Radioactivity

Q1: Construct a summary table for alpha, beta and gamma, showing their properties (include masses, composition, charges, typical speeds, typical energies, deflection in magnetic fields, penetrating powers, ionising power).

Q2: What is the main origin of natural background radiation ?

Q3: What is the main origin of artificial background radiation ?

Q4: Why is it more important for children to be exposed to less radiation than adults ?

Q5: What are the procedures governing the use of radioactive sources in schools ?

Who is the school’s officer responsible for radioactive sources ?

Under what conditions, if any, are students allowed to use the sources

Devise a set of rules for staff using the sources.

Q6: The ‘levelness’ of waste depends on the radiation emitted as well as the activity. For a sources, low level waste is defined as having an activity less than 4x10⁹Bq and below 1.2x10¹⁰Bq for g and b radiations. Why the difference ?

Exponential decay - many other phenomena show a decay like that of radioactive sources. For the next two examples, plot standard decay curves and then use your mathematical skills to plot straight lines from the data (this will give true verification of the nature of the decay, and you can find half life much more accurately in this way)

Q7: Spiderlings are cannibalistic. A tarantula breeder sadly counts his collection as they turn on each other. When will he have 50 spiderlings left ?

Spiderlings remaining	1000	595	354	210	125
Time/mins	0	15	30	45	60

Q8: Is it true that the number of chocolates in this tin of Quality Street shows an exponential decay ? The mass of the tin is 400g. What is the half life of the decay ?

Time/days	0	1	2	3	4	5	6
Mass/g	1000	760	620	536	480	450	421

Q9: What is the decay constant for the Quality Street decay ?

Q10: The half-life of krypton-92 is 3.00s. If we have 5.12 x 10¹² atoms of K92, then how many would you expect to be undecayed after:

a) 3.00s b)9.00s c)10.00s

Q11: Accidents do happen. Currently the operators of Dounreay nuclear power station face legal action after a leak of plutonium into the sea. Previous surveys show that there are more than 1500 patches of contamination in the area and 180 potentially lethal ‘hot particles’ had been released from the site. (New Scientist, 2 October 96).

(a) Locate Dounreay on a map. Give reasons for the location of the site there.

(b) How can the ‘hot particles’ be located ?

(One was actually found several miles away from the site, rumoured to be by a skeleton of a seagull....)

Q12: Droughtshire Water are concerned about the flow rates in their rivers so continually inject a radioisotope of activity 5x10⁶Bq into the River Wet. The isotope has a half-life of 2hours. Downstream 10 000m an activity of 3x10⁴Bq is detected. If the speed of the river is, on average on an ideal day, 8ms^-1

(a) what would the activity of the whole radioisotope be expected to be ? 4.4x10⁶Bq

(b) what is the ratio ‘actual flow rate:expected flow rate’

0.007

(NB the continual injection is necessary so that there is a steady flow of radioisotope while the sampling is done).

Q13: A patient is undergoing a red blood cell count using the radioisotope ⁹⁹Tc^m which has a half life of 6 hours. At the time of injection the source activity is 4 000 000 hr^-1. Twelve hours later the activity of a 2cm³ blood sample is found to be 400 hr^-1.

(a) what is the total volume of blood in the patient’s body, assuming the sample is evenly distributed ?

5000cm³

(b) what is the decay constant for ⁹⁹Tc^m ?

0.116hr^-1

(c) if the blood sample had in fact been taken after 8 hours, what would the activity have been then ?

635hr^-1

Q14: You will need to research this one. What isotope was responsible for the final interpretation of the Turin Shroud as an elaborate hoax ? Explain the procedure which was used how the final verdict came about.

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