# Bmat help!

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Thread starter 8 months ago
#1
Can anyone help with this question, please?
In an experiment concerning radioactive decay the count rate of radiation 5cm from source X was measured at 140 counts per min. 12 mins later with the detector at the same position the count rate was measured at 35 counts per min. Background radiation was measured at 20 counts per minute. Clculate the half life of source X?
A) 1 min
B)2 mins
C)3 mins
D) 4 mins
E)5 mins
0
8 months ago
#2
C?
0
8 months ago
#3
I got d) 4

heres my working but it might be wrong:

=120

half life
0- 120
1- 60
2- 30
3- 15

15 left after 3 half lives
12/3= 4

each half life is 4 mins
0
8 months ago
#4
(Original post by Medi-cry)
I got d) 4

heres my working but it might be wrong:

=120

half life
0- 120
1- 60
2- 30
3- 15

15 left after 3 half lives
12/3= 4

each half life is 4 mins
Actually yeah I get you, I didn’t realise I need to divide 12 by 3 😅
1
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