Radioactivity Flashcards
What are radioisotopes?
unstable nucleus that decay into stable states by emitting radiation in alpha, beta or gamma
define isotone
difference nuclides with same value of neutrons
define metastable
radionuclides being able to exist for a significant period of time with their nucleus in an excited/higher energy state before falling to ground state
define isomer
long-lived excited state of a nuclide
define activity in radioactivity
rate at which nuclei decay/ average number of disintegrations per second
define half-life
average time a radioactive substance takes to decay to half its initial activity
What causes alpha, beta+ (positron emission), beta- decay, electron capture?
alpha decay= too many protons and neutrons
beta- decay= too many neutrons
electron capture/beta+ = too few neutrons
Between particle, gamma ray, electron and x-ray emission, which are considered atomic or nuclear?
particle and gamma ray = nuclear
x-ray and electron = atomic
describe the formation of alpha decay
heavy radionuclide with too many nucleons decay releasing 2 protons and neutrons.
parent atomic mass reduces by 4
parent proton number reduces by 2
forms daughter element and alpha particle
describe the features of alpha particle
+ve charge, relatively heavy, short range and highly ionising
describe formation of beta minus decay
radionuclide with too many neutron decays, converting a neutron into a proton and electron
parent atomic mass stays same
parent proton number increases by 1
forms daughter element and beta - particle (electron)
describe formation of beta plus decay
radionuclide with too few neutrons decay converting a proton into a neutron and positron
parent atomic mass stays same
parents proton number decreases by one
forms daughter element and positron (anti electron)/ beta+ particle
describe electron capture
radionuclide with too few neutrons decay.
K-shell electron is captured by the nucleus
causing proton to be converted into neutron and the emission of an electron neutrino
parent atomic mass stays same
parent proton number stays same
parent element adds electron
forms daughter element with same atomic number but decrease 1 in proton number
How is a gamma ray formed during isomeric transition?
radionuclide in metastable state decays to ground state and during the isomeric decay, the energy difference between excited and ground nuclear states is emitted as gamma ray
what is an alpha, beta + beta- particles?
alpha = helium ion
beta+ = positron
beta- = electron
What is activity measured in?
Becquerel (Bq) or s^-1
What 3 things are radionuclides used for in medicine? (give description)
- imaging
- looking at physiological function - non-imaging investigations
-using multiple blood samples to measure a physiological rate - molecular therapies
-using destructive nature of ionising radiation to kill diseased cells
Describe alpha, beta and gamma particles charge, range and how they lose energy over distance
alpha: +ve charge, short range, impart a lot of energy over very short distance
beta: -ve charge, relatively short range but longer than alpha, impart their energy over a relatively short distance
gamma: no charge, very long range, act like photons/x-rays
What are favourable features of radionuclides used in imaging?
- high penetration (gamma rays)
- low half life so patient isnt radioactive for long
- long enough half time to allow time between injection and scanning
- emission energy to be detected by cameras of 10-100keV
What does SPECT stand for?
single photon emission computed tomography
What type of radiation does SPECT use?
gamma rays
what are most common gamma emitting radionuclides used in SPECT?
Tc-99m
Kr-81m
I-123
What type of radiation is used in PET?
Beta plus particles
How do beta plus particles interact in PET scan
beta plus particle/positron interacts with an electron annihilating it creating 2 back to back 511 keV gamma rays
What are 2 commonly used radionuclides in PET scans?
F-18
Ga-68
What is the dose of radioactivity prescribed to a patient in the form of activity?
100-900 MBq (dependant on study)
What piece of equipment is used to count radioactive plasma samples?
gamma counter
In non imaging activity administered to the patient is very small
What are the basic requirements for the radionuclide used in Non imaging?
- emission needs to escape plasma and interact with the detector (gamma rays)
- half-life needs to be long enough for blood samples to be taken then samples to be counted
What is the half life of Tc-99?
6 hours
What particles are used in molecular therapy and why?
alpha or beta as they are highly damaging charged particles
- short range
-half-life long enough to do damage but not long enough that the patient is radioactive longer than needed
What radionuclide is used to treat thyroid cancer and how does it work?
I-131 (iodine)
- thyroid takes up iodine
- most of iodine that doesnt go to the thyroid is excreted through urine
What is the values of radionuclide prescribed in MBq to overactive thyroid and thyroid cancer?
400, 600, 800 MBq prescribed for overactive thyroid
1.1, 3.7 or 7.4 GBq prescribed for thyroid cancer
What radionuclide is used to treat bone metastases for prostate cancer patient, how does it work?
Ra-223 (radium)
- behaves as calcium so is selectively taken up by bone
- majority of Ra-223 not taken uo by bone is excreted through faeces
- 55KBq per kg prescribed
What is the half life of Ra-223
11 days
