Experimental Sensitivities in Neutron Activation and Gamma Spectrometry with a 150-kVAccelerator J e a n Perdijon
SAMES, 21 rue Jean Mack, Grenoble (Zskre), France This study is a report of the possibilities offered in neutron activation analysis using a 150-kV accelerator. To do this, it was necessary to establish a catalogue of gamma spectra given by main elements under defined irradiation and counting conditions. The photoelectric peaks recognized on these spectra were listed in increasing order of energy so as to facilitate qualitative analysis. Finally, the potential limit of detection achievable with each photopeak was calculated, and optimum limits of detection for the elements under study were deduced. ANALYSIS BY NEUTRON ACTIVATION has been made available to industrial laboratories by use of small neutron generators (1-4). These generators are equipped with a tritium target which is bombarded with accelerated deuterons under a voltage of about 150 kV. Although the neutron flux produced is much lower than that of a reactor, the energy of neutrons is about 14 MeV, and they are capable of producing reactions different from those possible with a reactor. Unfortunately, there is still very little data published on the use of fast neutrons (5-10); tabulated sensitivities available tend to be the result of theoretical calculations made on the basis of cross-sections which are rarely known precisely (11, 12). Because fast neutrons can be slowed by means of a hydrogenated material, the data of this study have been completed with some limits of detection obtained with thermalization; the comparison with limits of detection obtained with a 2-MV Van de Graaff accelerator (13) or with a reactor (14) is interesting. EXPERIMENTAL
Apparatus. The SAMES-built activation analysis installation consists of the following elements: (1) neutron generator (SAMES 150-kV electrostatic accelerator with tritium target for producing 14-MeV neutrons); (2) flux
(1) 0. U. Anders and D. W. Briden, ANAL.CHEM., 36,287 (1964). (2) W. W. Meinke and R. W. Shideler, Nucleonics, 20, No. 3 , 60 (1962). (3) J. Perdijon, Revue de Mktallurgie, 63,27 (1966).
(4) R. A. Stallwood, W. E. Mott, and D. T. Fanale, ANAL.CHEM., 35, 6 (1963). (5) G. Aude and J. Laverlochtre, Commissariat B 1’Energie Atomique, Rept. SAR-G-63-38 (1963). (6) A. Chatterjee, Nucleonics, 22, No. 8, 108 (1964). (7) A. Chatterjee, Zbid., 23, No. 8, 112 (1965). (8) Y . Kusaka, H. Tsuji, and T. Adachi, Bull. Chem. Soc. Japan, 36, 1259 (1963). (9) H. Neuert and H. Pollehn, EURATOM, Rept. EUR 122.e (1963). (10) J. E. Strain and W. J. Ross, Rept. ORNL 3672 (1965). (11) R. F. Coleman, Analyst, 86, 39 (1961). (12) A. S. Gillespie and W. W. Hill, Nucleonics, 19, No. 11, 170 (1961). (13) 0. U. Anders, Nucleonics, 18, No. 11, 178 (1960). (14) H. P. Yule, ANAL.CHEM., 37, 129 (1965).
448
e
ANALYTICAL CHEMISTRY
monitoring equipment, consisting of a plastic scintillator with a photomultiplier and a single channel analyzer, giving a proportional quantity to the integrated flux passing through the sample during irradiation; (3) irradiation station with two positions: one surrounded with cadmium and placed against the target (for 14-MeV neutron irradiation), and the other in the middle of a polyethylene block (for thermal neutron irradiation); (4) gamma spectrometer, consisting of a 3 in. X 3 in. cylindrical NaI(T1) crystal scintillator with a 54 AVP photomultiplier (the assembly was placed in the middle of a Cu-Cd lined lead castle, 5 cm thick and about one cubic meter in volume, and connected to a 400-channel pulseheight analyzer); the background of the spectrometer is shown in Figure 1 for different calibrations of the analyzer; the distance between the crystal and the axis of the sample container, which is parallel to the crystal, is 20 mm; ( 5 ) a rapid sample transfer system between the irradiating and counting stations (this is a pneumatic system, with a programmer for setting irradiation, decay, and counting times); (6) cylindrical polyethylene sample containers, obtained from Olympic Plastics Corporation, Los Angeles, Calif. (inside volume, 1.5 cm3). Standards. One standard was made for each element studied, and each contained 200 m g of the element. Comparison between spectra is thus facilitated. The matrixes employed were pure bodies, preferably nonoxidizing and nonhygroscopic. If the matrix was a composite one, then the other elements bound with the element under study were activated as little as possible, and the exact formula of the composition was required (compositions with C or H atoms were chosen, or with 0, Ca, or Pb as a last resort). Powder matrixes were generally preferred, dispersed throughout the paraffin wax which completely filled the sample container; this was the case for all the composite bodies. For some noncomposite bodies, the standard was in the form of a piece of wire or solid fragment, which was placed along the axis of the sample container. The nature of the matrix employed for each element is given in Table I. It should be observed that the polyethylene and the paraffin wax cause a weak blank spectrum, which is shown in Figure 2 for different irradiation, decay, and counting conditions. Irradiation, Decay and Counting. The standards were irradiated and counted under well defined time and flux conditions. Three series of spectra were obtained: (1) 14MeV neutron spectra, favoring short half lives (half lives < 5 min): irradiation time, 30 sec, decay time, 3 sec, counting time (real time), 30 sec; (2) 14-MeV neutron spectra, favoring long half lives (half lives > 5 min): irradiation time, 5 min, decay time, 10 min, counting time (live time), 5 min; (3) thermal neutron spectra: irradiation time, 10 min, decay time, 3 sec, counting time (live time), 10 min. Uniformity of irradiation was ensured by rotating the sample container around its axis, which was parallel to the target. The spectra thus obtained are in Table I. A catalogue of the spectra will be published by the European Atomic Energy Community.
RESULTS List of Photopeaks. Data are divided into three series, corresponding to the three series of spectra (Tables 11, 111, and IV). Photopeaks, which can be clearly recognized on spectra, are filed in growing order of energy inside these series, and in growing order of half lives for the same energy
Counts/Channel (400 c)
factor. Certain photopeaks are too close to each other t o be dissociated, and where a photopeak has to be indicated in a different order from that which has just been stated, then its energy is given in brackets. The ditto sign is employed when characteristics are absolutely identical. Information concerning the radioisotopes formed was extracted from tables of isotopes (15-17). The explanation of photopeaks found with certain spectra led us to several reactions, pointed out by asterisks in the tables, which are not generally indicated in tabulated cross-sections (6, 7, 9). (15) J. F. Stehn, Nucleonics, 18, No. 11, 186 (1960). (16) D. Strominger, J. M. Hollander, and G. T. Seaborg, Reu. Mod. Phys., 30, 585 (1958). (17) W. H. Sullivan, “Trilinear Chart of Nuclides,” USAEC (1957).
200
)Pi-
I
Annihilation
1 oc
.. *.
-*
.....
1%.
........................
-99--*
b
0
100
200 nochannel
300
400
Figure 1. Spectrometer background for different calibrations of analyzer NaI(TI) crvstal. 3 in. X 3 in.. with a 54 AVP ahotornultiolierin a 1 rns lead castle
VOL 39, NO. 4, APRIL 1967
449
Table I. List of Spectra Studied
Element (Weight = 200 mg) Ag
AI
As Au B Ba Br Ca Cd
c1 co
cr
cu F Fe Ga Ge He I In K Me Mn Mo N Na Nb Ni 0 P Pb Pd
Pt S Sb Se Si Sn Sr Ta Te Ti U V W Zn Zr
Matrix powder powder AsiOa wire powder BaCOs BrPb caC0I solid Clzca CoCOa CrzOa powder FzG powder solid powder HgO flakes solid KHCOa powder solid MoOa NH4HCOa NaHCOs powder powder COaCa (PO4hCa8 powder wire wire powder SbzOs powder powder powder SrCOa powder powder TiOz UOa V2O6 WOJ ZnO sponge
14-MeV Neutrons Thermal neutrons ti, = 10 min, tir = 5 min, ti, = 30 Sec, tdsc = 10 min, tot = 5 min tdec = 3s, tCt = 10 min tdeo = 3 s a , tot 3 30 Sec (real) (live) (live) Analyzer AnalyzerAnalyzer Relative Relative calibration Relative calibration calibration integrated flux integrated flux integrated flux (MeV) (MeV) (MeV) 18.7 14.4 19.7 17.7 18.2 18.7
0-1 0-1 0-8 0-1 0-1
18.6
&4
15.3
0-2
{E 20.5
279.4 283.0 268.9 534.1
0-1
270.3 228.1
0-1 0-1
243.9
0-1
0-2
230.2
0-2
0-4 0-2 0-4 0-1 0-1 0-1 0-4
237.2 257.8 322.4 506.9 256.3
0-4 0-1 0-1 0-1 0-2
245.0
0-4
291.2
0-4
340.7
0-1
281.7
0-1
249.1 389.0
0-1 0-1
393.4 307.3 420.6 229.2 362.2
0-1 0-2 0-1 0-2 0-2
0-1
{z 0-1
18.6
0-1
17.2 18.6 18.2
0-2 0-2 0-2
15.7
0-4
19.8 18.5 18.3 20.4
0-8 0-4 0-2 0-1
20.8 16.1 16.0 18.1
0-4 0-1 0-1 0-4
19.7
0-1
18.4 16.3
0-1 0-1
13.4
0-4
153.7 144.3 149.1
0-4 0-1 0-1
157.5 155.1 154.7 131.2 147.9
0-2 0-4 0-1 0-4 0-4
125.7 126.2 158.8 138.5 169.8 145.8 151.1 140.9 146.0
0-4 0-2 0-1
0-4
148.0
0-2
153.0 189.9
0-2 0-2
158.6 148.2 178.3
0-2 0-1 0-1
181.2
0-1
129.4 156.5 143.6 152.7 131.7
0-1 0-2 0-1 0-1 0-2
163.2
0-2
Table II. List of Photopeaks Obtained with Fast Neutronsa Energy (MeV)
Half life 3.5 min
0.061 0.075 0.088 0.093
39.2 sec 44.3 sec
0.105
5.5 sec
(0.130) 0.117 (0.134) 0.130 0.130 0.134
1.7min 1.7min
,*
40 Sec 1.7 min 1.7min
--
450
ANALYTlCAL CHEMISTRY
Radioisotope 1amSb
,*
"Mn 9
losmRh 18SmW 67Mn
Element Sb I.
Fe 1.
Pd
W
Fe
Reaction n, 2n
.
":? n, P*
n, 2n* n, P
Counts Per mg
} 380
Minimum detectable activity
Limit of detection ( p g )
\75
)18000 60 1000 60 See photopeak at 0.105 MeV See photopeak at 0.117 MeV (Continued)
Table 11. (Continued)
Energy (MeV) 0.139
Half life 48 sec
0.142 0.160 0.165 0.20 0.21 0.21
19.5 sec 17.5 sec 1.7 min 29.4 sec 4.8 sec 21 sec
0.28 0.32
7.4 sec 5.79 min 60 sec 37.6 sec
,
0.40 0.44
,
Element As Ge Ti Se W F Br Ag Pd Au V Mg Na Mo
1.06 1.28 1.37 1.44
66 sec 15.5 min 2.55 rnin 15.5 rnin 16.4 rnin 24.0 rnin 41.9 rnin 1.87 hr 3.10 hr 0.84 sec 60 sec 4.4 min 2.4 min 15.3 sec 66 sec 2.60 min 6.7 sec 16.5 rnin 60 sec 1.7 rnin 0.84 sec 6.56 rnin 29.4 sec 3.76 min
1.53 1.61 (1.65) 1.63 (1.65) 1.65
4.4min 60 sec 37.6 sec 11.2 sec 37.6 sec 37.6 sec
1.78
2.30 rnin
2.12 2.13
13.7 sec 12.4 sec
Mg Na P Si B c1
2.32 5.90 (6.76) 6.13
10.83 sec 13.7 sec
Zr B
'7.4 Sec
6.76 7.12
13.7 sec '7.4 sec
F 0 B F 0
0.51
("1 9
0.57 0.58 0.59 0.63 0.66 0.66 0.66 0.83 0.92 0.98 1.00
,
,,
P Mo Sb Ag Cr F Ti Pb
Mg Zr Ag Se M O
Ba Pb Zr Mg Cr Pb Si F Cr Mn Zr Mg
,, 0
Minimum detectable activity
Limit of detection (fig)
65 65 65 70 65 80 85 60 80 75
90 460
95 1500 50 1100 460 25 1000 550
750 150 700 50 1300 70
180 2400 80 130 800 }750 1j: 420 }1600 90 70 800 See photopeak at 0.51 MeV, 66 sec 170 70 400 120 65 550 9 60 7000 35 60 1700 12 60 5000 20 65 3200 16 60 3600 100 85 850 65 55 900 16 55 3600 3 50 16OOO 600 65 110 16 55 3600 120 60 550 20 55 3000 12 50 40oo 9 50 5500 35 45 1400 110 50 480 85 55 650 30 55 1900 25000
:)
;1
Na
S
,
Counts per mg
}420 See photopeak See photopeak 180 500 25 12 5 4
;i:
17500
)100
45 at 1.61 MeV at 1.63 MeV 35 35 35 35 35 30
130 130 30 220 420 30 See photopeak at 5.90 MeV 10 30 20 30
190 65 1600 3000 7000 7500 )lloo
150 75 3000 1500
(Limits of detection norma.lized to a flux of 10Qn/cm2sec)
VOl. 39, NO. 4, APRIL 1967
451
The numbers given in the last three columns were rounded
off after the calculations had been finished-i.e., after the limit of detection had been determined. Above all, the calculation of the limit of detection gives an idea of the sen-
sitivities which can be expected under well defined irradiation and counting conditions. Calculation of Number of Counts under Photopeaks. The number of counts was calculated by the trapeze method:
Counts/Channel(400 c) x5
2.10'
I
b
in Container
I
I 1
I'
10'
I 1 I !
100
200
300
400
nochannel
Figure 2. Blank spectrum for different irradiation, decay, and counting conditions
Par&
polyethylene container . . . , . . . .wax-filled 14-MeV neutrons; t i , = 30 sec, tdeo = 3 sec, tot = 30 sec; 0-8 MeV; - - - - -14MeV neutrons; t i r = 5 min, fdeg = 10 min, t,t = 5 min; 0-4 MeV; Thermal neutrons; tir = 10 min, tdeo = 3 sec, tot = 10 min; 0-4 MeV;
452
ANALYTICAL CHEMISTRY
(O
= 18.7 = 136.9
(O
= 245.9
(O
Table III. List of Photopeaks Obtained with Fast Neutronsa Energy (MeV) 0.059 0.093 0.102 0.103 0.145 0.149 0.150 0.150 0.153 0.158 0.176 (0.188) 0.188 0.188 0.21 0.23 0.25 0.26 I,
Half life 10.5 rnin 8.15 hr
Element Ni Ta
Reaction n, P n, 2n
,6
56.8 rnin 32.4 min
Se c1 Au Cd Sr Sn
n, 2n n, 2n n, 2n
900 260 40 lo00 140 800 1600
,,
10.0 hr
48.6 rnin 70 rnin 40.0 rnin 44 min 10.0 hr 4.8 min 10.0 hr 3.60 hr 70 min 48.6 min 82 min ,9
0.28 0.34
52 hr 80 rnin
0.37 0.37 0.39 0.46 0.51
44 min
("1 ("1
, I
("1
("1 9,
,, 1
0.60
,,
0.62 0.62 0.66 0.83
,,
0.84 0.85 I,
,,
Hg Au 9
,, ,,
Counts Per mg
,,
68 min 2.80 hr 74 min 6.4 min 7.75 min 8.9 rnin 9.80 min 12.8 hr 10 min 15 min 24.0 min 55 rnin
32.4 min 35.0 rnin 38.3 min 12.8 hr 44 min 7.1 hr 55 min 68 rnin 7.1 hr 12.8 hr
,
39.6 hr 17.5 days 7.8 min 17.5 days 6.4 min 18.5 min 13.3 days 14.2 hr ,9
!3.45 min 2.58 hr
,,
l7.8 min 0.91 68 min 0.91 3.60 hr 0.94 0.96 38.3 min 1.83 day 0.99 (1.04) = ti, = 5 rnin, tdeo = 10 Elin, tot = 5 min (live) (Limits of detection normalized to a flux of 109 nlcma sec) 9
Pd Au Nb Sr Cd As Ge Se Pb Au
Pt Hg Pb Sr Te Br K Fe
cu I
N In Cd
,,
c1 Sn Zn
,.
Se Cd Ga Se cu Zn Ge As Ge As Br
.,
I As Ge AI co Fe Sr Pb Nb Zn Ti I,
rn:
n nr* 2n* n, 2n n, 2n*
{:; ,'::
Minimum detectable activity
}::
170 200 160 190 220 190 180
Limit of detection (rg)
2400 12200 190 750 4000 180 1700 240 110
n, 2n I,
n, 2n* n, 2n n, 2p* n, 2n
{:; 2:
n5 P n, 2n n, a* n, 2n* n9 P n, 2n
{;: 2:
n, n'*
P:
n nr* 2n n, 2n n, 2n n, 2n n, 2n n, 2n n, 2n n, 2n n, 2n* n, P n, 2n n, 2n n, 2n n, 2n n, P n, 2n
,
n, 2n n, 2n n, 2n n, 2n n, P n, 2n n, 2n n, P* n, 2n n, 2n n, 2n n, 2n n, ff n, P n, P n, cy n, P n, P n, n'* n, 2P* n, 2n
)35 190 )170 15000 170 1200 See photopeak at 0.176 MeV 45 220 4600 360 200 5 50 3000 200 70 45 180 4200 240 220 950 40 180 4400 7 170 24000 100 180 1800 40 180 4200 300 170 600 8 170 21000 1200 190 150 220 190 900 21000 190 9 550 200 360 120 190 1500 ]~7000 2400 }200 190 75 17 160 460 )180 ]I200 650 220 320 130 1400
1;:
13200 170 See photopeak 13000 See photopeak See photopeak See photopeak 100 15 140 10
}im 8 5
20 3000 140
600 35 7 30
!:::
Im 12400
170 at 0.51 MeV, 24 min 200 16 at 0.51 MeV, min at 0.51 MeV, 9.8 min at 0.51 MeV, 38 rnin 180 1800 130 8500 160 1100 130 13000 )i50 1150 120 15000 100 21000 150 7000 170 55 180 1300 170 280 140 4200 140 zoo00 130 4600
4
4Ooo
n*,p
]5m
(Continued on page 454)
VOL 39,
NO. 4, APRIL 1967
453
Table III. List of Photopeaks Obtained with Fast Neutrons (Continued) Energy (MeV)
Half life
1.02 1.04 1.04 1.10 1.13 1.15 1.17
9.45 min 5.15 rnin 1.83 day 7.8 rnin 22.0 min 32.4 min 13.9 min
Wu "SC 74Ga 'K 34mc1
1.29
1.83 hr
1
,,
Radioisotope
c1
cu Ni
W O
ca
'A
1.33 1.36 1.37
1.83 day 37.0 hr 15.0 hr
4sSc S7Ni 4Na
1.49 1.60 1.81
2.56 hr 37.5 min 2.58 hr
66Ni "C1 6oMn
1.85 2.07 2.13 2.13
17.8 22.0 32.4 2.58
rnin min rnin hr
88Rb
,
Element A1 Ga Ti Ge Ca
2'Mg
K Ti Ni A1 Mg Zn K co Fe Sr
ca
4K 34mC1 66Mn 4
c1 co Fe K
,I
7.75 min 37.5 min 7.8 min 2.58 hr 15.0 hr
2.16
,,
2.35 2.65 2.75
"K "C1 74Ga 66Mn 24Na
Ge Fe A1 Mg
1,
5.04 rnin
3.09
c1
"S
Reaction n, P n, a n, P n, P* n9 P n, 2n n, ff n, P n, a n, P n, P n, 2n n, ff n, P n, a n, a n, ff n, P n, P n, P n, 2n n, a n, P n, i n n, a n,. D* n, P n, (Y
n, P n, P
Counts Per mg
Minimum detectable activity
Limit of detection (rg)
1000 180
150 150 150 800 See photopeak at 0.99 MeV 18 120 7000 12 130 11000 20 150 8000 65 120 1800 14 120 9500 4 90 23000 25 100 4600 10 100 loo00 6 120 zoo00 150 130 850 240 140 600 8 130 17000 18 80 4400 18 80 4600 75 75 1100 25 75 2800 3 65 22000 40 80 2000 7 65 9000 35 75 2200 20 6 70 110 80
65
3400
60
loo00
70 65 45
1000 600
600
Minimum Detectable Activity (counts)
Minimum Detectable Activity (counts)
90
80
350
70
300
60
950
50
P00
40
150
30
100
_-
15
Q5
P
I
3
4
5
6 7 8910
PO
30
40
Background (counts)
100
Figure 3. Calculation of the minimum detectable activity (for a relative standard deviation of 2 0 z ) 454
0
ANALYTICAL CHEMISTRY
number of counts undl:r photopeak =
where nk represents the number of counts in the channel k, and where i and j represent the channel numbers of the valleys limiting the photopeak. In the very high energy zone (above 4 MeV-i.e., in the case of "Be and l6N, photcipeaks were counted with pair peaks), the background was Dimply subtracted from the total number of counts. In these calculations, the following factors were not taken into account: (1) Blank: it is very weak (see Figure 2) and can be disregarded when the trapeze method is employed, except perhaps with certain photopeaks at 0.51 MeV. However, these were mentioned only if they were considerably above the blank; (2) Dead time: counting is in live time for the last two series, but this correction is only correct for half lives which are fairly long in comparison with counting time; (3) Self-shielding and self-absorption (the containers are very small); (4) The possibility of certain photopeaks mixing with pair peaks or backscattering-only the most important origin has been considered; ( 5 ) The possibility of fast neutrons contributing to certain thermal neutron photopeaks, because it is impossible to eliminate all the fast neutrons, and the same r,adioisotope may be produced by (n, y) and (n, 2n) reactions. Nevertheless, the deviations due to the above sources are limited, and the main objective was to obtain an order of magnitude. Flux Calibration. In order to normalize the number of counts per milligram tc a given flux, it was necessary to find the relation between the flux going through the sample (which can be considered constant) and the relative integrated flux reading. This was achieved by using bodies of which the cross-section was known: fast neutrons, copper wire; thermal neutrons, aluminum standard. The following relation ships were thus defined : fast neutron flux (in neutrons/cm2 sec)-7.9 x 106 relative integrated flux over one minute, thermal neutron flux (in neutrons/cm* s e c e l . 8 X l o 5 relative integrated flux over one minute. Calculation of the Minimum Detectable Activity. The minimum detectable activity was defined as being the minimum number of counts emanating from the element only, so that, taking into account tb: background corresponding to the counting time and the energy range of the photopeak, the relative standard deviation for the number of counts emanating from the element orily was equal t o 20z (see Figure 3). Limits of detection in micrograms can be obtained by dividing the minimum detectable activity by the number of counts per microgram. Table of Optimum Limiit of Detection. The limits of detection for each photopeak studied in well defined conditions, as given in Tables 11,111,and IV, are not necessarily the best ones. Table V shows the elements listed according to limit of detection, under optimum conditions of irradiation and counting (tlr = tot = 4 half lives, or 20 rnin maximum, since tritium targets still wear out too quickly, tdeo = 3 sec). The following data are also given for each element: (1) The radioisotope permitting the most sensitive analysis of the element, with its half life and the energy of its main photopeak;
Table IV. List of Photopeaks Obtained with Thermal Neutrons4 MiniLimit mum of detectdetecEnergy Counts able tion Half life (MeV) per mg activity (pg) 10.5 min 0.059 6OOo 260 40 3.5 min 0.061 1280 (0.075) 14000 170 0.074 23.5 min 12000 280 25 0.075 3.5 min See photopeak at 0.061 MeV 0.130 1.7 rnin 150 240 1600 0.137 54.2 rnin loo00 340 35 0.139 48 sec 440 220 500 0.147 24.8 min 220 260 1200 0.150 70 min 45 220 4600 40.0 min 0.153 360 220 650 0.158 44 min 700 240 350 1.7min 0.165 80 280 3400 4.8 min 0.188 1700 300 180 0.23 70 min 140 240 1700 0.26 82 min 120 240 2000 0.32 5.79 min 150 260 1700 9.5 min 0.33 140 240 1700 0.37 44 min 110 220 1900 2.80 hr 0.39 500 240 480 54.2 min 0.41 35000 260 8 2.70 days 0.41 550 220 400 0.43 2.4 min 170 1200 140 0.45 24.8 min [loo 1240 12400 (0.46) 74 min 25.0 min 0.46 2200 260 120 0.46 74 min See photopeak at 0.45 MeV 24.0hr 0.48 120 240 2000 12.8 hr 0.51 11000 260 25 0.54 25.0 min 110 220 1900 26.6 hr 0.56 200 280 1400 18.5 min 0.62 1600 200 120 2.4 min 0.63 11800 1240 1140 24.2 sec (0.66) 26.6 hr 0.65 18 170 loo00 0.66 24.2 sec See photopeak at 0.63 MeV 0.66 2.60 min 2800 240 85 0.69 24.0 hr 80 180 2200 54.2 min 0.80 9500 200 20 14.2 hr 0.83 160 200 13W 2.58 hr 0.85 7500 240 30 5.15 min 1.04 160 180 1100 1.09 54.2 min 32000 190 6 1.21 26.6 hr 14 140 11OOO 1.27 54.2 min 41000 170 4 15.0 hr 1.37 100 190 1900 3.76 min 1.44 1 m 220 14 1.46 14.2 hr 20 180 9ooo 54.2 min 1.49 3800 190 50 1.78 2.30 min 1100 120 100 2.58 hr 1.81 950 110 120 2.13 450 100 230 14.2 hr 2.21 25 95 4OOo 2.51 18 85 4800 2.65 2.58 hr 55 75 1300 15.0 hr 2.75 40 75 1900 a (n,y) reaction, ti, = 10 min, tdeo = 3 sec, t,t = 10 rnin (live) (limits of detection normalized to a flux of 5.107n/cms sec).
(2) The other elements which may interfere by giving radioisotopes having both half life and photopeak energy too closely approaching those of the radioisotope produced by the element under study (with thermal neutrons, the interferences from fast neutrons, which cannot be completely eliminated, are taken into account); VOL 39, NO. 4, APRIL 1967
455
Table V. Table of Optimum Limits of Detection for the Elements under Study0 Limit of detection
(a)
From 1 to 10
From 10 to 100
Radioisotope
Ag AI Ba Br Cd cu Ga Hg Sb Si Sr Zn Zr
lo6Ag %?Mg l37mBa 78Br 111rnCd 62CU 68Ga 199mHg
From lo00 to loo00 tir and tCt =
l2oSb
28A1 *7mSr 63Zn 4Y
In Mn U
ll6mIn "Mn
c1
4mC1 62V
Cr
From 100 to lo00
0
Element
239u
3
F
190
Fe Ge K Mg Mo N Na 0 P Pd se Sn Te W
68Mn ?smGe BK 24Na 9~
MO
l3N 23Ne '8N
28A1 lO9mpd 81mSe l23Sn lZ8Te l86mW
co I V
1BI 62V
As Au Nb Ni
76mGe l9lmAu 9 2Y 62Co
Pt
197rnpt
Ta Ti
46mk
GOmCo
l8OmTa
Energy of Half life main peak (MeV) 14-MeV neutrons :10Qn/cm2sec 24.0 min 0.51 9.45 min 0.84 2.60 rnin 0.66 6.4 rnin 0.51 48.6 rnin 0.25 9.80 rnin 0.51 68 min 0.51 44 min 0.158 16.4 rnin 0.51 2.30 min 1.78 2.80 hr 0.39 38.3 rnin 0.51 16.5 rnin 0.92 Thermal neutrons: 5.107n/cm2 sec 54.2min 1.27-1.09 2.58hr 0.85 23.5 min 0,074 14-MeV neutrons: 10Qn/cm2sec 32.4 rnin 0.51 3.76 rnin 1.44 29.4 sec 0.20 2.58 hr 0.85 48 sec 0.139 7.75 min 0.51 15.0 hr 1.37-2.75 15.5 min 0.51 10 min 0.51 37.6 sec 0.44-1.65 7.4 sec 6.13 2.30 min 1.78 4.8 rnin 0.188 56.8 min 0.103 40.0 min 0.153 74 min 0.46 1.7 rnin 0.130 Thermal neutrons: 5.107n/cm2 sec 10.5 min 0,059 25.0 rnin 0.46 3.76 rnin 1.44 14-MeV neutrons : 10'Jn/cm*sec 48 sec 0.139 7.4 sec 0.28 3.60 hr 0.21-0.94 13.9 min 1.17 80 min 0.34 8.15 hr 0.093-0.102 19.5 sec 0.142
456
Sb, In, C1, Sn.
Ag Cu, N, K.
ANALYTICAL CHEMISTRY
..
l*Ag
..
Br, Sb, N, In, K.. Cd, Se, Cr. Cd, C1, Sn Ag, In, Mo. P
.. ..
C1, Sn, Se..
Sr
.
0.62
.
'ZGa 0.37 lZbSb
8omZr
Fe, Co
Zn, Sn. Mn Pd, Ag
..
8 7 s
1tN
co As, Pd Br, Cu, N. A1 Sb, In, Ag. . Cu,Br, K . . Mg F, B Si
.. . .
74Ga 2.16 laNe
Hg, Cd, C1 Fe, Pd
U-W
Ni Te Cr, Mn
6eMn
Ge, Pd
'6As
Cu
60mCO
"Ti
Au Se
Thermal neutrons : 5.107 n/cm* sec Au l98Au 2.70days 0.41 14-MeV neutrons: 10@n/cm2sec B 1% 13.7 sec 5.60-6.76 0,F Ca 44K 22.0 min 1.13 c1 207mpb 0.84 sec 0.57 Pb s 84P 12.4 sec 2.13 C1, B 4 halflives or maximum 20 min, tdec = 3 sec.
(3) If such interferences are numerous, then another photopeak given by the same radioisotope, or another radioisotope, which can be employed for analyzing the element, although the limit of detection will not be as good. Finally, it should be observed that the Compton continuum o r backscattering of a n energetic photopeak may mask a weaker and less energetic photopeak. Similarly, a photo-
Other peak or R.I. usable
Interference
6
'Ti
2.12
peak which is slightly energetic may easily be lost in the x-rays and background. Received for review January 20, 1966. Resubmitted May 17, 1966. Accepted September 12, 1966. This work was carried out under the auspices of the European Atomic Energy Community, contract NO. 02464-4IRAF/Eurisotop.
