Radiochemistry

Question 1

What causes radioactivity?

Answer 1

Spontaneous nuclear disintegration
Unstable isotopes

Question 2

What does nuclear stability depend on?

Answer 2

*ratio neutrinos to protons
*gives rise to spontaneous decay (radioactivity) with particle emission

Question 3

What are a (alpha) particles?

Answer 3

*nucleus of helium
*emitted by elements MW>140
*2 neutrons and 2 protons
*heavy
*slow moving

Question 4

What is the most commonly used radioisotopes in biochem?

Answer 4

b emitters

Question 5

What two forms do B emitters exist in?

Answer 5

*electron - b-
*positron- b+

Question 6

During decay a B particle is emitted- what other particle is emitted?

Answer 6

*antineutrino- almost massless particle- carries away from energy from decay

Question 7

How can anti neutrinos be stopped?

Answer 7

Small atomic number materials eg plastics

Question 8

What are y emitters (gamma)?

Answer 8

A photon of electromagnetic radiation
Usually secondary process after B emission

Question 9

What kinetics order is spontaneous disintegration?

Answer 9

First order

Question 10

What is the equation for radioactive disintegration? (Half life)

Answer 10

=0.693/y

Question 11

What are the units of radioactivity?

Answer 11

*Ci (curie)- large- usually use millicuries mCi and microcuries (uCi)
*Bq (becquerel) - small

Question 12

What are the units of radiation?

Answer 12

*roentgen (coulomb/kg)
*rad (gray)
*rem (sievert)

Question 13

What is the gray (rad) unit used for?

Answer 13

Amount of energy transferred by radiation to an object

Question 14

What two methods are used to detect radioactivity?

Answer 14

*liquid scintillation counter- best counting efficiency
*greiger-muller tube -high energy B emitters (Small ones struggle to enter tube)- counting efficiency not as good as LSC
(Both used for B emitters only)

Question 15

What does a recording instrument register?

Answer 15

Counters per min

Question 16

What is the equation for instrument efficiency?

Answer 16

%efficiency= observed cpm - background cpm / actual disintegration per min x 100

Question 17

What three components are used in liquid scintillation?

Answer 17

*radioactive material
*organic solvent
*one or more organic FLUORESCENT SUBSTANCES

Question 18

How is the scintillation counter process carried out?

Answer 18

B particle collides with solvent particle
B + S > B (less energy) + S
S reacted with primary Fluor F1
S* + F1 > S + F1*
F1 molecules emit photons at higher wavelength- often not enough so secondary Fluor added
F1* + F2 > F1 + F2*
F2* > F2 + hv2 (light)

Question 19

What is an example of fluors?

Answer 19

*PPO
*POPOP

Question 20

What are the components of a scintillator counter?

Answer 20

*PMT x2- photomultiplier tubes- two used due to tube damage from thermal noise
*pulse summation
*coincidence gate- pick up info from two PMT’s
*pulse height analyser- allows counting of pulses with DEFINED energy limits
*scaler
*printer

Question 21

What does channel 1 of scintillator detect?

Answer 21

All 3H

Question 22

What does channel 2 of scintillator detect?

Answer 22

14C

Question 23

What is the problem with quenching during scintillation?

Answer 23

*causes underestimation of activity of sample
*variable quenching causes similar sample to be counted differently

Question 24

What is chemical quenching?

Answer 24

Chemicals that interfere with energy transfer to fluors- capturing it and releasing it as heat

Question 25

What is colour quenching?

Answer 25

Unwanted dyes absorb in violet blue region act as filter- reducing intensity of photon

Question 26

How can quenching be corrected?

Answer 26

*use of internal standard
*channels ratio
*external standardisation

Question 27

What is an example of a quenching agent?

Answer 27

Chloroform