# PS 253 Lecture Notes - Lecture 1: Embry–Riddle Aeronautical University, Standard Deviation, Strontium

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Published on 7 May 2020

School

Department

Course

Professor

Radioactive Decay Process and Shielding Tests

Pakshal Shah, Dominic Perito, Hallie Jenkins, Audrey Buehler

PS 253, Section 01, Kaydian Quintero, Department of Physical Sciences,

Embry Riddle Aeronautical University, Daytona Beach, Florida

March 2020

In first part of the experiment, emissions from a sample of 8*1011 atoms

of Co-60 (Cobalt-60) are measured in short time intervals. The histogram

created from the 300 counts of data gives the value of mean and standard

deviation as 199 and 14 respectively. In the second part, lead (Pb) and

aluminum (Al) sheets are used to stop gamma rays and beta particles emitted

from Cobalt-60 and Strontium-90 (Sr-90) respectively.

Statement of Purpose

To measure the number of

emissions from a sample of 8*1011

atoms of Cobalt-60 (Co-60). To test

the efficacy of lead and aluminum

in stopping C0-60 gamma rays and

Sr-90 beta particles.

Experimental Method

To detect the emission, a Geiger-

Muller (GM) tube is used which

excites an electron of a neutral gas

atom using gamma rays. GM tube

is connected to Pasco interface and

pulse detector with voltage set to

450V. In order to obtain 300

counts, the emissions are recorded

for 25 minutes in total. At the end

of this part, a histogram is created

to obtain the mean and standard

deviation. For the second portion,

emissions from unshielded Co-60

are measured first. And then the

emissions are recorded with

2,3,4,6, and 8 sheets of Pb. It is

repeated one more time with a 10-

layer aluminum foil slide. The

same process is repeated for Sr-90

with first unshielded condition and

then 1 Pb sheet and 1, 2, 5, 10, 20,

25, and 30 layers of aluminum (Al)

foil slides. Since both Co-60 and

Sr-90 were tested with no

shielding, 1Pb sheet, and 1 10-layer

Al foil slide. The effectiveness of

lead and aluminum sheets are

obtained by comparing the number

of emissions obtained with and

without shielding.

Results – Part I

From the 300 data points, the

mean value and the standard

deviation of the Geiger Counts

(counts/sample) was found to be

199 and 14 respectively.

Analysis – Part I

A Gaussian distribution

statistical model can be prepared

from the results obtained. The

standard deviation, or uncertainty

of the data points can be obtained

by the following formula:

R =

R = = 14.1

As per the expectations, 68%

of data should fall under R, while

95% of data should fall under 2R.

Results – Part II

All lead sheets are measured

to have a thickness of (1.50.05)

mm. The 10-layer aluminum foil

slide has a thickness of

(0.0130.05) mm.

The mean values of the

number of decays obtained with

shielded and unshielded Cobalt-60

(Co-60) are as follows:

# of Lead

Plates

Total

Thickness

±.005 mm

(mm)

Mean

Baseline

511

1

1.5

580

2

3

504

3

4.5

453

4

6

396

6

9

323

8

12

260

10 Al Sheet

0.013

511

Table 1: Pb and Al shielding tests results on Co-60

The mean values of the

number of decays obtained with

shielded and unshielded Strontium-

90 (Sr-90) are as follows:

# of Al foil

slides

Total

thickness

±.005 mm

(mm)

Mean

Baseline

1272

1

0.013

1169

2

0.026

1208

5

0.065

1098

10

0.13

1039

20

0.26

930

25

0.325

866

30

0.39

773

1 Lead Sheet

1.5

23

Table 2: Pb and Al shielding tests results on Sr-90