Lecture 1 Flashcards
1
Q
Define radiochemistry
A
- Processes where the atomic nuclei (rather than bonds) undergo changes of various types
- e.g. 131,53I –> 131,54Xe + 0,-1 e-
2
Q
What did Becquerel do
A
- Discovered radiation from uranium
3
Q
What did p and m curie do
A
- Isolated radioactive Po and Ra- tried to isolate what caused radiation in U
- alpha radiation was identified as He particles and the produce of Ra decay as new element Rn
- Ra –> Rn + He
- Showed atomic nuclei can undergo changes
4
Q
How do smoke detectors work
A
- Air within the cell of a detector is ionised by the 4He2+
- A current flows under the influence of an electric potential- caused by ionisation
- If smoke is present, the ions become attached to the smoke particles and the current drops to a level which sets off an alarm- as ions not available to conduct electricity
- 241Am –> 4He2+ + 239 Np
5
Q
What is 1 curie
A
- 3.7 * 10^10 disintegrations or nuclear transformations per second
- Approx the amount of radioactivity emitted by one gram of radium 226.
6
Q
Where do inert noble gases arise from
A
- Natural U deposits e.g. in granite
7
Q
What is danger of Radon
A
- has a short half-life 3.82 days and is inert so not trapped
- it seeps into homes and breathed by humans, decaying in the lungs to 218Po and then further to 214Pb, 214Bi and 214Po
- All of these are high energy alpha-emitters and solids which damage DNA in lung tissues leading to cancer.
8
Q
How is radiochem used in foods
A
- Gamma ray irradiation of foods -
- retards growth of organisms so extends shelf life of foodstuffs
- used to treat meat used on space missions
9
Q
What is the nucleus composed of
A
- two nucleons- protons and neutrons
- Number of protons is atomic number (Z)
- Number of protons and neutrons (A) together is effectively the mass of the atom
10
Q
What is the mass of a proton
A
- 1.0073 a.m.u (atomic mass unit)
11
Q
What is the mass of a neutron
A
- 1.0087 amu
12
Q
What is the mass of an electron
A
- 0.00054
13
Q
What are the isotope symbols
A
- A is the number of nucleons (protons + neutrons)
- Z is number of protons in the isotope (charge)
- X is the atomic symbol for the isotope
14
Q
What is a radioisotope
A
- Is an isotope of an element that is unstable and undergoes radioactive decay
- When nuclides of one type emit radiation, they are changed into different nuclides
15
Q
What is radioactive decay
A
- Is spontaneous and does not require an input of energy to occur.
- The stability of a particular nuclide depends on the composition of its nucleus, including the number of protons, number of neutrons and the proton to neutron ratio
16
Q
Do elements always have stable isotopes
A
- Some have no stable isotopes
- So any atoms of that element is radioactive
- For other elements only certain isotopes are radioactive
17
Q
What is the radius of hydrogen atoms
A
- 5.29*10^-11m (Bohr radius) 1/2Angstrom
18
Q
What is the radius of a nucleus with nucl number A
A
- approx =A^1/3 * (1.2*10^-15m)
19
Q
What is radioactivity
A
- The spontaneous breakdown of an atom’s nucleus by the emission of particles and/or radiation
- Radiation is the emission of energy through the space in the form of particles and/or waves
20
Q
What are the two types of radiation
A
- Ionising
- non-ionising
21
Q
Describe ionising radiation
A
- Removes electrons from atoms
- High energy
- Particulate (alphas and betas)
- Waves (gamma and x-rays (non radioactive in origin))
22
Q
Describe non-ionising radiation
A
- Electromagnetic
- Cannot remove electrons from atoms
- Infrared, visible, microwaves, radar, radio waves, lasers
23
Q
What are the decay rules
A
- Nucleon number A is conserved
- Atomic number (charge) Z is conserved
- Energy and momentum are conserved
24
Q
What is alpha decay and give generic equation
A
- 4,2 Alpha particle emitted (He)
- A,Z X –> (A-4), (Z-2) X’ + 4,2a
25
Q
What is beta decay and give generic equation
A
- 0, -1 beta particle emitted (e-)
- A neutron in the nucleus is capable of turning into a proton and an electron. decreases neutron to proton ratio when too high, increasing stability
- The electron is immediately ejected at a high speed from the nucleus.- Beta particle
- A,Z X –> A, Z+1 X’ + 0,-1b
- Atomic number increases by 1, mass stays same
6.https://chem.libretexts.org/Bookshelves/Introductory_Chemistry/Map%3A_Fundamentals_of_General_Organic_and_Biological_Chemistry_(McMurry_et_al.)/11%3A_Nuclear_Chemistry/11.04%3A_Nuclear_Decay
25
Q
What is positron decay and give generic equation
A
- Type of beta decay
2.proton in the nucleus can turn into a neutron and another particle called a positron.- increases neutron to proton ratio, increasing the stability - 0,+1 beta particle emitted (positron, anti-electron)
- A,Z X –> A, (Z-1) X’ + 0,+1Beta particle
- Atomic number decreases by 1 but mass stays the same
26
Q
What is electron or K capture decay and give generic equation
A
- An alternate way for a nuclide to increase its neutron to proton ratio
- An electron from an inner orbital is captured by the nucleus of the atom and combined with a proton to form a neutron.
- X-Rays emitted
- A,Z X + 0,-1 e –> A, (Z-1)X’ + X-ray
- Atomic number decreases by 1 but mass stays the same
27
Q
What are gamma rays
A
- Gamma rays (γ) are very high energy electromagnetic waves emitted from a nucleus.
- Gamma rays are emitted by a nucleus when nuclear particles undergo transitions between nuclear energy levels.
- This is analogous to the electromagnetic radiation emitted when excited electrons drop from higher to lower energy levels
- The only difference is that nuclear transitions release much more energetic radiation.
28
Q
What is gamma emission decay and give generic equation
A
- 0,0 gamma particle emitted
- A,Z X* –> A,Z X +0,0 gamma
- No effect on mass or atomic number but relaxes from excited to relaxed state- loses energy
29
Q
What is spontaneous fission
A
- neutrons are emitted
- nuclei break apart into big chunks
- (A+B+C), Z+Y X –> A,Z X’ + B,Y X’ + c(1,0)n
30
Q
What are two other types of nuclear decay which are very rare
A
- Neutron - rare as binding energy of neutrons is high
- proton emission (rarest)
