This document discusses actinometry, which is a technique used to determine the number of photons in a beam of light or absorbed per unit time. It defines quantum yield as the number of moles of product formed per Einstein of light absorbed. An actinometer is a chemical system or physical device that determines the rate of photon absorption. There are two main types of actinometers - physical detectors such as thermopiles and photocells, and chemical actinometers which measure radiation intensity through chemical reaction yields, such as the uranyl oxalate actinometer discussed in the document.

1. Actinometry

2. Presentation Outline
Quantum Yield
Actinometer
History
Physical Detectors (Physical
Actinometer)
Chemical Actinometer
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Example (Uranyl oxalate
Actinometer)

3.  The quantum yield (ϕ) is defined as the number of
moles of product formed per Einstein (Numbers of
quanta) of light absorbed by the photosensitive agent.
 Its value can be unity, less than unity or may be greater
than it.

4. Countingphoton is inefficient, there is a
tendencyto miss a lot of photonsduring
counting .

5.  An actinometer is a chemical system or physical device
which determines the number of photons in a beam of
light or absorbed per unit time.
 This phenomenon is known as Actinometery.

6. The first actinometer was invented by John
Herschel in 1825 for the investigation of solar
radiation in relation to meteorology
research, based on temperature changes induced
by absorption of light by a copper sulfate
solution.

7.  It works based on the principle that “the rate of
photolytic conversion of molecules within an
actinometer cell is equal to the rate of absorption of
photons in the actinometer”.

8. Actinometer are of two type. It can be a
1. Physical Detectors
2. Chemical Actinometer
(Chemical Actinometer is also known as dosimeter.)

9. Physical detector may be a
 Thermophile
 Photocell
 Photomultiplier

10.  It is an electronic device that converts
thermal energy into electrical energy.
 It is composed of several
thermocouples connected usually in
series or, less commonly, in parallel.
 Thermophiles are thermocouples
connected in series and generate e.m.f
on heating.

13.  A device that detects light and converts light energy directly into electrical
energy.
 A photocell consist of a Photosensitive cathode and collector anode
enclosed in an evacuated bulb.
 Light quanta of energy greater than the threshold value of metal cause
ejection of electron which are collected by anode and current flow in
circuit.
 The intensity of current generated will be linearly proportional to the
incident light intensity.

15.  Although these instruments, based on photo physics,
are
 Accurate
 user-friendly
 mostly cheap
But still their direct application in photochemistry is very
limited compared with chemical actinometer.

16.  Chemical Actinometery involves measuring the
radiation intensity through the yield of the chemical
reaction.
 There are several types of chemical actinometer such
as
 Uranyl Oxalate Actinometer
 Ferrioxalate actinometer
 Reinecke’s salt Actinometer

17.  Uranyl oxalate actinometer consist of liquid solution
of oxalic acid containing uranyl sulfate.
 Light in the wavelength range of ultraviolet
region decomposes the oxalic acid.
 Decomposition occur (through a complex region
involve initial absorption of light energy by uranyl
ion) into mixture of Carbon dioxide, carbon
monoxide and water molecules.

18.  A standard solution is generally irradiated with light of the proper
wavelength and of known intensity, and the quantity of oxalic acid
decomposed is accurately measured by titration with potassium
permanganate.
 The quantity of oxalic acid decomposed and the quantity of light energy
absorbed can then be used as a scale from which to predict either quantity
when the other is known or measured.
 UO2
+2 + hv ( UO2
+2 )
 ( UO2
+2 ) + C2H2O4 UO2
+2 + H2O + CO2 +CO

19. Thank
you
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