Radioactive Decay

Question 1

Alpha (α) particle

Answer 1

A particle emitted by the nucleus through α decay, containing 2 protons and 2 neutrons.

Identical to a helium nucleus.

Question 2

Beta (β) particle:

Answer 2

A particle emitted by the nucleus through β decay, either negatively or positively charged.
β- particle: electron (“negatron”).
β+ particle: positron (antimatter, positively charged version of electron).

Question 3

β- particle

Answer 3

electron (“negatron”)

Charge: 1.602 × 10^−19 coulombs.

Question 4

β+ particle

Answer 4

A positron. (antimatter, positively charged version of electron)

Question 5

Gamma (γ) ray

Answer 5

A photon emitted by the nucleus.

(different from an x-ray which is from an electron interaction (Bremsstrahlung) but may have the same energy range).

Question 6

Internal conversion electron

Answer 6

Emitted when a nucleus transfers energy to an orbital electron instead of emitting a gamma ray

Question 7

Characteristic X-ray

Answer 7

A photon emitted by an electron transitioning from one shell to another.

Other than the source of production, a 30-keV X-ray is identical to a 30-keV γ - ray.

(Compare with Auger electron)

Question 8

Alpha (α) Decay

Answer 8

The nucleus is bloated, proton heavy and wants to lose weight!

Emission of alpha particles (2 neutrons and 2 protons)
Occurs in very heavy (Z > 52) nuclei.

Typical alpha energies range from 2 to 8 MeV.
Alpha particles are monoenergetic

Question 9

Beta-Minus (β-) decay

Answer 9

The nucleus is proton-poor and wants more protons!

One of the neutrons is able to turn into a proton

Atomic number goes up by 1; mass stays the same.

electron and antineutrino is emitted.

Question 10

Beta-Plus (β+) decay

Answer 10

The nucleus is proton-rich and wants more neutrons!

One of the protons turns into a neutron,

Atomic number goes down by 1; mass stays the same.

Positron (anti-electron) and a neutrino is emitted.

Question 11

Electron Capture (EC)

Answer 11

The nucleus is proton-rich and wants more neutrons!

When nucleus is proton rich but does not have an excess of 1.02 MeV, the nucleus eats one of its electrons.

Electron combines with Proton to form a neutron. A Neutrino is emitted.

Remaining energy is emitted as a gamma ray or as internal conversion electrons

Characteristic X-rays due to filling of electron vacancy in inner shells.

Question 12

Gamma Emission

Answer 12

The nucleus is excited and wants to settle down!

No change in atomic mass or atomic number.

Excess energy is released as a photon.

Question 13

Internal Conversion

Answer 13

The nucleus is excited and it kicks out an electron!

The nucleus transfers internal energy to an inner shell electron which is freed.

Resulting vacancy is filled by higher electrons -> characteristic X-rays or Auger electrons.

Question 14

Activity

Answer 14

Disintegration per second, Becquerel (Bq).

Question 15

Exponential Decay

Answer 15

A = -λ · N

A(t) = A_0 · exp(-λ t)

Question 16

Half-Life

Answer 16

How long it takes to decay to half the original activity

T_1/2 = ln(2)/λ

Question 17

Mean Life

Answer 17

t_avg = 1 / λ

Question 18

Effective half-life

Answer 18

How long an isotope is effective in the body.

1 / t_eff = 1 / t_phys + /1 t_bio

(Hint: Parallel resistors)

Question 19

If a electron and a positron collide they …

Answer 19

Might scatter from each other (Bhabha scattering )

or

Annihilation (conversion of mass in energy) resulting in two 0.511 MeV x-rays in opposite directions.