Benchmarking fission rate simulations throughcomparison with neutron activation data

Project in Applied Physics

AuthorPeter Karlsson

SupervisorsZhihao Gao and Andreas Solders

Applied Nuclear Physics DivisionDepartment of Physics and Astronomy

Angstromslaboratoriet

Abstract

Metal foils were implemented in a measurement of neutron-induced fission at the IGISOLfacility in 2016. These foils were activated by a neutron flux during the experiment andmeasured after the beam was turned off. The radioactive products from the neutron activationwere identified in an analysis of γ-ray spectroscopy data. The results were then used tobenchmark the neutron flux simulated by MCNPX, which is used for a simulation model ofan ion guide that was implemented in the experiment in 2016. The predicted number ofneutron activation products were calculated using the simulated neutron flux and comparedto results from the experiment. This comparison benchmarked the neutron flux and showed aconsistency with the results from a previous study. This is a step in the process to validate thepredictive power of the simulation model which is developed for the study of neutron-inducedfission.

1

Contents

1 Introduction 11.1 Background and motivation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11.2 Application . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

2 Spectroscopy measurement 22.1 Measurements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22.2 Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

3 Theoretical calculation 63.1 Neutron activation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63.2 Neutron flux Φ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 73.3 Formula . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

3.3.1 Production of activation products during irradiation . . . . . . . . . . . . . 73.4 Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

4 Comparison and discussion 12

5 Conclusion 13

6 Outlook 13

References 14

2

1 Introduction

1.1 Background and motivation

It is not easy to measure neutrons because they only interact with matter through nuclear reac-tions. One way to indirectly measure neutrons is by measuring the products of neutron activation.Some products of neutron activation decay by beta or positron decay, usually accompanied withγ-rays. If the activation products have a suitable half life, we can measure the electron or positronand gamma ray after the activation. An experiment of neutron induced fission[1] was conducted atthe IGISOL facility at the University of Jyvaskyla in Finland[2] in 2016. In this experiment metalfoils were implemented in the setup. One motivation for implementing the foils was to measurethe neutron flux.

Figure 1: Shematic layout of the IGISOL facility[3]. (1) Ion guide, (2) sextupole ion guide (SPIG),(3) dipole magnet, (4) switchyard, (5) β-γ spectroscopy setup, (6) radiofrequency cooler-buncher,(7) beam line towards a collinear laser spectroscopy setup, (8) Penning trap (JYFLTRAP), (9)microchannel plate (MCP) detector.

Traditionally, proton beams have been used to create fission products at the IGISOL facilitybut research has shown that neutron induced fission has a higher yield of neutron rich fissionproducts[3]. In the past neutron beams have been created at IGISOL by nuclear reactions or bythe breaking up of deutrons. The energy of the neutrons created from the breakup of deuterium islimited to 15 MeV. To produce neutrons with higher energies proton induced reactions are used[4].A proton beam with energy up to 30 MeV from the MCC30/15 light ion cyclotron is made tocollide with a 6mm thick beryllium disc with a radius of 25mm to produce neutrons with energiesup to 29.6 MeV[5] via the 9Be(p,n) reaction as described in [4]. The beryllium target acted asa proton-neutron converter (see figure 2) in the 2016 experiment that studied neutron inducedfission. A MCNPX simulation model of the setup has previously been developed[4] and from thecomparison of the results from the model with the results from the experiment, it was assumedthat the the simulation model overestimated the fission rate. In order to verify that assumptionthe neutron flux used in model should be benchmarked. This can be done because another factorof the fission rate, the cross section for nuclear reactions, is well known. In the 2016 experiment theneutrons interacted with activation foils made of Titanium, Indium, Cobalt and Nickel. When theproton beam was turned off the metal foils were left to cool down for several days after which theirγ-ray spectra was measured. Counts of γ-rays was extracted from the spectroscopy data. Thepredicted number of γ-rays resulting from the neutron activation can be found from a calculationbased on the simulated neutron flux from the MCNPX model. By comparing the number of γcounts from the two sides the simulated neutron flux can be benchmarked. The focus of thisproject were the Titanium and Indium foils. Details will be presented in the following sections.

1

1.2 Application

The project concerns the analysis of γ-ray data from a HPGe-detector and the estimation of theexpected activation of a material in a neutron field. This particular case concerns the determinationof neutron flux for a study of neutron induced fission but the method could be applied to manyfields, for example radiation safety, material studies, contamination issues etc.

(a) Pn-converter (b) Ion guide

Figure 2: Schematic view (top view (a), side veiw (b)) of ion guide used in the test of neutroninduced fission at the IGISOL facility[3]. (I) pn-converter, (II) ion guide, (1) cooling water, (2)Beryllium target, (3) viton-o-rings (4) extraction nozzle (5) target material, (6) helium gas inlet,(7) implantation foil, (8) gas diffuser. The blue arrow represents the primary ion beam. A commonscale is given at the bottom of (b). The yellow line indicates the position of the Indium activationfoil.

2 Spectroscopy measurement

An experiment with neutron induced fission was conducted at IGISOL in 2016. The experi-ment was conducted with a proton beam with an energy of 30 MeV. In the experiment thea Titanium activation foil was implemented in position 7 in figure 2. The foil had a size of24.5mm×50mm×10mg/cm2. Another activation foil, made of Indium, was placed in the gap be-tween the pn-converter and the ion guide (parts I and II in figure 2, respectively) as indicated bythe yellow line in figure 2a. The indium foil had a size of 2.54cm×2.54cm×1mm[1]. The locationof the ion guide at the IGISOL facility is shown at position 1 in figure 1.

2.1 Measurements

After the proton beam had been turned off the activation foils were taken out of the chamber.Because the radiation from the neutron activation was too high, the activation foils were left tocool down for a few days before the γ-ray spectroscopy measurements started. Because of thisonly products with a half-life of at least two days were investigated. The Titanium foil was placed16 cm in front of a HGPe detector in a low background station. The Indium foil was measured atanother station and placed at a distance of 40 cm in front of the detector. Both activation foilswere measured twice. See table 1 for more information about the measurement campaigns.

2

Titanium activation foilEvent Dates and time Detector dead timeStart of irradiation 2016-12-09 at 19:40End of irradiation 2016-12-12 at 07:00Time of 1st measurement 2016-12-20 at 10:30End of 1st measurement 2016-12-21 at 10:33 0.22%Time of 2nd measurement 2017-01-23 at 16:10End of 2nd measurement 2017-01-24 at 00:08 0.17%

Indium activation foilEvent Dates and time Detector dead timeStart of irradiation 2016-12-09 at 19:40End of irradiation 2016-12-12 at 07:00Time of 1st measurement 2016-12-17 at 12:23End of 1st measurement 2016-12-17 at 06:43 7.20 %Time of 2nd measurement 2016-12-17 at 12:23End of 2nd measurement 2016-12-19 at 13:23 7.04 %

Table 1: Timeline of events for measurements of the Titanium and Indium activation foils

The γ-spectroscopy spectra from the first measurement of Titanium is shown in figure 3. Theenergy calibration and efficiency calibration (including geometry and energy efficiency) was doneusing a mixed source of 152Eu and 133Ba.

Figure 3: Experimental γ-ray spectra for first measurement of Titanium[6]

Figure 4 shows the efficiency curve. The measured count of a γ-ray in the detector is correctedby the total efficiency to represent counts in 4π space. For the Indium foil the energy calibrationwas done but not the efficiency calibration.

3

Figure 4: Efficiency correction formula for the detector used for the measurement of the Titaniumactivation foil calculated by Genie 2000[6]

2.2 Results

From the spectroscopy data the peak area can be extracted as counts of γ-rays. In table 2 thecounting rates as the peak area divided by the live time with uncertainties is shown. The γ-rayspectra from the experiment in 2016 was analyzed by finding prominent peaks and noting at whichenergy they were centered together with the peak area, peak area uncertainty, detector dead timeand time duration of the measurement. The prominent peaks were chosen because they were moreclearly separated from the registered background radiation which made them easier to identify bycomparing their γ-ray energy to tabulated γ-ray energies of radioactive isotopes[7]. Table 2 showsthe energies of the γ-rays from the peaks from the experimental spectra selected for study togetherwith the isotope with which it was identified. Correcting the counting rate extracted from thespectroscopy data using the efficiency formula:

ln(Eff) = −1.348e1 + 5.268e0ln(E) − 9.593e−1ln(E)2 + 4.818e−2ln(E)3 (1)

in figure 4 gave the number of counts of γ-rays that was compared to the number predicted bythe calculation. The number of counts of γ-rays are shown in the column ”Σγ-rays from allreactions” in table 2. The uncertainties used for the experimental data are the uncertaintiesbased on Poisson statistics calculated by the software. For the uncertainties in the theoreticalcalculation, the uncertainties in the simulated neutron flux and the uncertainties in the branchratio for the decay γ-radiation are taken into account. For the calculation of the uncertainties inthe theoretical calculation the propagation of uncertainties formula in equation 2 was used.

∆Z =

√(∂Z

∂x

)2

(∆x)2

+

(∂Z

∂y

)2

(∆y)2. (2)

4

Titanium 1st measurementexperimental data

Peak energy [MeV] Isotope Counting rate [s−1] Count rate uncertainty [s−1]888.9 46Sc 984 ± 31120.2 46Sc 1010 ± 4159.5 47Sc 5860 ± 4175.4 48Sc 133 ± 1983.2 48Sc 1402 ± 41037.2 48Sc 1375 ± 41212.6 48Sc 35 ± 11311.8 48Sc 1449 ± 51296.7 47Ca 61 ± 1

Titanium 2nd measurementexperimental data

Peak energy [MeV] Isotope Counting rate [s−1] Count rate uncertainty [s−1]889 46Sc 730 ± 4

1120.2 46Sc 743 ± 4159.5 47Sc 7 ± 0.3

Titanium 1st measurementcalculation

Peak energy [MeV] Isotope Σγ-rays from Uncertainty [s−1]all reactions [s−1]

888.9 46Sc 1398 2·10−6

1120.2 46Sc 1398 2·10−7

159.5 47Sc 3741 4·10−3

175.4 48Sc 171 6·10−5

983.2 48Sc 2283 3·10−3

1037.2 48Sc 2226 4·10−3

1212.6 48Sc 54 2·10−4

1311.8 48Sc 2283 4·10−3

1296.7 47Ca 71 2·10−8

Titanium 2nd measurementcalculation

Peak energy [MeV] Isotope Σγ-rays from Uncertainty [s−1]all reactions [s−1]

888.9 46Sc 1055 2·10−6

1120.2 46Sc 1055 2·10−7

159.5 47Sc 5 1·10−5

175.4 48Sc 4·10−4 1·10−10

983.2 48Sc 5·10−3 7·10−9

1037.2 48Sc 5·10−3 8·10−9

1212.6 48Sc 1·10−4 4·10−10

1311.8 48Sc 5·10−3 8·10−9

1296.7 47Ca 4·10−1 2·10−8

Table 2: Energies of chosen peaks in experimental spectra for Titanium and the isotopes identifiedwith the γ-ray energy.

5

3 Theoretical calculation

3.1 Neutron activation

To benchmark the neutron flux from the MCNPX simulation a theoretical calculation was per-formed. Which radioactive isotopes to use in the calculation was determined by looking at whatnuclear reactions that could have occurred between the materials of the foils and the neutrons.Because the metal foils were thin, 22.2µm and 1mm for Titanium and Indium respectively, it wasassumed that each of the neutrons only underwent a one chance reaction. That means that theneutrons did not interact with the activation products. A reaction with a single neutron wouldproduce radioactive isotopes belonging to elements with a mass number close to the mass numberof the parent. The reaction resulting in the largest difference in mass number that was consideredwas the reaction (n,α), which would lead to a reduction of the mass number by three, comparedto the parent nuclei. In figure 5 parts of the periodic table for Titanium and Indium are showntogether with the surrounding elements. The isotopes to be studied according to table 2, wherethe parent nuclei are identified with the γ-rays from the experimental γ-ray spectra, are markedby colored squares in figure 5.

(a) Titanium (b) Indium

Figure 5: Excerpts from the periodic table[7] showing the isotopes studied for Titanium (redsquares) and Indium (pink squares).

The reactions and isotopes used in the calculation for the Titanium and Indium activation foilsare shown in table 3. These reactions were chosen on the grounds that they all lead to reactionproducts which, when they decay, give off γ-rays with energies found in the experimental γ-rayspectra(see table 2). Since the isotopes in the foils and the activation products are known, theactivation reactions likely to occur can be determined.

Target element product Isotope Reaction Secondary product50Ti 47Ca 50Ti(n,α)47Ca 47Sc49Ti 48Sc 49Ti(n,d)48Sc48Ti 48Sc 48Ti(n,p)48Sc48Ti 47Sc 48Ti(n,d)47Sc47Ti 47Sc 47Ti(n,p)47Sc47Ti 46Sc 47Ti(n,d)46Sc46Ti 46Sc 46Ti(n,p)46Sc113In 111In 113In(n,3n)111In 111mCd113In 114mIn 113In(n,g)114mIn 114In115In 114mIn 115In(n,2n)114mIn 114In115In 115mCd 115In(n,p)115mCd 115Cd

Table 3: Reactions chosen for theoretical calculation for the activation foils. (n,α)= α decay,(n,d)= deutron decay, (n,p) = proton decay, (n,2n)= double neutron decay, (n,3n)= triple neutrondecay

6

3.2 Neutron flux Φ

The objective of the project was to benchmark the neutron flux from the MCNPX-simulation.The flux data text file contained columns of neutron flux energies ranging from 0 to 30 MeV withthe corresponding flux values in units of neutrons/cm2/proton. The values of the flux energywas converted into units of eV by multiplying them with 1 · 106 in order to be compatible withthe units of the experimental cross section. The values for the flux was converted into units ofneutrons/cm2 by the following procedure:The number of protons/s in proton beam of magnitude 10µA are:

10µA = 10µC

s= 10µ · 1

1.602e−19

protons

s= 6.242e13

protons

s(3)

This is used to convert the units of the neutron flux

neutrons

cm2proton· 6.242e13

protons

s= 6.242e13

neutrons

cm2s(4)

Experimental cross section σ

The values for the experimental cross section for the reactions studied used in the theoreticalcalculations was acquired from Evaluated Nuclear Data File (ENDF)[8]. The experimental crosssection data was linearly interpolated in order for the data points in the tabulated cross sectionto match the data points for the flux from the MCNPX-simulation.

Branching fractions and branch ratios

Some isotopes can have several decay modes, such as β− and e+ decay. The probability of eachis given by the branching fraction. Each decay also has a probability of giving off one or severaldecay γ-rays of an energy characteristic of that isotope. The probability of an isotope giving offa decay γ is given by the branch ratio for that γ-energy. The values of the branch fractions andthe branch ratios used in the calculation was acquired from the nuclear data base NuDat 2.7[7].

3.3 Formula

As can be seen in table 1 , there were three distinct stages involved in the experiment. The firststage was the time for which the foils were irradiated, the second stage was the cool down timebetween the time the beam was turned off until the HPGe measurement of the foils began. Thethird stage was the HPGe measurement. The calculation was done using different formulas foreach stage.

3.3.1 Production of activation products during irradiation

When the foils were irradiated, activation products were created in the material. Mathematicallythis is described by the radioactive decay law with a source term

dN(t)

dt= P − λN(t), (5)

which has the solution

N(t) =P

λ(1 − e−λt), (6)

where N(t) is the number of nuclei at time t, λ is the decay constant of the nuclei and P =ΦσNtarget is the production of activation products per unit time, where Φ is the neutron flux inunits of [neutronscm2s ], σ is the reaction cross in units of barns and Ntarget is the number of targetatoms in the sample. P is assumed to be constant because the number of atoms in the materialis many orders of magnitude greater than the amount of activation products produced. In some

7

cases there might be several sources of production of a radioactive isotope. It can be produced byneutron activation and also as a decay product of another activation product. If this is the case,the radioactive decay law for the isotope is found by starting from the radioactive decay law[9]

dN2(t)

dt= −λ2N2(t) + λ1N1(t) + P2, (7)

where the right side of the equation has one component, −λ2N2(t), for the decay of the isotope,one component, λ1N1(t), for the creation of isotopes from the decay of a parent nuclei and onecomponent, P2, for the creation of isotopes by neutron activation and λ is the decay constant ofthe nuclei. Equation 7 is solved by inserting equation 6 for N1 into equation 7 and multiplying byan integrating factor eλ2t.

eλ2tdN2(t)

dt= −λ2eλ2tN2(t) + λ1e

λ2tP1

λ1(1 − e−λ1t) + eλ2tP2. (8)

Collecting all N2(t) on the left side and simplifying gives

d

dt(eλ2tN2(t)) = P1(eλ2t − e(λ2−λ1)t) + eλ2tP2. (9)

Integrating both sides with respect to time gives∫ t

0

d

dt(eλ2tN2(t))dt =

∫ t

0

P1(eλ2t − e(λ2−λ1)t)dt+

∫ t

0

P2eλ2tdt. (10)

Performing the integration leads to

eλ2tN2(t) −N2(0) = P1

[eλ2t

λ2− e(λ2−λ1)t

(λ2 − λ1)

]t0

+ P2

[eλ2t

λ2

]t0

, (11)

where N2(0) = 0 because there are no N2 present at time 0. This simplifies to

N2(t) =P1

λ2

(1 +

λ1e−λ2t − λ2e

−λ1t

(λ2 − λ1)

)+P2

λ2

(1 − e−λ2t

), (12)

which is the equation for the total number of a specific radioactive nuclei at time t. Equation6 and equation 12 were used to calculate the number of activation products as function of timeduring the irradiation of the foils.

Decay of activation products during cool down time

After the irradiation of the activation foils had stopped the radioactive activation products in thefoils started to decay. The amount that were left at time t was calculated with equation[9]

N1(t) = N1(0)e−λ1t (13)

for a single activation product or the first activation product in a decay chain and with

N2(t) = N2(0)e−λ2t +λ1N1(0)

(λ2 − λ1)

(e−λ1t − e−λ2t

)(14)

for a radioactive nuclei in a decay chain, where N(t) and N(0) are the number of activation productsat time t and t=0 respectively.

8

Decay of activation products during HPGe measurement

The total amount of decays for a single activation product or the first activation product in a decaychain during the measurement time is given by the difference between how many were present attime t=0 and time t:

∆N1(t) =(N1(0) −N1(0)e−λ1t) = N1(0)(1 − e−λ1t

)(15)

For the daughter nuclei N2 there is an additional term that comes from the number of parent nucleiN1 that has decayed into N2 and then decayed further. To find the total number of decays forthe daughter nuclei during the measurement time the activity of the daughter nuclei is integratedwith respect to time

∆N2(t) =

∫ t

0

λ2N2(t)dt, (16)

where ∆ N2(t) are the number of daughter nuclei that have decayed and N2(t) on the right handside is given by equation 14.

Inserting equation 14 into equation 16 and performing the integration gives

∆N2(t) =

∫ t

0

λ2

(N2(0)e−λ2t +

λ1N1(0)

(λ2 − λ1)

(e−λ1t − e−λ2t

))dt =

=

∫ t

0

(λ2N2(0)e−λ2t +

λ1λ2N1(0)

(λ2 − λ1)

(e−λ1t − e−λ2t

))dt =

= λ2N2(0)

[−e

−λ2t

λ2

]t0

+λ1λ2N1(0)

(λ2 − λ1)

[−e

−λ1t

λ1+e−λ2t

λ2

]t0

=

= N2(0)(1 − e−λ2t

)+λ1λ2N1(0)

(λ2 − λ1)

(λ1e

−λ2t − λ2e−λ1t

λ1λ2− (λ1 − λ2)

λ1λ2

),

(17)

which simplifies to

∆N2(t) = N2(0)(1 − e−λ2t

)+N1(0)

(1 +

λ1e−λ2t − λ2e

−λ1t

λ1 − λ2

)(18)

To express the decays of the nuclei in decays/s, the decays per branch ratio were divided bythe total measurement time of the HPGe-measurement. In order to be able to compare thetheoretical prediction to the experimental value, the number of predicted decays/s were adjustedto compensate for the detector dead time(see section 2.1).

3.4 Results

Based on the reactions in table 3 the product rates for different reactions were calculated. Theproduct rate is defined as PR = ΦσNtarget, where Φ is the neutron flux and σ is the cross sectionfor a specific reaction. Figure 6 shows the neutron flux together with cross sections for differentreactions and the corresponding product rate. The simulated neutron flux is shown in the top partof the graphs. The neutron energy is distributed between zero up to 30 MeV although there is ahigher concentration of neutrons at the lower part of the energy scale. The reaction cross sectionis shown in the middle part of the graphs. The cross sections are zero up to a certain energy.This is the threshold energy for the specific reaction to occur, which is dependent on the Q-valueof the reaction. The bottom parts of the graphs show the product rate, which is the product ofthe top two parts of the graph. This represents the probability per unit time of a certain reactionoccurring.

9

To perform the theoretical calculation the reaction rate R = ΦσNtarget was calculated for all thereactions studied. The results are shown in figure 6.

(a) Reaction rate for 46Sc

(b) Reaction rate for 47Sc

Figure 6: Reaction rates for production of studied isotopes.

10

(c) Reaction rate for 48Sc

(d) Reaction rate for 47Ca

Figure 6: Reaction rates for production of studied isotopes.

11

Ratio of predicted over experimental number of γ-rays

To compare the predicted number of γ-rays from calculation with the counts of γ-rays from thespectroscopy measurement, the ratio defined as Nc/Ne is shown in figure 7, where Nc representsthe calculated count of a specific γ-ray and Ne is the experimental count of the same γ-ray.

Figure 7: Ratio of calculated over experimental number of γ counts. The error bars representsthe uncertainty in the calculations.

4 Comparison and discussion

Figure 7 shows that most of the points representing the ratio of Nc over Ne are distributed around1.5. This result is consistent with results reported in the work of Zhihao[5] and suggests that theneutron flux is overestimated by about 50%.

There were some problems with the calculation of the Indium foil. One is that the efficiencycalibration for the spectroscopy setup used to measure the Indium foil was not done and withoutthat there is no reliable data to compare the calculations to. Another issue is that 114mIn and115mCd are products of the neutron activation and there is no information about the isomericyield ratio for these two nuclides. There were plans to put weights on the production of metastates in order to guess the production but there was no time to perform the calculations. When115mCd and 115Cd decay to the daughter nucleus they will first decay to an isomeric state witha half life of several hours. The equation to use for the calculation was found but there was notime to perform the calculations.

The formulas for a single activation product gave consistent results where the predicted activity atthe second measurement had lowered at the same rate as the experimental activity. The formulafor a decay chain consistently underestimated the number of created activation products. Thereason is most likely a reaction missing in the analysis or a faulty assumption. One assumptionwas that an activation product does not interact with the neutrons in the neutron flux. Buta reaction such as 48Sc(n,2n)47Sc, where 48Sc is a neutron activation product, could solve twoproblems at once. It has a reasonably high reaction cross section (0.9 barns), so it is likely tooccur, and the calculated values of 48Sc are higher than expected whereas the values for 47Sc aretoo low. If some of the 48Sc isotopes were to be transformed into 47Sc isotopes the theoretical

12

results would agree better with the experimental results. This was not investigated due to a lackof time.

5 Conclusion

The predicted counts of γ-rays were calculated based on the neutron flux and cross section forthe Titanium foil. The sources of the γ-rays in the spectroscopy measurements for Titaniumand Indium foils have been identified. By comparing the predicted counts with the experimentalcounts it was concluded that the neutron flux is overestimated by approximately 50%. This agreeswith Zhihao’s result[5]. Because the lack of the efficiency calibration and isomeric yield ratio theanalysis was not finished in the case of the Indium foil.

6 Outlook

Many of the potential candidates for activation products in the Indium activation foil were isotopeswith meta states. The tabulated data for the cross sections do not take into account the numberof activation products that are created in the more energetic meta state. How many that arecreated in the meta state is important because some meta states have a longer half life than theground state. For instance 114mIn, with a half life of 49.51 days as compared to its ground statewith a half life of 71.9 seconds. This difference is crucial if the activation product is to surviveuntil it can be measured. An accurate knowledge of the meta state yield in the activation processwould be beneficial in creating better results. Since an upgrade of the IGISOL facility in 2017 itis possible to separate metastable states with energies of a few keV[10]. That information couldbe used to perform studies that could verify the MCNPX simulation with a higher accuracy.

13

References

[1] Mattera A, Pomp S, Lantz M, Rakopoulos V, Solders A, Al-Adili A,et al. Production of Snand Sb isotopes in high-energy neutron-induced fission of nat U. Eur. Phys.J A, 54(33), 2018.

[2] University of Jyvaskyla. IGISOL[internet], [cited 2020 Jan 12]. Available at https://www.jyu.fi/science/en/physics/research/infrastructures/accelerator-laboratory/

nuclear-physics-facilities/the-exotic-nuclei-and-beams.

[3] Gorelov D, Penttila H, Al-Adili A, Eronen T, Hakala J, Jokinen A,et al. Developments forneutron-induced fission at igisol-4. Nucl. Instr. Meth. B, 376(46-51), 2016.

[4] Jansson K, Al-Adili A, Nilsson N, Norlin M and Solders A. Simulated production rates ofexotic nuclei from the ion guide for neutron-induced fission at igisol. Eur. Phys.J A, 53(243),2017.

[5] Gao Z, Solders A, Al-Adili A, Canete L, Eronen T, Gorelov D, et al. Fission studies atigisol/jyfltrap: Simulations of the ion guide for neutron-induced fission and comparison withexperimental data, 2019 (Unpublished).

[6] MIRON Technologies, The Detection and Measurement Division. GenieTM 2000, basic spec-troscopy software basic spectroscopy software[internet], 2020 [cited 2020 Jan 12]. Availableat https://www.mirion.com/products/genie-2000-basic-spectroscopy-software.

[7] Alejandro Sonzogni. Nudat 2.7 [internet], [cited 2020 Jan 12]. Available at https://www.

nndc.bnl.gov/nudat2/.

[8] Viktor Zerkin. Evaluated nuclear data file (endf) [internet], 2020[cited 2020 Jan 12]. Availableat https://www-nds.iaea.org/exfor/endf.htm.

[9] Osterman J Nordling C. Physics Handbook for Science and Engineering. Studentlitteratur,Lund, Sweden, 7 ed. edition, 2004.

[10] Rakopoulos V, lantz M, Solders A, Al-Adili A, Mattera A, Canete L,et al. First isomericyield ratio measurements by direct ion counting and implications for the angular momentumof the primary fission fragments. Phys. Rev. C, 98(024612), 2018.

14