22Ne(a,n)25Mg status and perspectives (for an underground experiment) GIANTS, Padova 28-30 Aprile 2015 22Ne(a,n)25Mg status and perspectives (for an underground experiment) F. Cavanna & P. Prati INFN - Genova

Astrophysical motivations: AGB stars GIANTS, Padova 28-30 Aprile 2015 Astrophysical motivations: AGB stars Thermally pulsing stage (TP) Temperatures in the base of the convective zone high enough to ignite the 22Ne(a,n)25Mg 22Ne produced via: 14N(a,g)18F(b+n)18O(a,g)22Ne

Astrophysical motivations: AGB stars GIANTS, Padova 28-30 Aprile 2015 Astrophysical motivations: AGB stars Thermally pulsing stage (TP) Temperatures in the base of the convective zone high enough to ignite the 22Ne(a,n)25Mg 22Ne produced via: 14N(a,g)18F(b+n)18O(a,g)22Ne

Astrophysical motivations: AGB stars GIANTS, Padova 28-30 Aprile 2015 Astrophysical motivations: AGB stars Pignatari et al. Nucl Phys A 758 (2005) Study of the abundance variation for Ne, Mg, Si, Ca, Fe, Ni, Kr, Rb and Zr by varying the 22Ne(a,n)25Mg reaction rate

Astrophysical motivations: massive stars GIANTS, Padova 28-30 Aprile 2015 Astrophysical motivations: massive stars Core hydrogen burning -> hydrogen processed into helium Enrichment of the 14N content in the core Core helium burning 22Ne produced via: 14N(a,g)18F(b+n)18O(a,g)22Ne Enrichment of the 22Ne content 22Ne : 4He = 1: 10 If the core temperature T ≈ 0.15 GK, 22Ne(a,n)25Mg starts to produce neutrons

Astrophysical motivations: massive stars GIANTS, Padova 28-30 Aprile 2015 Astrophysical motivations: massive stars L.-S. The A.J. 533 2000 Dashed and solid lines represent abundances calculated with two different stellar models 22Ne abundance decreases much more dramatically in one model than in the other The neutron flux in stellar environments is an important factor influencing the amount of material that is produced in the s-process. The reaction rate of 22Ne(a,n)25Mg and the competing 22Ne(a,g)26Mg reaction must be well known

GIANTS, Padova 28-30 Aprile 2015 Jaeger et al., 2001

The direct measurement by Jaeger et al. (2001) GIANTS, Padova 28-30 Aprile 2015 The direct measurement by Jaeger et al. (2001) Experimental setup: Stuttgart DYNAMITRON accelerator with a He+ beam (Ibeam = 100-150 mA) Windowless gas target facility RHINOCEROS 4p neutron detector Gas target setup: 99.9% enriched 22Ne gas Three purification elements: Cryogenic trap at liquid nitrogen temperature Zeolite trap Getter purifier Pressure was reduced by the differential pumping stages to several times 10-8 mbar. Jaeger et al., PRL 87, 2001

The direct measurement by Jaeger et al. (2001) GIANTS, Padova 28-30 Aprile 2015 The direct measurement by Jaeger et al. (2001) 4p neutron detector: Neutrons thermalized in a cylindrical polyethylene moderator Neutrons captured by 12 proportional counters Absolute detection efficiency up to 50% Plastic scintillator detector to suppress cosmic-ray-induced background

Band of uncertainty normalized to NACRE GIANTS, Padova 28-30 Aprile 2015 Jaeger et al. (2001) results Band of uncertainty normalized to NACRE Large uncertainties in the reaction rate at T9 < 0.8

Band of uncertainty normalized to NACRE GIANTS, Padova 28-30 Aprile 2015 Jaeger et al. (2001) results Band of uncertainty normalized to NACRE Large uncertainties in the reaction rate Resonance at Er,lab = 635 keV corr. to Elevel = 11152 keV ?

Parity of the level at 11152 keV GIANTS, Padova 28-30 Aprile 2015 Parity of the level at 11152 keV Jp (22Ne) = 0+ Jp (a) = 0+ Only natural parity states can be populated (i.e. 0+, 1-, 2+, etc.) in 22Ne + a reactions NACRE collab., Käppeler et al., Koehler, and Karakas et al. Elevel = 11152 keV state in 26Mg natural parity (Jp = 1-) Most recently Longland et al. and deBoer et al. Elevel = 11152 keV state in 26Mg unnatural parity (Jp = 1+)

Most recent review: Longland et al. 2012 GIANTS, Padova 28-30 Aprile 2015 Most recent review: Longland et al. 2012 95 % c.l. Jaeger et al. 2001 Reasons for the disagreement: Inflated weighted averages of the reported resonance strengths for different measurements Excluded the contribution of the tentative Er,lab = 630 keV (Elevel = 11154 keV) 68 % c.l. Longland et al., PRC 2012

Most recent review: Longland et al. 2012 GIANTS, Padova 28-30 Aprile 2015 Most recent review: Longland et al. 2012 Ratio of final abundances resulting from the 22Ne(a,g)26Mg and 22Ne(a,n)25Mg new recommended rates to those obtained from old recommended rates Comparison of abundance variations versus mass number arising from the Longland et al. 2012 rate uncertainties and the literature ones (Nacre and Jaeger)

Expected rate @ LUNAMV By Alberto Lemut GIANTS, Padova 28-30 Aprile 2015 Expected rate @ LUNAMV By Alberto Lemut

~ 3 OoM lower than the maximum production with 13C(a,n) GIANTS, Padova 28-30 Aprile 2015 n production @ LUNAMV En max = 0.4 MeV ~ 3 OoM lower than the maximum production with 13C(a,n) By Alberto Lemut

(To be compared with ~ 5.5 106 m-2 d-1 at sea level GIANTS, Padova 28-30 Aprile 2015 Neutron background @ Gran Sasso P.Belli et al., Nuovo Cimento 101A n. 6 (1989) Neutron Energy Flux (cm-2 s-1) 0.025 eV (1.98 ± 0.05) 10-6 0.05 – 103 eV (1.08 ± 0.02) 10-6 > 2.5 MeV (0.23 ± 0.07) 10-6 ~ 2.85 103 m-2 d-1 (To be compared with ~ 5.5 106 m-2 d-1 at sea level (cosmic neutrons) A background rate of hundreds of count/day is expected with a real detector installed in Gran Sasso Passive shielding is required to achieve a background rate of 1-20 count/day

GIANTS, Padova 28-30 Aprile 2015 Not only shielding.. Spectrum collected at Boulby mine with the 4p Stuttgart detector Spectrum collected at Bochum with the 4p Stuttgart detector The flat bck. is most likely intrinsic a background in the 3He tubes and extends to about 5 MeV. Similar indications from Notre Dame.

GIANTS, Padova 28-30 Aprile 2015 10.6 MeV Moreover, 22Ne(a,n)25Mg competes with 22Ne(a,g)26Mg and therefore the s of both the reactions is needed Even with such low-energy neutrons, a coupled n-g detector could be a step forward

GIANTS, Padova 28-30 Aprile 2015 Conclusions Significant room to improve the study of 22Ne(a,n): 0.1 < Ea < 1 MeV  LUNAMV New neutron (-gamma) detectors Proper passive shielding and clean detecting materials must be selected to fully exploit the advantages offered by the underground environment. New gas target with technical solution to prevent beam induced n background and contaminations

Summary and open issues Significative room for improve the study of 13C(a,n) and 22Ne(a,n): in the first case very likely an underground experiment could definitively solve the problem. 0.1 < Ea < 1 MeV for both the experiments. New neutron detectors: Maybe a combination of previous designs (e.g. an “active” moderator + Cd foils + high resolution g detectors ). Proper passive shielding and clean detecting materials must be developed to fully exploit the advantages offered by the underground environment. Technical solution for using the same detector for both the experiments. 13C target production to enhance purity, stability, etc. New gas target with technical solution to prevent beam induced n background and contaminations

Possible development: high efficiency, (moderate) energy resolution, bck. reduction E spectrum TAC spectrum PSA spectrum

GIANTS, Padova 28-30 Aprile 2015 Level scheme

(To be compared with ~ 5.5 106 m-2 d-1 cosmic neutrons at sea level) Neutron background @ Gran Sasso P.Belli et al., Nuovo Cimento 101A n. 6 (1989) Neutron Energy Flux (cm-2 s-1) 0.025 eV (1.98 ± 0.05) 10-6 0.05 – 103 eV (1.08 ± 0.02) 10-6 > 2.5 MeV (0.23 ± 0.07) 10-6 ~ 2.85 103 m-2 d-1 (To be compared with ~ 5.5 106 m-2 d-1 cosmic neutrons at sea level) Unless the fast component is resolved (with a neutron spectrometer), a background rate of hundreds of count/day is expected with a real detector installed at Gran Sasso Passive shielding is required to achieve a background rate of 1-20 count/day

10.6 MeV Moreover, 22Ne(a,n)25Mg competes with 22Ne(a,g)26Mg and therefore the s of both the reactions is needed Even with such low-energy neutrons, a coupled n-g detector could be a step forward

0.4 m3 Pb and Cu shield  bck reduction: 105 Passive shielding is very effective underground: e.g. the LUNA set-up for 3He(a,g)7Be 0.4 m3 Pb and Cu shield  bck reduction: 105 ≈ 0.7 counts/(day keV) ROI 1230 - 1765 80 T = 21.68 d 60 40K 40 20 500 1000 1500 2000 E(keV)

Not only shielding.. Spectrum collected at Boulby mine with the 4p Stuttgart detector Thermalized neutrons peak (~ 1 MeV in a 3He counter) Courtesy of. F. Strieder Spectrum collected at Bochum with the 4p Stuttgart detector The flat bck. is most likely intrinsic a background in the 3He tubes and extends to about 5 MeV. Similar indications from Notre Dame. Courtesy of. F. Strieder

Expected sensitivity at LUNA GIANTS, Padova 28-30 Aprile 2015 Expected sensitivity at LUNA

The RHINOCEROS windowless gas-target (developed in Stuttgart now in Notre Dame, IN) The 99.9% enriched 22Ne target gas was continuously re-circulated to allow long term experiments in a specially designed reaction chamber with highly polished gold-plated walls. The high chemical purity of the gas was sustained by three purification elements: a cryogenic trap at liquid nitrogen temperature, a zeolite trap, and a getter purifier. The pressure was reduced by the differential pumping stages of the RHINOCEROS facility to several times 10-8 mbar.

LUNA estimate Q = -0.473 MeV Last estimate by A. Lemut, LBL, Ca But the pattern of low-energy resonances is very confused Last estimate by A. Lemut, LBL, Ca

Expected sensitivity @ LUNA