# Half-Life Flashcards

1
Q

what is the rate at which unstable nuclei decay measured with

A

activity and half-life

2
Q

what is the radiation given out from the nuclei of atoms measured with

A

a geiger-muller tube and counter

3
Q

what does the geiger-muller tube and counter do

A

records count rate which is the number of radiation counts reaching per second

4
Q

what is radioactive decay in terms of patterns

A

totally random, so you cant pinpoint which nucleus in the sample will decay and at what time, its a wild beast!

5
Q

although radioactive decay doesnt have patterns, what can you predict

A

how long it takes for the radiation emitted by the nuclei to halve known as the half life. all about the time

6
Q

what can knowing about the life span of a half life allow you to do

A

radioactive sources arent so unpredictable when you can predict make predictions about them even when its random

7
Q

what is the activity of a radioactive source

A

the rate at which the source decays using its half life to figure it out

8
Q

what is activity measured in

A

becquerels or Bq (1 Bq = 1 decay per second)

9
Q

why do radioactive nuclei even decay in the first place

A

to become more stable

10
Q

what happens when a radioactive nucleus decays to become more stable

A

its activity as a whole decreases as old sources emit less radiation, like old people emit less life

11
Q

tell me son, just how diverse are the lives of nuclei all around the world

A

some isotopes only need a handful of hours to decay all their unstable nuclei, but some dons can take millions of years

12
Q

half life sounds like an interesting way to measure decay, but why is this used in the first place and why not full life

A

because the activity never actually reaches zero, so half lives are used to measure the rate of activity drop off

13
Q

what is a half life anyway

A

the time taken for the number of radioactive nuclei in an unstable isotope to be cut in two

14
Q

so if the definition of the half life is correct, what does the half life also measure

A

the time taken for the activity and count rate to half with it

15
Q

ite quick mental logic - a short half life means the activitiy…

A

falls quickly as the nuclei are unstable and rapidly decay

16
Q

why are sources with tiny half lives dangerous to be around

A

they emit a high level of radiation in their youth, but they quickly become safe and old

17
Q

even more mental logic - a long half life means the activity…

A

falls slowly obviously because most of the nuclei dont decay for a long time… just kinda sits there… releasing small amounts of radiation for a long time… dead life

18
Q

why can a source with a ling half life be dangerous as well

A

because the release of radiation for a long time exposes nearby areas to radiation for millions of years, not healthy mate

19
Q

quick maths - the initial activity of a sample is 640 Bq. calculate the final activity as a percentage of the initial activity after 2 years

A

1 half life = 640 / 2 = 320
2 half life = 320 / 2 = 160
160 / 640 = 0.25
0.25 x 100 = 25%

20
Q

in a graph of activity against time (activity on y and time on x), how will the line be shaped

A

an inside drooping slide from the top of the activity down to time

21
Q

how do you find the half life from a graph of activity against time

A

finding the time interval on the bottom axis corresponding to halving of the activity on the vertical axis (like a median in a cumilative frequency graph)

22
Q

what does the tube and the counter do in the gieger muller tube and counter

A
• the gieger muller tube clicks every time it detects radiation
• the counter displays the number of clicks per second
23
Q

what does the tube and the counter do in the gieger muller tube and counter

A
• the gieger muller tube clicks every time it detects radiation
• the counter displays the number of clicks per second