CHM2046 Ch21

what happens to atoms in nuclear reactions

they are typically converted to atoms of another element

what particles take part in nuclear reactions

protons, neutrons, and other nuclear particles are involved, electrons have a lesser role (unlike chemical reactions)

what are nuclear reactions accompanied by

relatively large changes and energy and measurable changes in mass

what does reaction rate of nuclear reaction depend on

the number of nuclei, not affected by temp, catalysts, or compounds

nuclide

a nucleus of a particular composition, different for each isotope

radioactive decay

when nuclides are unstable and spontaneously emit radiation

what are the 3 natural types of radioactive emission

alpha particles, beta particles, and gamma rays

positron emission

emission of a B+ particle from the nucleus, the antiparticle of the electron→ proton in nucleus is converted into a neutron and positron is emitted

electron capture

when nucleus interacts w an electron in a low atomic energy level, proton is transformed into a neutron

alpha decay

loss of an alpha particle from the nucleus

Beta - decay

a neutron is converted into a proton, which remains in the nucleus, and a B- particle

gamma emission

usually occurs together w other forms of radioactive decay, results in no change in either A or Z since gamma rays have no mass or charge

what determines the stability of a nuclide

the ratio of N/Z, # of N, # of Z, and total mass of the nuclide

all nuclides with what Z are unstable

Z > 83

elements with an even # of protons (Z) usually have a larger # of

stable nuclides

what leads to greater stability in nucleons

if the nucleons are paired by like spins in the nucleon energy levels

if N=Z then what is the atom

stable, for lower mass elements

what are the only stable nuclides that are N/Z <1

1 1 H, 3 2 He

Odd Z and N

unstable

exceptionally stable if N or Z are what

magic numbersw

what are the magic numbers

2, 8, 20, 28, 50, 82, 126

If A is close to periodic table mass, then the atom is

stable

If A> periodic table mass

B- decay

if A < periodic table mass then

positron or e- capture

ionization counter

detects radioactive emissions as they ionize a gas, produces free electrons and gaseous cations which produce an electric current

scintillation counter

detects radioactive emissions by their ability to excite atoms and cause them to emit light, photons produce electric current

what is SI unit of radioactivity

becquerel (Bq) defined as one disintegration per second (d/s)

rate of radioactive decay (A)

aka activity, proportional to # of nuceli present → number of nuclei divided by time

what order reaction does radioactive decay follow

first-order kinetics, K is called decay constant

what does radiocarbon dating measure

isotopes of Carbon-12 and carbon-14 in materials of biological origin

nuclear transmutation

the induced conversion of the nucleus of one element into the nucleus of another, achieved by high-energy bombardment of nuclei in a particle accelerator

linear accelerator

uses a series of tubes w alternating voltage, particle is accelerated from one tube to the next by repulsion

cyclotron accelerator

evacuated chamber, alternating voltage sources, proton, magnet, target

transuranium nuclides

atomic #s higher than uranium (92), scientists use accelerators to make these for medical application and studying matter

radioactive emissions collide w surrounding matter,

dislodging electrons and causing ionization, each such event producing a cation and free electron

the # of cation-electron pairs is directly related to

the energy of the incoming ionizing radiation

what does the damage incurred by ionizing radiation depend on

the type of radiation, its half life, and its biological behavior

Si unit for energy absorption

the gray, 1 Gy= 1 J absorbed per kg of body tissue

RBE

relative biological effectiveness factor, assess actual tissue damage by taking into account strength of radiation, exposure time, and type of tissue

penetrating power of radioactive emission is inversely related to

mass, charge, and energy of the emission

molecular interactions of radiation result in

free radicals, one or more unpaired e-

two models of radiation risk

linear response model- radiation effects accumulate over time regardless of dose\

s shaped response model- there is a threshold above which the effects are more significant

tracers

a small amount of radioactive isotope mixed w stable isotope will undergo the same chemical reactions and can act as a tracer on xrays

the mass of the nucleus is less than

the combined masses of its nucleons, lost mass is released as energy

nuclear binding energy

the energy required to break 1 mol of nuclei into individual nucleons

where does binding energy per nucleon peak at

elements w mass number A = 60, stability decreases after this number but increases up to it

fission

heavier nuclei can split into lighter ones by undergoing fission

fusion

lighter nuclei can combine to form a heavier nucleus in a process called fusion

fusion and fission both what

increase a nuclides binding energy per nucleon

what does fission release

energy and generates more high-energy neutrons and stimulate further fission

because it further advances fission, what is the process

self-sustaining chemical reaction, critical mass is required to achieve this