Haller, E.E.

Hansen, W.L.

Hindi, M.M.

Larimer, R.-M.

Lesko, K.T.

Luke, P.N.

Norman, E.B.

Sur, B.

Wietfeldt, F.E.

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Lawrence Berkeley National LaboratoryRecent WorkTitleReply to a Comment by N.K. ShermanPermalinkhttps://escholarship.org/uc/item/8548m8gzJournalPhysical Review Letters, 68(9)AuthorsSur, B.Norman, E.B.Wietfeldt, F.E.et al.Publication Date1991-10-01eScholarship.org Powered by the California Digital LibraryUniversity of California. . ':j-LBL-31366 Preprint Lawrence Berkeley Laboratory UNIVERSITY OF CALIFORNIA Submitted to Physical Review Letters Reply to a Comment by N.K. Sherman B. Sur, E.B. Norman, F.E. Wietfeldt, K.T. Lesko, M.M. Hindi, R.-M. Larimer, P.N. Luke, W.L. Hansen, and E.E. Haller October 1991 U. C. Lawrence Berkeley Laboratory Library, Berkeley FOR REFERENCE Not to be taken from this room Prepared for the U.S. Department of Energy under Contract Number DE-AC03· 76SF00098 IXJ ~ Do IQ . U1 S r .... O"n '1 0 111'0 '1'< '< . t-r IXJ r I Co) t-Co) (J'I (J'I DISCLAIMER This document was prepared as an account of work sponsored by the United States Government. Neither the United States Government nor any agency thereof, nor The Regents of the University of Califor-nia, nor any of their employees, makes any warranty, express or im-plied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe pri-vately owned rights. Reference herein to any specifiC commercial product, process, or service by its trade name, trademark, manufac-turer, or otherwise, does not necessarily constitute or imply its en-dorsement, recommendation, or favoring by the United States Gov-ernment or any agency thereof, or The Regents of the University of California. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or any agency thereof or The Regents of the University of California and shall not be used for advertising or product endorsement pur-poses. Lawrence Berkeley Laboratory is an equal opportunity employer. .. ! DISCLAIMER This document was prepared as an account of work sponsored by the United States Government. While this document is believed to contain correct information, neither the United States Government nor any agency thereof, nor the Regents of the University of California, nor any of their employees, makes any warranty, express or implied, or assumes any legal responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by its trade name, trademark, manufacturer, or otherwise, does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States Government or any agency thereof, or the Regents of the University of California. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or any agency thereof or the Regents of the University of California. Reply to a Comment by N.K. Sherman B. Sur(1), E.B. Norman(2), F.E. Wietfeldt(2), K.T. Lesko(2), M.M. Hindi(3), R.-M. Larimer(2), P.N. Luke(4), W.L. Hansen(4), and E.E. Haller(5),(6) (1)Physics Dept., Queen's University, Kingston, ON K71 9N6 Canada (2)Nuclear Science Division, Lawrence Berkeley Laboratory, Berkeley, CA 94720 (3)Physics Dept., Tennessee Technological University, Cookeville, TN 38505 (4)Engineering Division, Lawrence Berkeley Laboratory, Berkeley, CA 94720 (5)Material Science Division, Lawrence Berkeley Laboratory, Berkeley, CA 94720 (6)Dept. of Materials Science and Mineral Engineering, Univ. of California, Berkeley, CA 94720 To be submitted to Physical Review Letters This work was supported by the Director, Office of Energy Research, Office of High Energy and Nuclear Physics, Nuclear Physics Division of the U.S. Department of Energy under Contract No. DE-AC03-76SF00098. Sur et al. Reply: In the preceding Comment1, Sherman raises the interesting question of whether the channeling of electrons and x-rays in Ge could account for the distortion we observed2 in the p spectrum of 14C. We have addressed this question in two ways. First, we remeasured the response function of our detetctor to look for evidence of channeling. Secondly, we reanalyzed our 14C data to see if the observed distortion is compatible with that expected from channeling. We irradiated our 14C-doped Ge detector with 166-keV y-rays using an external 139Ce source. At this energy, the fraction of y-interactions in Ge which occur via the photoelectric effect is 84%, and approximately 87% of these occur on a K-shell electron.3 Thus, 73% of all interactions of this y-ray in our detector produce -photoelectrons with an energy of 166 - 11 = 155 keV. These electrons are emitted from Ge lattice sites throughout the crystal and have a fairly broad angular distribution relative to the initial y-ray's direction. Because of the large mass of the recoiling Ge+ ion, the energy spread of these electrons is very small. Thus, if 156-keV p's from 14C decays undergo the channeling proposed by Sherman, then this should also happen to these photoelectrons. The effect of this would be that in a few percent of all events tV 22 keV would escape from the crystal and thus not show up in the ionization signal. This would produce an energy spectrum which contains both a full-energy peak and a small satellite peak t\J 22 keV below it. Figure 1 shows the relevant portion of the spectrum observed with the 139Ce source placed on the front face of our 14C-doped Ge detector. These data are events in which a signal was observed in the center region of the crystal and nothing was observed above threshold in the guard ring (Le. type 2 events).2 The full-energy peak contains 2.93x105 counts. A small Ge x-ray escape peak (,..., 125 net counts) is observed at 166-10 = 156 keV. At the point 22 keV below the full-energy peak, no peak-like structure is observed. The limit we can place on the net number of counts in such a hypothetical peak is approximately 100 for any proposed energy loss from 1 10-50 keV. The same limits were obtained in a second measurement performed with the source mounted on the side of the detector which sent the 'Y rays through the edge of the crystal. Nearly identical limits were also obtained for center-region singles (Le. type 1)2 events. Thus, our measurements show that if channeling does occur, it produces an energy loss of this size less than 0.05% of the time for a 155-keV electron in Ge. This is a much smaller fraction than that estimated by Sherman. The second approach we took was to assume that Sherman's proposed effect actually occurs and that a small number of J3's lose a fraction of their energy to a process that does not produce ionization. We modified our analysis programs2 to perform six different fits to a 420 point type-2 data set containing 224 days of counting with the 14C-doped crystal and 111 days of counting with the background crystal. This represents all the data we previously reported2 plus an additional 102 days of 14C counting and an additional 59 days of background counting. If one assumes that mv = 0 and that no channeling occurs, the lowest X2 obtained is 479. The absolute minimum value of X2 = 461 is found for mv = 17 keV and an emission probability of 1.2%. If instead, one assumes that mv = 0 but that 1.2% of alll3's lose 17 keV through channeling, the best fit X2 is 500. If the amount of energy lost to channeling and the fraction of events affected are allowed to vary, the lowest X2 obtained is again 479 for an energy loss of 50 keV and a fraction = 0.01 %. This shows that even if Sherman's channeling mechanism did occur at the level he estimated, it would not produce a spectrum that quantitatively fits our data. We also performed fits which assumed that mv = 0 but that our data contained two beta spectra whose endpoint energies differ. Assuming that 1.2% of all events are associated with a spectrum whose endpoi nt is 156 - 17 = 139 keV, the lowest X2 r" obtained is 496. Allowing the second component's endpoint energy and fractional area to vary yields a minimum value of X2 = 475 for an endpoint shift of 4 keV and a fractional area of 3%. 2 The reason for these results is that the shape of a ~ spectrum near the endpoint is very different for massless and massive neutrinos. If rTly=O, the ~ energy spectrum goes to zero with a slope of zero, while a massive neutrino produces a ~ spectrum that goes to zero with an infinite slope. The above analyses demonstrate that our 14C experiment is sensitive not only to the position of the spectral distortion, but also to its detailed shape. So far, the only model which quantitatively explains this result is that a neutrino with a mass of 17± 1 keY is emitted 1.2+0.3% of the time in the ~ decay of 14C. B. Sur,(1) E. B. Norman,(2) F. E. Wietfeldt,(2) K. T. Lesko, (2) M. M. Hindi,(3) R.-M. Larimer, (2) P. N. Luke,(4) W. L. Hansen,(4) and E. E. Haller(5),(6) Received _August 1991 PACS numbers: 23.40.Bw, 14.60.Gh, 27.20.+n References >':, 1. N. K. Sherman, preceding Comment. 2. B. Sur et al., Phys. Rev. Lett. 66, 2444 (1991). 3. E. Storm and H. I. Israel, Nucl. Data Tables A7, 590 and 681 (1970). 3 t 'J..",,; Q) s:: s:: CIS .s:: .!2. en .... s:: ::s 0 U 106 166 105 104 Ge x-ray Escape 103 (166-22) ~ 102 101 850 975 1100 Channel Number Figure 1. Type-(2) spectrum observed in our 14C-doped germanium detector when a 'I 139Ce souce was placed on the front face of the detector. All ene~ies are given in '~J keY. Note that the weak 14C beta spectrum was measured separately and was subtracted from the raw data to produce this plOt. 4 LAWRENCE BERKELEY LABORATORY UNIVERSITY OF CALIFORNIA INFORMATION RESOURCES DEPARTMENT BERKELEY, CALIFORNIA 94720 -

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Reply to a Comment by N.K. Sherman

Reply to a Comment by N.K. Sherman

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