Physics
Radioactivity:
A: Beta particles loose kinetic energy upon impact, and are absorbed by
the phosphor, they cant penetrate through the thick glass tube.
A: Activity is due to the radioactive decay of nuclei, as time goes on
there are fewer number of nuclei left, decay rate falls, hence activity
falls.
A: Lea is the best absorber as it results in the lowest count rate for
barium 133, the Strontium-90 data cant be used to evaluate as most of
the results are close to the background level.
A: Stone is the best absorber for strontium 90 as it results in the lowest
count rate of 13, but the worst absorber for barium 133 as it results in
the highest count rate of 10,408. It may not be worse than paper as
paper is not tested for barium 133.
A: (NO EXPERIMENTAL DETAILS) Beta radiation can penetrate paper but
is absorbed by lead and aluminium.
A: Scientists know the original proportion (or activity) of uranium in the
rock when it formed. They measure the proportion of uranium (or its
activity) in the granite now. They compare the current activity to the
original activity to determine how much uranium has decayed. From this
they can work out how many half-lives have passed and use the known
half-life of uranium to calculate the age of the rock.
OR
When granite forms, it contains a known proportion of uranium. Over
time, uranium decays through a chain of radioactive decay into a stable
daughter element. Scientists can measure the amount of this stable
daughter element in the granite now. By comparing it to the original
uranium amount, they can determine how many half-lives have passed.
Using the known half-life of uranium, they can then calculate the age of
the granite.
A: Three FROM – MP1. Neutrons released; MP2. neutrons slowed by
moderator; MP3. Can be absorbed by other (U) nuclei; MP4. Causing
further fissions;
A: Stable isotopes do not emit ionising radiation.
A: Any TWO of 1.Range / penetration of alpha radiation is low; 2.Radon
(is a gas so) particles /atoms mobile OR americium (solid so) particles /
atoms stay in place; 3.Radon can be inhaled / damage internal tissue OR
radiation from americium stays within smoke detector / absorbed by the
plastic;
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