Expt 2B. Preparation of radioactive samples by precipitation and filtration:
A study of self-absorption
Esther Kim
Student #: 301096230
NUSC 346 Spring 2015
Experiment date: Feb 20th 2015
Submission date: Mar 1st 2015
ABSTRACT
36
Cl source is prepared in NaCl solution and Cl from NaCl acts as a carrier. From the active
solution prepared, AgCl precipitate is formed. With varying amount of the active solution, we obtained different masses of AgCl. This solid product is measured with silicon detector in a lead box to measure the constant activity of the source. We observed that with for very small thickness (smaller mass) has linear relationship with its activity. However, as the thickness increased, the activity was not increased proportional to its mass. This indicates that the sample is self-absorbing.
INTRODUCTION
When the solid samples are compared with other samples, few corrections should consider: chemical yield, self-scattering and self-absorption, and geometric factors. The chemical yield correction can be made by standard analytical methods [1]. The self-scattering and selfabsorption corrections are related to both the type and energy of the radiation [1]. In a sample containing the beta emitter, the beta particle can also be absorbed by the sample itself in a process called “self-absorption”[2]. The effect of self-absorption needs to be taken into a consideration for the precise and accurate measurement. The effect of self-absorption can be corrected in two ways: the method of constant activities for high beta energies, and the method of specific activities for low beta energies. In this experiment, we will be using the method of constant activities with varying mass (ie. different thickness) to correct for self-absorption.
EXPERIMENTAL
The procedure of this lab follows as the Lab Manual of Experiment 2B, page 29 to 33.
We used 5mL of 36Cl source (ID: CL-36-07) provided from the instructor. There was a change in the procedure for the amount of Cl labeled NaCl solution used in 5 test tubes. We use 1, 2, 4, 8,
~15mL of this active solution to prepare the AgCl sample.
Filtration apparatus is shown in Figure 3 of the lab manual.
OBSERVATIONS AND DATA:
AMOUNT OF ACTIVE
SOLUTION
0.1ML(STANDARD)
0ML
1ML
2ML
4ML
8ML
~15ML
MASS OF AGCL
(MG)
0
6.2
11.5
23.8
46.6
86.4
COUNTS
DURATION (S)
CPS
ERROR OF
CPS
7684
0
10443
10012
10029
10018
10034
5487.0
0
363.4
194.2
91.6
87.6
68.3
1.40
0
28.74
51.56
109.49
114.36
146.91
0.02
0
0.28
0.52
1.09
1.14
1.47
AgCl mass vs. count rate 150.00
146.91
135.00 120.00
cps
114.36
109.49
105.00 90.00 75.00 60.00
51.56
45.00 30.00
28.74
15.00 0.00
0 0.0
10.0
20.0
30.0
40.0
50.0
mass(mg)
60.0
70.0
80.0
90.0
CALCULATION
Error of counts calculation: √ counts
Error of cps: (√counts)/ time
RESULTS AND DISCUSSION
In this experiment, natural stable chloride in NaCl was an isoptic carrier for the radioactive label
36Cl[1]. The non-isotopic carrier is an inactive atom of a different element, having close chemical properties [1]. This allows handling normal quantities of materials and to us regular chemical procedures [1]. By adding the carriers, the chemical yield can be obtained from a comparison of the amount of carrier recovered to the initial amount used [1]. Therefore, with
