radioactivedecay berçincemremurat z
fundamental particles • electron • proton • neutron ?
leptons • one of the families of fundamental particles • first generation leptons:electronsand neutrinos; • their anti-particles:positrons and antineutrinos • found in normal matter • are not affected by thestrong nuclear force
leptons • there are second and third generations, which are extremely short lived, so not observed in daily life
hadrons • not fundamental • made up of even smallerparticles, quarks • 3 different generations of quarks
hadrons • the combination of these 6 types of quarks make up hundreds of hadrons • 1st generation quarks (up/down)found in the proton and the neutron, the nucleons of normal matter • other quarks are found in experiments, not in daily life
é é é é é é 1st generation quarks updowndown upupdown proton neutron 2/3+2/3 -1/3 = +1 -1/3-1/3 +2/3 = 0
binding the nucleus the nucleus of helium contains two protons which are both positively charged. they should repel each other but they do not. why? + +
the strong force • an attractive force • has an effect over a very short range(10-15 m, about the size of the nucleus) • leptons don’t feel this force, but particles in the quark family do. + + strongnuclear force
bdecay • occurs when a nucleus has either too many protons or neutrons. one of the neutron or protons is transformed to the other.
what causesbdecay? it cannot be the strong nuclear force because this has no effect on electrons and the beta particle is an electron. neither, as physicists know, can it be the electromagnetic force. in order to explain it, we need to identify a new force called the weak force. the weak force is very short range and, as the name implies, it is not at all strong. its effects are felt by all fundamental particles - quarks and leptons
- b-decay • the atom has too many neutrons to be stable. • does it just kick out one of the neutrons? • but the neutrons arestuck too tightly,it can’t do that • what it can do is...convert the neutroninto a proton!
- b-decay • a neutron decays intoa proton, an electron (b- particle), and an antineutrino 1 = 1 + 0 0 = 1 - 1
how does a neutron turn into a proton? one of the down quarks changeinto an up quark. é é é proton neutron
neutrinos • same exact beta decay produced an electron with variable energies. • Li-8 becoming Be-8 • Each atom of Li-8 produces an electron • the theory says all should have the same energy. • this was not the case. • the electrons were coming out with any old value they pleased up to a maximun value, characteristic of each specific decay. • Pauli suggested the energy was being split randomly between two particles - the electron and an unknown light particle that was escaping detection. Enrico Fermi suggested the name "neutrino," which was Italian for "little neutral one."
neutrinos • discoveredbecause momentum and charge didn't seem to be conserved in nuclear reactions • neutrinos have some mass, maybe about one ten-millionth the mass of an electron. Wolfgang Pauli suggested the existence of a neutrino.
- ¾ ¾ ® + + A A 0 X Y ν b Z Z+1 e -1 b-decay neutron -1, proton +1,so no change in mass number - ¾ ¾ ® + + 14 14 0 C N ν b 6 7 e -1 proton +1,so atomic number increases by one
+ b+decay • a proton decays intoa neutron, a positron (b+ particle), and a neutrino 1 = 1 + 0 1 = 0 + 1
+ ¾ ¾ ® + + A A 0 X Y ν b Z Z-1 e 1 b+decay neutron +1, proton -1,so no change in mass number + ¾ ¾ ® + + 18 18 0 F O ν b 9 8 e 1 proton -1,so atomic number decreases by one
bdecay • all reactions occur because in different regions of the Chart of the Nuclides, one or the other will move the product closer to the region of stability • these particular reactions take place because conservation laws are obeyed
conservation oflepton number leptonnumber0 leptonnumber0 leptonnumber1 leptonnumber-1 0 = 0 + 1 - 1 the leptons emitted in beta decay did not exist in the nucleus before the decay–they are created at the instant of the decay.
mass/energy conservation in bdecay • the mass of an electron is very small • neutrons are a little heavierthan protons • keeping the same mass number doesn't necessarily mean you end up with exactly the same mass • but we have just converted a neutron to a proton- how does it happen?
mass/energy conservation in bdecay we haven’t talked about relativity, but last year we studied the famous equation of Einstein: which means that mass (m) and energy (E) are really the same thing, and that you can convert one into the other using the speed of light. • if you add up all the mass and energy that's around before and after a nuclear reaction, you'll find that the totals come out exactly the same. E=mc2
mass/energy conservation in bdecay let’s take this as an example. the proton has slightly less mass than the neutron. the mass of the electron makes up for this somewhat, but if you do the math, you'll see that there's still some mass "missing" from the right side of the reaction. energy takes up the slack: the electron comes out moving very fast, i.e., with lots of kinetic energy.
mass/energy conservation in bdecay in other reactions, the "leftover" energy sometimes shows itself in different ways. for example, the nucleus that comes out is sometimes in an excited state--the remaining protons and neutrons have more energy than usual. The atom eventually gets rid of this extra energy by giving off a gamma ray.
spontaneity ofb decay beta decay satisfies the minimum energy condition because the nucleus tends to give off energy after becoming more stable. beta decay also satisfies the maximum randomness condition because after decay, a beta particle and an anti/neutrino is given out, so the number of particles, therefore possible micro states increase. satisfying both of these tendencies, it’s possible to conclude that beta decay is spontaneous.
uses of b decay • carbon dating. carbon-14 decays by emitting beta particles. • beta particles are used for radiotheraphy
electron capture decay Electron capture is not like any other decay – alpha or beta, All other decays shoot something out of the nucleus. In electron capture, something ENTERS the nucleus. • An electron from the closest energy level falls into the nucleus, which causes a proton to become a neutron. • A neutrino is emitted from the nucleus. • Another electron falls into the empty energy level and so on causing a cascade of electrons falling. The atomic number goes DOWN by one and mass number remains unchanged.
electron capture decay • unstable nuclei capture electrons from the K energy level. • according to theconversion, while a new nucleus is being formed, the atom emits photons.
electron capture decay K L M N 19P21N 18P22N 1 8 8 8 2 2 8 7 1 7 1s2 2s22p6 3s23p6 1s2 2s22p6 3s23p6 4s1