Page 571 - Instrumentation Reference Book 3E

Materials analysis 553

Table 23.1 Exciting sources for X-ray fluorescence analysis
Isotopt. Hay-l{fe Principal photori eneFgies [lie L:i Eniissioiz
([YO)
433 yr 11.9-22.3 -40
59.5 35.3
453 d 22.1. 25.0 102.3
2.63-3.80 -10
88.0 3.6
j7c0 170.5 d 6.40. 7.06 -55
14.4 9.4
122.0 85.2
136.5 11.1
2.7 yr 5.89. 6.49 -28
241.5d 41.3, 47.3 -110
69.7 2.6
97.4 3c
103.2 20
60.0 d 17.4, 3 1.1 138
35.5 7
21.3 yr 9.42-1 6.4 -2 1
46.5 -4
+ Bremsstrahlung to 1.16 MeV
14'prn 2.623 yr Characteristic X-rays of target -0.4
+ target +Bremsstrahlung to 225 keV
23XPU S7.75yr 1 1.6-2 1.7 -13
lrjmTe 119.7 d 27.4, 31.1 -50
159.0 83.5
128d 52.0. 59.7 -5
84.3 3.4
+ Bremsstrahlung to 968 keV
Tritium ('H) 12.35yr
+ Ti target 4.51. 4.93 -10-2
+ Bremsstrahlung to 18.6 keV
+ Zr target 1.79-2.5 -10-2
+ Bremsstrahlung to 18.6 keV

systems which can operate for limited periods at for coal ash analysis, lead in paint, and other non-
liquid-nitrogen temperatures, but as long as they specific elemental analysis.
remain in a vacuum enclosure they can be
allowed to rise to room temperature without 23.2.3 Moisture measurement: by neutrons
damage to the detector, as would occur with the
earlier Ge (Ei) detector, where the lithium would If a beam of fast neutrons is passed through a
diffuse out of the crystal at ambient temperature. substance any hydrogen in the sample will cause
As Si (La) detectors are really only useful for X- the fast neutrons to be slowed down to thermal
rays up to about 30keV, the introduction of the energies, and these slow neutrons can be detected
Ge (HP) detector alllows X-ray non-dispersive by means of a BF3- or 3He-filled gas proportional
fluorescence analysis to be used for higher ener- counter system. As the major amount of hydro-
gies in non-laboratory conditions. gen present in most material is due to water con-
In the early 1980s with the availability of tent, and the slowing down is directly
microprocessors as well as semiconductor detec- proportional to the hydrogen density, this offers
tors such as HgI (mercuric iodide), it became a way of measuring the moisture content of a
possible to build small, lightweight non-disper- great number of materials. Some elements such
sive 'devices that could be operated on batteries as cadmium, boron, and the rare-earth elements
and itaken into the field. These devices were able chlorine and iron, however, can have an effect on
to operate at near-room temperature, due to the the measurement of water content since they have
incorporation of Peltier cooling circuitry in their high thermal-neutron capture probabilities.
designs. and made In-situ non-destructive elem- When these elements are present this method of
ental analysis possible. Typically their use has been moisture measurement has to be used with cau-
for positive material identification, especially spe- tion. On the other hand, it provides a means of
cialty metal alloys, but they have also been used analyzing substances for these elements, provided