25.4 Radioactivity

Question 1

how are protons and neutrons held together?

Answer 1

strong nuclear force

Question 2

what is stronger:

a) strong nuclear force
b) electrical force between charged particles?

Answer 2

a) strong nuclear force

=> has to overcome the electrical repulsion betw protons in the nucleus

Question 3

what is the main condition for the strong nuclear force?

Answer 3

only works at very short distances (ie in a nucleus)

Question 4

radioactive

Answer 4

atoms with unstable nuclei

Question 5

how do nuclei become more stable? (2)

Answer 5

1) alter # or ratio of protons:neutrons

2) lower energy

Question 6

radioactive decay

Answer 6

process through which atoms with unstable nuclei undergo to become more stable

Question 7

types of radioactive decay

Answer 7

1) α
2) β
3) γ

Question 8

parent

Answer 8

nucleus undergoing radioactive decay

Question 9

daughter

Answer 9

resulting stable nucleus after a nucleus undergoes radioactive decay

Question 10

α decay (cause, releases, change and what it’s stopped by)

Answer 10

cause: too many neutrons and protons
releases: 4 He / α
________2
change: Z - 2, AW -4
stopped by: human skin

Question 11

β (-) decay

Answer 11

cause: too many neutrons
releases: 0 β (converts N-> P)
________ -1
change: Z + 1
stopped by: Al foil + plastic + glass

Question 12

β (+) decay

Answer 12

cause: too many protons
releases: 0 β (converts P-> N)
+1
change: Z - 1
stopped by: Al foil + plastic + glass

Question 13

electron capture

Answer 13

cause: too many protons
releases: 0 e (converts P-> N by capturing e)
-1
change: Z - 1
stopped by: Al foil + plastic + glass

Question 14

γ decay

Answer 14

cause: too high energy
releases: 0 γ
________ 0
change: nothing
stopped by: lead + concrete

Question 15

half-life

Answer 15

time it takes for a sample of radioactive substance to decay by (1/2)

Question 16

how does radioactive decay change overtime?

Answer 16

radioactive decay decreases exponentially with time

Question 17

k

Answer 17

decay constant: value that is inversely proportional to half-life (shorter half-life = larger k = faster decay)

Question 18

Eb

Answer 18

nuclear binding energy: energy required to break up intact nucleus into individual nucleons

Question 19

what is required for an atom to have an Eb?

Answer 19

1) protons

2) neutrons

Question 20

what does a greater or lower Eb indicate?

Answer 20

greater Eb = more stable nucleus

lower Eb = less stable nucleus

Question 21

Δm

Answer 21

mass defect: the change in mass as individual nucleons bind to form a nucleus

Question 22

Δm equation

Answer 22

(total mass of separate nucleons) - (mass of nucleus)

Question 23

what does a negative or positive Δm value indicate?

Answer 23

positive Δm = stable nucleus
negative Δm = unstable nucleus

=> want Δm to be more positive (indicates that the overall mass decreases when you bind the nucleons together -> better binding -> decrease mass)

Question 24

Eb equation (2)

Answer 24

1) Eb = (Δm)(c^2)

2) Eb (in eV) = (Δm in amu) x 931.5 MeV