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                                                                     EXHIBIT 4.6

                          REGISTRATION RIGHTS AGREEMENT


          This Registration Rights Agreement (this "AGREEMENT") is made and
entered into as of May 28, 2002, by and among American Science and Engineering,
Inc., a Massachusetts corporation (the "COMPANY"), and the investors signatory
hereto (each a "PURCHASER" and collectively, the "PURCHASERS").

          This Agreement is made pursuant to the Securities Purchase Agreement,
dated as of the date hereof, among the Company and the Purchasers (the "PURCHASE
AGREEMENT").

          The Company and the Purchasers hereby agree as follows:

       1. DEFINITIONS. Capitalized terms used and not otherwise defined
herein that are defined in the Purchase Agreement shall have the meanings given
such terms in the Purchase Agreement. As used in this Agreement, the following
terms shall have the following meanings:

          "EFFECTIVE DATE" means the date on which the Registration Statement is
declared effective by the Commission.

          "EFFECTIVENESS DATE" means the earlier of (i) the 90th day following
the Closing Date and (ii) the fifth Trading Day following the date on which the
Company is notified by the Commission that the Registration Statement will not
be reviewed or is no longer subject to further review and comments PROVIDED,
that such period shall be extended by the number of Trading Days in excess of
the third Trading Day following the delivery of the Registration Statement
pursuant to Section 3(a)(i), that the Holders or their Special Counsel shall
fail to respond or provide comments to the Company upon delivery of such
Registration Statement.

          "EFFECTIVENESS PERIOD" shall have the meaning set forth in Section
2(a).

          "FILING DATE" means the 15th day following the Closing Date; provided,
however, that if the Company's independent accountant has not issued its report
with respect to the Company's financial statements to be included in the
Company's Annual Report on Form 10-K for the fiscal year ended March 31, 2002,
then the Registration Statement required to be filed hereunder shall be filed
prior to the 30th day following the Closing Date PROVIDED, that such period
shall be extended by the number of Trading Days in excess of the third Trading
Day following the delivery of the Registration Statement pursuant to Section
3(a)(i), that the Holders or their Special Counsel shall fail to respond or
provide comments to the Company upon delivery of such Registration Statement.

          "HOLDER" or "HOLDERS" means the holder or holders, as the case may be,
from time to time of Registrable Securities.

          "INDEMNIFIED PARTY" shall have the meaning set forth in Section 5(c).

          "INDEMNIFYING PARTY" shall have the meaning set forth in Section 5(c).


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          "LOSSES" shall have the meaning set forth in Section 5(a).

          "PROCEEDING" means an action, claim, suit, investigation or proceeding
(including, without limitation, an investigation or partial proceeding, such as
a deposition), whether commenced or threatened.

          "PROSPECTUS" means the prospectus included in the Registration
Statement (including, without limitation, a prospectus that includes any
information previously omitted from a prospectus filed as part of an effective
registration statement in reliance upon Rule 430A promulgated under the
Securities Act), as amended or supplemented by any prospectus supplement, with
respect to the terms of the offering of any portion of the Registrable
Securities covered by the Registration Statement, and all other amendments and
supplements to the Prospectus, including post-effective amendments, and all
material incorporated by reference or deemed to be incorporated by reference in
such Prospectus.

          "REGISTRABLE SECURITIES" means the Shares and Warrant Shares, together
with any securities issued or issuable upon any stock split, dividend or other
distribution, recapitalization or similar event with respect to the foregoing.

          "REGISTRATION STATEMENT" means the registration statement which is
required to register the resale of the Registrable Securities including the
Prospectus, amendments and supplements to each such registration statement or
Prospectus, including pre- and post-effective amendments, all exhibits thereto,
and all material incorporated by reference or deemed to be incorporated by
reference in such registration statement.

          "RULE 144" means Rule 144 promulgated by the Commission pursuant to
the Securities Act, as such Rule may be amended from time to time, or any
similar rule or regulation hereafter adopted by the Commission having
substantially the same purpose and effect as such Rule.

          "RULE 415" means Rule 415 promulgated by the Commission pursuant to
the Securities Act, as such Rule may be amended from time to time, or any
similar rule or regulation hereafter adopted by the Commission having
substantially the same purpose and effect as such Rule.

          "RULE 424" means Rule 424 promulgated by the Commission pursuant to
the Securities Act, as such Rule may be amended from time to time, or any
similar rule or regulation hereafter adopted by the Commission having
substantially the same purpose and effect as such Rule.

          "SHARES" means the shares of Common Stock issued to the Purchasers at
the Closing pursuant to the Purchase Agreement.

          "SPECIAL COUNSEL" means Purchaser Counsel who will be reimbursed by
the Company pursuant to Section 4.

          "WARRANT SHARES" means the shares of Common Stock issuable upon
exercise of the Warrants.


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          "WARRANTS" means the Warrants issued or issuable under the Purchase
Agreement.

       2. REGISTRATION.

          (a) On or prior to the Filing Date, the Company shall prepare and file
with the Commission the Registration Statement covering the resale of all
Registrable Securities required to be included in such Registration Statement
for an offering to be made on a continuous basis pursuant to Rule 415. The
Registration Statement shall be on Form S-3 (except if the Company is not then
eligible to register for resale the Registrable Securities on Form S-3, in which
case such registration shall be on another appropriate form in accordance
herewith) and shall contain (except if otherwise required by the Commission) the
"PLAN OF DISTRIBUTION" attached hereto as ANNEX A. The Company shall use its
best efforts to cause the Registration Statement to be declared effective under
the Securities Act as promptly as possible, but in any event prior to the
Effectiveness Date, and shall use its best efforts to keep the Registration
Statement continuously effective under the Securities Act until the date which
is five years after the Effective Date or such earlier date when all Registrable
Securities covered by the Registration Statement have been sold or may be sold
without volume restrictions pursuant to Rule 144(k) as determined by the counsel
to the Company pursuant to a written opinion letter to such effect, addressed
and acceptable to the Company's transfer agent and the affected Holders (the
"EFFECTIVENESS PERIOD").

          If: (a) the Registration Statement is not filed on or prior to its
Filing Date (if the Company files the Registration Statement without affording
the Holder the opportunity to review and comment on the same as required by
Section 3(a), the Company shall not be deemed to have satisfied clause (a)), or
(b) the Company fails to file with the Commission a request for acceleration in
accordance with Rule 461 promulgated under the Securities Act, within five
Trading Days of the date that the Company is notified (orally or in writing,
whichever is earlier) by the Commission that the Registration Statement will not
be "reviewed," or not subject to further review, or (c) prior to the Effective
Date, the Company fails to file a pre-effective amendment and otherwise respond
in writing to comments made by the Commission in respect of the Registration
Statement within 15 Trading Days after the receipt of comments by or notice from
the Commission that such amendment is required in order for the Registration
Statement to be declared effective, or (d) the Registration Statement filed or
required to be filed hereunder is not declared effective by the Commission by
its Effectiveness Date, or (e) after the Effective Date, the Registration
Statement ceases for any reason to remain continuously effective as to all
Registrable Securities for which it is required to be effective, or the Holders
are not permitted to utilize the Prospectus therein to resell such Registrable
Securities, for in any such cases an aggregate of twenty Trading Days (which
need not be consecutive Trading Days) (any such failure or breach being referred
to as an "EVENT," and for purposes of clause (a) or (d) the date on which such
Event occurs, or for purposes of clause (b) the date on which such five Trading
Day period is exceeded, or for purposes of clauses (c) the date which such 15
Trading Day period is exceeded, or for purposes of clause (e) the date on which
such twenty Trading Day period is exceeded being referred to as "EVENT DATE"),
then in addition to any other rights the Holders may have hereunder or
applicable law: (x) on each such Event Date the Company shall pay to each
Purchaser (as defined in the Purchase Agreement) of the Shares an amount in
cash, as liquidated damages and not as a penalty, equal to 1% of the aggregate
Investment Amount


                                      -3-


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paid by such Purchaser of the Shares pursuant to the Purchase Agreement; and (y)
on each monthly anniversary of each such Event Date (if the applicable Event
shall not have been cured by such date) until the applicable Event is cured, the
Company shall pay to each Purchaser of the Shares an amount in cash, as
liquidated damages and not as a penalty, equal to 2% of the aggregate Investment
Amount paid by such Purchaser of the Shares pursuant to the Purchase Agreement;
PROVIDED, HOWEVER, in no event may the total amount of liquidated damages
payable to any Holder exceed 18% of the aggregate Investment Amount paid by such
Purchaser of the Shares pursuant to the Purchase Agreement. If the Company fails
to pay any liquidated damages pursuant to this Section in full within seven days
after the date payable, the Company will pay interest thereon at a rate of 12%
per annum (or such lesser maximum amount that is permitted to be paid by
applicable law) to the Purchaser of the Shares, accruing daily from the date
such liquidated damages are due until such amounts, plus all such interest
thereon, are paid in full. . The liquidated damages pursuant to the terms hereof
shall apply on a pro-rata basis for any portion of a month prior to the cure of
an Event.

          (c) The Registration Statement required to be filed hereunder shall
include not less than 1,393,750 shares of Common Stock.

       3. REGISTRATION PROCEDURES

          In connection with the Company's registration obligations hereunder,
the Company shall:

          (a) Not less than five Trading Days prior to the filing of the
Registration Statement or any related Prospectus or any amendment or supplement
thereto, the Company shall, (i) furnish to the Holders and their Special Counsel
copies of all such documents proposed to be filed (including documents
incorporated or deemed incorporated by reference) which documents will be
subject to the review of such Holders and their Special Counsel, and (ii) cause
its officers and directors, counsel and independent certified public accountants
to respond to such inquiries as shall be necessary, in the reasonable opinion of
respective counsel to conduct a reasonable investigation within the meaning of
the Securities Act. The Company shall not file the Registration Statement or any
such Prospectus or any amendments or supplements thereto to which the Holders of
a majority of the Registrable Securities and their Special Counsel shall
reasonably object in good faith.

          (b) (i) Prepare and file with the Commission such amendments,
including post-effective amendments, to the Registration Statement and the
Prospectus used in connection therewith as may be necessary to keep the
Registration Statement continuously effective as to the applicable Registrable
Securities for the Effectiveness Period and prepare and file with the Commission
such additional Registration Statements in order to register for resale under
the Securities Act all of the Registrable Securities; (ii) cause the related
Prospectus to be amended or supplemented by any required Prospectus supplement,
and as so supplemented or amended to be filed pursuant to Rule 424; (iii)
respond as promptly as reasonably possible, to any comments received from the
Commission with respect to the Registration Statement or any amendment thereto
and, as promptly as reasonably possible provide the Holders true and complete
copies of all correspondence from and to the Commission relating to the
Registration Statement; and (iv) comply in all material respects with the
provisions of the Securities Act and the Exchange Act


                                      -4-


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with respect to the disposition of all Registrable Securities covered by the
Registration Statement during the applicable period in accordance with the
intended methods of disposition by the Holders thereof set forth in the
Registration Statement as so amended or in such Prospectus as so supplemented.

          (c) Notify the Holders of Registrable Securities to be sold and their
Special Counsel as promptly as reasonably possible (and, in the case of (i)(A)
below, not less than two Trading Days prior to such filing) and (if requested by
any such Person) confirm such notice in writing no later than one Trading Day
following the day (i)(A) when a Prospectus or any Prospectus supplement or
post-effective amendment to the Registration Statement is proposed to be filed;
(B) when the Commission notifies the Company whether there will be a "review" of
such Registration Statement and whenever the Commission comments in writing on
the Registration Statement (the Company shall provide true and complete copies
thereof and all written responses thereto to Special Counsel); and (C) with
respect to the Registration Statement or any post-effective amendment, when the
same has become effective; (ii) of any request by the Commission or any other
Federal or state governmental authority for amendments or supplements to the
Registration Statement or Prospectus or for additional information; (iii) of the
issuance by the Commission of any stop order suspending the effectiveness of the
Registration Statement covering any or all of the Registrable Securities or the
initiation of any Proceedings for that purpose; (iv) of the receipt by the
Company of any notification with respect to the suspension of the qualification
or exemption from qualification of any of the Registrable Securities for sale in
any jurisdiction, or the initiation or threatening of any Proceeding for such
purpose; and (v) of the occurrence of any event or passage of time that makes
the financial statements included in the Registration Statement ineligible for
inclusion therein or any statement made in the Registration Statement or
Prospectus or any document incorporated or deemed to be incorporated therein by
reference untrue in any material respect or that requires any amendment or
supplement to the Registration Statement, Prospectus or other documents so that,
in the case of the Registration Statement or the Prospectus, as the case may be,
it will not contain any untrue statement of a material fact or omit to state any
material fact required to be stated therein or necessary to make the statements
therein, in light of the circumstances under which they were made, not
misleading.

          (d) Use its best efforts to avoid the issuance of, or, if issued,
obtain the withdrawal of (i) any order suspending the effectiveness of the
Registration Statement, or (ii) any suspension of the qualification (or
exemption from qualification) of any of the Registrable Securities for sale in
any jurisdiction, at the earliest practicable moment.

          (e) Furnish to each Holder and their Special Counsel, without charge,
at least one conformed copy of the Registration Statement and each amendment
thereto, including financial statements and schedules, and all exhibits to the
extent requested by such Person (including those previously furnished or
incorporated by reference) promptly after the filing of such documents with the
Commission.

          (f) Promptly deliver to each Holder and their Special Counsel, without
charge, as many copies of the Prospectus or Prospectuses (including each form of
prospectus) and each amendment or supplement thereto as such Persons may
reasonably request. The Company hereby consents to the use of such Prospectus
and each amendment or supplement


                                      -5-


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thereto by each of the selling Holders in connection with the offering and sale
of the Registrable Securities covered by such Prospectus and any amendment or
supplement thereto.

          (g) Prior to any public offering of Registrable Securities, use its
best efforts to register or qualify or cooperate with the selling Holders and
their Special Counsel in connection with the registration or qualification (or
exemption from such registration or qualification) of such Registrable
Securities for offer and sale under the securities or Blue Sky laws of such
jurisdictions within the United States as any Holder reasonably requests in
writing, to keep each such registration or qualification (or exemption
therefrom) effective during the Effectiveness Period and to do any and all other
acts or things necessary or advisable to enable the disposition in such
jurisdictions of the Registrable Securities covered by the Registration
Statement; PROVIDED, that the Company shall not be required to qualify generally
to do business in any jurisdiction where it is not then so qualified or subject
the Company to any material tax in any such jurisdiction where it is not then so
subject.

          (h) Upon the occurrence of any event contemplated by Section 3(c)(v),
as promptly as reasonably possible, prepare a supplement or amendment, including
a post-effective amendment, to the Registration Statement or a supplement to the
related Prospectus or any document incorporated or deemed to be incorporated
therein by reference, and file any other required document so that, as
thereafter delivered, neither the Registration Statement nor such Prospectus
will contain an untrue statement of a material fact or omit to state a material
fact required to be stated therein or necessary to make the statements therein,
in light of the circumstances under which they were made, not misleading.

          (i) Comply with all applicable rules and regulations of the
Commission, the failure to comply with which would have a Material Adverse
Effect.

          (j) The Company may require each selling Holder to furnish to the
Company a certified statement as to the number of shares of Common Stock
beneficially owned by such Holder, whether now or during the last three years
the Holder has held or holds any position, office or has other material
relationship with the Company or any of its affiliates, and if requested by the
Commission, the controlling person of such Holder.

       4. REGISTRATION EXPENSES. All fees and expenses incident to the
performance of or compliance with this Agreement by the Company shall be borne
by the Company whether or not any Registrable Securities are sold pursuant to
the Registration Statement. The fees and expenses referred to in the foregoing
sentence shall include, without limitation, (i) all registration and filing fees
(including, without limitation, fees and expenses (A) with respect to filings
required to be made with the Trading Market on which the Common Stock is then
listed for trading, and (B) in compliance with applicable state securities or
Blue Sky laws), (ii) printing expenses (including, without limitation, expenses
of printing certificates for Registrable Securities and of photocopying
Prospectuses, (iii) messenger, telephone and delivery expenses, (iv) fees and
disbursements of counsel for the Company (but not including any fees or
disbursements of Special Counsel for the Holders which fees and disbursements
are included in those paid pursuant to Section 5.1 of the Purchase Agreement),
(v) Securities Act liability insurance, if the Company so desires such
insurance, and (vi) fees and expenses of all other Persons retained by the
Company in connection with the consummation of the transactions


                                      -6-


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contemplated by this Agreement. In addition, the Company shall be responsible
for all of its internal expenses incurred in connection with the consummation of
the transactions contemplated by this Agreement (including, without limitation,
all salaries and expenses of its officers and employees performing legal or
accounting duties), the expense of any annual audit and the fees and expenses
incurred in connection with the listing of the Registrable Securities on any
securities exchange as required hereunder.

       5. INDEMNIFICATION

          (a) INDEMNIFICATION BY THE COMPANY. The Company shall, notwithstanding
any termination of this Agreement, indemnify and hold harmless each Holder, the
officers, directors, agents, brokers (including brokers who offer and sell
Registrable Securities as principal as a result of a pledge or any failure to
perform under a margin call of Common Stock), investment advisors and employees
of each of them, each Person who controls any such Holder (within the meaning of
Section 15 of the Securities Act or Section 20 of the Exchange Act) and the
officers, directors, agents and employees of each such controlling Person, to
the fullest extent permitted by applicable law, from and against any and all
losses, claims, damages, liabilities, costs (including, without limitation,
reasonable costs of preparation and reasonable attorneys' fees) and expenses
(collectively, "LOSSES"), as incurred, arising out of or relating to any untrue
or alleged untrue statement of a material fact contained in the Registration
Statement, any Prospectus or any form of prospectus or in any amendment or
supplement thereto or in any preliminary prospectus, or arising out of or
relating to any omission or alleged omission of a material fact required to be
stated therein or necessary to make the statements therein (in the case of any
Prospectus or form of prospectus or supplement thereto, in light of the
circumstances under which they were made) not misleading, except to the extent,
but only to the extent, that (1) such untrue statements or omissions are based
solely upon information regarding such Holder furnished in writing to the
Company by such Holder expressly for use therein, or to the extent that such
information relates to such Holder or such Holder's proposed method of
distribution of Registrable Securities and was reviewed and expressly approved
in writing by such Holder expressly for use in the Registration Statement, such
Prospectus or such form of Prospectus or in any amendment or supplement thereto
(it being understood that the Holder has approved Annex A hereto for this
purpose) or (2) in the case of an occurrence of an event of the type specified
in Section 3(c)(ii)-(v), the use by such Holder of an outdated or defective
Prospectus after the Company has notified such Holder in writing that the
Prospectus is outdated or defective and prior to the receipt by such Holder of
the Advice contemplated in Section 6(d). The Company shall notify the Holders
and the Holders shall notify the Company promptly of the institution, threat or
assertion of any Proceeding of which the Company is aware in connection with the
transactions contemplated by this Agreement.

          (b) INDEMNIFICATION BY HOLDERS. Each Holder shall, severally and not
jointly, indemnify and hold harmless the Company, its directors, officers,
agents and employees, each Person who controls the Company (within the meaning
of Section 15 of the Securities Act and Section 20 of the Exchange Act), and the
directors, officers, agents or employees of such controlling Persons, to the
fullest extent permitted by applicable law, from and against all Losses, as
incurred, arising solely out of or based solely upon: (x) such Holder's failure
to comply with the prospectus delivery requirements of the Securities Act or (y)
any untrue statement of a material fact contained in any Registration Statement,
any Prospectus, or any form


                                      -7-


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of prospectus, or in any amendment or supplement thereto, or arising solely out
of or based solely upon any omission of a material fact required to be stated
therein or necessary to make the statements therein not misleading to the
extent, but only to the extent, that such untrue statement or omission is
contained in any information so furnished in writing by such Holder to the
Company specifically for inclusion in such Registration Statement or such
Prospectus or to the extent that (1) such untrue statements or omissions are
based solely upon information regarding such Holder furnished in writing to the
Company by such Holder expressly for use therein, or to the extent that such
information relates to such Holder or such Holder's proposed method of
distribution of Registrable Securities and was reviewed and expressly approved
in writing by such Holder expressly for use in the Registration Statement (it
being understood that the Holder has approved Annex A hereto for this purpose),
such Prospectus or such form of Prospectus or in any amendment or supplement
thereto or (2) in the case of an occurrence of an event of the type specified in
Section 3(c)(ii)-(v), the use by such Holder of an outdated or defective
Prospectus after the Company has notified such Holder in writing that the
Prospectus is outdated or defective and prior to the receipt by such Holder of
the Advice contemplated in Section 6(d). In no event shall the liability of any
selling Holder hereunder be greater in amount than the dollar amount of the net
proceeds received by such Holder upon the sale of the Registrable Securities
giving rise to such indemnification obligation.

          (c) CONDUCT OF INDEMNIFICATION PROCEEDINGS. If any Proceeding shall be
brought or asserted against any Person entitled to indemnity hereunder (an
"INDEMNIFIED PARTY"), such Indemnified Party shall promptly notify the Person
from whom indemnity is sought (the "INDEMNIFYING PARTY") in writing, and the
Indemnifying Party shall assume the defense thereof, including the employment of
counsel reasonably satisfactory to the Indemnified Party and the payment of all
fees and expenses incurred in connection with defense thereof; provided, that
the failure of any Indemnified Party to give such notice shall not relieve the
Indemnifying Party of its obligations or liabilities pursuant to this Agreement,
except (and only) to the extent that it shall be finally determined by a court
of competent jurisdiction that such failure shall have proximately and
materially adversely prejudiced the Indemnifying Party.

          An Indemnified Party shall have the right to employ separate counsel
in any such Proceeding and to participate in the defense thereof, but the fees
and expenses of such counsel shall be at the expense of such Indemnified Party
or Parties unless: (1) the Indemnifying Party has agreed in writing to pay such
fees and expenses; (2) the Indemnifying Party shall have failed promptly to
assume the defense of such Proceeding and to employ counsel reasonably
satisfactory to such Indemnified Party in any such Proceeding; or (3) the named
parties to any such Proceeding (including any impleaded parties) include both
such Indemnified Party and the Indemnifying Party, and in the opinion of counsel
to such Indemnified Party there will be a conflict of interest if the same
counsel were to represent such Indemnified Party and the Indemnifying Party (in
which case, if such Indemnified Party notifies the Indemnifying Party in writing
that it elects to employ separate counsel at the expense of the Indemnifying
Party, the Indemnifying Party shall not have the right to assume the defense
thereof on behalf of the Indemnified Party and such additional counsel shall be
at the expense of the Indemnifying Party). The Indemnifying Party shall not be
liable for any settlement of any such Proceeding effected without its written
consent, which consent shall not be unreasonably withheld. No Indemnifying Party
shall, without the prior written consent of the Indemnified Party, effect any
settlement of any pending Proceeding in respect of which any Indemnified Party
is a party,


                                      -8-


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unless such settlement includes an unconditional release of such Indemnified
Party from all liability on claims that are the subject matter of such
Proceeding.

          All reasonable fees and expenses of the Indemnified Party (including
reasonable fees and expenses to the extent incurred in connection with
investigating or preparing to defend such Proceeding in a manner not
inconsistent with this Section) shall be paid to the Indemnified Party, as
incurred, within ten Trading Days of written notice thereof to the Indemnifying
Party (regardless of whether it is ultimately determined that an Indemnified
Party is not entitled to indemnification hereunder; PROVIDED, that the
Indemnifying Party may require such Indemnified Party to undertake to reimburse
all such fees and expenses to the extent it is finally judicially determined
that such Indemnified Party is not entitled to indemnification hereunder).

          (d) CONTRIBUTION. If a claim for indemnification under Section 5(a) or
5(b) is unavailable to an Indemnified Party (by reason of public policy or
otherwise), then each Indemnifying Party, in lieu of indemnifying such
Indemnified Party, shall contribute to the amount paid or payable by such
Indemnified Party as a result of such Losses, in such proportion as is
appropriate to reflect the relative fault of the Indemnifying Party and
Indemnified Party in connection with the actions, statements or omissions that
resulted in such Losses as well as any other relevant equitable considerations.
The relative fault of such Indemnifying Party and Indemnified Party shall be
determined by reference to, among other things, whether any action in question,
including any untrue or alleged untrue statement of a material fact or omission
or alleged omission of a material fact, has been taken or made by, or relates to
information supplied by, such Indemnifying Party or Indemnified Party, and the
parties' relative intent, knowledge, access to information and opportunity to
correct or prevent such action, statement or omission. The amount paid or
payable by a party as a result of any Losses shall be deemed to include, subject
to the limitations set forth in Section 5(c), any reasonable attorneys' or other
reasonable fees or expenses incurred by such party in connection with any
Proceeding to the extent such party would have been indemnified for such fees or
expenses if the indemnification provided for in this Section was available to
such party in accordance with its terms.

          The parties hereto agree that it would not be just and equitable if
contribution pursuant to this Section 5(d) were determined by pro rata
allocation or by any other method of allocation that does not take into account
the equitable considerations referred to in the immediately preceding paragraph.
Notwithstanding the provisions of this Section 5(d), no Holder shall be required
to contribute, in the aggregate, any amount in excess of the amount by which the
proceeds actually received by such Holder from the sale of the Registrable
Securities subject to the Proceeding exceeds the amount of any damages that such
Holder has otherwise been required to pay by reason of such untrue or alleged
untrue statement or omission or alleged omission.

          The indemnity and contribution agreements contained in this Section
are in addition to any liability that the Indemnifying Parties may have to the
Indemnified Parties.

       6. MISCELLANEOUS

          (a) REMEDIES. In the event of a breach by the Company or by a Holder,
of any of their obligations under this Agreement, each Holder or the Company, as
the case may be,


                                      -9-


<PAGE>


in addition to being entitled to exercise all rights granted by law and under
this Agreement, including recovery of damages, will be entitled to specific
performance of its rights under this Agreement. The Company and each Holder
agree that monetary damages would not provide adequate compensation for any
losses incurred by reason of a breach by it of any of the provisions of this
Agreement and hereby further agree that, in the event of any action for specific
performance in respect of such breach, it shall waive the defense that a remedy
at law would be adequate.

          (b) OTHER REGISTRATIONS. Prior to the Effective Date, the Company
shall not, directly or indirectly, file any other registration statement (other
than on Form S-8 or equivalent form as promulgated under the Securities Act)
with the Commission with respect to any securities of the Company. Except as and
to the extent specified in SCHEDULE 6(b) hereto, neither the Company nor any of
its security holders (other than the Holders in such capacity pursuant hereto)
may include securities of the Company in the Registration Statement other than
the Registrable Securities, and the Company shall not after the date hereof
enter into any agreement providing any such right to any of its security
holders. Except as and to the extent specified in SCHEDULE 6(b) hereto, the
Company has not previously entered into any agreement granting any registration
rights with respect to any of its securities to any Person which have not been
fully satisfied.

          (c) COMPLIANCE. Each Holder covenants and agrees that it will comply
with the prospectus delivery requirements of the Securities Act as applicable to
it in connection with sales of Registrable Securities pursuant to the
Registration Statement.

          (d) DISCONTINUED DISPOSITION. Each Holder agrees by its acquisition of
such Registrable Securities that, upon receipt of a notice from the Company of
the occurrence of any event of the kind described in Section 3(c), such Holder
will forthwith discontinue disposition of such Registrable Securities under the
Registration Statement until such Holder's receipt of the copies of the
supplemented Prospectus and/or amended Registration Statement or until it is
advised in writing (the "ADVICE") by the Company that the use of the applicable
Prospectus may be resumed, and, in either case, has received copies of any
additional or supplemental filings that are incorporated or deemed to be
incorporated by reference in such Prospectus or Registration Statement. The
Company may provide appropriate stop orders to enforce the provisions of this
paragraph.

          (e) PIGGY-BACK REGISTRATIONS. If at any time during the Effectiveness
Period there is not an effective Registration Statement covering all of the
Registrable Securities and the Company shall determine to prepare and file with
the Commission a registration statement relating to an offering for its own
account or the account of others under the Securities Act of any of its equity
securities, other than on Form S-4 or Form S-8 (each as promulgated under the
Securities Act) or their then equivalents relating to equity securities to be
issued solely in connection with any acquisition of any entity or business or
equity securities issuable in connection with stock option or other employee
benefit plans, then the Company shall send to each Holder written notice of such
determination and, if within five days after receipt of such notice, any such
Holder shall so request in writing, the Company shall include in such
registration statement all or any part of such Registrable Securities such
holder requests to be registered. In the case of the registration of shares of
Common Stock by the Company in


                                      -10-


<PAGE>


connection with an underwritten public offering at any time during the
Effectiveness Period when there is not an effective Registration Statement, (a)
the Company shall not be required to include any Registrable Securities in such
underwriting unless the Holders thereof accept the terms of the underwriting as
agreed upon between the Company and the underwriter(s) selected by it, and (b)
if the underwriter(s) determines that marketing factors require a limitation on
the number of Registrable Securities to be offered, the Company shall not be
required to register Registrable Securities of the Holders in excess of the
amount, if any, of shares of the capital stock which the principal underwriter
of such underwritten offering shall reasonably and in good faith agree to
include in such offering in excess of any amount to be registered for the
Company, and in the event of any such limitation, the number of Registrable
Securities of any Holder requesting inclusion in such registration shall be
based upon the relative holdings of Registrable Securities of all Holders
requesting such registration (and if any Holder would thus be entitled to
include more Registrable Securities than such Holder requested to be registered,
the excess shall be allocated among other requesting Holders pro rata based upon
their relative holdings of Registrable Securities).

          (f) AMENDMENTS AND WAIVERS. The provisions of this Agreement,
including the provisions of this sentence, may not be amended, modified or
supplemented, and waivers or consents to departures from the provisions hereof
may not be given, unless the same shall be in writing and signed by the Company
and the Holders of at least a majority of the then outstanding Registrable
Securities.

          (g) NOTICES. Any and all notices or other communications or deliveries
required or permitted to be provided hereunder shall be in writing and shall be
deemed given and effective on the earliest of (i) the date of transmission, if
such notice or communication is delivered via facsimile at the facsimile
telephone number specified in this Section prior to 5:00 p.m. (New York City
time) on a Trading Day, (ii) the Trading Day after the date of transmission, if
such notice or communication is delivered via facsimile at the facsimile
telephone number specified in this Agreement later than 5:00 p.m. (New York City
time) on any date and earlier than 11:59 p.m. (New York City time) on such date,
(iii) the Trading Day following the date of mailing, if sent by nationally
recognized overnight courier service, or (iv) upon actual receipt by the party
to whom such notice is required to be given. The address for such notices and
communications shall be as follows:

       If to the Company:                American Science and Engineering, Inc.
                                         829 Middlesex Turnpike
                                         Billerica, MA 01821-3907
                                         Attn: Chief Financial Officer
                                         Fax No.: (978) 262-8812

       With a copy to:                   Brown Rudnick Berlack Israels LLP
                                         One Financial Center
                                         Boston, MA 02111
                                         Attn: Steven R. London, Esq.
                                         Fax No.: (617) 856-8201


                                      -11-


<PAGE>


       If                         to a Purchaser: To the address set forth
                                  under such Purchaser's name on the signature
                                  pages hereto.

       If to any other Person who is then the registered Holder:

                                  To the address of such Holder as it appears in
                                  the stock transfer books of the Company

or such other address as may be designated in writing hereafter, in the same
manner, by such Person.

          (h) SUCCESSORS AND ASSIGNS. This Agreement shall inure to the benefit
of and be binding upon the successors and permitted assigns of each of the
parties and shall inure to the benefit of each Holder. The Company may not
assign its rights or obligations hereunder without the prior written consent of
each Holder. Each Holder may assign its rights hereunder in the manner and to
the Persons as permitted under the Purchase Agreement.

          (i) EXECUTION AND COUNTERPARTS. This Agreement may be executed in any
number of counterparts, each of which when so executed shall be deemed to be an
original and, all of which taken together shall constitute one and the same
Agreement. In the event that any signature is delivered by facsimile
transmission, such signature shall create a valid binding obligation of the
party executing (or on whose behalf such signature is executed) the same with
the same force and effect as if such facsimile signature were the original
thereof.

          (j) GOVERNING LAW. All questions concerning the construction,
validity, enforcement and interpretation of this Agreement shall be governed by
and construed and enforced in accordance with the internal laws of the State of
New York, without regard to the principles of conflicts of law thereof. Each
party agrees that all Proceedings concerning the interpretations, enforcement
and defense of the transactions contemplated by this Agreement and any other
Transaction Documents (whether brought against a party hereto or its respective
affiliates, directors, officers, stockholders, employees or agents) shall be
commenced exclusively in the state and federal courts sitting in the City of New
York, Borough of Manhattan. Each party hereto hereby irrevocably submits to the
exclusive jurisdiction of the state and federal courts sitting in the City of
New York, Borough of Manhattan for the adjudication of any dispute hereunder or
in connection herewith or with any transaction contemplated hereby or discussed
herein (including with respect to the enforcement of the any of the Transaction
Documents), and hereby irrevocably waives, and agrees not to assert in any
Proceeding, any claim that it is not personally subject to the jurisdiction of
any such court or that such Proceeding is improper. Each party hereto hereby
irrevocably waives personal service of process and consents to process being
served in any such Proceeding by mailing a copy thereof via registered or
certified mail or overnight delivery (with evidence of delivery) to such party
at the address in effect for notices to it under this Agreement and agrees that
such service shall constitute good and sufficient service of process and notice
thereof. Nothing contained herein shall be deemed to limit in any way any right
to serve process in any manner permitted by law. Each party hereto hereby
irrevocably waives, to the fullest extent permitted by applicable law, any and
all right to trial by jury in any legal proceeding arising out of or relating to
this Agreement or the transactions contemplated hereby. If either party shall
commence a Proceeding to enforce any provisions of a Transaction


                                      -12-


<PAGE>


Document, then the prevailing party in such Proceeding shall be reimbursed by
the other party for its reasonable attorney's fees and other reasonable costs
and expenses incurred with the investigation, preparation and prosecution of
such Proceeding.

          (k) CUMULATIVE REMEDIES. The remedies provided herein are cumulative
and not exclusive of any remedies provided by law.

          (l) SEVERABILITY. If any term, provision, covenant or restriction of
this Agreement is held by a court of competent jurisdiction to be invalid,
illegal, void or unenforceable, the remainder of the terms, provisions,
covenants and restrictions set forth herein shall remain in full force and
effect and shall in no way be affected, impaired or invalidated, and the parties
hereto shall use their reasonable efforts to find and employ an alternative
means to achieve the same or substantially the same result as that contemplated
by such term, provision, covenant or restriction. It is hereby stipulated and
declared to be the intention of the parties that they would have executed the
remaining terms, provisions, covenants and restrictions without including any of
such that may be hereafter declared invalid, illegal, void or unenforceable.

          (m) HEADINGS. The headings in this Agreement are for convenience of
reference only and shall not limit or otherwise affect the meaning hereof.

          (n) INDEPENDENT NATURE OF PURCHASERS' OBLIGATIONS AND RIGHTS. The
obligation of each Purchaser hereunder is several and not joint with the
obligations of any other Purchaser hereunder, and no Purchaser shall be
responsible in any way for the performance of the obligations of any other
Purchaser hereunder. Nothing contained herein or in any other agreement or
document delivered at any closing, and no action taken by any Purchaser pursuant
hereto or thereto, shall be deemed to constitute the Purchasers as a
partnership, an association, a joint venture or any other kind of entity, or
create a presumption that the Purchasers are in any way acting in concert with
respect to such obligations or the transactions contemplated by this Agreement.
Each Purchaser shall be entitled to protect and enforce its rights, including
without limitation the rights arising out of this Agreement, and it shall not be
necessary for any other Purchaser to be joined as an additional party in any
proceeding for such purpose.

                   [REMAINDER OF PAGE INTENTIONALLY LEFT BLANK
                           SIGNATURE PAGES TO FOLLOW]






                                      -13-


<PAGE>


                  IN WITNESS WHEREOF, the parties have executed this
Registration Rights Agreement as of the date first written above.



                                      AMERICAN SCIENCE AND ENGINEERING, INC.


                                      By: /s/ Andrew R. Morrison
                                         ---------------------------------------
                                      Name: Andrew R. Morrison
                                      Title: Vice President and CFO



                   [REMAINDER OF PAGE INTENTIONALLY LEFT BLANK
                     SIGNATURE PAGES OF PURCHASER TO FOLLOW]


















                                      -14-


<PAGE>


         IN WITNESS WHEREOF, the parties hereto have caused this Registration
Rights Agreement to be duly executed by their respective authorized
signatories as of the date first indicated above.


                               PINE RIDGE FINANCIAL, INC.

                               By:  /s/ Kenneth L. Henderson
                                   --------------------------------------------
                                   Kenneth L. Henderson
                                   Attorney-in-fact



                               Address for Notice:
                               c/o Cavallo Capital Corp.
                               660 Madison Avenue, 18th Floor
                               New York, NY 10021
                               Facsimile No.:(212) 651-9010
                               Attn: Danny Golan

           With copies to:     Robinson Silverman Pearce Aronsohn & Berman LLP
                               1290 Avenue of the Americas
                               New York, NY  10104
                               Facsimile No.: (212) 541-4630 and (212) 541-1432
                               Attn: Eric L. Cohen, Esq.


                                      -15-

<PAGE>


         IN WITNESS WHEREOF, the parties hereto have caused this Registration
Rights Agreement to be duly executed by their respective authorized
signatories as of the date first indicated above.


                            RADYR INVESTMENTS LIMITED

                            By:  /s/ David Sims
                                --------------------------------------------
                                Name: David Sims
                                Title: Director


                            Address for Notice:
                            c/o Rhino Advisors Inc.
                            130 West 29th Street, 5th Floor
                            New York, NY 10001
                            Facsimile No.:(212) 594-7181
                            Attn: Rose Alaimo

        With copies to:     Robinson Silverman Pearce Aronsohn & Berman LLP
                            1290 Avenue of the Americas
                            New York, NY  10104
                            Facsimile No.: (212) 541-4630 and (212) 541-1432
                            Attn: Eric L. Cohen, Esq.


                                      -16-

<PAGE>


         IN WITNESS WHEREOF, the parties hereto have caused this Registration
Rights Agreement to be duly executed by their respective authorized
signatories as of the date first indicated above.


                               CLEVELAND OVERSEAS LTD.

                               By:  /s/ Primeway S.A.
                                   --------------------------------------------
                                   Name:
                                   Title: Director


                               Address for Notice:
                               c/o Vertical Ventures, LLC
                               900 Third Avenue, 26th Floor
                               New York, NY 10022
                               Facsimile No.:(646) 274-1728
                               Attn: Joshua Silverman

           With copies to:     Robinson Silverman Pearce Aronsohn & Berman LLP
                               1290 Avenue of the Americas
                               New York, NY  10104
                               Facsimile No.: (212) 541-4630 and (212) 541-1432
                               Attn: Eric L. Cohen, Esq.



                                      -17-


<PAGE>


         IN WITNESS WHEREOF, the parties hereto have caused this Registration
Rights Agreement to be duly executed by their respective authorized
signatories as of the date first indicated above.


                               ZLP MASTER TECHNOLOGY FUND LTD.

                               By:  /s/ Stuart J. Zimmer
                                   --------------------------------------------
                                   Name: Stuart J. Zimmer
                                   Title: Director


                               Address for Notice:
                               c/o Zimmer Lucas Partners
                               45 Broadway, 28th Floor
                               New York, NY 10006
                               Facsimile No.:(212) 440-0750
                               Attn: John Lee

           With copies to:     Robinson Silverman Pearce Aronsohn & Berman LLP
                               1290 Avenue of the Americas
                               New York, NY  10104
                               Facsimile No.: (212) 541-4630 and (212) 541-1432
                               Attn: Eric L. Cohen, Esq.



                                      -18-

<PAGE>


         IN WITNESS WHEREOF, the parties have executed this Registration
Rights Agreement as of the date first written above.


                           CRANSHIRE CAPITAL, L.P.

                           By:  /s/ Mitchell Kopin
                               --------------------------------------------
                           Name: Mitchell Kopin
                           Title: President - Downsview Capital


                           Address for Notice:

                           666 Dundee Road, Suite 1901

                           Northbrook, IL 60062


                           with a copy to:


                                      -19-

<PAGE>


         IN WITNESS WHEREOF, the parties hereto have caused this Registration
Rights Agreement to be duly executed by their respective authorized
signatories as of the date first indicated above.


                          SF CAPITAL PARTNERS LTD.

                          By:  /s/ Brian H. Davidson
                              --------------------------------------------
                          Name: Brian H. Davidson
                          Title: Authorized Signatory


                          Address for Notice:
                          1500 West Market Street, Suite 200
                          Mequon, WI 53092
                          Facsimile No.:(262) 240 3215
                          Attn: Brian H. Davidson

      With copies to:     Robinson Silverman Pearce Aronsohn & Berman LLP
                          1290 Avenue of the Americas
                          New York, NY  10104
                          Facsimile No.: (212) 541-4630 and (212) 541-1432
                          Attn: Eric L. Cohen, Esq.



                                      -20-

<PAGE>


         IN WITNESS WHEREOF, the parties hereto have caused this Registration
Rights Agreement to be duly executed by their respective authorized
signatories as of the date first indicated above.


                               SPECIAL SITUATIONS PRIVATE EQUITY FUND, L.P.

                               By: /s/ Austin Marxe
                                   --------------------------------------------
                               Name:
                               Title:


                               Address for Notice:

                               Special Situations Funds
                               153 E. 53rd Street, 55th Floor
                               New York, NY 10022
                               Attn: Steven R. Becker
                               Facsimile No.:(212) 207-6515

                               With Copy to:

                               Lowenstein Sandler PC
                               65 Livingston Avenue
                               Roseland, NJ 07068
                               Facsimile No.(973) 597-2383
                               Attn.: John D. Hogoboom, Esq.



                                      -21-

<PAGE>


         IN WITNESS WHEREOF, the parties hereto have caused this Registration
Rights Agreement to be duly executed by their respective authorized
signatories as of the date first indicated above.


                               SPECIAL SITUATIONS TECHNOLOGY FUND, L.P.

                               By: /s/ Austin Marxe
                                   --------------------------------------------
                               Name:
                               Title:


                               Address for Notice:

                               Special Situations Funds
                               153 E. 53rd Street, 55th Floor
                               New York, NY 10022
                               Attn: Steven R. Becker
                               Facsimile No.:(212) 207-6515

                               With Copy to:

                               Lowenstein Sandler PC
                               65 Livingston Avenue
                               Roseland, NJ 07068
                               Facsimile No.(973) 597-2383
                               Attn.: John D. Hogoboom, Esq.



                                      -22-

<PAGE>


         IN WITNESS WHEREOF, the parties hereto have caused this Registration
Rights Agreement to be duly executed by their respective authorized
signatories as of the date first indicated above.


                               DEEPHAVEN PRIVATE PLACEMENT TRADING LTD.

                               By:  /s/ Bruce Lieberman
                                   --------------------------------------------
                               Name: Bruce Lieberman
                               Title: Director Private Placements


                               Address for Notice:
                               c/o Deephaven Capital Management LLC
                               130 Cheshire Lane, Suite 102
                               Minnetonka, MN 55305
                               Facsimile No.:(952) 249-5320
                               Attn: Bruce Lieberman

           With copies to:     Robinson Silverman Pearce Aronsohn & Berman LLP
                               1290 Avenue of the Americas
                               New York, NY  10104
                               Facsimile No.: (212) 541-4630 and (212) 541-1432
                               Attn: Eric L. Cohen, Esq.



                                      -23-

<PAGE>


         IN WITNESS WHEREOF, the parties hereto have caused this Registration
Rights Agreement to be duly executed by their respective authorized
signatories as of the date first indicated above.


                               CAPITAL VENTURES INTERNATIONAL

                               By:  /s/ Martin Kobinger
                                   --------------------------------------------
                               Name: Martin Kobinger
                               Title: Investment Manager


                               Address for Notice:
                               c/o Heights Capital Management
                               401 City Avenue, Suite 220
                               Bala Cynwyd, PA 19004
                               Facsimile No.:(610) 617 3013
                               Attn: Michael Mollen


                                      -24-


<PAGE>


                                     ANNEX A

                              PLAN OF DISTRIBUTION

     The Selling Stockholders and any of their pledgees, assignees and
successors-in-interest may, from time to time, sell any or all of their shares
of Common Stock on any stock exchange, market or trading facility on which the
shares are traded or in private transactions. These sales may be at fixed or
negotiated prices. The Selling Stockholders may use any one or more of the
following methods when selling shares:

o    ordinary brokerage transactions and transactions in which the broker-dealer
     solicits purchasers;

o    block trades in which the broker-dealer will attempt to sell the shares as
     agent but may position and resell a portion of the block as principal to
     facilitate the transaction;

o    purchases by a broker-dealer as principal and resale by the broker-dealer
     for its account;

o    an exchange distribution in accordance with the rules of the applicable
     exchange;

o    privately negotiated transactions;

o    short sales;

o    broker-dealers may agree with the Selling Stockholders to sell a specified
     number of such shares at a stipulated price per share;

o    a combination of any such methods of sale; and

o    any other method permitted pursuant to applicable law.

     The Selling Stockholders may also sell shares under Rule 144 under the
Securities Act, if available, rather than under this prospectus.

     Broker-dealers engaged by the Selling Stockholders may arrange for other
brokers-dealers to participate in sales. Broker-dealers may receive commissions
or discounts from the Selling Stockholders (or, if any broker-dealer acts as
agent for the purchaser of shares, from the purchaser) in amounts to be
negotiated. The Selling Stockholders do not expect these commissions and
discounts to exceed what is customary in the types of transactions involved.

     The Selling Stockholders may from time to time pledge or grant a security
interest in some or all of the shares of common stock or warrants owned by them
and, if they default in the performance of their secured obligations, the
pledgees or secured parties may offer and sell the shares of common stock from
time to time under this prospectus, or under an amendment to this prospectus
under Rule 424(b)(3) or other applicable provision of the Securities Act of 1933
amending the list of Selling Stockholders to include the pledgee, transferee or
other successors in interest as Selling Stockholders under this prospectus.


                                      -25-


<PAGE>


     The Selling Stockholders also may transfer the shares of common stock in
other circumstances, in which case the transferees, pledgees or other successors
in interest will be the selling beneficial owners for purposes of this
prospectus.

     The Selling Stockholders and any broker-dealers or agents that are involved
in selling the shares may be deemed to be "underwriters" within the meaning of
the Securities Act in connection with such sales. In such event, any commissions
received by such broker-dealers or agents and any profit on the resale of the
shares purchased by them may be deemed to be underwriting commissions or
discounts under the Securities Act. Each Selling Stockholder has informed the
Company that it does not have any agreement or understanding, directly or
indirectly, with any person to distribute the Common Stock.

     The Company is required to pay all fees and expenses incident to the
registration of the shares. The Company has agreed to indemnify the Selling
Stockholders against certain losses, claims, damages and liabilities, including
liabilities under the Securities Act.













                                      -26-