The I127(3He,t)127Xe reaction has been measured for low-lying states in Xe127 which may play a role in neutrino capture by I127. High-spin states at excitation energies Ex=309 and 646 keV are found to be much more strongly populated than the Jπ=((3/2-(7/2)+ states relevant to neutrino capture by I127

Benton, D.R.

Champagne, A.E.

Coulter, K.P.

Kouzes, R.T.

Lowry, M.M.

Mao, Z.Q.

McDonald, A.B.

Carolina Digital Repository

PHYSICAL REVIEW C VOLUME 39, NUMBER 1Brief ReportsJANUARY 1989Brief «po«s are shor~ papers which rcport on completed research or are addenda to papers~reviously published in the physica]Review A. Brief Report may be no longer than 3~t printed pages and must be accompanied by an abstract.&( He, t )' Xe reaction with relevance to neutrino detectionA. E. Champagne, R. T. Kouzes, A. B.McDonald, M. M. Lowry,D. R. Benton, and K. P. CoulterDepartment ofPhysics, Princeton University, Princeton, Xew Jersey 08544Z. Q. MaoDepartment of Physics and Atmospheric Science, Drexel University, Philadelphia, Pennsylvania l9l04(Received 9 September 1988)The ' I( He, t)' Xe reaction has been measured for low-lying states in ' Xe which may play arole in neutrino capture by ' I. High-spin states at excitation energies E„=309and 646 keV arefound to be much more strongly populated than the J"=(2-2 )+ states relevant to neutrino captureby 127IRecently, Haxton' examined the feasibility of ' I asthe basis for a new radiochemical detector of astrophysi-cal neutrinos. From estimates of the ' I(v„e )' Xecross section, he concluded that the capture rate per unitvolume for this detector could be an order of magnitudegreater than that of the existing Cl detector of Daviset al. At this level, a detector based on ' I would notonly be a sensitive detector of Be and B solar neutrinos,but could also be used to detect neutrinos produced bysupernovae.At present, the Gamow-Teller (GT) strength for neutri-no capture by ' I has not been measured. This strengthcan be obtained from the ' I(p, n)' Xe reaction at inter-mediate energies where the forward-angle cross section isa direct measure of the GT matrix elements. However,the energy resolution for such (p, n) studies is expected tobe no better than about 200 keV, making it dificult toresolve the low-lying levels of ' Xe, which have been in-ferred indirectly from gamma-ray studies. ' The presentstudy was therefore undertaken to observe the low-lyinglevel structure of ' Xe via the ' I( He, t)' Xe reaction,with an overall energy resolution of about 25 keV. The( He, t) reaction is too complex to permit the Gamow-Teller strength function to be inferred directly, but thegeneral characteristics of this charge-exchange reactionshould result in relative cross sections similar to those ex-pected in the (p, n) reaction. Neutrino capture by ' Iwill produce states in ' Xe with J =(—,'-—,')+ and there-fore particular attention was directed toward these states.It was thus hoped that this measurement might assist inthe interpretation of the (p, n) reaction and might also in-dicate the presence of energy levels missed in thegamma-ray studies. In addition, the reaction Q value wasmeasured to compare with the value derived from a re-cent mass table.The ' I( He, t)' Xe reaction was investigated usingHe beams [F. ( He) =29.78 MeV] provided by thePrinceton cyclotron. Outgoing tritons were momentumanalyzed in the focal plane of a quadrupole-dipole-dipole-dipole (QDDD) magnetic spectrometer. A tritonspectrum collected at 0&,b= 7' using a KI target is shownin Fig. 1. The energy dispersion in the spectrometer wasmeasured using the energies of well-known states popu-lated in the 'Br( He, t) 'Kr and Zn( He, t) Ga reac-tions. The triton-energy difference between the E =125keV, J = —,'+ first-excited state in ' Xe and the groundstate of Ga (measured using a KI+ Zn sandwich tar-get) implies Q = —0.676(6) keV for the ' 7I( He, t)'27Xereaction. This result is in good agreement withQ = —0.680(7) keV obtained from a recent mass compi-lation. All observed peaks could be identified as ' Xelevels proposed from the gamma-decay measurements.No clear evidence of the expected states at F. =297 keV( —', ) and 322 keV ( —,'+ ) was obtained. On the basis of itsspin, the latter state may play a role in neutrino captureby ' I. The most strongly populated states in the spec-trum shown in Fig. 1 are the high-spin states at E„=309keV ( —", ) and E =646 keV ( —,'+) previously observed byUrban et al. For comparison, the strongest low-lyingstate of interest for neutrino capture is the 125-keV state( —+ ) which is weaker than the nearby 309-keV state by afactor of 6.5. Angular distributions were measured up to39 248 1989 The American Physical Society39 BRIEF REPORTS 24980600 40-O202000) u)h- OCQtA M(O M,(gjN&&300 400 500CHANNEL"Ca„«&'4& ~r«600'"I('He, t)'"Xe E('He) = 29.8 Me~L9 70O„.b=30, but were found to be relatively featureless.At the best resolution currently achieved in (p, n ) mea-surements (on the order of 200 keV), the 309-keV and646-keV high-spin states could obscure the GT state be-tween 110 keV» E„»850 keV. This has particularsignificance when determining the cross section for cap-ture of Be neutrinos, since these captures would popu-late the 125-keV state which will not be resolved from the309-keV state in (p, n) measurements. The astrophysical-ly interesting J"= =,'+ states are formed via L =0angular-momentum transfer with angular distributionsthat are quite different from the L =2 or L =3 distribu-tions of the high-spin states. Thus, considerable caremust be taken in the (p, n) measurements to extract theL =0 strength in the presence of the stronger L )0states.FIG. 1. Triton spectrum from the ' I( He, t)' Xe reaction at0&,b=7'. The locations of known states in ' Xe are indicated.Excitation energies (in keV) and spin parities are from Refs. 3and 4.This work was supported in part by the National Sci-ence Foundation.'W. C. Haxton, Phys. Rev. Lett. 60, 768 (1988).~J. K. Rowley, B. T. Cleveland, and R. Davis, Jr., in Solar Neu-trinos and Neutrino Astronomy (Lead High Schooi, Lead,South Dakota), Proceedings of a Conference on Solar Neutri-nos and Neutrino Astronomy, sponsored by Homestake Min-ing Company, AIP Conf. Proc. No. 126, edited by M. L.Cherry, K. Lande, and W. A. Fowler (AIP, New York, 1984).A. D. Irving, P. D. Forsyth, I ~ Hall, and D. G. E. Martin, J.Phys. G 9, 1245 (1983).4W. Urban, T. Morek, Ch. Droste, B. Kotlinski, J. Srebrny, J.Wrzesinski, and J. Styczen, Z. Phys. A 320, 327 (1985).5A. H. Wapstra and G. Audi, Nucl. Phys. A432, 1 (1985}.

I127(3He,t)127Xe reaction with relevance to neutrino detection

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I127(3He,t)127Xe reaction with relevance to neutrino detection

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