation in a sample of glucose containing 11C atoms. Both samples have the same mass.
Which sample has the higher intensity of radiation?
Give a reason for your sample. / 1
(3)
10. / The element iodine has only one isotope that is stable. Several of the radioactive isotopes of iodine have medical uses, Iodine-131, for example, is used in the study of the thyroid gland and it decays by beta emission.
(a) / Complete the balanced nuclear equation for the beta decay of iodine-131.
/ 1
(b) / The graph shows how the mass of iodine-131 in a sample changes over a period of time.

i) What is the half-life of this isotope?
ii) A sample of sodium iodide solution contained 100 mg of iodine-131 when it was prepared.
Sixteen days later it was injected into a patient. What mass ofions would the 16 day old sample contain?
/ 1
1
1
(4)
11. / Phosphorus-32 and strontium-92 are two radioisotopes used to study how far mosquitoes travel.
(a) / Strontium-92 decays by emission of a beta particle.
Complete the nuclear equation for the decay of strontium-92.
92
Sr
38 / 1
(b) / In an experiment, 10g of strontium-92 chloride was added to a sugar solution used to feed mosquitoes.
The strontium-92 chloride solution was fed to the mosquitoes in a laboratory at 20oC. When the mosquitoes were released, the outdoor temperature was found to be 35oC.
What effects would the increase in temperature have on the half-life of the strontium-92 chloride ? strontium-92 chloride / 1
(c) / A mosquito fed on a solution containing phosphorus-32 is released.
Phosphorus-32 has a half-life of 14 days.
When the mosquito is recaptured 28 days later, what fraction of the phosphorus-32 will remain. / 1
(3)

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