- #1

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I am very new too Matlab and how it all works but I am having trouble understanding at what axis the numerical integration is occurring from on the graph that I plotted.

So I am currently doing an experiment in gamma ray spectroscopy and due to issue with the software we found it hard to integrate under a specific photo peak so it was suggest to use Matlab to integrate under the area, but the photo peak is off the x-axis so which I have highlighted in my picture below.

But my issue is I don't know how to integrate that specific area in Matlab, so what I have done so far is cherry pick the data and fit a Gaussian to it which produced the given function and graph.

Firstly here is my data set I picked for the curve

1117.4 7

1120.4 9

1123.4 7

1126.4 13

1129.4 6

1132.4 14

1135.4 15

1138.4 11

1141.4 20

1144.4 16

1147.5 16

1150.5 18

1153.5 33

1156.5 20

1159.5 19

1162.5 24

1165.5 35

1168.5 35

1171.5 43

1174.5 42

1177.5 40

1180.5 38

1183.5 38

1186.5 37

1189.5 34

1192.5 39

1195.5 34

1198.5 25

1201.6 23

1204.6 23

1207.6 19

1210.6 19

1213.6 13

1216.6 10

1219.6 16

1222.6 10

1225.6 6

1228.6 2

1231.6 11

1234.6 11

1237.6 5

1240.6 7

Next here is my code to plot the data

Ignore comment out parts Im currently experimenting

this produced the following graph

so now this is the part hat get confusing for me I need to calculate the area in the red but when i used the trapz(x,y) I think it is finding the area of both red and green, my only option at the moment I think is to shift the graph down so it aligns with the x=0 axis and it should integrate just the red area is this correct?

So I am currently doing an experiment in gamma ray spectroscopy and due to issue with the software we found it hard to integrate under a specific photo peak so it was suggest to use Matlab to integrate under the area, but the photo peak is off the x-axis so which I have highlighted in my picture below.

But my issue is I don't know how to integrate that specific area in Matlab, so what I have done so far is cherry pick the data and fit a Gaussian to it which produced the given function and graph.

Firstly here is my data set I picked for the curve

1117.4 7

1120.4 9

1123.4 7

1126.4 13

1129.4 6

1132.4 14

1135.4 15

1138.4 11

1141.4 20

1144.4 16

1147.5 16

1150.5 18

1153.5 33

1156.5 20

1159.5 19

1162.5 24

1165.5 35

1168.5 35

1171.5 43

1174.5 42

1177.5 40

1180.5 38

1183.5 38

1186.5 37

1189.5 34

1192.5 39

1195.5 34

1198.5 25

1201.6 23

1204.6 23

1207.6 19

1210.6 19

1213.6 13

1216.6 10

1219.6 16

1222.6 10

1225.6 6

1228.6 2

1231.6 11

1234.6 11

1237.6 5

1240.6 7

Next here is my code to plot the data

Code:

```
dataset = xlsread('Lab 3 Results 11.10.18 (1).xlsx','Sheet3','C390:D431');
x=dataset(:,1);
%y=dataset(:,2);
%plot(x,y,'-')
a1=37.43 ;
b1=1178 ;
c1=39.28 ;
d1=0
y=a1*exp(-((x-b1)/c1).^2)-d1;
%int1=trapz(x,y)
%int2=trapz(y)
plot(x,y)
%xlabel('Energy : KeV', 'FontSize', 15)
%ylabel('Number Of Interactions','FontSize', 15)
```

Ignore comment out parts Im currently experimenting

this produced the following graph

so now this is the part hat get confusing for me I need to calculate the area in the red but when i used the trapz(x,y) I think it is finding the area of both red and green, my only option at the moment I think is to shift the graph down so it aligns with the x=0 axis and it should integrate just the red area is this correct?