Neutron-capture cross-sections of ²⁴⁴Cm and ²⁴⁶Cm measured with an array of large germanium detectors in the ANNRI at J-PARC/MLF

Figures & data

Figure 1. A side view of NNRI. The neutron beam emitted from the moderator goes through the T0 chopper, neutron filter, disk choppers, collimators and the two detector systems, and then is dumped into the beam stopper. The sample positions for the array of large Ge detectors and NaI detectors are 21.5 and 27.9 m from the moderator, respectively.

Figure 2. Layout of the array of Ge detectors. The array is composed of two cluster-Ge detectors, eight coaxial-Ge detectors and anti-coincidence shields around each Ge detector.

Table 1. Isotopic and chemical impurities of curium oxide in the ²⁴⁴Cm and ²⁴⁶Cm samples [15].

	^244Cm sample		^246Cm sample
	TIMS (mole%)	α-Ray spectrometry*	TIMS (mole%)	α-Ray spectrometry*
^244Cm	90.1 ± 1.7	90.1	27.5 ± 0.5	27.5
^245Cm	2.71 ± 0.34	Not detected	1.06 ± 0.28	Not detected
^246Cm	7.22 ± 0.34	7.0 ± 0.6	59.4 ± 1.3	55.6 ± 1.7
^247Cm	Not detected	Not detected	2.9 ± 0.4	Not detected
^248Cm	Not detected	Not detected	9.10 ± 0.24	Not detected
^240Pu	–	13.6 ± 0.6	–	2.97 ± 0.14
Note: *The values are obtained by normalizing to the results of ^244Cm with TIMS.

Figure 3. γ-ray pulse-height spectra from the ²⁴⁴Cm sample with neutron beam (red solid line), the dummy case (black dotted line), and a decay γ-ray pulse-height spectrum from the ²⁴⁴Cm sample without neutron beam (blue dashed line) measured with one of the crystals.

Figure 4. γ-ray pulse-height spectra from the ²⁴⁶Cm sample with neutron beam (red solid line), the dummy case (black dotted line), and a decay γ-ray pulse-height spectrum from the ²⁴⁶Cm sample without neutron beam (blue dashed line) measured with one of the crystals.

Figure 5. The resonance-gated net spectrum (black solid line) and the sum of the resonance-gated γ-ray pulse-height spectra (gray solid line) in the first resonance of ²⁴⁰Pu in the ²⁴⁶Cm sample data.

Figure 6. The resonance-gated net spectra in the first resonance of ²⁴⁴Cm from the ²⁴⁴Cm sample (black dashed line) and the ²⁴⁶Cm sample (gray solid line). Asterisks (*) indicate previously unknown γ-rays.

Table 2. Observed γ-ray energies and transition assignments.

γ-Ray energies (keV)	Transition assignment [2] (keV)
^244Cm
252.4 ± 1.5	252.84 ± 0.02 → g.s.
380.8 ± 1.7	633.64 ± 0.011 → 252.84 ± 0.02
3250 ± 3*	Not assigned
3260 ± 3*	Not assigned
3865 ± 3*	Not assigned
4122 ± 3*	Not assigned
4524 ± 3*	c.s. → 633.64 ± 0.011
4885 ± 3*	c.s. → 252.84 ± 0.02
^246Cm
438.3 ± 1.6*	439 ± 3 → g.s.
892.4 ± 1.8*	897 ± 5 → g.s.
3634 ± 3*	Not assigned
4206 ± 3*	c.s. → 947 ± 2
4493 ± 3*	c.s. → 668 ± 5
Note: *Previously unknown γ-rays.

Figure 7. The resonance-gated net spectrum in the first resonance of ²⁴⁶Cm from the ²⁴⁶Cm sample. Asterisks (*) indicate previously unknown γ-rays.

Figure 8. Typical TOF spectra of the ²⁴⁴Cm and ²⁴⁶Cm samples measured with one of the 14 crystals.

Figure 9. Flow chart of data analysis procedures.

Figure 10. A typical time dependence of the live-to-real time ratio (red dotted line) and the corresponding TOF spectra with (blue dashed line) and without (black solid line) the dead-time correction from the ²⁴⁶Cm sample measured with one of the Ge crystals.

Figure 11. A typical TOF spectrum measured with one of the crystals (blue dotted line), the corresponding TOF dependence of the area count due to the random timing pulses (red dashed line), the TOF spectra with the dead-time correction (light-blue solid line), the fitted curve (black dashed-dotted line), and the deduced background (black solid line) in the 0–80 ms TOF range from the ²⁴⁶Cm sample.

Figure 12. A typical estimated background of the ²⁴⁶Cm sample measured with one of the crystals (red dashed line) and the corresponding TOF spectrum minus the background due to overlapping neutrons and decay γ-rays (black solid line).

Figure 13. The sum TOF spectra of the ²⁴⁴Cm sample (black solid line) and the ²⁴⁶Cm sample (gray solid line) and the uncertainties of the ²⁴⁴Cm sample (black dashed line) and the ²⁴⁶Cm sample (gray dashed line).

Figure 14. Correction factors for neutron self-shielding and multiple scattering for the ²⁴⁶Cm sample (gray solid line) and the ²⁴⁴Cm sample (black dashed line).

Figure 15. The averaged neutron flux at the 21.5-m sample position (black solid line) and neutron-energy-dependent errors (gray dashed line).

Figure 16. The normalized yields weighted by the abundance listed in Table 1 (red solid line); the contributions from neutron-capture events of ²⁴⁰Pu, ²⁴³Am, and ^{244, 246}Cm (black dashed line); and uncertainties in the contributions (blue dotted line) from the ²⁴⁴Cm sample in the neutron energy region from 1 to 100 eV.

Figure 17. The normalized yields weighted by the abundance listed in Table 1 (red solid line); the contributions from neutron-capture events of ²⁴⁰Pu, ²⁴³Am, and ^{244, 246, 248}Cm (black dashed line); and uncertainties in the contributions (blue dotted line) from the ²⁴⁶Cm sample in the neutron energy region from 1 to 100 eV.

Table 3. Obtained resonance parameters along with the evaluations of JENDL-4.0 [16].

^244Cm sample			^246Cm sample			Belongs	Averaged			JENDL-4.0
E (eV)	Γγ (meV)	Γ n (meV)	E (eV)	Γγ (meV)	Γ n (meV)		E (eV)	Γγ (meV)	Γ n (meV)	E (eV)	Γγ (meV)	Γ n (meV)
1.0551 ± 0.0015	30.6 ± 0.6	2.446 ± 0.018	1.0550 ± 0.0015	30.6 ± 0.6	2.445 ± 0.018	^240Pu	1.0551 ± 0.0013	30.6 ± 0.4	2.446 ± 0.013	1.06	29.1 ± 0.6	2.45 ± 0.02
1.350 ± 0.004	51 ± 4	1.02 ± 0.06	1.350 ± 0.003	45 ± 8	1.07 ± 0.10	^243Am	1.350 ± 0.003	47 ± 5	1.05 ± 0.06	1.360 ± 0.001	50.0 ± 1.2	1.10 ± 0.01
4.317 ± 0.007	26.7 ± 2.6	0.266 ± 0.013	4.311 ± 0.007	29.5 ± 3.1	0.300 ± 0.009	^246Cm	4.314 ± 0.006	28.1 ± 2.0	0.283 ± 0.008	4.320 ± 0.003	28.0 ± 5.6	0.31 ± 0.01
−			7.242 ± 0.012	25 ± 4	1.78 ± 0.10	^248Cm	7.242 ± 0.012	25 ± 4	1.78 ± 0.10	7.250 ± 0.005	23.3 ± 4.7	1.89 ± 0.03
7.659 ± 0.012	38.1 ± 2.9	8.90 ± 0.25	7.662 ± 0.012	38 ± 5	8.6 ± 0.4	^244Cm	7.661 ± 0.011	37.8 ± 2.9	8.77 ± 0.22	7.67 ± 0.03	37.0 ± 3.7	9.6 ± 0.4
−			15.31 ± 0.03	33 ± 6	0.50 ± 0.04	^246Cm	15.310 ± 0.027	33 ± 6	0.50 ± 0.04	15.30 ± 0.02	31.0 ± 6.2	0.55 ± 0.01
16.790 ± 0.029	38 ± 4	1.74 ± 0.06	16.79 ± 0.03	38 ± 7	1.70 ± 0.12	^244Cm	16.79 ± 0.03	38 ± 4	1.72 ± 0.07	16.80 ± 0.08	37.0 ± 3.7	1.95 ± 0.30
20.45 ± 0.05	28 ± 5	2.8 ± 0.4	20.45 ± 0.04	27 ± 5	2.9 ± 0.4	^240Pu	20.45 ± 0.04	28 ± 4	2.88 ± 0.29	20.4	27.0 ± 1.4	2.75 ± 0.3
22.85 ± 0.04	40 ± 4	0.90 ± 0.04	22.86 ± 0.04	41 ± 8	0.93 ± 0.09	^244Cm	22.86 ± 0.04	40 ± 4	0.91 ± 0.05	22.90 ± 0.05	37.0 ± 3.7	0.84 ± 0.10
–			26.90 ± 0.05	33 ± 6	17.8 ± 2.2	^248Cm	26.90 ± 0.05	33 ± 6	17.8 ± 2.2	26.90 ± 0.02	32.0 ± 6.4	19.2 ± 0.9

Figure 18. The obtained capture yields weighted by the abundance in Table 1 (gray circles), with the corresponding uncertainties (black dashed line), the SAMMY [26]-fitted results for all nuclides (purple solid line), ²⁴⁴Cm (red dashed line), ²⁴⁶Cm (blue dashed line), ²⁴³Am (orange dashed line), and ²⁴⁰Pu (green dashed line) using the parameters shown in Table 4 (below 30 eV) and the JENDL-4.0 [16] (above 30 eV) in the neutron energy region from 1 to 100 eV for the ²⁴⁴Cm sample.

Figure 19. The obtained capture yields weighted by the abundance in Table 1 (gray circles), with the corresponding uncertainties (black dashed line), the SAMMY [26]-fittedresults for all nuclides (purple solid line), ²⁴⁶Cm (red dashed line), ²⁴⁴Cm (blue dashed line), ²⁴⁸Cm (light green dashed line), ²⁴³Am (orange dashed line), and ²⁴⁰Pu (green dashed line) using the parameters shown in Table 4 (below 30 eV) and the JENDL-4.0 [16] (above 30 eV) in the neutron energy region from 1 to 100 eV for the ²⁴⁶Cm sample.

Figure 21. The capture yields weighted by the abundance in Table 1 from the ²⁴⁶Cm sample with error bars (blue circles), the SAMMY [26] fits using the parameters shown in Table 4 (blue solid line), and comparison to JENDL-4.0 [16] (broadened with SAMMY, black dashed line) around the first resonance of ²⁴⁶Cm.

Figure 20. The capture yields weighted by the abundance in Table 1 from the ²⁴⁴Cm sample (red circles) and the ²⁴⁶Cm sample (blue triangles) with error bars, the results of the SAMMY [26] fits using the parameters shown in Table 4 (²⁴⁴Cm sample: red solid line, ²⁴⁶Cm sample: blue solid line), and comparison to JENDL-4.0 [16] (broadened with SAMMY, ²⁴⁴Cm sample: black dotted line, ²⁴⁶Cm sample: black dashed line) around the first resonance of ²⁴⁴Cm.

Figure 22. Deduced neutron-capture cross-sections of ²⁴⁴Cm (black circles with gray error bars) and comparison to those measured by Moore [4] (blue triangles with blue err bars) and broadened JENDL-4.0 [16].

Figure 23. Deduced neutron-capture cross-sections of ²⁴⁶Cm (black circles with gray error bars) and comparison to those measured by Moore [4] (blue triangles with blue err bars) and broadened JENDL-4.0 [16].

Figure 24. The ratios of sensitivities of the first and second resonances of ²⁴⁶Cm and the first, second, third, and forth resonances of ²⁴⁴Cm to that of ²⁴⁰Pu at the first resonance were calculated.

Figure 25. The deduced neutron-capture cross-sections of ²⁴⁴Cm (black circles; contribution from error sources to the uncertainties of the cross-sections, total error: red solid line; the abundances of ²⁴⁰Pu: black solid line; the evaluated value of JENDL-4.0 [16] of the first resonance of ²⁴⁰Pu: black dashed line; the contribution of fission events: blue dashed line; statistic: green solid line; self-shielding and multiple scattering: green dashed line; and systematic one in the normalization: purple solid line) around the first resonance of ²⁴⁴Cm.

Figure 26. The deduced neutron-capture cross-sections of ²⁴⁶Cm (black circles; contribution from error sources to the uncertainties of the cross-sections, total error: red solid line; the abundances of ²⁴⁰Pu: black solid line; the evaluated value of JENDL-4.0 [16] of the first resonance of ²⁴⁰Pu: black dashed line; isotopic ratio of ²⁴⁴Cm to ²⁴⁶Cm: blue solid line; the contribution of fission events: blue dashed line; statistic: green solid line; self-shielding and multiple scattering: green dashed line; and systematic one in the normalization: purple solid line) around the first resonance of ²⁴⁶Cm.

Table 4. Contributions to the non-neutron-energy-dependent errors in this work.

	^244Cm sample (%)	^246Cm sample (%)
SAMMY fitting error	0.6	0.3
Errors in the abundances of ^240Pu	4.4	4.7
Errors in the evaluated value of JENDL-4.0 [16] of the first resonance of ^240Pu	2.2	2.2
Systematic errors in the normalization (shown in section 5.1.1.1)	2.4	2.4
Systematic errors in influences of the scattered neutrons (shown in section 5.1.1.2)	0.3	0.3
Error in the isotopic ratio of ^244Cm to ^246Cm	–	2.7
Total (only the non-energy-dependent errors)	5.5	5.9