Exam 3

Question 1

What is the decay valley?

Answer 1

Where unstable isotopes decay into a more stable valley

Question 2

What is beta decay?

Answer 2

ejection of a beta particle and neutron is turned into proton

Question 3

What is positron decay?

Answer 3

ejection of a positron and proton is turned into a neutron

Question 4

What is electron capture?

Answer 4

an electron is capture with a proton and converted into a neutron

Question 5

What is an alpha decay?

Answer 5

ejected of 2N2P (4He nucleus)

Question 6

What is fission?

Answer 6

nucleus spiles into 2 fragments and free neutrons (232Th, 235 U, 238U)

Question 7

What is gamma emission?

Answer 7

release of excess energy of decay products to get to ground state

Question 8

What is neutron capture?

Answer 8

neutron brought into nucleus

Question 9

What is the movement of beta decay?

Answer 9

up and left

Question 10

what is the movement of positron decay/electron capture?

Answer 10

down and right

Question 11

what is the movement of alpha decay?

Answer 11

2 down and 2 left

Question 12

what is the movement of neutron capture?

Answer 12

right

Question 13

What is the process of a star?

Answer 13

Fusion, neutron capture, and beta decay

Question 14

What happens with a super nova explosion?

Answer 14

neutrons are released (rapid process)

Question 15

What happens to abudance as you go to heavier elementrs?

Answer 15

decrease

Question 16

Why are odd elements in less abundance?

Answer 16

physics of nucleus leads to less stability

Question 17

How many radioactive elements were produced by nucleosynthesis?

Answer 17

10

Question 18

What is the radioactive decay equation?

Answer 18

N = Noe(-lambda*t)

Question 19

What is the daughter equation?

Answer 19

D = Do + N(e(lamda*t) -1)

Question 20

Why can the radioactive decay equation be a problem?

Answer 20

two unknowns: t and Do

Question 21

What do we do to be able to use the radioactive decay equation?

Answer 21

measure 2 minerals & normalize use slope = (e(lambda*t -1) to find time (assume they evolved from the same magma at the same time; isochron) & use intercept to find where the magma came from

Question 22

What is the isochron equation?

Question 23

Why do we normalize?

Answer 23

bc diff minerals incorp diff amnts of an element

Question 24

How does a whole rock isochron work?

Answer 24

even if theres an open system maybe a fist sized sample wont be

Question 25

What is better Rb-Sr or K-Ar?

Answer 25

K-Ar

Question 26

Why can we sometimes assume intial Ar is negligible?

Answer 26

Ar is a noble gas and is excluded from mineral

Question 27

How do we measure Ar?

Answer 27

gas source mass spec

Question 28

What causes Ar to release from minerals?

Answer 28

heating 200-700C

Question 29

How do we do Ar-Ar age dating?

Answer 29

send to nuclear reactor, send standards, zap w/laser, measure 40Ar, 39Ar, 36Ar

Question 30

Why is zircon good for age dating?

Answer 30

its U rich and Pb poor

Question 31

What is the trend for Pb loss?

Answer 31

decreases along a straight like towards the origin at time of metamorphism

Question 32

When would He accumulate in a zircon?

Answer 32

when its lower than the closure temp

Question 33

What is the closure temp of He in zircon?

Answer 33

150-200C

Question 34

What is the closure temp of He in apatite?

Answer 34

50-100C

Question 35

Why is the He closure temp diff for diff minerals?

Answer 35

radiation damage

Question 36

What does U, Th do as it decays?

Answer 36

gives of He

Question 37

Is Sm more compatible in the mantle or the crust?

Answer 37

Mantle

Question 38

Is Nd more compatible in the mantle or the crust?

Answer 38

Crust

Question 39

Is Rb more compatible in the mantle or the crust?

Answer 39

crust

Question 40

How do we do Nd geochronology?

Answer 40

Measure Nd/Nd and Sm/Nd to project back in time until we intersect the mantle (only on volcanic rock)

Question 41

Does Re go in melt or stay behind?

Answer 41

goes in melt

Question 42

Does osmium go in melt or stay behind?

Answer 42

stays behind

Question 43

What is a good number for crust Re/Os ratio?

Answer 43

19.3

Question 44

What is Os a trace for?

Answer 44

subducted/recycled crust

Question 45

How big is zircons Lu/Hf ratio?

Answer 45

small, Hf loves zircon, locks in Hf at time of formation

Question 46

How are the radiogenic isotope trends for the crust?

Answer 46

hight Sr, Very high Re, low Nd and low Hf

Question 47

How do recent volcanic rocks in the east african rift compare to rocks outside the rift?

Answer 47

recent volcanics are close to mantle, old Rb-rich rocks outside have much higher ratios

Question 48

What do carbonate rocks record?

Answer 48

the ocean 87Sr/86Sr ratios from their time of formation (seds would have higher Rb)

Question 49

What is the Sr value for the mantle?

Answer 49

0.705

Question 50

What would suggest 2 component mixing is valid?

Answer 50

a straight line on a plot of R vs. 1/C

Question 51

What can Sr isotopes in seawater tell us?

Answer 51

amnt of continent weathering, stratigraphic indicators, hot water circ

Question 52

How have Sr ratios changes from the cambrian to last 30Ma?

Answer 52

High in Cambrian from weathering, Mesozoic lower from less weathering & hot water circ, current rising from collision of India into Asia creating the Himalayas

Question 53

How can enamel and bone tell us about humans?

Answer 53

enamel grows & doesnt change. but bones can tell us change

Question 54

WHat is U-series/Th-series?

Answer 54

each decay chain is fed by a long-lived parent

Question 55

What does everything decay to?

Answer 55

206Pb

Question 56

What do nuclides depend on?

Answer 56

its decay and decay of the preceding that evolves toward a balance

Question 57

What happens if there is a short half life?

Answer 57

there is fast decay meaning we will reach equili. quickly

Question 58

What is a geochron?

Answer 58

evolution of a system back towards equili.

Question 59

How does the activity ratio evolve for 231Pa/235U?

Answer 59

goes towards 1

Question 60

how much does disequil. decrease by for every 1/2 life of daughter element?

Answer 60

by a factor of 2

Question 61

what is the time scale of nuclide approaching equili.

Answer 61

proportional to 1/2 life

Question 62

Why is U high in seawater?

Answer 62

its soluble

Question 63

how does seawater get a U value of 1?

Answer 63

alpha decay of 238U leading to 234 being ejected into the water

Question 64

What does 230Th/238U & 234U/238U activity evolve to?

Answer 64

Th/U up to 1, U/U down to 1 (inital excess U)

Question 65

What can Pb decay tell us about?

Answer 65

age & sedimentation rate

Question 66

What can U/Th-series disequili. tell us about igneous processes?

Answer 66

time scales of magmatic processes and processes in the source zone

Question 67

What instrument do we use for 210Pb?

Answer 67

Geiger counter

Question 68

What are the 2 most abundant elements in the atmos.?

Answer 68

N and O

Question 69

What does 14N + n turn into?

Answer 69

14C + p

Question 70

What creates 10B?

Answer 70

solar proton + N/O

Question 71

What form from collision w/Ar?

Answer 71

32Si, 35S, 36C (longest 1/2 life), 39Ar

Question 72

How does radiocarbon dating work?

Answer 72

plants take C from atmos., decay, analyze wood

Question 73

Why has initial 14C changes over time?

Answer 73

industrialization

Question 74

How is 14C changing over time?

Answer 74

decreasing