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Introduction

Astronomy is all about the observation and

movement of heavenly bodies objects like

Sun, Moon, planets, comets, asteroids, and

stars. Astrophysics studies the physical pro- perties of these objects: how they evolve, and how they form. It emerged as a science in the late nineteenth century.

Nuclear astrophysics is the marriage of nu

clear physics, a laboratory science concerned with the infinitely small, and astrophysics, the science of what is far away and infini tely large. It sets out to explain the origin, evolution and abundance of all the chemi cal elements in the Universe. It was born in 1938 with the work of physicist Hans

Bethe on the nuclear reactions occurring at

the core of stars; reactions that produce the incredibly powerful energy that keeps stars shining for billions of years.

Nuclear astrophysics is still booming as a

science.The matter all around us, and from which we are made, is made up of 92 chemical elements that can be found even in the

deepest confines of the Universe. Nuclear astrophysics explains the origin of these che mical elements by nucleosynthesis, which is the synthesis of atomic nuclei in different astrophysical environments such as the core of stars.

Nuclear astrophysics provides answers to

fundamental questions, like: • How can our Sun and the stars keep shining for billions of years? • What is the origin of elements essential to life, like carbon, oxygen, nitrogen and iron? • How do the nuclei formed by nucleosynthe- sis get dispersed into space? • How are the heaviest chemical elements formed, like gold, platinum and lead?

The history of matter: a timeline

© F.Legrand/CEA

group 1 1 4 2 5 3 6 72

375914

1116
4813
61015

121718

La-Lu Ac- Lr TaH LiBe Na

KCaScTi

LaV CeCr PrMn NdFe PmCo SmNi EuCu GdZn TbGa DyGe HoAs ErSe TmBr YbKr

LuRbSrYZr

AcNb ThMo PaTc URu NpRh PuPd AmAg CmCd BkIn CfSn EsSb FmTe MdI NoXe

LrCsBaHfWReOsIrPtAuHgTiPbBiPoAtRnHe

BCNOFNe

AlSiPSClAr

FrRaRfDbSgBhHsMtDsRgCnUutFlUupLvUusUuoMg

1,007 9 6.94

19.0122

22.989

8

39.098

340.07844.955947.867

138.905

550.9415

140.11

651.9961

140.907

754.9380

144.24

255.845

[145 ]58.9332 150.3

658.6934

151.96

463.546

157.2

565.38

158.925

369.723

162.50

072.64

164.930

374.9216

167.25

978.96

168.934

279.904

173.05

483.798

174.966

8

85.467

887.6288,905891,224

[227 ]92.9064

232.038

195.96

231.035

9[98]

238.028

9101.07

[237 ]102,9055 [244 ]106.42 [243 ]107.8682 [247 ]112.411 [247 ]114.818 [251 ]118.710 [252 ]121.760 [257 ]127.60 [258 ]126.9045 [259 ]131.293 [262

132.905

10.81

112.010714.006715.999418.998420.1797

26.981

528.085530.973832.06535.45339.948

[223 hyd rogen lithiumberyllium sodium potassiumcalciumscandiumtitanium lanthanumvanadium ceriumchromium praseodymium manganese neodymeiron prométhiumcobalt samariumnickel europiumcopper ga doliniumzinc terbiumgallium dys prosiumgermanium holmiumarsenic er biumselenium thu li umbromine yt terbiumkrypton actiniumniobium th orium molybdenum protactinium technetium uraniumruthenium neptu niumrhodium plutoniumpalladium americiumsilver curiumcadmium ber kéliumindium californiumTin einsteiniumantimony fermiumtellurium mendelevium io din e nob eliumxenon boroncarbonnitrogenoxygenfluorineneon franciumradium magnésium 26
Fe 55.84
5Iron Sy mbo l (in white and green : no stable isotope)

Atomic m

ass, based on 12

CNameAtomic

number alkali metals alkaline earth metals transition metals other metals metalloids other nonmetals halogens noble gases lanthanides actinides

Periodic table of chemical elements

Lanthanides

Actinides

Its light-radiating

outer shell.The many isotopes of a particular chemical element are nuclei variants that differ only in number of neutrons. For example, carbon-12 (6 protons and

6 neutrons) and carbon-14

(6 protons and 8 neutrons) are two isotopes of carbon. €8

It took until the early twentieth century and the

development of nuclear physics for astrophysi- cists, who were primarily looking to understand the mechanism that keeps a star shining, to be able to answer the big question: where do the nuclear reactions that produce nuclei happen?

A star is a sphere of hot gas held together by

gravitational attraction, which tends to pull its particles as closely as possible together. The star does not collapse under its own gravity, as its internal gas pressure counteracts the gravitatio nal contraction. For this balance to stay stable, the internal pressure has to increase steadily along a gradient with depth into the star, such that each shell of inward-pressing material is counterbalanced on either side between a more compressive and a less compressive shell. As a compressed gas releases heat, the stellar material gets hotter with increasing depth and with increasing pressure. Working in from a few thousand degrees at the outer surface, the temperature can, depending on the mass of the star, reach tens or even hundreds of mil lions of degrees in its central-core regions. This temperature gradient between inner core and outer surface generates an energy transfer that takes excess thermal energy from the hot inner region and gives it out to the cooler outer region.

At the star's surface, this energy flux escapes

before diluting as radiation this makes the star shine, and it can only keep shining if there is an internal source of energy to compensate for the radiation emitted at the surface.quotesdbs_dbs42.pdfusesText_42

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