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Magnetic trapping of neutrons


Accurate measurement of the lifetime of the neutron (which is unstable to beta decay) is important for understanding the weak nuclear force1 and the creation of matter during the Big Bang2. Previous measurements of the neutron lifetime have mainly been limited by certain systematic errors3; however, these could in principle be avoided by performing measurements on neutrons stored in a magnetic trap. Neutral-particle and charged-particle traps are widely used for studying both composite and elementary particles, because they allow long interaction times and isolation of particles from perturbing environments4. Here we report the magnetic trapping of neutrons. The trapping region is filled with superfluid 4He, which is used to load neutrons into the trap and as a scintillator to detect their decay. Neutrons in the trap have a lifetime of 750+330-200 seconds, mainly limited by their beta decay rather than trap losses. Our experiment verifies theoretical predictions regarding the loading process and magnetic trapping of neutrons. Further refinement of this method should lead to improved precision in the neutron lifetime measurement.

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Figure 1: Half-section view of the neutron trapping apparatus.
Figure 2: Counting rate as a function of time after the neutron beam is turned off (pooled background-subtracted data).

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  1. Dubbers,D. Test of the standard model with free neutron beta decay. Nucl. Phys. A 527, 239–250 (1991).

    Article  ADS  Google Scholar 

  2. Lopez,R. E. & Turner,M. S. Precision prediction for the big-bang abundance of primordial 4He. Phys. Rev. D 59, 103502/1–14 (1999).

    Article  ADS  CAS  Google Scholar 

  3. Doyle,J. M. & Lamoreaux,S. K. On measuring the neutron beta-decay lifetime using ultracold neutrons produced and stored in a superfluid-4He-filled magnetic trap. Europhys. Lett. 26, 253–258 (1994).

    Article  ADS  CAS  Google Scholar 

  4. Phillips,W. D. in Laser Manipulation of Atoms and Ions (eds Arimondo, E., Phillips, W. & Sturmia, F.) 289–344 (North Holland, Amsterdam, 1992).

  5. Caso,C. et al. Review of particle physics. Eur. Phys. J. C 3, 1–794 (1998).

    Google Scholar 

  6. Byrne,J. et al. A revised value for the neutron lifetime measured using a Penning trap. Europhys. Lett. 33, 187–192 (1996).

    Article  ADS  CAS  Google Scholar 

  7. Mampe,W., Ageron,P., Bates,C., Pendlebury,J. M. & Steyerl,A. Neutron lifetime measured with stored ultracold neutrons. Phys. Rev. Lett. 63, 593–596 (1989).

    Article  ADS  CAS  Google Scholar 

  8. Nesvizhevskii,V. V. et al. Measurement of the neutron lifetime in a gravitational trap and analysis of experimental errors. Sov. Phys. JETP 75, 405–412 (1992).

    Google Scholar 

  9. Paul,W., Anton,F., Paul,L., Paul,S. & Mampe,W. Measurement of the neutron lifetime in a magnetic storage ring. Z. Phys. C 45, 25–30 (1989).

    Article  CAS  Google Scholar 

  10. Golub,R., Richardson,D. & Lamoreaux,S. K. Ultra-Cold Neutrons (Adam Hilger, Bristol, UK, 1991).

    Google Scholar 

  11. Vladimirskı˘,V. V. Magnetic mirrors, channels and bottles for cold neutrons. Sov. Phys. JETP 12, 740-746 (1961).

    Google Scholar 

  12. Abov, Yu. G., Borovlëv,S. P., Vasil'ev,V. V., Vladimirskii,V. V. & Mospan,E. N. Measurement of the time of storage of ultracold neutrons in a magnetic trap. Sov. J. Nucl. Phys. 38, 70–73 (1983).

    Google Scholar 

  13. Niehues,N. Untersuchungen an einer magnetischen Flasche zur Speicherung von Neutronen. (Investigations on a magnetic bottle for the storage of neutrons. ) Thesis, Friedrich Wilhelm Univ. Bonn (1983).

  14. Hess,H. F. et al. Magnetic trapping of spin-polarized atomic hydrogen. Phys. Rev. Lett. 59, 672–675 (1987).

    Article  ADS  CAS  Google Scholar 

  15. van Roijen,R., Berkhout,J. J., Jaakkola,S. & Walraven,J. T. M. Experiments with atomic hydrogen in a magnetic trapping field. Phys. Rev. Lett. 61, 931–934 (1988).

    Article  ADS  CAS  Google Scholar 

  16. Doyle,J. M., Friedrich,B., Kim,J. & Patterson,D. Buffer-gas loading of atoms and molecules into a magnetic trap. Phys. Rev. A 52, R2515–R2518 (1995).

    Article  ADS  CAS  Google Scholar 

  17. Chu,S. in Laser Manipulation of Atoms and Ions (eds Arimondo, E., Phillips, W. & Sturmia, F.) 239–288 (North Holland, Amsterdam, 1992).

    Google Scholar 

  18. Golub,R. & Pendlebury,J. M. The interaction of ultra-cold neutrons (UCN) with liquid helium and a superthermal UCN source. Phys. Lett. A 62, 337–339 (1977).

    Article  ADS  Google Scholar 

  19. Golub,R. et al. Operation of a superthermal ultracold neutron source and the storage of ultracold neutrons in superfluid helium-4. Z. Phys. B 51, 187–193 (1983).

    Article  ADS  CAS  Google Scholar 

  20. Hendry,P. C. & McClintock,P. V. E. Continuous flow apparatus for preparing isotopically pure 4He. Cryogenics 27, 131–138 (1987).

    Article  ADS  CAS  Google Scholar 

  21. Adams,J. S., Kim,Y. H., Lanou,R. E., Maris,H. J. & Seidel,G. M. Scintillation and quantum evaporation generated by single monoenergetic electrons stopped in superfluid helium. J. Low Temp. Phys. 13, 1121–1128 (1998).

    Article  ADS  Google Scholar 

  22. McKinsey,D. N. et al. Radiative decay of the metastable He2 (a3 Σ+u) molecule in liquid helium. Phys. Rev. A 59, 200–204 (1999).

    Article  ADS  CAS  Google Scholar 

  23. McKinsey,D. N. et al. Fluorescence efficiencies of thin scintillating films in the extreme ultraviolet spectral region. Nucl. Instrum. Methods B 132, 351–358 (1997).

    Article  ADS  CAS  Google Scholar 

  24. Habicht,K. Szintillationen in flüssigem Helium—ein Detektor für ultrakalte Neutronen. (Scintillations in liquid helium—a detector for ultracold neutrons.) Thesis, Tech. Univ. Berlin (1998).

  25. Kilvington,A. I., Golub,R., Mampe,W. & Ageron,P. Scattering of ultra-cold neutrons (UCN) by superfluid helium at temperatures around 1 K. Phys. Lett. A 125, 416–420 (1987).

    Article  ADS  CAS  Google Scholar 

  26. Yoshiki,H. et al. Observation of ultracold-neutron production by 9-Å cold neutrons in superfluid helium. Phys. Rev. Lett. 68, 1323–1326 (1992).

    Article  ADS  CAS  Google Scholar 

  27. Happer,W. Optical pumping. Rev. Mod. Phys. 44, 169–249 (1972).

    Article  ADS  CAS  Google Scholar 

  28. Golub,R. & Lamoreaux,S. K. Neutron electric-dipole moment, ultracold neutrons and polarized 3He. Phys. Rep. 237, 1–62 (1994).

    Article  ADS  CAS  Google Scholar 

  29. Golub,R. Ultracold neutrons: their role in studies of condensed matter. Rev. Mod. Phys. 68, 329–347 (1996).

    Article  ADS  CAS  Google Scholar 

  30. Butterworth,J. S. et al. A removable cryogenic window for transmission of light and neutrons. Rev. Sci. Instrum. 69, 3998–3999 (1998).

    Article  ADS  CAS  Google Scholar 

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We thank J. M. Rowe, D. M. Gilliam, G. L. Jones, J. S. Nico, N. Clarkson, G. P. Lamaze, C. Chin, C. Davis, D. Barkin, A. Black, V. Dinu, J. Higbie, H. Park, R. Ramakrishnan, I. Siddiqi and G. Brandenburg for their help with this project. We thank P. McClintock, D. Meredith and P. Hendry for supplying the isotopically pure helium. We acknowledge the support of the NIST, US DOC, in providing the neutron facilities used in this work. This work is supported in part by the US NSF. The NIST authors acknowledge the support of the US DOE.

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Huffman, P., Brome, C., Butterworth, J. et al. Magnetic trapping of neutrons. Nature 403, 62–64 (2000).

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