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1. In the determination of iron in aluminium alloys the 29 MeV
gamma of iron - 59 was measured. A decay period of 1 week
before chemical processing is allowed for the decay of the
(15.0 hr) sodium 24 formed from the reaction 27Al (n, α) 24Na
will the gamma radiation from sodium - 24 would constitute an
interference to iron determination.
2. At 120 min after discharge from the reactor all of the
aluminium – 28 (2.58 hr half-life) and most of the other short-
lived isotopes will have decayed to negligible activity and the
activity of manganese – 56 has dropped to 2.153 X 106
counts/sec. Calculate the activity of Manganese – 56 at the time
of removal from the reactor.
3. If a 10.0 mg sample of aluminium foil were irradiated for 30
min in a neutron flux of 5 X 1011 neutrons cm -2 sec -1 how long
the sample be allowed to cool before chemical processing so that
aluminium activity will have decayed to less than 1 count/min
half-life for aluminium is 2.58 hr, natural abundance is 100%
and reaction cross - section is 0.235 X 10-24 cm 2/nuclei.
4. For the irradiation time and flux stated in Problem 3, what is
the limit of detection (40counts/sec) for traces of sodium as
sodium – 24 in “pure” aluminium foil after the aluminium
activity has decayed to less than 1 count/min. Counting
geometry is 100%. Assume no other activities are present and
ignore corrections for the absorption of sodium beta particles
by the aluminium foil.
5. What weight of sample should be taken for the activation
analysis of an aluminium alloy that contains 0.019% zinc if
the irradiation time is 62 hr with a flux of 5 X 1011 neutrons
cm -2 sec -1 followed by a cooling period of 24 hr. A rate of
1000 counts/ min is desirable for Zn abundance is 18.6%,
reaction cross-section is 0.01 X 10-24 cm2/nuclei and halflife is 13.8 hrs.
6. In a particular aluminium alloy, 0.59% of present 65Ni is
present. If the sample weigh 10.0 mg, how long, should the
irradiations be continued for the determination of the element?
Assume a rate of 10,000 counts/min in a 5-min counting period
is desirable after a cooling period of 0.7 day. Flux is 5 X 1011
neutrons/cm2/sec.
7. Calculate the activity for a 10.0-mg sample of an aluminium
alloy containing 0.041% manganese after a 0.50-hr
irradiation in a flux of 5 X 1013 neutrons cm -2 sec-1.