05 - Radioactive properties

Question 1

Z

A
Element
Z

Answer 1

number of protons

= atomic number

Question 2

N

Answer 2

number of neutrons

Question 3

A

Answer 3

= protons + neutrons

= mass number

Question 4

isotope

Answer 4

same proton number

various neutron number
various number of mass

Question 5

beta- decay

Answer 5

neutron to
–> Proton, Negraton and antineutrino

daughter: Z+1, N-1, Z+1+N-1=A
e. g. 87Rb -> 87Sr

Question 6

beta+ decay

positron decay

Answer 6

Proton to
–> Neutron, Positron, Neutrino

daughter: Z-1, N+1, Z-1+N+1 =A
e. g. 18F -> 18O

Question 7

e- capture decay

Answer 7

Electron -> split proton
–> Neutron & Neutrino

daughter: Z-1, N+1, Z-1+N+1
e. g. 40K -> 40Ar

Question 8

alpha decay

Answer 8

2 Protons + 2 Neutrons

• -> charge 2+
• -> 4He-nucleus

daughter: Z-2, N-2, Z-2+N-2=A-4
e. g. 238U -> 234Th

Question 9

Decay chains

Answer 9

U and Th isotops can’t reach stable via a single decay

Question 10

!!
Dacay of unstable isotopes
!!
(formula)

Answer 10

N = N0 * e^( -lambda * t )

N = numer of remaining mother isotopes at time t

N0 = number of mother isotopes at time t=0

lambda = isotope specific decay constant

Question 11

half life time

for daugther isotopes

Answer 11

D* = N0 * /1-e^(-lambda*t)

t = 1/lambda * ln( D* / N + 1 )

Question 12

depth of penetration
of
radiation

Answer 12

extremely small
for apha & beta particles

thats why gamma ray is used

Question 13

which radioactive decays produse measureable gamma rays?

Answer 13

uranium-radium series
(4.4 * 10^9 years half life)

Thorium series (1.4 * 10^9 years half life)

Potassium K40 (1.3 * 10^9 years half life)

Question 14

characteristic peak

Potassium

Answer 14

1.46 MeV

Question 15

characteristic peak

Thorium

Answer 15

2.62 MeV

Question 16

characteristic peak

Uranium

Answer 16

1.76 MeV

Question 17

major occurence

Potassium

Answer 17

micas
feldspars (K)
micaceous clays (illite)
radioactive evaporates

Question 18

major occurence

Thorium

Answer 18

shales

heavy minerals

Question 19

major occurence

Uranium

Answer 19

Phoshates

organic matter

Question 20

Potassium

sources

Answer 20

• clay minerals: illite high, Kaolinite low
• rock-forming minerals: feldspars, mica
• evaporates: sylvite

Question 21

Thorium

sources

Answer 21

• acid & intermediate rocks
• stable (ddon’t go in solution)
• with detrital sediments, never with pure chemical sediments (carbonates,aragonite)
• clay indicator
• in marine element

Question 22

Uranium

sources

Answer 22

• acid & intermediate rocks
• result of weathering & alteration
• unstable salt
• in detrial & chemical sediments
• reducing,anoxic

Question 23

K U Th in

Carbonates

Answer 23

all low

oxidizing env.

Question 24

K U Th in

Stylolites, Phosphates

Answer 24

K, Th low
U high

reducing env.

Question 25

K U Th in Clay, marl

Answer 25

K, Th high | U low

Question 26

K U Th in Algal, glauconite

Answer 26

K (U) high | Th low

Question 27

K U Th in Igneous rocks

Answer 27

K, Th, U | increasing from mafic (basic) to felsic ( acid) rocks

Question 28

K U Th in sedimentary rocks

Answer 28

K, Th, U | increase with clay content

Question 29

K U Th in Carbonates

Answer 29

Th, K near 0, when pure K,(U) algal origin or glauconite U = 0 -> oxidizing env. U variable reducing env or stylolithes Th,K,U -> clay content - marl

Question 30

Gammalog

Answer 30

lithological profiling - > sediments: clean sand,carbonates and shaly and fining/coarening upwards - >correlations

Question 31

Gamma Ray Index I_GR

Answer 31

determine clay content I_GR = ( GR -GR(noshale) ) / ( GR(shale) - GR(noshale) ) ``` I_GR = 0 =clean rocks I_GR = 1 = shale ```

Question 32

Th/K ratio indicates?

Answer 32

various clay minerals

Question 33

Th/U ratio indicates?

Answer 33

organic carbon content >7 continental oxidizing <7 marine, grey-green shales <2 black shale, phosphate

Question 34

Radioactive Heat Generation

Answer 34

Mean heat flow at the surface: 65 mW/m² Mean heat flow between mantle and continental crust: 20 mW/m² Difference due to radioactive heat generation: 45 mW/m²

Question 35

Total heat production Heat generation A

Answer 35

A = 0.01 rho (9.52 U + 2.56 Th + 3.48 K)