physics - chapter 14

nuclear reaction

the nucleus of an element is hit by another particle

if the nucleus changes…

it has been transmutated

what is conserved in a nuclear reaction?

energy + momentum

equation for rxn. energy

(inital - final) x c² = Q

+Q

exothermic, will proceed no matter what

-Q

endothermic, needs a certain amount of Ek

why are neutrons used?

very effective + lack charge

what happens after absoring a neutron

an element will split cleanly into 2, will also release neutrons

why are neutrons released during fission?

lower amounts of neutrons = more stability

nuclear reactors must be

self-sustaining + controlled

role of moderators?

slow down neutrons (ie. graphite, heavy water)

do escaped neutrons contribute to the rxn?

no

what happens if a fission rxn. doesn’t hit a critical mass

the rxn. will not proceed, too many neutrons lost

role of control rods

can be raised and lowered for fine tuning of n0, will absorb them

cons of nuclear energy

appropriate waste managment, accidental radiation

how do atomic bombs use fission?

uncontrolled

what is fusion?

lighter nuclei combining and releasing A LOT of energy

how can the energy be increased in fusion?

using heavier H (ie. deuterium, tritium)

are there fusion reactors?

no, only fusion bombs (thermonuclear bombs) so far

how can plasma be controlled?

by inserting charged particles and using a strong magnet

which type of radiation will affect the DNA level

every type

what is ionizing radiation?

radiation that ionizes the materials it passes through

source activity units

Ci - 3.7 × 10^10 disintegrations/second

source activity SI unit

Becquerel - 1 disintegration/second

absorbed dose unit

rad - 1.00 × 10^-2 J/kg

absorbed dose SI unit

Gray - 1J/Kg = 100 rads

why is radiation poisoning so harmful?

effects are accumulative

which rays are most damaging to humans?

alpha rays

effective dose formula

effective dose = dose x relative biological effectiveness

effective dose units

rem

effective dose SI unit

Sievert (Sv)

short 1000 rem dose mortality

100%

400 rem dose mortality

50%

how is radiation minimized in therapy?

the source is constantly rotated around the body to lower dose to normal cells

how are radioactive isotopes used?

in screening, isotopes are different n0 #s, non-invasive scans

how is radation used in PET/SPECT

3D imaging with gamma rays