Modern Physics LaboratoryMP8 Radioactive Decay and Radiation Absorption

D. Summary of the experiment (20 pts)Summarize what you have done and your interpretation of the results, especially in respect to how

they match the goal of the experiment and what you have learnt from this experiment (2-3 paragraphs,

less than 45 words!"

#his experiment aimed at investigating the nuclear phenomena associated with

radioactive decay of uranium-23$ and radiation a%sorption of caesium-&3' with various

thicnesses of polyethylene a%sor%ers"

)e divided the experiment into two parts" *efore the %eginning of the first part of 

experiment, we measured the %acground radioactive counts in &s" #he measured value

was '4&" #herefore, the %acground count rate would %e741

1000 s=0.741 s

−1

" #his value

could %e used to find the corrected count rate %y su%tracting the measured count rate with

 %acground count rate" +or the first part of experiment, we were mainly focusing on

measuring the radioactive counts of uranium-23$ in &s-interval from s to 4&s %y using the

tu%e" )e o%served that the radioactive counts in &s-interval decreased gradually from

2. counts to 2. counts" )e could then wor out the corrected count rate" /t decreased from

2$"3s-& to 2"2s-&" *y plotting a graph of natural logarithm of corrected count rate versus time t,

we could found the decay rate 0 %y the slope of graph" #he experimental decay rate 0 was

"1.s-&" ence, we could further wor out the half-life time of uranium-23$ %y euation of 

t 1

2

=ln2

 R" #he experimental half lifetime was &"5s, which was not so accurate when

comparing with the pu%lished value of '2s" #his might %e attri%uted to the fact that the

 %acground radiation and radioactive decay of uranium-23$ were random" onducting more

trials of the experiment could reduce this inaccuracy" owever, due to the time limitation, we

could not mae it so accurate" +or the second part of experiment, we were going to measure

the radioactive counts of caesium-&3' %y varying the thicness of 6 a%sor%ers from cm (no

a%sor%er! to "&5'5cm" #he counts decreased from 533$ to 443, so the corrected count rate

decreased from 52"14s-&  to 3"1.s-&" *y plotting the graph of natural logarithm of corrected

count rate versus thicness of a%sor%er  x, we could find out the linear a%sorption coefficient μ  %y the slope of the graph" #he experimental linear a%sorption coefficient   μ   was

&'"&4&cm-&" 7fter o%taining  μ , we further wored out the half-value thicness of 6 %y

euation of  x1

2

=ln2

 μ" #he experimental half-value thicness was "44cm" #hus, we

could say that 6 was a good radiation a%sor%er as a relatively thin layer of 6 could already

a%sor% half of the radiation emitted" Similar to the first part of experiment, errors might %e

 present due to the randomness of %acground radiation and ceasium-&3'" #his could %e

improving %y doing more trials"

#o conclude, we successfully investigate the nuclear phenomena with radiation decay

and radiation a%sorption" #he experimental half-life time of uranium-23$ was &"5s" #he

experimental half-value thicness of 6 was "44cm"