Lecture 10 Chemistry

Question 1

Threshold E to produce e transitions in water

Answer 1

7.4 ev

Question 2

Depending on the amount of E transferred to the e, the molecule can undergo

Answer 2

ionization (E threshold in water 13eV, excitation (7.4 ev), thermal transfer (vibrational rotation)

Question 3

Average E loss and most probably E loss

Answer 3

E straggling

Question 4

E needed to break C=C

Answer 4

4.9 ev

Question 5

cell composition

Answer 5

70-85% H2O, 10-20% protein, 10% carbs, 2-3% lipids

Question 6

Initial physical event

Answer 6

transfer of 7-100 ev to cause ionizations or excitations in H2O molecule

Question 7

E of subexcitation e in H2O

Answer 7

<7.4 ev

Question 8

The time scale for physical stage

Answer 8

10^(-16)s

Question 9

Species produced at the physical stage of the interaction of particle in water

Answer 9

H2O* (excitation), H2O+ (ionization), e (E=7.4 ev)

Question 10

Prechemical stage

Answer 10

initial reactants produce radicals as they diffuse in medium.

Question 11

what is a radical

Answer 11

atom that contains an unpaired e and thus is very reactive (can be neutral or charged)

Question 12

what is a e aq

Answer 12

e captured by water through dipolar interactions, becoming solvated

Question 13

E needed to break O-H bond

Answer 13

5 ev

Question 14

Name radicals produced in water due to irradiation

Answer 14

H2O8=HO. (oxidizer)+ H., H2O+ = H+ + OH., H2O-= H. +OH-, ,and e aq from H2O

Question 15

what is oxidation

Answer 15

the loss of e. e transferred to an oxidizing agent which becomes reduced

Question 16

Time scale for prechemical stage

Answer 16

10^-15-10^-12 s

Question 17

Chemical stage time scale

Answer 17

10^-12s

Question 18

Characterize the chemical stage

Answer 18

the radicals and ions react with each other HO. +HO. = H2O2, HO. +e aq = OH-, HO. +H. = H2O , H+ + e aq=H. and etc. Most of the reactions remove the chemically reactive species

Question 19

Time when most of the radicals and ions diffuse that far that the further reaction is unlikely

Answer 19

10^-6. The chemical stage is over by this time. G value will not change after

Question 20

the formula for radical diffusion

Answer 20

D = distance^2/6 time

Question 21

Simulations of the track of charged particle is possible via

Answer 21

Monte Carlo method : generation of e, passage model. generations of reactive species, diffusion of species, recombination events.

Question 22

G value

Answer 22

Radiochemical yield: # of species produced/100 ev of E loss by charged particle and its secondaries when it stops in water.

Question 23

How different the species produced by a, b, e radiation in 10^-15s in track regions

Answer 23

they are the same H2O*, H2O+, e. The difference in the spatial E deposition patterns (track density)

Question 24

Limitation of Fricke dosimeter

Answer 24

stong LET dependence

Question 25

Fricke dosimeter characteristics

Answer 25

a most useful method to measure # of reactive species in solution; 1mM FeSO4 in 0.8M H2SO4: when irradiated Fe2+ oxidized to Fe3+ which has blue color (spectrophotometer measurement), D response linear up to 400 Gy and up to 700Gy

Question 26

How many Fe3+ are produced in Fricke dosimeter

Answer 26

G= 2G(H2O2)+3G(H.)+G(HO.) if O2 is present, otherwise: | G(H)+G(OH)+2G(H2O2)

Question 27

What is the use of a Fricke dosimeter?

Answer 27

to test scavengers and the effect of LET on E deposition as an effect on scavengerable species

Question 28

Direct effect of radiation

Answer 28

E deposited into a molecule (DNA): ionization, excitation leading to radicals formation inside the biomolecule. The dose-response relationship is linear

Question 29

Indirect action of radiation

Answer 29

ionization of the solvent molecules. Indirect actions are diffusion-limited and the dose-response rate can be complex.

Question 30

Primary species that are responsible for rad damage in DNA

Answer 30

HO.

Question 31

For high LET radiations

Answer 31

direct action is a predominant mechanism of DNA damage

Question 32

Repair processes of DNA damage

Answer 32

Recombination, restoration, repair

Question 33

Recombination of DNA

Answer 33

recombination: reaction of nearby radical with the DNA radical to regenerate the original DNA (<10^-11s);

Question 34

Restoration

Answer 34

restitution: chem restoration of DNA (no enzyme involved). Some intracellular agents can react with radicals

Question 35

The most important intracellular agent that reacts with radicals

Answer 35

gsh glutathione. It donates one H. to the DNA and restores it. <10^-3s

Question 36

Repair stage of DNA

Answer 36

cellular enzymes recognize damage and repair DNA within min and hours

Question 37

Scavengers

Answer 37

Chemicals that can react with reactive species like HO. can block indirect effects of radiation: can be helpful in estimating the relative contributions of direct and indirect effects; define chemistry, and they showed that 60-70% of all damages from low LET are caused by HO.

Question 38

name several scavenger reactants

Answer 38

N2O, O2, Acid