Nucleus and Radiation Flashcards
What is the nucleus composed of?
Protons and neutrons
What do each chemical element have?
Given atomic number (no. of protons)
Define Isotope
Atoms with the same number of protons but a different number of neutrons
What are 3 naturally occurring isotopes?
12-6C
13-6C
14-6C
What do different isotopes have?
Different probabilities of being found naturally (e.g. they have a different natural abundance)
C-12 = 98.93
C-13 = 1.109
C-14 = 1 part per trillion
How do you convert amu –> kg?
1amu = 1.6605x10^-27
?What are the particles in the nucleus held together by?
Strong nuclear force
What are the 4 fundamental forces of nature?
- Gravitational
- Electromagnetic
- Strong nuclear
- Weak nuclear
What are the properties of Gravitational?
Range: Infinite
Act between: All masses
Effect: Holds stars and planets in orbit
Relative magnitude: 10^-36
What are the properties of Electromagnetic?
Range: Infinite
Act between: All charge
Effect: Holds atom together
Relative magnitude: 1
What are the properties of Strong Nuclear?
Range: Within nucleus
Act between: Nucleons
Effect: Hold nuclei together
Relative magnitude:1
What are the properties of weak nuclear?
Range: within nucleus
Act between: Nucleons and electrons
Effect: Responsible for radioactivity
Relative magnitude: 0.01
How does the strong nuclear force overcome repulsion?
Between positively charged protons to hold nucleus together
The binding energy
- Energy radiated away when protons and neutrons are brought together to form the nucleus
- Energy required to overcome strong nuclear force and break apart nucleus
When is mass of nucleus < sum of masses of protons and neutrons observed?
Experimentally
When nucleus is formed from protons and neutrons
Define mass defect
the difference between the mass of an isotope and its mass number, representing binding energy.
What is mass defect due to?
Equivalence of mass and energy
What equation brings together the binding energy and mass defect?
E=mc^2
What is binding energy?
the energy that holds a nucleus together. This is equal to the mass defect of the nucleus.
What is a measure of stability of nucleus?
Binding energy per nucleon
How can a light nuclei become more stable?
Fusing together to form a heavier nuclei
How can a heavy nuclei become more stable?
By splitting (fission) to form a light nuclei
What is 1eV?
1.6x10^-19
What is the speed of light?
3x10^8ms-1
What are alpha particles emitted by?
Radioactive nuclei
alpha decay
What is the charge of alpha particle
2+
What has the same composition as a helium nucleus?
alpha particles
What are conserved?
Nucleons and charges
How are alpha decay written symbollically?
A Z X —> A-4 , Z-2 Y + 4,2He
The mass number A is reduced by 4 and proton 2
What do alpha particles have?
short range in air (<10cm)
What is the consequence of alpha radiation outside the body?
Less hazardous as they would be stopped by outer layers of skin
What is the consequence of alpha radiation inside the body?
Very hazardous
All energy would be deposited in small volume of living tissue e.g. lungs
What can alpha particles ionize?
Atoms and molecules with which they collide
i.e. knock electrons out of orbitals leaving a charged ion
How can ions cause damage to living tissue?
They can break chemical bond and produce damaging free radicals
What are the two types of beta decay?
B- and B+
What is B- decay?
A neutron in the nucleus decays to a proton, an electron and an electron antineutrino
How can B- decay be written as symbollically?
A,Z X –> A, Z+1 Y + e- + Ve
What is B+ decay?
A proton in the nucleus decays to a neutron, a positron and electron neutrino
How can B+ decay be written as symbollically?
A, Z X –> A, Z-1 Y + e+ + Ve
What are called beta particles?
Both electrons (e-) and positrons (e+)
What range do Beta particles have?
several metres in air but can be stopped by a sheet of aluminium
What are less densely ionizing than alpha particles?
Beta particles
What are gamma radiation?
High energy (high frequency) photons of electromagnetic radiation
How are gamma radiation produced?
By product of Alpha/Beta decay
What happens when a nucleus emits a beta particle?
It will be in an excited state. It can return to its ground state by emitting a gamma ray
Where is 99mTc extensively used in?
Nuclear medicine e.g. to perform bone scans to look for metastases
How can gamma radiation be stopped?
Very energetic
Thick sheet of lead or several metres of concrete
What can gamma radiation cause?
Ionization
lower probability than alpha or beta particles
what is PET?
Imaging technique based on B+ decay and Gamma radiation
What is electron mass?
9.11 x 10^-31
How do you conserve momentum of gamma radiation?
Two gamma ray photons must travel in opposite directions
What is momentum of photon given by?
p=h/wavelength
What is mode of decay of a nucleus dependent on?
Relative number of protons and neutrons
Proton rich nuclei tend to decay via b+ decay
Neutron rich nuclei tend to decay via b- decay
Heavy nuclei tend to decay via alpha decay
