Nuclear Chemistry Flashcards

Question

What is half life? GIve an example

Answer 1

It is the time required for half of the nuclei in a sample to undergo a decay event For example, I - 131 has a half life of 8 days, so if we start with 160 nuclei, after 8 days, only 80 original I-131 nuclei will remain

Answer 2

N = N0 x e ^-kt N = number of nuclei N0 = initial number of nuclei k = decay constant t = time

Answer 3

The decay constant (k) is characteristic of the particular radioactive nuclide

Answer 4

It depends on the number of the original nuclei present

Answer 5

The activity (A) of a radioactive isotope is a specific measure of the rate of decay, defined as the number of nuclei that disintegrates per second

Answer 6

It is defined when the atom is unstable and spontaneously emits energy in the form of radiation

Answer 7

It is the becquerel (Bq). 1 becquerel = 1 disintegration per second

Answer 8

A = kN (where N is the no. of nuclei in sample), and k is the decay constant

Answer 9

A = A0 x e^ -kt

Answer 10

Specific Activity and Molar activity

Answer 11

Is the activity per gram of radioactive nuclide

Answer 12

It is the activity per mole of radioactive nuclide

Answer 13

Small decay number and long half life

Answer 14

High decay number and short half life

Answer 15

t(1/2) = ln2 / k

Answer 16

1. Measure the C-14 activity of the archaeological sample (this is 'At') 2. Measure the C-14 activity of an equivalent modern day sample (this is 'A0') 3. Substitute these values into the equation for C-14 age: t = 8033 x ln(A0 / At) - note C-14 dating is only appropriate from objects less than 60000 years old

Answer 17

Stable and radioactive

Answer 18

Involves the competition between two main forces: Electrostatic (coulomb) repulsion between protons act to push the nucleons apart over a long range The strong nuclear force, which is a short range attraction between all nucleus

Answer 19

Decay occurs when the electrostatic repulsion by the protons overwhelms the strong nuclear attraction by nucleons. In nuclides with too few neutrons, the electrostatic repulsion overwhelms the strong nuclear attraction. This causes it to be radioactive. As the nucleus gets larger, the long range electrostatic repulsion between protons accumulate and overwhelms the strong nuclear attraction. This causes the nucleus to become too big (because all the nucleons are repelled from each other). This causes radiation. When there are too many neutrons, the nucleus is unstable as well.

Answer 20

Alpha decay (Helium atom) Beta decay (B- / electron) Positron decay (B+) Electron Capture Neutron emission Gamma emission

Answer 21

Alpha decay involves the emission of an alpha particle, which is a helium nucleus with a mass number of 4 and charge 2+. Alpha decay occurs because the nucleus becomes too heavy with protons and neutrons. It is too heavy to keep itself together. There are too many protons as well so it starts decaying This decreases both neutrons and protons

Answer 22

This is when an electron is ejected from the nucleus. One neutron is changed into a proton and an electron. The proton is added to the nucleus and electron is ejected. Beta decay occurs because there are too many neutrons to protons. the n/z ratio is too high. This helps decrease it This decreases neutrons and increases protons n/z increases

Answer 23

B+ (positron) is the antimatter of an electron, and is emitted from the nucleus. One proton is changed into a neutron in this nuclear reaction to balance the charge. The ejected positron will collide with the electron in the surrounding environment, producing 2 gamma rays This occurs because there are too many protons to neutrons. n/z ratio is too low. This helps increase it whilst emitting a positron This decreases the number of protons and increases neutrons

Answer 24

This is when an electron from the outer cloud is captured by the nucleus and combines with a proton to form a neutron This is typically followed by emissions of x rays and electrons fall into lower energy states to fill vacancy left by the captured electron This increases the number of neutrons and decreases the number of protons I.e. Iron - 55 + electron --> Manganese - 55 n/z increases

Answer 25

This involves a simple emission of a neutron, which changes mass but leaves no of protons unchanged This reduces the number of neutrons Example: Helium - 7 --> helium 6 + neutron

Answer 26

This is the high frequency radiation that often acompanies other forms of decay. It is essentially energy. I.e. Tc - 99m --> Tc - 99 + gamma

Answer 27

neutron to proton ratio

Answer 28

Size of nucleus (too many protons or neutrons) Composition of nucleus (n/z ratio)

Answer 29

Lead - 208

Answer 30

It is where all known stable nuclides fall inside the 'zone of stability'. The zone has a n/z ratio near to one for light electrons, but as the nucleus gets larger, the n/z ratio increases until 1.5 for heavier elements. Unstable isotopes must decay towards the zone of stability

Answer 31

It can only go diagonally for decaying in the zone of stability. It can go either up or down the zone of stability to become stable.

Answer 32

It has a harmful interaction with biological tissue. This can cause effects such as radiation sickness, cancers and nuclear weapons

Answer 33

The radiation is probably responsible for saving many more lives than it takes through forms such as cancer therapy and medical imaging

Answer 34

It is produced by radioactive decay and has high energy, and can eject electrons from the orbit of an atom

Answer 35

10eV, so each unit of radiation can ionise a large number of molecules

Answer 36

5MeV = 5000000 eV = 5 x 10^5 ionised molecules

Answer 37

0.05 to 1 MeV = 5 x 10^3 to 1 x 10^5 ionised molecules

Answer 38

1 MeV = 1000000eV = 1 x 10^5 ionised molecules

Answer 39

This is because the body is 50-70% water by weight, so large proportions of reactions will be with water. When exposed to radiation, water is ionised to a cation and electron: H2O + ionising radiation --> H2O (+) + e(-) The H2O(+) then reacts with water to form: H2O(+) +H2O --> H3O (+) + OH * Meanwhile, the e- reacts with water to form: e(-) + H2O --> OH (-) + H * Both OH * and H * are free radicals. Free radicals are very reactive, and can damage: DNA strands --> genetic damage, cancer Cell membranes --> cells break apart Proteins --> enzymes lose function

Answer 40

Type of radiation Length of exposure Source of exposure

Answer 41

alpha, beta and gamma (need to remember their properties such as energy and pentration)

Answer 42

energy = 5 MeV penetration (air) = 40 mm Penetration (biological) = 0.05mm relative biological effectiveness = 20

Answer 43

energy = 0.05 - 1 MeV penetration (air) = 6-300 mm Penetration (biological) = 0.06 - 4mm relative biological effectiveness = 1-1.7

Answer 44

energy = 1 MeV penetration (air) = 400 mm Penetration (biological) = 50cm relative biological effectiveness = 1

Answer 45

RBE (relative biological effectiveness) is a relative measure of the damage done by a given type of radiation per unit of energy deposited in biological tissues.

Answer 46

Short term (acute): called radiation poisoning. Involves high doses for a short period of time, causing acute cell damage and often death Long term (chronic): Radiation induced cancer. Anything that interrupts DNA can lead to cancer

Answer 47

Internal exposure: Ingestion or inhalation. Here, alpha and beta radiation are the most dangerous as although they have bad pentration they have high ionising power, and once they're in its easier to suffer radiation damage External exposure: alpha cant pentrate through air and skin. Beta might be able to cause some damage, Gamma radiation can pentrate skin, and is likely more dangerous

Answer 48

The Sievert (Sv)

Answer 49

Radon - It is part of decay of Uranium 238. COlourless and odourless gas which damages lungs. Contributes to 55% of natural radiation dose Potassium - 40 - This is naturally occurring, such as through bananas, kidney beans and sunflower seeds. It provides a low form of radiation Cosmic rays - high kinetic energy particles. This is usually absorbed in the upper atmosphere, but some still goes through and provides radiation

Answer 50

Focusing ionising radiation onto tumour Internal admission of a radiopharmaceutical

Answer 51

It uses gamma radiation as it must penetrate air and skin, and this is tuned into the cancerous cells to cause the cancer cells to be destroyed

Answer 52

The radiopharmaceutical must be targeted to the tumour. It uses alpha or beta emitters, which have short range effect. For example, iodine naturally accumulates in the thyroid, so I-131 (beta emission, with half life of 8 days) is used to treat thyroid cancer Current focus / research is attempting to attach radionuclides to antibodies which guide radiopharmaceuticals to other cells or organs

Answer 53

Radioimaging uses radiation emitted from within the body to map the body. The radiation used must be highly penetrating so that it can be detected and isn't harmful to the patient --> uses gamma radiation Distribution of radioisotope is imaged by scintilallation counting ( no need to know this) Computer tomography can give a 3d reconstruction of the body Radiation can come from a number of sources such as technetium - 99m and positron emitters

Answer 54

Because it is easily incorporated into drugs. It is also easily prepared from Mo - 99. It also doesn't change chemistry when it decays, and emits only high penetrating gamma rays, not any harmful alpha and beta particles

Answer 55

It uses a radionuclide that emits positrons. Inside the body, the positron reacts with electrons, producing two high energy gamma rays, which are detected outside the body The most common PET imaging agent is fludeoxyglucose (FDG), in which an oxygen atom of glucose is replaced by a fluorine - 18 FDG is used to observe parts of the body that use high levels of glucose, such as tumours, and the brain

Answer 56

s^-1 per second

Nuclear Chemistry Flashcards

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