radioactivity, decay, radioisotopes

lecture 2 radpharm

radioactive decay properties determine what two things?

method of detection, whether it can be used for diagnostic/therapeutic application

chemical and physical properties determine

localization in the body

electron configuration determines the

chemical properties of an element, i.e. chemical bonds

nuclear configuration determines the

stability of the atom’s nucleus, i.e. radioactive decay

nuclide

atom characterized by number of protons and neutrons in its nucleus

nomenclature: X

elemental symbol

nomenclature: Z

number of protons

nomenclature: N

number of neutrons

nomenclature: A

atomic mass number (protons and neutrons)

isotope

nuclide that has same number of protons but differing number of neutrons; same element, different mass

at the level of a single atom, radioactive decay is

a random process

in radioactive decay, what is produced

daughter isotopes, which interact with other products to become radiation

in general: radioactive decay is

spontaneous emission of radiation from an atom due to transformation in the nucleus

alpha decay- what changes about the isotope

helium nucleus is produced, new element is produced (-2p, -2n)

alpha particles are relatively ___ and poorly ___

massive, penetrating

why are alpha particles poorly penetrating?

very high LET

what is the end result of beta decay?

results in an electron and a new element (+1p, -1n)

most beta emitters also emit…

gamma rays

betas have ___ LET

high

gamma rays (isomeric transition) decay process

results in element staying the same and releasing a photon

in gamma decay, the nucleus composition

does not change

when nucleons rearrange/drop energy levels, they

release the extra energy (the photon)

gamma rays have ___ LET

low

positron decay occurs with nuclei that have…

too many protons (an n/p ratio too low for stability)

the proton and neutron numbers of nucleus in positron decay do what?

they change (-1p, +1n) and creates a new element while a positron is emitted

positrons go on to pair up with…

free electrons and annihilate

why do nuclei decay

unstable balance of neutrons and protons

linear energy transfer

heavy/charged particles have high LET, waves/photons have low LET

some radionuclides emit ___

several types of radiation

radioactivity

rate of decay of a radioactive source

radioactivity can be described mathematically without…

regard to specific mechanisms of decay

1 disintegration(decay) per 1 second equals

1 Becquerel (Bq)

nuclear transformations per second is referred to as

dps

how many Bq is 1 Curie (Ci)

3.7×10^10 Bq OR 37 MBq = 1 mCi

Activity formula

A = 𝜆N

𝜆 =

ln2/T_(1/2)

activity is inversely proportional to

nuclide’s half life (T_1/2)

activity is directly proportional to

decay constant (𝜆) and number of radioactive atoms (N)

what is the decay constant 𝜆

probability that radioactive atom will decay

unit for 𝜆

1 over time (1/sec), or inverse time (sec^-1)

the decay constant is a true constant, meaning

not affected by external influences

radioactive decay equation

A_t = (A_0)e^(-𝜆t)

half life means

time at which activity is decreased to half its original value

decay factor method

e^-𝜆t

if you want to know activity going back, __ activity by decay factor

divide

if you want to know activity going forward, ___ by decay factor

multiply

ideal characteristics in diagnostic radioisotopes

gamma(photons), low LET; long enough half life to transport to site; low to medium energy

higher radioisotope energy does what

gives more exposure to pt and staff

radioisotopes w multiple gamma energies require

special setup on imaging system

ideal characteristics of therapeutic radioisotopes

alphas/betas, high LET; longer half lives so RP stays in body for extended periods of time; high energies ideal for damaging tissue