ISSN 0101-3084
CMENÍSP
ipen Instituto de Pesauisas Energéticas e Nucleares
THERMAL NEUTRON CAPTURE CROSS SECTION OF CHROMIUM, VANADIUM, TITANIUM AND NICKEL ISOTOPES
Luiia VENTURINI and Brigitt» R.S. PECEQUILO
PUBLICAÇÃO IPEN 300 ABRIL/1990
SAO PAULO
PUBLICAÇÃO IPEN MO A M I L / 1 M 0
THERMAL NEUTRON CAPTURE CROSS SECTION OF CHROMIUM.
VANADIUM, TITANIUM AND NICKEL ISOTOPES
Luzia VENTURINI and Brittle HS. PECEQUILO
DEPARTAMENTO DE PROTEÇÃO RAOIOLÓOICA
CNCM/fP
INSTITUTO DE PESQUISAS ENERGÉTICAS E NUCLEARES SAO PAULO - BRASIL
Siri* PUBLICAÇÃO IPEN
IN IS Categories and Descriptors
A31.00
CHROMIUM VANADIUM TITANIUM NICKEL
CROSS SECTIONS THERMAL NEUTRONS
I PEN • Doc • 3562
Aprovado para publleaçfo tm 29/03/90.
Nota: A rtdaçéo, ortografia, concaftof a revlifo final «16 da reipontabllldide dot*) autor <••).
THERMAL NEUTRON CAPTURE CROSS SECTION OF CHROMIUM,VANADIUM.TITANIUM AND NICKEL ISOTOPES.
Luzia VENTURINI and Brigitte R.S. PECEQUILO
INSTITUTO DE PESQUISAS ENERGÉTICAS E NUCLEARES-IPEN-CNEN/SP DIVISÃO DE MONITORAÇÃO AMBIENTAL -NPA*
Caixa Postal - 11049 - Pinheiros 05499-São Paulo-Brasil
ABSTRACT
The thermal neutron cross section of chromium,vanadium, titanium and nickel can be determined by measuring the pair spectrum of prompt gamma-rays emitted when targets of these elements are Irradiated by a thermal neutron beam.Such measurements were carried out by irradia- ting the natural element mixed with a nitrogen standard (melamine) in the tangential beam hole of the IEA-R1 research reactor.
The pair spectrometer efficiency calibration curve in the 1.5 to 11 MeV energy range was performer! with a mel ami ne plus ammonium chloride mixed target. The cross section was calcinated for the most prominent gamma transitions of each isotope, using nitrogen as standard and averaged over the obtained values. The resulting mean cross sections are as follows:
(13.4 t o.7)b for 5 0Cr,(0.79 ± 0,02)b for 5 2Cr,(18.1 * 0,7)b for ^ r , (4.9 rO.2)b for 5 1V,(8.4 r O . U b for 4 8T 1 , (4.41 r 0.08)b 5 8N 1 , (2.54i0.07)b for 6 ON1,(15.2rO.5)b for 62N1 and (1.6 £ 0.1) for
The present Mork was performed at the Nuclear Physics Division of the IPEN-CNEN/SP.
SECÇÂO DE CHOQUE DE CAPTURA DE NEUTRONS TÉRMICOS DCS ISOTOPOS DO CRÔ- Ó, VANÁDIO, TITÂNIO E NÍQUEL.
Luzia VENTURINI e Brigitte R.S. PECEQUILO
INSTITUTO DE PESQUISAS ENERGÉTICAS E NUCLEARES - IPEN-CNEN/SP DIVISÃO DE MONITORAÇÃO AMBIENTAL - NPA*
Caixa Postal - 11049 - Pinheiros 05499 - São Paulo - Brasil
RESUMO
A secção de choque de captura de neutrons térmicos dos Isótopos do crômio, vanádio, titânio e níquel pode ser determinada pela medi- da do espectro de ralos gama prontos quando alvos destes elementos são Irradiados num feixe de neutrons térmicos. Estas medidas fora, realizadas Irradiando uma mistura do elemento natural com um padrão de nitrogênio ( mel ami na) no canal tangendal de Irradiação do reator de pesquisa IEA-R1. A curva de calibração em eficiência do espectrome tro de pares na região de energias de 1,5 ali MeV foi obtida com um alvo misto de mel amina e cloreto de amônia.
A secção de choque foi calculada como um valor médio a partir dos va- lores Individuais das transições gama mais Intensas de cada um dos 1- sótopos, usando o nitrogênio como padrão. Os valores médios obtidos são, como segue: (13,4 ± 0,7)b para Cr,(0,79 ± 0,02)b para Cr, (18,1 * 0,7)b para 5 3Cr, (4,9 ± 0,2)b para 5 1V, (8,4 ± O.Dpara 4 8T 1 , (4,4 ±0,08b)para 5 8N 1 , (2,54 t 0,07)b para 6 0N 1 , (15,2 ± 0,5)b para
62Ni e (1,6 ±0,l)b para 6 4N 1 .
* 0 presente trabalho foi realizado na Divisão de Fisica Nuclear do IPEN-CNEN/SP.
INTtODUCTHM
The determination of the total thermal neutron capture cross section for the (n,> ) reaction can be arrived in two ways.First, If all the primary transitions are identified, one can calculate their partial cross sections and, by summing all of then, one can deter- mine the total neutron capture cross section. Hawever, for most nuclei, the identification of all primary transitions is extremely difficult.
The second procedure to determine the total thermal neutron c«£
ture cross section is to normalize to the known total cross section of another element mixed with the sample before Irradiation.Assuming thermal neutron capture alone, the thermal radioactive cross section can be readily obtained from a ( n,y ) spectrum by the relation :
A Ns es ls
os 5 5 — o Ac N E I S
where a , A, N and I are the thermal neutron capture cross section, peak area, number of atoms, detection efficiency and the intensity of the transition respectively, and s refers to the standard.
Since both the Isotope and the standard present many ganra transitions, one can calculate the cross section for each prominent transition of the isotope using all prominent transitions of the standard and av- erage over all the obtained values.
Using the equation (1), for j standard transitions and n Iso- tope transitions, the mean thermal neutron capture cross section e for the Isotope is given by:
oc N 1 • J k = n A(E. ) e{E.) I (E.) ' 1 - 1 k « 1 A(E,) «(Ek) I (Efc)
U)
where E denotes the energy of the gamma transition being considered.
The radioative capture cross sections for Cr, Cr, Cr, V, Ti, Ni, Ni and Ni were determined by irradiating, in a thermal neutron beam, composite targets of the natural elements well mixed with mel ami ne (C.H.N.) and by measuring the pair spectrum of
J o b
the prompt gamma rays. Nitrogen was used as standard because I t s well known and precise cross section, energies and i n t e n s i t i e s .
EXPEtIMENTAL METHOD
The measurements were c a r r i e d out through the use of the tangencial i r r a d i a t i o n f a c i l i t y [ 1 ] of the IEA-R1 r e - search r e a c t o r . At the sample i r r a d i a t i o n p o s i t i o n the thermal neutron f l u x 1s of the order of 5 x 10 n / c m ' . s . C h a r a c t e r i s t i c s of the t a r g e t s are d e t a i l e d 1n Table I .
The prompt gamma rays f o l l o w i n g thermal neutron cap*
t u r e were detected by an improved p a i r spectrometer N a I ( T l ) - G e ( L i ) - N a l ( T l ) described elsewhere [ 2 ] ,
Spectra were accumulated in a Hewlett-Packard 8192 chan nels multichannel analyzer and d i g i t a l s t a b i l i z a t i o n was used t o guard against gain and baseline s h i f t s .
Spectral analysis was achieved by means of the FORTRAN IV computer code Analysis [ 3 ] which provided the peak areas used in equation ( 2 ) .
59 The prompt gamma rays intensities H E ) for the N I ,
*lu* 03»,, 6bUi 52., 5 1r 5 3r 5 4 . . T 9T.
Ni, N1, N1, V, Cr, Cr, Cr and T1 Iso- topes were taken from reference [4] to [ 9 ] .
In equantion (2) the number of atoms 1s calculated as:
m N f
°- (3)
M
where « - mass of the natural element.
No = Avogadro's number,
M = atomic «ass of the Isotope,
f - isotopic abundance of the Isotope.
EFFICIERCV CALIBRATION CURfE
For a given gamma transition of energy E, we ca» de- fine detector efficiency as:
A(E)
Id)
Where A(E) and HE) are the corresponding peak area and I n t e n s i t y , respectively. So, we can determine the efficien- cy c a l i b r a t i o n curve by measuring the prompt gamma-ray spec trum of a target with a set of well-known energies and in- t e n s i t i e s .
The pair spectrometer efficiency c a l i b r a t i o n curve was determined by measuring a mixed sample of 14.2487g of mel amine (C,H N ) and 0.4167g of ammonium chloride (NH.C1)
j o b 4
in the energy region of 1.5 to 11 MeV. For this range of energy, the nitrogen and chlorine Isotope have a large num ber of transitions with well known values of energy and i n t e n s i t y .
The gamma transition energies and I n t e n s i t i e s con- sidered 1n our calculation were taken from Kenneth[10] for the nitrogen and from Krusche [11]for the chlorine and the respective cross sections taken from references [12] and 113].
The peak area 1s proportional to the cross section and to the number of atoms being Irradiated.
So, i t 1s possible to normalize the results for the chlorine to those
8
of nitrogen. This Mas done fay using a normlization factor equal to 0.20 - 0.01.
The efficiency calibration curve from 1.5 to 11.2 HeV Mas per- formed through three prompt gamma spectra measured 1n the energy range of 1.5 to 6.1 MeV, 3.4 to 8.0 MeV and 5.0 to 11 NeV.
The curves were normalized to the Intermediate energy range and the experimental points were fitted to the polynomial function l n U ) = aQ • a] In (E) + a? [ln(E)]*.
RESULTS AMD DISCUSSION
50 52 53 The thermal neutron capture cross section of Cr, Cr, Cr,
5 1V, 4 8T 1 , 5 8N 1 , 6 0N 1 , 62N1 and 6 4N1 were determined by measuring the pair spectrum of the (n, Y ) reactions on natural element targets (Ta- ble I), using nitrogen as standard. The calculations were performed through equation (2). As an example, Table II shows the values ob- tained for Cr and the resulting average cross section. The final results for the considered Isotopes are presented In Table III, together with the cross section values reported 1n the litera- ture.
As It can be seen from Table III, our results are In good agree 50 48 "~
ment with those reported In the literature, except for Cr, T1 and N1. We can consider these values as new contributions to the60
52 53 58 determination of the real values. In the case of Cr, Cr, N1 and T1, the precision of the results has been Increased and we be48 11eve that 1t means an advance 1n the reseache of the nuclear prop- erties.
TABLE I : CHARACTERISTICS OF THE TARGETS.
1 ) 1 I I I
Target Isotope Mass of the I s o t o p i c Mass of . I I natural e l e I A b u n d a n c e I ^ »
_ I . JiL J
• I
Titanium
I I
48 1.0332
I
73.94
7
11.0994 I
Vanadium I 51
4.0196 99.75 10.2166
Chromium
" I I I
50 52 53
4.0566 4.35
83.79 9.50
11.5445
Nickel 58
60 62 64
4.1726 67.88 26.23 3.66
1.08
11.0994
10
TABLE I I : CALCULATED ¥ALUES ( I N 1ARNS) FOR THE THERNAL NEUTRON CROSS SECTION OF 5 3C r .
^Standard *
\
isotopeX.
6645.34
7099.71
8884.71
9718.82
5297.81
17.9 * 2.2
17.7 * 2.1
17.3 ± 3.2
18.5 * 3.5
5533.38
1
18.2 * 2.3
18.0 * Z.Z
17.6 * 3.3
18.8 * 3.6
5562.06
18.5 * 2.3
18,3 * 2.3
17.9 * 3.4
19.1 ± 3.7
7298.91
18.0 * 2.3
17.8 * 2.2
17.4 * 3.3
18.6 * 3.6
Average theraal neutron cross section » 18. 1 * 0.7 barns
Transition energy 1n keV.
11 TABLE III : THERMAL NEUTRON CROSS SEC T I M III BARNS.
Isotope
5 0Cr
5 2C r
5 3Cr
51y
4 8Ti
5 8N1
6 0Ni
6 2N1
6 4N1
This
13.4 *
, : *
18.1 i
4.9 i
8.4 i
4.41 t
2.54 t
15.2 ±
| 1.6 ±
Work ' 1
1
0.7 |
0.02!
| 0.7 |
0.2 |
0.1 1
1
0.08!
1
0.07|
1
0.5 | I
1
0.1 |
1
15.9
0.79 18.2
4.9 7.84 4.6 2.9 14.5 1.52
Rcf.
•
•
i
t
i
±
*
t
t
(14 ]
0.2 0.06
1.5 0.1
0.25
0.3 0.2 0.3 0.03
12
REFERENCES
1. PECEQUILO.B.R.S. Nova técnica para a determinação de Impurezas em compostos de urânio e de tório pela análise dos ralos ga- ma pontos de captura, são Paulo, Instituto de Energia Atomi^
ca, 1978 (IEA-DT-078).
2. PECEQUILO.B.R.S.; VANDENPUT, G.C.; STOPA, C.R.S. and SUAREZ,A.A.
Prompt neutron capture gamma ray analysis of nuclear fuel
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3. ANALYSIS - A FORTRAN IV Computer code for spectral analysis.
Not published.
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Thermal neutron capture 1n Isotopes of n i c k e l . Z.Phys. 2 8 1 : 3 6 5 , 1 9 7 7 .
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6 . AU6LE, R.L. Revised A-cha1n f o r A= 5 3 . Nucl.Data Sheets, 2 1 ( 3 ) : 3 4 9 , 1 9 7 7 .
7 . AMBLE, R.L, Revised A-cha1n f o r A« 5 1 . Nucl.Data Sheets, 2\ ( 2 ) : 208, 1978
13 8. VERHEUL, H. and AUBLE, R.L. Revised A-cha1n for A* 54.
Nuci.Data Sheets, 23 (4) : 487, 1978.
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Methods, A=249, 366, 1986.
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BORNER, H.G.; BRISSOT,R.; HOFMEYER.C. and RASCHER.R. Gamma ray energies and Cl level scl36
Nucl. Phys., As386, 245, 1982.
36 35
ray energies and Cl level scheme from the reaction Cl (n,ir)
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M e t h o d s . 188, 243, 1981 .
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13. ENDT,P.M. and VAN DER LEUN.C. Energy levels of A-21-44 nuclei (VI/. Nucl. Phy* A310, 1, 1978.
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