Lecture 9

Question 1

when we talk about nucleosynthesis we mean

Answer 1

the formation of the light elements

Question 2

the abundances of the light elements reflect the

Answer 2

primordial state of the universe

Question 3

the theory of primordial nucleosynthesis is able to

Answer 3

successfully predict these abundances over about nine orders of magnitude

strongest piece of evidence for hot big bang theory

Question 4

protons are lighter than

Answer 4

neutrons

Question 5

free neutrons decay into

Answer 5

protons with a half life of 610s

Question 6

neutrons bound into

Answer 6

stable isotopes of the light elements don’t decay

Question 7

neutrinos decouple from

Answer 7

the rest of the cosmic plasma at a temperature of about 10^10K

Question 8

the ratio between the number of neutrons and protons is

Answer 8

1 when kbT&raquo_space; difference in rest masses

Question 9

when kbT = 0.8MeV

Answer 9

neutrinos decouple and the CNB is formed

the reactions can no longer occur and neutrons freeze out

Question 10

free neutrons can still

Answer 10

decay

Question 11

R = Nn/Np =

Answer 11

1/5

Question 12

Deuterium can be formed via

Answer 12

p + n -> d + γ

Question 13

γ causes

Answer 13

photo-disintegration of the deuterium d

Question 14

the mass abundance ratio

Answer 14

Y4 = mass of 4He / total mass

Y4 = 2R/1+R

where R = Nn/Np

Question 15

Increasing the neutron half-life increases

Answer 15

Y4

fewer neutrons decayed = more neutrons available to form helium

Question 16

increasing Nv increases

Answer 16

Y4

relativistic energy density at nucleosynthesis is increased giving a higher value of R

Question 17

Increasing η increases

Answer 17

Y4

less high energy photons, decrease in deuterium

Question 18

Lower temperatures decreases

Answer 18

Y4

neutrinos fill up fermi level
fewer neutrons available