ARTICLE IN PRESS

Nuclear Instruments and Methods in Physics Research A 562 (2006) 710–713 www.elsevier.com/locate/nima

Status of the photonuclear activation file: Reaction cross-sections, fission fragments and delayed neutrons Danas Ridikasa,, Marie-Laure Giacria, Mark B. Chadwickb, Jean-Christophe Davida, Diane Dore´a, Xavier Ledouxc, Aymeric Van Lauwea, Wiliam B. Wilsonb a

CEA Saclay, DSM/DAPNIA/SPhN, 91191 Gif/Yvette, France Los Alamos National Laboratory, Los Alamos, NM 87545, USA c CEA/DIF, DAM/DPTA/SPN, 91680 Bruye`res-le-Chaˆtel, France b

Available online 2 March 2006

Abstract Recently a renewed interest in photonuclear reactions has appeared. It is motivated by a number of different applications where progress in reliable and, in some cases, very high-intensity electron accelerators was awaited. In particular, today’s interest is linked to the nuclear material interrogation and non-destructive nuclear waste characterization, both based either on prompt neutron, or delayed neutron, or delayed gamma detection following photofission. The knowledge of photonuclear reactions is also extremely important in the design of electron accelerators used for medical applications, nuclear physics, photoneutron sources, radioactive ion beam production, etc. In this paper we present the photonuclear activation file (PAF) under development to be included into any material depletion code. By now the PAF contains the photonuclear cross-sections for more than 600 isotopes, fission fragment distributions and delayed neutron evaluations for most of the actinides in the photon energy range from 0 up to 25 MeV. Theoretical predictions, evaluated data files and available experimental data were used to construct the PAF, and some benchmarks are in progress to ensure its quality. The release of the first version of PAF is planned in 2006. r 2006 Elsevier B.V. All rights reserved. PACS: 25.20. x; 25.85.Jg Keywords: Photonuclear reactions; Photofission; Delayed neutrons

1. Introduction Although photo-neutrons typically provide only a small additional neutron source in technologies involving particle accelerators and nuclear reactors, photoneutrons and photofission are of significant importance in applications based on electron accelerators and Bremsstrahlung targets [1]. For example, intense neutron sources for physics experiments as ORELA at ORNL (USA), GELINA at Geel (Belgium), and, more recently, ELBE at Dresden (Germany) are based on photonuclear reactions. In these and other similar cases, photoneutrons certainly pose a serious concern for radiation protection, shielding and decommissioning. Photonuclear processes and photofisCorresponding author. Tel.: +33 1 69087847; fax: +33 1 69087584.

E-mail address: [email protected] (D. Ridikas). 0168-9002/$ - see front matter r 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.nima.2006.02.028

sion, in particular, can also play a significant role in the detection of nuclear materials. Here both the prompt and the delayed photoneutrons and g-rays can provide the unique signature of presence of fissile nuclei in massive cargo containers [2]. Therefore, new simulation capabilities are urgently needed to help develop this technology. This is also important in order to design and optimize the electron accelerators, conversion targets and neutron detectors. Equally, simulations are essential for interpreting new measurements. Major problems in modeling photonuclear reactions are the lack of photonuclear data on corresponding crosssections despite huge efforts of the IAEA, where evaluations are provided for 164 isotopes only [3]. In addition, no material evolution-depletion code including photonuclear reactions is available. In a close collaboration with the LANL we have been working on the development of a new

ARTICLE IN PRESS D. Ridikas et al. / Nuclear Instruments and Methods in Physics Research A 562 (2006) 710–713

photonuclear activation file (PAF) to be included into the CINDER’90 evolution code or any other material depletion code [4,5]. Below we present the PAF structure, different photonuclear data sources and methodology used to construct a general purpose photoactivation data library, including some benchmark examples in order to ensure its quality. The release of the first version of PAF is previewed in 2006. 2. The structure of PAF As in the case of neutron activation libraries, PAF contains very similar structure. In brief, for each isotope the library includes:

  

decay half-lives and branching ratios, energy of the decay particles, number of possible reaction products for each reaction.

(a) the reaction product, (b) the corresponding group cross-section, including (c) fission fragment distributions, and (d) delayed neutron tables if photofission can occur. The photon flux is described by a 25 group structure from 0 to 25 MeV in equal steps of 1 MeV. As shown in Fig. 1, we start the construction of PAF including all 164 isotopes available from the IAEA evaluations [3]. For the remaining more than 500 isotopes the HMSALICE and GNASH reaction codes have been used to calculate photonuclear reaction cross-sections [4]. For photofission fragment distributions we employ the evaporation–fission code ABLA from GSI [5]. The PAF also includes the 6-group tables of photofission delayed neutrons. These were obtained by the summation

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techniques of delayed neutron precursors at equilibrium, resulting from the ABLA predictions [5]. 3. The quality of PAF Within PAF we considered that the IAEA evaluations and corresponding experimental data can serve as a reference for the reaction codes used in this work [3]. In this context, a number of comparative calculations were performed to evaluate the quality of the constructed data library for PAF [4,5]. 3.1. HMS-ALICE calculations The major advantage of the HMS-ALICE code is that results can be obtained very quickly for a large number of nuclei [4]. As an example shown below in Fig. 2 we compare the HMS-ALICE predictions with the IAEA files for 181Ta. Although the HMS-ALICE predictions are rather good for heavy nuclei, much bigger discrepancies were observed in the case of light (e.g., C, O, etc.) and intermediate mass nuclei (e.g., Al, S, etc.) [4]. In some cases the disagreement was found within a factor of 2 or 3 [4]. It is clear that HMS-ALICE needs some improvements to predict photonuclear reactions for light nuclei, while for heavy nuclei, including actinides, the predictions are rather satisfactory [4]. 3.2. Evaluations with GNASH We employed GNASH for some actinides in order to construct the ENDF libraries at the same time. The use of GNASH to evaluate photonuclear reactions was already discussed in Ref. [6] for nonfissile nuclei and in Ref. [7] for fissile nuclei. By now PAF includes only 3 isotopes evaluated with GNASH, namely 237Np, 240Pu and 241Am, which were not available in the IAEA evaluations. Our results for 241Am together with existing but scarce data in this case are given in Fig. 3. Thanks to good physics incorporated in GNASH, this code gives very satisfactory 400 σ(γ,1n) IAEA

Cross section (mbarn)

σ(γ,1n) HMS-ALICE σ(γ,2n) HMS-ALICE

(γ,n) 200

100

0

Fig. 1. A schematic view of the PAF structure: different sources of data flow are indicated explicitly.

σ(γ,2n) IAEA

300

(γ,2n)

5

10

15 Energy (MeV)

20

25

Fig. 2. Neutron production cross-sections for 181Ta as a function of photon energy obtained with HMS-ALICE (dashed and dotted curves) and compared with the IAEA files (solid curves).

ARTICLE IN PRESS D. Ridikas et al. / Nuclear Instruments and Methods in Physics Research A 562 (2006) 710–713

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400

Cross section (mb)

300

Table 1 Comparison of relative photo-fission rates: function of endpoint Bremsstrahlung energies

Am-241

GNASH (γ,fiss) Soldatov (94) Korestaya (79) Findlay (92) GNASH (γ,1n) GNASH (γ,2n)

Energy (MeV) Experiment GNASH

11.5 2.4570.07 2.54

241

Am versus

14.5 2.4270.06 2.51

238

U as a

20.0 2.1870.12 2.34

(γ,fiss) 200 Table 2 Comparison of calculated and experimental total and partial DN yields and half-lives for photo-fission of 235U with the 15 MeV endpoint Bremsstrahlung photons

(γ,n) 100 (γ,2n)

Group

0 5

10 15 Photon Energy (MeV)

20

Fig. 3. Comparison between GNASH and experimental data for (g,n) (g,2n) and (g,fiss) in the case of 241Am.

predictions in the case of actinides [7]. In addition, these results are also confirmed in the case of integral measurements [8] as shown in Table 1.

1 2 3 4 5 6 Total

Yield, DN/per fission

T1/2, s

Exp.

Calc.

Exp.

Calc.

0.05270.01 0.19370.04 0.14670.03 0.35470.07 0.13470.03 0.08370.05 0.96713

0.061 0.424 0.243 0.381 0.074 0.010 1.193

54.772.5 20.371.0 5.4570.60 2.0170.25 0.5070.10 0.1970.04

55.6 19.1 5.21 2.13 0.47 0.17

3.3. Fission yields with ABLA 15 MeV 6

YIELD (%)

Similarly, as for photonuclear cross-sections, we tested the predictive power of the ABLA code for photofission fragment distributions when data were available [5]. Fig. 4 presents the mass distribution of fission yields in the case of 15 MeV endpoint Bremsstrahlung photons on 235U. Our calculations (histogram) are quite satisfactory compared to the available experimental data (squares) [9]. Similar quality predictions were also obtained for 238U, 239Pu, 237 Np and 232Th [5]. We note that some parameter adjustments were necessary in order to reproduce the data. Unfortunately, very little data exist for the isotopic photofission yields, which would give more detailed validation of ABLA. Equally, the presence of data on isotopic yields would be very helpful in predictions of delayed-neutron yields.

4

2

0 80

100

120 140 Fragment Mass (A)

160

Fig. 4. Mass distribution of photofission fragments for 235U with 15 MeV endpoint Bremsstrahlung photons (see text for details).

3.4. Delayed neutrons (DN) The independent isotopic distributions of fission fragments, resulting from ABLA, were converted to the cumulative yields. Those were classified in six groups (according to their half-lives) and the DN parameters in terms of 6-group tables were obtained for all actinides [5]. Table 2 presents our predictions compared to existing experimental data [10] in the case of photofission of 235U. As expected, our results for the half-lives are closer to data than the yields are. The calculated total number of DN is in rather good agreement with data. On the other hand, the groups 2 and 3 are overestimated, while the groups 5 and 6 are underestimated. The relative contributions of different isotopes inside each group still have to be

investigated in detail for nuclei, where the experimental DN data is available. 4. Conclusions and outlook The status of PAF under development was presented. By now PAF includes the photoactivation cross-sections for more than 600 isotopes in the energy range of photons from 0 to 25 MeV. In the case of actinides, PAF also contains isotopic photofission fragment distributions and DN tables. Both existing experimental data (IAEA evaluations for 164 isotopes) and different reaction codes (for more than 500 isotopes) were used to construct this data file. The quality of code predictions was tested

ARTICLE IN PRESS D. Ridikas et al. / Nuclear Instruments and Methods in Physics Research A 562 (2006) 710–713

extensively with existing experimental data. The release of the first version of PAF is planned in 2006 and should be applicable for activation analysis in photon fluxes. Finally, we add that we started the experimental program to measure DN decay curves from photofission for a number actinides, and the first results will be reported elsewhere in the near future.

References [1] D. Ridikas, P. Bokov, M.-L. Giacri, Potential applications of photonuclear processes: renewed interest in electron driven systems, Proceedings of the International Conference on Accelerator Applications ADTTA’03, 1–5 June 2003, San Diego, California, USA. [2] D. Ridikas, F. Damoy, A. Plukis, R. Plukiene, Nuclear material interrogation via high-energy b-delayed neutrons and g-rays from photofission, Proceedings of the International Conference NEMEA2, 20–23 October 2004, Bucharest, Romania.

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[3] M.B. Chadwick, P. Oblozinsky, A.I. Blokhin, T. Fukahori, Y. Han, Y.-O. Lee, M.N. Martins, S.F. Mughabghab, V.V. Varlamov, B. Yu, J. Zhang, IAEA TECH-DOC 1178 (2000). [4] M.L. Giacri, M.B. Chadwick, J.C. David, D. Dore´, D. Ridikas, A. Van Lauwe, W.B. Wilson, Status of the photonuclear data library for CINDER’90, in: Proceedings of the International Conference ND2004, September 26–October 1 2004, Santa Fe, New Mexico, USA; published in AIP Conf. Proc. 769 (2005) 195. [5] J.C. David, D. Dore´, M.L. Giacri, D. Ridikas, A. Van Lauwe, Fission fragment distributions and delayed neutron yields from photon induced fission, in: Proceedings of the International Conference ND2004, September 26–October 1 2004, Santa Fe, New Mexico, USA; published in AIP Conf. Proc. 769 (2005) 1120. [6] M.B. Chadwick, P.G. Young, R.E. MacFarlane, M.C. White, R.C. Little, Nucl. Sci. Eng. 144 (2003) 157. [7] M.L. Giacri, M.B. Chadwick, D. Ridikas, P.G. Young, W.B. Wilson, Photonuclear physics in radiation transport III: actinide crosssections and spectra, Nucl. Sci. Eng. 153 (2006) 1. [8] J.R. Huizenga, J.E. Gindler, R.B. Duffield, Phys. Rev. 95 (1954). [9] E. Jacobs, et al., Phys. Rev. C 21 (1980) 237. [10] O.P. Nikotin, K.A. Petrzhak, At. Energy. 20 (3) (1966) 268.