Fission Product Yields for Neutrino Physics and Non- prolifera7on

Transcription

1 Fission Product Yields for Neutrino Physics and Non- prolifera7on

2 The nuclear physics proper7es of fission products are important for many fields Neutrino Physics Nuclear Forensics Monitoring Reprocessing Facili6es Weapons Physics Reactor Safeguards Stellar Astrophysics Nuclear Medicine In many cases more detailed experimental data is needed - Here are some examples from from the first two fields

3 Neutrino Physics

4 Reactors represent intense sources of anti-neutrinos and are used for neutrino oscillation studies A 3 GW reactor emits antineutrinos per second - All produced by the beta-decay of fission products E ν ~ 0 10 MeV Detected by Reines & Cowan via: ν e + p n + e +

5 Reactor Neutrino Experiments Discoveries since the 1950s: Short Middle Long Neutrino discovered in by Reines and Cowan. Short baseline expts determined an6neutrino spectrum/flux (maybe) Upper limit of mixing angle θ 13 to sin 2 2θ 13 <0.17 (Chooz, Palo Verde), s An6- neutrino disappearance at KamLAND in Precision measurements of θ 13 (Daya Bay, Double Chooz, RENO), present

6 An7- neutrino spectra are determined by the cumula7ve yields and the beta- decay spectra of the fission products Equilibrium aggregate beta spectra: S k (E) = FF Y FF (Z,A,m)S(E,Z,A,m) S(E,A,Z,m) = B i S(E,Z, A,m,E 0 i ) i Spectra are quite ac6nide dependent β- decay branching ra6os and end- point energies only known for ~95% of the decays Many of the cumula6ve fission yields are uncertain

7 Neutrino community determined the an7neutrino spectra from measurements of aggregate beta- decay spectra Measurements at ILL of thermal fission beta spectra for 235 U, 239 Pu, 241 Pu Converted to an6neutrino spectra by fidng to 30 end- point energies Use Vogel et al. and Mueller et al. database es6mates for 238 U 238 U ~ 7-8% of fissions =>small error K. Schreckenbach et al. PLB118, 162 (1985) A.A. Hahn et al. PLB160, 325 (1989) FIT S β (E) = A i S i (E, E i o ) i=1,30 S i (E, E 0 i ) = E β p β (E 0 i E β ) 2 F(E, Z)

8 As Burn Proceeds: Different Combination of Isotopes Fissioning 239 Pu steadily grows in via: 238 U+nà 239 Uà 239 Npà 239 Pu Followed by higher mass Pu This change translates into a change in the antineutrino spectrum emitted from the beginning to the end of a burn cycle T=0/T=1yr 5% fewer detected an6neutrinos ager 1 yr Must be taken into account in osc expts. Basis of non- prolifera6on schemes Bugey-3 energy-dependent decrease after 1 year

9 Calcula7ng the an7neutrino flux at a given reactor 1. Measure thermal power in primary & secondary loop W th uncertainty ~<2%, but KamLAND quote % Uncertainty usually dominated by water flow measurement. 2. Calculate number of fissions from W th E f good to ~0.5-1% (?) Kopeiken et al. Phys. Atom Nucl. 67 (2004) Power company reactor burn simula7on to determine which isotopes are fissioning N f = W th / E f E f = E tot < E ν > ΔE βγ + E (n,γ ) isotopes SE ( ν) = fs i i( Eν) i 4. Knowledge of individual an7neutrino spectra for each fissioning isotope 4. has recently become a serious problem observing an anomaly and a `bump

10 Men6on et al. PRD Short Baseline Reactor An7- Neutrino Anomaly Improved An7neutrino Spectra: Th. A. Mueller, et al. PRC, C83 (2011) A reanalysis of the conversion of the aggregate beta- spectrum to an an6- neutrino spectrum All short baseline experiments saw ~6% too few an6neutrinos If oscilla6ons would require 1 ev sterile neutrino

11 Known correc7ons to β- decay are the main source of the anomaly S(E e,z,a) = G 2 F 2π p E (E E 3 e e 0 e )2 C(E)F(E e,z, A)(1+δ(E e,z, A)) Frac7onal correc7ons to the individual beta decay spectra: δ(e e,z, A) = δ rad +δ FS +δ WM { δ rad = Radiative correction (used formalism of Sirlin) δ FS = Finite size correction to Fermi function δ WM = Weak magnetism Originally approximated as: δ FS +δ WM = (E ν 4MeV )) The difference between this original treatment and an improved treatment of these correc7ons is the main source of the anomaly

12 However, 30% of the transi7ons are forbidden => the uncertaunty in the anomaly large A~95 Peak Forbidden: Br, Kr, Rb, Y, Sr, Zr mostly forbidden Not Fermi (0+) or GT (1+) Nb, Mo, Tc ogen allowed GT i.e, ΔL>0, Δπ=+/- 1 A~ 137 Peak Sb, I, Te, Xe, Cs, Ba, Pr, La - mostly forbidden The forbidden transi6ons tend to dominate the high energy component of spectrum This makes the weak magne6sm and finite size correc6on quite uncertain If all allowed the fit to Schreckenbach => An6neutrino spectrum +3% If 25% forbidden Find an equally good fit with no increase in the an6neutrino spectrum

13 A significant shoulder (the bump) is seen in the near and far detectors at all current reactor neutrino experiments at E prompt =4-6 MeV Εν=Eprompt MeV

14 Analyses of the Bump using ENDF versus JEFF cumula7ve yields differ ENDF, Dwyer + Langford, Phys. Rev. Ler (2015) A. A. Sonzogni, T. D. Johnson, and E. A. McCutchan, Phys. Rev. C 91, (R) (2015)

15 ENDF versus JEFF predic7ons for the BUMP Normailzed ratio to Huber-Mueller Huber-Mueller uncert. JEFF ENDF/B-VII.1 RENO The two evalua6ons disagree on many of the fission yields for nuclei domina6ng the bump Normalized Ratio to Huber-Mueller Huber-Mueller uncert. JEFF ENDF/B-VII.1 Daya Bay E Prompt (MeV)

16 ENDF versus JEFF predic7ons for the normaliza7on of the an7neutrino spectra σ ν N ν (E ν ) (10-16 mb/mev/fission) Huber-Mueller Daya Bay ENDF/B-VII Eν (MeV) Huber-Mueller Daya Bay JEFF The ENDF/B- VII.1 predic7ons are closer to Daya Bay, while the JEFF predic7ons are closer to the Huber- Mueller model that suggests an anomaly

17 The hardness of the reactor spectrum could be an issue The original fission aggregate beta spectra were measured at ILL, France - Heavy water reactor 10 Extremely thermal 7 The Daya Bay, RENO and Double Chooz measurements are all at PWR reactors Significant epithermal neutron component to the flux Fisison Cross cross section (b) Φ(E)*σ(E) σ(e) fission 239 Pu Φ(E) for 3% Enriched PWR 1 st epithermal resonance at 0.3 ev E (ev) Could the JEFF yields be closer to thermal And the ENDF/B- VII.1 yields be thermal/epithermal? Experimental measurements of the dominant fission yields would be very valuable in addressing the these neutrino issues

18 Nuclear Forensics

19 Nuclear Forensics relies on measuring the ac7nide ra7os in the debris Timescale is controlled by the difficult U & Pu chemistry: Separate key ac6nides and measure their isotopic ra6os by mass spectroscopy. Ac6nides provide the most detailed informa6on But there is a pressing need to get key informa6on on a faster 6mescale

20 The vola7le fission products could be collected and measured rapidly by flying into the plume 1. Collect the vola7le fission products on special filters 2. Assay key fission products on a rapid 7mescale using γ- ray spectroscopy 3. Deduce the fuel and whether the device was boosted from blocked Cs and I isotopes Timescale possible because no major chemical separa7on is needed for Cs and I

21 Sensi7vity of Cesium and Iodine to the type of explosion - blocked fission products retain fission informa7on The required cesium R- values are measured But the iodine isotopes of interest are not Radiochemistry always evaluated in terms of R- values: ( ) Y x 99Mo R = Y x 99Mo ( )thermal Varies by orders of magnitude Always ~1 Varies by orders of magnitude Close to ~1

22 Debris Frac7ona7on - always occurs but can be corrected for 136 Cs& 13$days$ 136 Xe& Stable&&! 137 Cs& 30$yrs$ β" 0.23% 137 Xe& 3.82$mins$ β" 3.5% 2.4% &&&&137 I& 24.5$sec$ 235 U fission β" 0.16% 137 Te& 2.5$sec$ The transport of 137 Cs depends 137 I and 137 Xe. 136 Cs has no precursors. => 136 Cs and 137 Cs from one another. 136Cs [R-value] R-value needed for Pu Cs [R-value] Frac7ona7on is corrected for by using the fact that the 137Cs/99Mo ra7o is close to unity for all fissions Uncertain7es in the method are small compared to the sensi7vity of 136 Cs/ 99 Mo to the nature of the fission

23 Summary Reactor neutrino physics is currently facing two major puzzles The anomaly, which is a 6% deficit in the an6neutrino flux at all short baseline experiments The shoulder (bump) at Eν= MeV ENDF and JEFF give very different predic6ons for these because their yields for the important fission product are different handful of fission products, that dominate the high- energy spectrum, need to be measured Nuclear Forensics could involve a new early phase The blocked cesium and iodine fission products can be used to determine whether the fuel is uranium and plutonium and whether 14 MeV fission is involved the 130 I and 135 I thermal, fast and 14 MeV fission yields need to be measured

24 Summary cont. Nuclear Forensics could involve a new early phase The blocked cesium and iodine fission products can be used to determine whether the fuel is uranium and plutonium and whether 14 MeV fission is involved the 130 I and 135 I thermal, fast and 14 MeV fission yields need to be measured