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
What is beta decay and give generic equation
1. 0, -1 beta particle emitted (e-)
2. 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
3. The electron is immediately ejected at a high speed from the nucleus.- Beta particle
4. A,Z X --> A, Z+1 X' + 0,-1b
5. 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
What is positron decay and give generic equation
1. 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
3. 0,+1 beta particle emitted (positron, anti-electron)
4. A,Z X --> A, (Z-1) X' + 0,+1Beta particle
5. Atomic number decreases by 1 but mass stays the same
26
What is electron or K capture decay and give generic equation
1. An alternate way for a nuclide to increase its neutron to proton ratio
2. An electron from an inner orbital is captured by the nucleus of the atom and combined with a proton to form a neutron.
3. X-Rays emitted
4. A,Z X + 0,-1 e --> A, (Z-1)X' + X-ray
5. Atomic number decreases by 1 but mass stays the same
27
What are gamma rays
1. Gamma rays (γ) are very high energy electromagnetic waves emitted from a nucleus.
2. Gamma rays are emitted by a nucleus when nuclear particles undergo transitions between nuclear energy levels.
3. This is analogous to the electromagnetic radiation emitted when excited electrons drop from higher to lower energy levels
4. The only difference is that nuclear transitions release much more energetic radiation.
28
What is gamma emission decay and give generic equation
1. 0,0 gamma particle emitted
2. A,Z X* --> A,Z X +0,0 gamma
3. No effect on mass or atomic number but relaxes from excited to relaxed state- loses energy
29
What is spontaneous fission
1. neutrons are emitted
2. nuclei break apart into big chunks
3. (A+B+C), Z+Y X --> A,Z X' + B,Y X' + c(1,0)n
30
What are two other types of nuclear decay which are very rare
1. Neutron - rare as binding energy of neutrons is high
2. proton emission (rarest)
