Radiation Prac 4: Half-Life of Protactinium

Aim:

In this experiment, you will be determining the half-life of the radioactive isotope Protactinium-234 (Pa-234)

Apparatus:

Geiger Counter Uranium-238 and H20 in a bottle

Method:

1. Background count established2. Uranium/Thorium/Protactinium mix is shaken vigorously and then turned upside

down so that the organic layer near the flat base can be placed near the Geiger counter

3. Once the organic solvent/water layers have established, the counter is started.4. A cumulative count is recorded every 20 seconds for about 7 or so minutes.

Results: (Background Count = 20 seconds)

Mid- Time (s)

Cumulative Count

Corrected Count Net Count Percentage

10 224 209 209 100.00%30 445 430 221 105.74%50 632 617 187 89.47%70 800 785 168 80.38%90 932 917 132 63.16%

110 1060 1045 128 61.24%130 1215 1200 155 74.16%150 1342 1327 127 60.77%170 1464 1449 122 58.37%190 1606 1591 142 67.94%210 1726 1711 120 57.42%230 1840 1825 114 54.55%250 1926 1911 86 41.15%270 2029 2014 103 49.28%290 2144 2129 115 55.02%310 2273 2258 129 61.72%330 2375 2360 102 48.80%350 2487 2472 112 53.59%370 2600 2585 113 54.07%390 2698 2683 98 46.89%410 2795 2780 97 46.41%

0 50 100 150 200 250 300 350 400 4500

50

100

150

200

250

Net Count vs Time

Time (s)

Net

Cou

nt (1

0s In

terv

als)

The graph follows a general progression down, however the results are very sloppy and hence it is difficult to determine a good line of best fit.

Discussion:

3. Count 1: 187 at 50 seconds Count 2: 97 at 410 (The 86 appears to be a statistical outlier and therefore has been ignored). 360 Second half life.3b. Count 1: 209 at 10 seconds Count 2: 103 at 270 seconds. 260 second half life.Unfortunately there are no remaining measurements where some of them can be halved to somewhat degree of accuracy, therefore the average will have to be found as 315s.

Written discussion (Questions):

1. U238Th23491 + α(He)4

2 Th234 Pa23491 + β- Pa234

91 U23492 + β-

2. U238 Half Life – 4.468 Billion Years Th234 Half Life – 24.1 days Pa234 Half Life – 6.7 hours (Though Pa234m has a half life of 1.17 minutes)

3. The calculated value is very far off the correct value of 1.17 minutes. There are multiple reasons for this inaccuracy. The method used was quite poor in terms of accuracy. Firstly, there was a sample space of a single cumulative measure, which is far from enough to determine an accurate averaged half life. Secondly, the Uranium product was in a bottle with uranium dissolved oil that also contained multiple other radioactive elements dissolved in water which could have significantly influenced and hence muddled the results. Other than this, there are also the difficulties of taking a measurement exactly on 10 seconds when the Geiger counter is constantly going up, including perhaps a level of human error.

4. Immiscible means for a liquid to not form a single homogenous mixture when shaken or mixed. This can be said for the mixture formed in the bottle, as the oil stayed on top of the water despite solvents in the liquid.

5. Because it can influence the results of the measurements and hence can make the radiation levels seem higher than they actually are.

6. Because it has a variety of functions such as dating objects, and it is also important for safety precautions such as determining when radioactive waste is safe as well as medical uses in radioactive traces.

7. 15.8 atoms

Conclusion:

This practical involved multiple errors and as a consequence the results obtained are riddled with anomalies, making it difficult to state achievement of the aim. Multiple improvements could have been made, however despite this, it still demonstrated a basic decrease of half-life radiation and on that metric could be considered to have achieved its aim.